Sacramento City Council
October 21, 2025

URBAN LEVEL OF FLOOD PROTECTION
ENGINEER’S REPORT

FOR THE

ROBLA-ARCADE LEVEE SYSTEM
AUGUST 2025
PREPARED UNDER: SACRAMENTO AREA FLOOD CONTROL
AGENCY, CONTRACT NO. 1588
(Back of title page)
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CERTIFICATION
This Engineer’s Report was prepared by the Sacramento Area Flood Control Agency (SAFCA) certification team including Psomas, Kleinfelder, Mead & Hunt, AECOM, and MBK Engineers (MBK). The purpose of this report is to support a finding that the Robla-Arcade Levee System, which was constructed and is owned by the Central Valley Flood Protection Board (CVFPB) and operated and maintained by the American River Flood Control District (ARFCD), provides an urban level of flood protection (ULOP) in accordance and consistent with the requirements, definitions, and descriptions provided by:

State of California Department of Water Resources (DWR) ULOP Criteria (November 2013), Section 2, EVD-1.

State of California DWR Urban Levee Design Criteria (ULDC) (May 2012), Section

7.0. The supporting documentation, calculations, data, definitions, limitations, and/or other pertinent information contained or referenced in this report form the basis of this certification. This certification does not constitute a warranty or guarantee of performance, express or implied. The certification is made for the Robla-Arcade Levee System. Individual certification statements are provided in Appendix A for each ULDC topic, which have been endorsed by the certification team member responsible.
455 University Ave. Suite 100  Sacramento, California 95825  Phone: (916) 456-4400  Fax: (916) 456-0253  Website: www.mbkengineers.com Water Resources  Flood Control  Water Rights DON TRIEU, P.E. FOUNDERS:

DARREN CORDOVA, P.E
NATHAN HERSHEY, P.E., P.L.S. ANGUS NORMAN MURRAY
LEE G. BERGFELD, P.E. 1913-1985
BEN TUSTISON, P.E. JOSEPH I. BURNS
THOMAS ENGLER, P.E., CFM 1926-2021
MICHAEL MONCRIEF, P.E. DONALD E. KIENLEN
NICOLE ORTEGA-JEWELL, PMP 1930-2023
KYLE KNUTSON, P.E.

ANNE WILLIAMS, P.E.

PATRICK HO, P.E.

CERTIFICATION
This certification is provided to the Sacramento Area Flood Control Agency (SAFCA) for the sole purpose of supporting an Urban Level of Flood Protection (ULOP) finding. This certification is made in accordance with the requirements, definitions, and descriptions in the State of California Department of Water Resources’ (DWR) Urban Level of Flood Protection Criteria (November 2013), Section 2, Subsection EVD1 and Urban Levee Design Criteria (ULDC) (May 2012), Section 7.0 Urban Levee Design Criteria.

All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained or referenced in this document form the basis of this certification. This certification does not constitute a warranty or guarantee of performance, express or implied. This certification is made with respect to the RoblaArcade Levee System (Levee System), as described in the Urban Level of Flood Protection Engineer’s Report, August 2025 (Engineer’s Report).

Limits and Conditions of This Certification
This certification shall expire or become invalid at the earliest time any of the following conditions are met for any portion of the levee system:
 Integrity of the levee system has degraded to the point that the identified improvements will not be adequate to provide an urban level of flood protection, as determined by me, or a duly qualified designated successor.  Discovery of any substantive defect in the condition of any component of the levee system that was not known at the time this certification was made, and which materially affects the system’s ability to provide protection relative to a 1-in-200 chance of annual flood, as determined by me, or a duly qualified designated successor.
 20-years from the date of certification or until the ULOP finding is superseded, whichever is sooner, provided that a periodic review of the finding, which may ii
include a full or partial engineering re-evaluation as deemed necessary, is performed every 5 years.

Certification Statement
At the request of SAFCA, as supported by the information contained and referenced within the Engineer’s Report, this is to certify the following:
 Certification of Data and Information – The data and information presented in this report are accurate to the best of my knowledge.
 Certification of Analysis – To the best of my knowledge, the analyses conducted were performed in accordance with DWR’s ULDC and/or sound engineering practices, in a manner consistent with the degree of skill and care ordinarily exercised by members of the civil engineering profession currently practicing in the same locality under similar conditions.

I, Thomas F. Engler, PE, a professional registered civil engineer in the State of California, certify that the aforementioned levee system, as described in this Urban Level of Flood Protection Engineer’s Report, August 2025, provides an urban level of flood protection.

Signature: Date: September 9, 2025
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TABLE OF CONTENTS
Table of Contents ...................................................................................................................................i List of Figures ....................................................................................................................................................................iii List of Appendices ..........................................................................................................................................................iv Acronyms and Abbreviations ........................................................................................... v

1.0 Introduction ............................................................................................................7

2.0 Description of Robla Arcade Levee System.........................................................8

3.0 Physical Description ...............................................................................................9 Robla Creek South Levee..................................................................................................................................9 Natomas East Main Drainage Canal East Levee – Robla Creek to Arcade Creek.......... 10 Arcade Creek North Levee ............................................................................................................................ 10

4.0 Performance History ............................................................................................11 Robla Creek South Levee............................................................................................................................... 11 Natomas East Main Drainage Canal East Levee ............................................................................... 12 Arcade Creek North Levee ............................................................................................................................ 12

5.0 Evaluation of Robla-Arcade Levee System........................................................12 ULDC 7.1: Design Water Surface Elevation.......................................................................................... 13 ULDC 7.2: Minimum Top of Levee.......................................................................................................... 14 ULDC 7.3: Soil Sampling, Testing, and Logging ................................................................................ 14 Robla Creek South Levee............................................................................................................................... 14 Natomas East Main Drainage Canal East Levee – Arcade Creek to Robla Creek.......... 15 Arcade Creek North Levee ............................................................................................................................ 15 ULDC 7.4: Slope Stability For Intermittently Loaded Levees......................................................... 16 Robla Creek South Levee............................................................................................................................... 16 Natomas East Main Drainage Canal East Levee – Robla Creek to Arcade Creek.......... 16 Arcade Creek North Levee ............................................................................................................................ 17 ULDC 7.5: Underseepage For Intermittently Loaded Levees........................................................ 17 Robla Creek South Levee............................................................................................................................... 18 Natomas East Main Drainage Canal East Levee – Robla Creek to Arcade Creek.......... 18 Arcade Creek North Levee ............................................................................................................................ 18 ii
ULDC 7.6: Frequently Loaded Levees .................................................................................................... 19 ULDC 7.7: Seismic Vulnerability ............................................................................................................... 19 ULDC 7.8: Levee Geometry........................................................................................................................ 19 Robla Creek South Levee............................................................................................................................... 20 Natomas East Main Drainage Canal East Levee – Robla Creek to Arcade Creek.......... 20 Arcade Creek North Levee ............................................................................................................................ 21 ULDC 7.9: Interfaces and Transitions ..................................................................................................... 21 Robla Creek South Levee (RCSL) ............................................................................................................... 22 Natomas East Main Drainage Canal East Levee – Robla Creek to Arcade Creek.......... 22 Arcade Creek North Levee ............................................................................................................................ 23 ULDC 7.10: Erosion ....................................................................................................................................... 24 Robla Creek South Levee............................................................................................................................... 25 Natomas East Main Drainage Canal East Levee – Robla Creek to Arcade Creek.......... 25 Arcade Creek North Levee ............................................................................................................................ 26 ULDC 7.11: Right-of-Way........................................................................................................................... 26 Robla Creek South Levee............................................................................................................................... 27 Natomas East Main Drainage Canal East Levee – Robla creek to Arcade Creek........... 28 Arcade Creek North Levee ............................................................................................................................ 28 ULDC 7.12: Encroachments ....................................................................................................................... 28 ULDC 7.13: Penetrations............................................................................................................................. 29 ULDC 7.14: Floodwalls, Retaining Walls, and Closure Structures................................................ 30 Robla Creek South Levee............................................................................................................................... 30 Natomas East Main Drainage Canal East Levee – Robla Creek to Arcade Creek.......... 31 Arcade Creek North Levee ............................................................................................................................ 31 ULDC 7.15: Animal Burrows....................................................................................................................... 32 ULDC 7.16: Levee Vegetation ................................................................................................................... 33 ULDC 7.17: Wind Setup and Wave Runup........................................................................................... 33 Robla Creek South Levee............................................................................................................................... 33 Natomas East Main Drainage Canal East Levee – Robla Creek to Arcade Creek.......... 34 Arcade Creek North Levee ............................................................................................................................ 34 ULDC 7.18: Security ...................................................................................................................................... 34 iii
ULDC 7.19: Sea Level Rise.......................................................................................................................... 35 ULDC 7.20: Emergency Actions and Flood Safety Plans................................................................. 35 ULDC 8.0 Operations & Maintenance................................................................................................... 36

6.0 Bibliography .................................................................................................................... 36

LIST OF FIGURES
Figure 1. Robla-Arcade Levee System
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LIST OF APPENDICES
Appendix A. Consultant Certification Statements
Appendix B. Independent Panel of Experts Report and Comment Closeout Appendix C. ULDC Water Surface Elevation Profiles – MBK Appendix D. Robla-Arcade ULDC Due Diligence, Geotech – AECOM Appendix E. Robla-Arcade ULDC Due Diligence, Geotech – Kleinfelder Appendix F. ULDC and FEMA Levee Inspection – MBK
Appendix G. O&M Right of Way Maps – Psomas
Appendix H. Robla-Arcade ULDC Due Diligence, Civil – Mead & Hunt Appendix I. ULDC Required Plans
Appendix I1 – Right of Way Plan – MBK Engineers
Appendix I2 – Encroachment Remediation Plan – MBK Engineers Appendix I3 – Penetrations Exception Work Plan – Mead & Hunt Appendix I4 – ARFCD Rodent Control & Abatement Program
Appendix I5 – ARFCD Security Plan
Appendix I6 – ARFCD Flood Safety Plan
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ACRONYMS AND ABBREVIATIONS
ACNL Arcade Creek North Levee
AEP annual exceedance probability
APF Adequate Progress Finding
ARCF American River Common Features
ARFCD American River Flood Control District
cfs cubic feet per second
City City of Sacramento
CPT Cone Penetration Test
CVFPB Central Valley Flood Protection Board
DWR California Department of Water Resources
DWSE Design Water Surface Elevation
EC Engineering Circular
EM Engineering Manual
ETL Engineering Technical Letter
FEMA Federal Emergency Management Agency
H:V horizontal-to-vertical ratio
fps feet per second
HTOL Hydraulic Top of Levee
IPE Independent Panel of Experts
MBK MBK Engineers
MTOL Minimum Top of Levee
NEMDC Natomas East Main Drainage Canal
O&M operation and maintenance
pcf pounds per cubic foot
RCSL Robla Creek South Levee
RM River Mile
SAFCA Sacramento Area Flood Control Agency
SB Senate Bill
SOP Standard Operating Procedure
SPFC State Plan of Flood Control
SPK Sacramento District (USACE)
ULDC Urban Levee Design Criteria
ULOP Urban Level of Flood Protection
UPRR Union Pacific Railroad
USACE U.S. Army Corps of Engineers
USGS United States Geological Survey
WSE water surface elevation
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URBAN LEVEL OF FLOOD PROTECTION ENGINEER’S REPORT

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7 1.0 INTRODUCTION
In 2008, the California Legislature passed the Central Valley Flood Protection Act (Senate Bill [SB] 5), which requires all cities and counties within the Sacramento-San Joaquin Valley to make findings related to an urban level of flood protection for urban and urbanizing lands within a flood hazard zone. The bill defined “urban level of flood protection” as the level of flood protection necessary to withstand flooding that has a 1-in-200 chance of occurring in any given year (annual exceedance probability or AEP) using criteria consistent with, or developed by, the California Department of Water Resources (DWR). The Urban Level of Flood Protection Criteria (ULOP Criteria) implementation guidance, issued by the State in November 2013, requires that these findings be based on substantial evidence in the record.

This document and its associated appendices provide substantial evidence that the levee system protecting a portion of the urban area in Sacramento County protected by the Robla Creek South Levee, Natomas East Main Drainage Canal East Levee, and Arcade Creek North Levee meets ULOP Criteria for a 1-in-200 AEP1 in accordance with the State of California’s Urban Levee Design Criteria (ULDC), issued in May 2012. The technical assessments performed as part of this effort are not an assessment of how floods may impact improvements (i.e., impacts to structures, facilities, docks, parks, etc.). Instead, the assessments considered a single flood event – the 1-in-200 AEP flood.

ULOP Criteria (EVD-1) requires that the substantial evidence include, at a minimum, “a report prepared by a Professional Civil Engineer registered in California to document the data and analyses for demonstrating the property, development project, or subdivision has an urban level of flood protection.” The ULOP Criteria indicates that the Engineer’s Report should include the following:
 A list of the flood management facilities, including, but not limited to, State Plan of Flood Control (SPFC) facilities;
 The location of the flood management facilities;
 The entities that operate and maintain the flood management facilities; and  A list of, and consideration of, reports, evaluations, inspections, and performance history of the flood management facilities.

This Engineer’s Report relies on other documents, reports, analyses, and evaluations, some of which are listed in the bibliography at the end of this report. This report does not, nor is it intended to, present all the evidence in the record. Instead, this Engineer’s Report and its bibliography are limited to presenting the substantial evidence required to demonstrate that an urban level of flood protection exists.

Documents that evaluate and describe the condition and performance of the facilities that are not included in the bibliography are incorporated by reference and have been provided separately. If the evaluation does not explicitly meet the criteria an exception has been written and is included in the supporting documentation provided in the Appendices.
1 The 1-in-200 AEP flood is also referred to as the 200-year flood.

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ROBLA-ARCADE LEVEE SYSTEM
8 The ULOP Criteria also requires a report by an Independent Panel of Experts (IPE Panel) on the review of this Engineer’s Report. The Panel’s report and responses to the Panel’s comments are provided separately in Appendix B.

In October 2023, the City of Sacramento (City) adopted an Adequate Progress Finding (APF) for the six levee systems protecting the Sacramento metropolitan area within their jurisdictions. This included the Robla-Arcade Levee System. The APF was based on a report prepared by SAFCA titled, 2023 Urban Level of Flood Protection Annual Report, dated August 2023. This report presented substantial evidence that once the planned improvements identified in the report were completed, the structural flood control facilities protecting the urban areas of the City from flooding would be able to withstand flooding from a 1-in-200 AEP flood event, in accordance with the State of California’s ULDC, issued in May 2012.

Since the Robla-Arcade Levee System does not require structural improvements, and non-structural actions have been completed, this Engineer’s Report certifies the Robla-Arcade Levee System as meeting ULDC and the 1-in-200 AEP urban level of flood protection. This Engineer’s Report presents the substantial evidence needed to support this certification.

2.0 DESCRIPTION OF ROBLA ARCADE LEVEE SYSTEM
The Robla-Arcade Levee System is comprised of three levees: Robla Creek South (left) levee; Natomas East Main Drainage Canal (NEMDC) East (left) Levee, extending between Robla Creek and Arcade Creek; and Arcade Creek North (right) Levee (Figure 1). The system is approximately 7 miles in length. Left and right designations are locations of the levees based on looking downstream. All three levees are operated and maintained by the American River Flood Control District (ARFCD).

A detailed description of each levee is included under the Physical Description below.

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9 Figure 1. Robla-Arcade Levee System

3.0 PHYSICAL DESCRIPTION

ROBLA CREEK SOUTH LEVEE
The Robla Creek South Levee, also known as the Linda Creek levee in the USACE 1956 construction documents, and referred to as Dry Creek Left Bank (South) Levee by USACE, is the left bank or south levee of Robla Creek, which is located within the Dry Creek floodway. The levee is approximately 2.3 miles in length. The downstream portion of Robla Creek South Levee (Station 6000+00 to 6052+00) was originally constructed in the 1950s by the USACE. In the 1990s, the existing levee was raised and the landside slopes were reconstructed by SAFCA, at which time the levee was extended from Station 6052+00 to 6106+66 and at which point the levee ties into high ground and continues eastward to Dry Creek Road (Station 6118+20) along the Magpie Creek Diversion Channel. A short spur levee starting at Station 6052+00, approximately 0.3 miles in length, and oriented parallel to and directly north of Claire Avenue, was constructed as part of the 1950s project and remains a Project levee although its regional flood protection URBAN LEVEL OF FLOOD PROTECTION ENGINEER’S REPORT

ROBLA-ARCADE LEVEE SYSTEM
10 purpose was overcome by the improvements made in the 1990s. The existing Claire Avenue levee reach was raised by SAFCA in 2006 and still provides local flood protection.

The Union Pacific Railroad (UPRR) crosses the Robla Creek South Levee near the confluence with the NEMDC East Levee where a reinforced concrete closure structure is present. Stoplogs are used as closures for this transportation crossing during flood events. There is no waterside development. Landward of the levee, land use is a mix of former agricultural (currently vacant), residential, and commercial uses. Where present, residential and commercial development is adjacent to the levee toe. The levee is crossed by the Rio Linda Boulevard bridge where floodwalls are integrated with the bridge abutment and extend approximately 20 feet along the levee on each side of the bridge crossing.

NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE – ROBLA CREEK TO ARCADE CREEK
The NEMDC East Levee was constructed in the 1950s by the USACE and extends from the American River to Robla Creek. The portion of the NEMDC East Levee from Robla Creek to Arcade Creek is a part of the Robla-Arcade Levee system.

The NEMDC East Levee from Robla Creek to Arcade Creek (Station 3056+00 to 3192+25) is 2.4 miles long.

In the 1990s, the levee was raised and the waterside and landside slopes were reconstructed.

A railroad embankment that predates the levee is located along the landside of the levee. A swale is present between the railroad and the NEMDC East Levee crest. This swale collects drainage and has a collection system to convey the water under the railroad and into a landside ditch. This landside ditch, lined and unlined depending on location, is located approximately 50 feet from the landside railroad embankment toe (100 feet from the projected levee prism toe) for the majority of the levee reach. This ditch is associated with the City of Sacramento Drainage Sumps 157 and 158. Additionally, an unlined drainage swale is located approximately 50 feet from the projected landside levee toe between Stations 3187+00 and 3192+25 associated with a 24-inch gravity culvert through the Robla Creek South Levee.

There is no waterside development. Landward of the levee, aside from the railroad, land use is primarily residential and commercial with several vacant and unimproved properties. The levee is crossed by Silver Eagle Road, Interstate 80, and Del Paso Road/Main Avenue. These bridges extend up and over the levee.

ARCADE CREEK NORTH LEVEE
The Arcade Creek North Levee was constructed in the 1950s by the USACE and extends from its connection to the NEMDC East Levee upstream approximately 2 miles to Marysville Boulevard (Station 5000+00 to 5112+43). Levee raises or floodwalls and corresponding embankment widenings were constructed along the entire Arcade Creek North Levee by SAFCA in the late 1990s. Specifically, a floodwall was constructed along the waterside edge of the levee crest between Stations 5075+00 and 5112+43 to meet FEMA freeboard requirements at the time of construction. Floodwall heights range between 1.3 and 6 feet above the levee embankment crest/existing ground with wall heights increasing upstream up to the tie-in location at the Marysville Boulevard bridge abutment. Additional work was completed in 2019 to install seepage cutoff walls, waterside slope reconstruction, and other related work to remediate seepage and stability deficiencies along Arcade Creek North Levee in order to meet ULDC (AECOM, 2024).

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11 The UPRR crosses the Arcade Creek North Levee near the NEMDC East Levee where a stoplog closure structure is present. The levee is crossed by Norwood Avenue, Rio Linda Boulevard, and the Sacramento Northern Bike Trail where bridge structures are within the levee prism. There is no waterside development.

The land use of the properties adjacent to the landside of the levee are primarily residential.

4.0 PERFORMANCE HISTORY
Past performance issues were reported from ARFCD maintenance personnel that included overtopping of the temporary sandbag berm located across Norwood Avenue Bridge during the 1986 flood. The overtopping flow inundated homes in the Strawberry Manor area (north of Arcade Creek, east of NEMDC) with up to 8 feet of water. The flooding was attributed to backwater from the American River impeding the flow from NEMDC and Arcade Creek, which was a historic low spot in the levee system. Overtopping of the sandbag berm in 1986 caused standing water at the landside levee toe which would have obscured any potential seepage within this area. The Norwood Avenue Bridge was raised after the 1986 flood event and SAFCA tied the levee into the bridge railings with short floodwalls in 1996; the Rio Linda Boulevard Bridge was subsequently raised. No closure structures are currently present at these crossings as they are elevated above the levee or isolated from the channel with abutment floodwalls.

The high-water event in 1986 triggered the installation, in 1987, of several stoplog structures throughout the Robla-Arcade levee system at railroad and road crossings where the rail or roadbed was lower than the levee crest. These structures were further modified by SAFCA as part of the North Area Local Project in the mid-1990s.

No past performance issues were observed during the 1997 high-water event.

ROBLA CREEK SOUTH LEVEE
Due to a lack of historical observed data on Robla and Magpie Creeks, and due to the fact that Dry Creek flows have more influence than Robla Creek and Magpie Creek flows on the WSE along the Robla Creek South Levee downstream of the Bike Trail bridge, the performance history for the Robla Creek South Levee is based on review of available gage records on Dry Creek.

There are 25 years of available gage records for Dry Creek at Vernon Street in Roseville, starting with water year 1997. Vernon Street is about 11 miles upstream of the start of the Dry Creek North Levee at Rio Linda Boulevard. The monitor stage of 119 feet (NGVD29) was exceeded in 10 of these 25 years, with a maximum of 126.72 (NGVD29) feet on January 22, 1997. There is a Sacramento County ALERT gage on the West Branch of Dry Creek at Elkhorn, about 0.7 miles upstream of Rio Linda Boulevard, with records starting in water year 2015. The defined flood stage at the Elkhorn Boulevard gage is 45.9 feet (NAVD88).

Comparison of the gage records indicates that the Vernon Street monitor stage of 119 feet (NGVD29) approximately coincides with the Elkhorn Boulevard flood stage of 45.9 feet (NAVD88), therefore it can be estimated that the flood stage at Elkhorn Boulevard has been exceeded in 10 out of 25 years with available record going back to 1997, with a maximum not exceeding 47 feet (NAVD88). It is worth noting the computed ULDC 200-year design flood stage on the West Branch of Dry Creek at Elkhorn Boulevard is

49.2 feet (NAVD88), a little over 3 feet above the ALERT defined flood stage. All of these have been below the 200-year DWSE.

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12 NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE
The nearest gage on the NEMDC with defined monitor and flood stages is the Sacramento County ALERT gage on the downstream side of the D-15 pump station (47344), located a little over 3 miles upstream of the Arcade Creek North Levee. The monitor stage for the D-15 downstream gage is 31.3 feet (NAVD88), and the flood stage is 40.5 feet (NAVD88). Gage data is available for water years 2015 through 2024. In that period, the flood stage has never equaled or exceeded, with a maximum recorded stage of 37.05 feet (NAVD88), on 1/11/2017. In the 10 years of record, there have been 34 occurrences of the monitor stage being equaled or exceeded. All of these have been below the 200-year DWSE.

Beginning in 2017, seepage was observed near the landside toe of the railroad embankment at the NEMDC and Arcade Creek North Levee intersection. The source of this seepage was evaluated over many years and was not deemed to be a levee safety issue. A drained stability berm was constructed in this area in 2025 (MBK, 2025a).

ARCADE CREEK NORTH LEVEE
The performance history assessment for the Arcade Creek North Levee is based on review of available records and information at the United States Geological Survey (USGS) Arcade Creek near Del Paso Heights gage (11447360) and the co-located Sacramento County Automated Local Evaluation in Real Time (ALERT) Arcade Creek at Watt Avenue gage (47336). The ALERT gage uses USGS gage height data, converted to NAVD88 by adding 49.19 feet. The gage is located just upstream of Watt Avenue and about

5.5 miles upstream of the start of the Arcade Creek South Levee. The ALERT gage has a defined “monitor stage” of 62.4 feet (NAVD88) and a “flood stage” of 63.4 feet (NAVD88).

Annual peak stage data is available for the USGS gage for 43 water years, starting in 1964. The monitor stage has been equaled or exceeded in 18 years, and the flood stage was equaled or exceeded in 9 years.

All of these have been below the DWSE.

There was no reported seepage or stability distress from either the 1986 or 1997 high-water events, however, overtopping of the sandbag wall was observed during the 1986 event at Norwood Avenue bridge which inundated the adjacent residential area. Reports from ARFCD indicate the stoplog structure was altered during a dip in the water surface elevation (WSE) to allow access through the roadway and was not rebuilt prior to the rise in WSE. This deficiency led to the overtopping in 1986. The Norwood Avenue bridge was raised to remediate this condition.

5.0 EVALUATION OF ROBLA-ARCADE LEVEE SYSTEM
The ULDC requires analysis under the 20 categories listed below. SAFCA’s certification team evaluated the Robla-Arcade Levee System for compliance with each of the 20 ULDC categories. The evaluations are summarized in the following report subsections, and detailed documentation of the analyses are provided as appendices to this report.

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13 ULDC Category ULDC Category

7.1 Design Water Surface Elevation 7.11 Right-of-Way

7.2 Minimum Top of Levee 7.12
Encroachments (Excluding
Penetrations, Closure Structures, and
Levee Vegetation)

7.3 Soil Sampling, Testing, and Logging 7.13 Penetrations

7.4 Slope Stability for Intermittently
Loaded Levees 7.14 Floodwalls, Retaining Walls, and
Closure Structures

7.5 Underseepage for Intermittently
Loaded Levees 7.15 Animal Burrows

7.6 Frequently Loaded Levees 7.16 Levee Vegetation

7.7 Seismic Vulnerability 7.17 Wind Setup and Wave Runup

7.8 Levee Geometry 7.18 Security

7.9 Interfaces and Transitions 7.19 Sea Level Rise

7.10 Erosion 7.20 Emergency Actions
ULDC 7.1: DESIGN WATER SURFACE ELEVATION
The ULDC DWSE is the 1-in-200 AEP WSE used to design and evaluate levees and floodwalls for the purposes of providing an urban level of flood protection.

The ULDC offers two options for determination of the DWSE: 1) the Federal Emergency Management Agency (FEMA) approach, and 2) the USACE approach. The evaluation for the Robla-Arcade Levee System conforms to the FEMA approach. In accordance with the ULDC, debris loading on bridge piers was included in the hydraulic analysis. The ULDC also requires adjustments for sea level rise and superelevation. Sea level rise was incorporated into the modeling downstream boundary conditions and there are no locations along the Robla-Arcade Levee System subject to superelevation. Climate change is considered optional in the ULDC and was not adjusted for in this modeling. Hydrology and hydraulics modeling were updated in the model based on a new model provided by the Central Valley Hydrology Study (CVHS, 2015). A detailed description of the determination of the DWSE is found in Technical Memorandum, Robla-Arcade Levee System - Determination of the Urban Levee Design Criteria Design Water Surface Elevation, Minimum Top of Levee, and Hydraulic Top of Levee (MBK, 2024a).

An additional elevation required by the ULDC is the hydraulic top of levee (HTOL), which is defined as the lower of the DWSE plus 3 feet or the median 500-year WSE.

The computed DWSEs for the Robla-Arcade Levee System are provided in Appendix C The Robla-Arcade Levee System meets the requirements for ULDC 7.1 for development of the DWSE.

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14 ULDC 7.2: MINIMUM TOP OF LEVEE
The Minimum Top of Levee (MTOL) is the required minimum elevation for the physical top of levee to provide a reasonable assurance of containing the DWSE and is defined as the higher of the DWSE plus 3 feet or the DWSE plus wind setup and wave runup. The determination of the MTOL is described in (MBK, 2024a) and provided in Appendix C.

Wind setup and wave runup were computed by Mead & Hunt (Mead & Hunt, 2024a) and are discussed below in ULDC 7.17. There are no locations along the Robla-Arcade Levee System where the combined wind setup and wave runup is greater than 3 feet; therefore, the MTOL is the DWSE plus 3 feet. Figures 9, 10, and 11 in Technical Memorandum, Robla-Arcade Levee System - Determination of the Urban Levee Design Criteria Design Water Surface Elevation, Minimum Top of Levee, and Hydraulic Top of Levee (MBK, 2024a) provides a profile showing the computed MTOL and actual top of levee profile. The levee exceeds the MTOL for NEMDC East Levee, Arcade Creek North Levee, and Robla Creek South Levee between Station 6000+00 and 6114+00. Between Robla Creek South Levee Station 6114+00 and 6118+20 the MTOL is not met. However, along this levee segment, the DWSE is below the landside toe of the levee (MBK, 2024a). Therefore, an exception is requested based on the channel being incised, which drops the WSE within the channel and keeps the levee dry.

The Robla-Arcade Levee System meets the requirements for ULDC 7.2 for MTOL, by exception.

ULDC 7.3: SOIL SAMPLING, TESTING, AND LOGGING
ULDC 7.3 requires soil sampling, testing, and logging, as per standard procedures prescribed in guidance documents, including the USACE Sacramento District (SPK) Standard Operating Procedure 3 Geotechnical Levee Practice (SOP-3) [USACE, 2022] and DWR Division of Flood Management’s Soil and Rock Logging, Classification, Description and Presentation Manual (DWR, 2009). This includes an evaluation of soil exploration quantity and location as outlined in the SPK SOP-3. Based on this document, explorations for levee evaluation should be obtained at the waterside toe, levee crest, landside toe, and landside field areas performed at a spacing of 1,000 feet for feasibility/tentatively selected plan studies, and at a spacing of 500 to 1,000 feet for design and preconstruction engineering studies. The SPK SOP-3 also recommends a thorough evaluation of existing information, as available, including construction documents, improvements, performance history, existing subsurface information, and regional and local geomorphology. The standard also recommends the use of cone penetrometers (CPTs) and geophysics to supplement borings, where appropriate.

ROBLA CREEK SOUTH LEVEE
The Robla Creek South Levee was evaluated by Kleinfelder. The required quantity and spacing of explorations following current USACE protocols was not met, and an exception is needed for this ULDC topic. The justification for this exception is described in the due diligence report prepared by Kleinfelder provided in Appendix E. In general, additional field observations, mapping, geophysical HEM (helicopterbased electromagnetics surveys), and documentation to understand the construction interaction with the subsurface stratigraphy was performed along the Robla Creek South Levee. This additional documentation, along with as-built plans and construction records are considered sufficient URBAN LEVEL OF FLOOD PROTECTION ENGINEER’S REPORT

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15 documentation to meet this requirement through exception. Improvements in 1995 to 1997 as part of a SAFCA flood control improvement project were observed and tested by Kleinfelder, including observation of key trench excavation to confirm the levee rested on firm, low permeability soils.

Construction records include keyway inspection and observation of earthwork placement and compaction of materials; prior geotechnical explorations performed by USACE and other consultants; geomorphology and geologic map interpretations; as-built documentation for the original levees and improvements, and QC/QA laboratory testing results.

Therefore, the Robla Creek South Levee meets the requirements for ULDC 7.3 Soil Sampling, Testing, and Logging, by exception.

NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE – ARCADE CREEK TO ROBLA CREEK
The NEMDC East Levee between Robla Creek and Arcade Creek was evaluated by Kleinfelder. The required quantity and spacing of explorations following USACE protocols was not met, and an exception is needed for this ULDC topic. The justification for this exception is described in the due diligence report prepared by Kleinfelder which is provided as Appendix E. In general, additional field observations, mapping, geophysical HEM, and documentation to understand the construction interaction with the subsurface stratigraphy was performed along the NEMDC East Levee. This additional documentation, along with as-built plans and construction records are considered sufficient documentation to meet this requirement through exception. Improvements in 1995 to 1997 as part of a SAFCA flood control improvement project were observed and tested by Kleinfelder, including observation of key trench excavation to confirm the levee rested on firm, low permeability soils; prior geotechnical explorations performed by USACE and other consultants; geomorphology and geologic map interpretations; as-built documentation for the original levees and improvements, and QC/QA laboratory testing results.

Therefore, the NEMDC East Levee between Robla Creek and Arcade Creek meets the requirements for ULDC 7.3 Soil Sampling, Testing, and Logging by exception.

ARCADE CREEK NORTH LEVEE
The Arcade Creek North Levee was evaluated by AECOM and Kleinfelder. The required quantity and spacing of explorations, following USACE protocols, was not met and an exception is needed for this ULDC topic. The justification for this exception is described in the due diligence reports prepared by AECOM and Kleinfelder which are provided in Appendices D and E, respectively. AECOM and Kleinfelder reviewed the explorations performed along this levee segment, along with as-builts, construction documentation, surficial geologic mapping and geomorphic assessments, geophysical HEM, resistivity surveys, and previous engineering documents. Improvements in 1995 to 1997 as part of a SAFCA flood control improvement project were observed and tested by Kleinfelder, including observation of key trench excavation to confirm the levee rested on firm, low permeability soils. The recent construction activity included construction of a cutoff wall that involved full time trench logging by AECOM and waterside slope reconstruction. This compilation of data, lack of past performance issue observations, and construction inspection provides justification for this exception.

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16 Therefore, the Arcade Creek North Levee meets the requirements for ULDC 7.3 Soil Sampling, Testing and Logging, by exception.

ULDC 7.4: SLOPE STABILITY FOR INTERMITTENTLY LOADED
LEVEES
ULDC 7.4.1 requires a minimum factor of safety of 1.4 for landside slope stability under steady state seepage conditions, based on the DWSE, for failure surfaces that intersect the levee crest and are greater than a few feet deep in the levee slope. It also requires a minimum factor of safety of 1.2, based on the Hydraulic Top of Levee (HTOL)2, for failure surfaces that intersect the levee crest and are greater than a few feet deep in the levee slope. ULDC 7.4.2 requires a minimum factor of safety of 1.0 to 1.2 for waterside slope stability during rapid drawdown conditions for the DWSE, depending on how long the embankment is saturated, with the higher factor of safety used for events of a longer duration. An intermittently loaded levee is defined as “a levee that does not experience a water surface elevation of one foot or higher above the elevation of the levee toe at least once a day for more than 36 days per year on average.” This system is considered intermittently loaded as discussed under ULDC 7.6 below.

ROBLA CREEK SOUTH LEVEE
Kleinfelder assessed slope stability conditions of the subject levee by reviewing prior slope stability analyses, which met criteria, and comparing them to the DWSE and HTOL water levels. Levee crest profiles and levee cross sections used previously for slope stability analysis are consistent with recent surveys (Psomas, 2024) and reevaluation at critical sections is not necessary. Kleinfelder also compared the DWSE used in prior analysis with the current DWSE and determined that the WSE was equal to or lower than values used in prior evaluations. In addition, based on a review of available construction records, geotechnical data, construction materials, construction quality control and quality assurance testing, historic performance, and the slope stability analysis referenced in the due diligence report prepared by Kleinfelder (Appendix E) the Robla Creek South Levee meets slope stability criteria.

Therefore, the Robla Creek South Levee meets the requirements for ULDC 7.4 Slope Stability for Intermittently Loaded Levees.

NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE – ROBLA CREEK TO ARCADE CREEK
The NEMDC East Levee between Robla Creek and Arcade Creek (NEMDCEL Station 3056+00 to 3192+25) was evaluated by Kleinfelder. Prior engineering analyses performed by Kleinfelder was reviewed to confirm the existing levee configurations meet ULDC and USACE minimum factor of safety requirements for slope stability. These analyses were reviewed to compare the prior evaluated WSE to the revised DWSE prepared for this evaluation (Appendix C). A summary of slope stability analyses is described in the due diligence reports prepared by Kleinfelder (Appendix E). Kleinfelder concluded that the analysis was performed at critical sections and results of the evaluated WSE which is higher than the current DWSE, 2 The hydraulic top of levee is defined by ULDC as the lower of the median 200-year WSE plus 3 feet or the median 500-year WSE. The HTOL was developed using the approach described in ULDC 7.1.

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17 met analysis criteria. These results are summarized in the due diligence reports prepared by Kleinfelder (Appendix E), which provide the condition evaluated, water surface designation, and the calculated slope stability factor of safety.

Therefore, the NEMDC East Levee between Robla Creek and Arcade Creek meets the requirements for ULDC 7.4 Slope Stability for Intermittently Loaded Levees.

ARCADE CREEK NORTH LEVEE
AECOM and Kleinfelder assessed slope stability conditions of the subject levee by reviewing prior slope stability analyses, which met criteria, and comparing them to the DWSE and HTOL water levels. Levee crest profiles and levee cross sections used previously for slope stability analysis are consistent with recent surveys (Psomas, 2024) and reevaluation at critical sections is not necessary. AECOM and Kleinfelder also compared the DWSE used in prior analysis with the current DWSE and determined that the WSE was equal to or lower than values used in prior evaluations. In addition, based on a review of available construction records, geotechnical data, construction materials, construction quality control and quality assurance testing, historic performance, and the slope stability analysis referenced in the due diligence reports prepared by AECOM (Appendix D) and Kleinfelder (Appendix E), the Arcade Creek North Levee meets slope stability criteria.

Therefore, the Arcade Creek North Levee meets the requirements for ULDC 7.4 Slope Stability for Intermittently Loaded Levees.

ULDC 7.5: UNDERSEEPAGE FOR INTERMITTENTLY LOADED
LEVEES
This section describes the levee documentation and general requirements for ULDC 7.5 Underseepage for Intermittently Loaded Levees. An intermittently loaded levee is defined as “a levee that does not experience a water surface elevation of one foot or higher above the elevation of the levee toe at least once a day for more than 36 days per year on average.” This system is considered intermittently loaded as discussed under ULDC 7.6 below.
“Levee underseepage criteria for intermittently loaded levees are as follows:
• The underseepage exit gradient for levees is required to be 0.5 or less at the landside levee toe using a steady-state seepage analysis for a water surface set at the DWSE. For levees with a landside blanket layer with a saturated unit weight less than 112 pounds per cubic foot (pcf), a minimum factor of safety for underseepage of 1.6 is required at the landside levee toe. • The underseepage exit gradient is required to be 0.8 or less at the toe of a seepage berm less than 300 feet wide using steady-state seepage analysis for a water surface set at the DWSE. If the saturated unit weight of the blanket layer is less than 112 pcf, a minimum factor of safety for underseepage of 1.0 is required at the toe of the seepage berm.” • The underseepage exit gradient for levees is required to be 0.6 or less at the landside levee toe using a steady-state seepage analysis for a water surface set at the HTOL. For levees with a landside URBAN LEVEL OF FLOOD PROTECTION ENGINEER’S REPORT

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18 blanket layer with a saturated unit weight less than 112 pounds per cubic foot (pcf), a minimum factor of safety for underseepage of 1.3 is required at the landside levee toe.

ROBLA CREEK SOUTH LEVEE
Kleinfelder assessed seepage conditions of the subject levee by reviewing prior seepage evaluations, which met criteria, and comparing them to DWSE and HTOL water levels. Kleinfelder concluded the analysis was performed at critical sections and met analysis criteria. Levee crest profiles and levee cross sections used previously for seepage analyses are consistent with recent surveys (Psomas, 2024) and reevaluation of critical sections is not necessary. Kleinfelder also compared the DWSE used in prior analysis with the current DWSE and determined that the WSE was equal to or lower than values used in prior evaluations. In addition, based on a review of available construction records, geotechnical data, construction materials, construction quality control and quality assurance testing, historic performance, and the post-construction seepage analyses referenced in the due diligence report prepared by Kleinfelder (Appendix E), the Robla Creek South Levee meets underseepage requirements.

Therefore, the Robla Creek South Levee meets the requirements for ULDC 7.5 Underseepage for Intermittently Loaded Levees.

NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE – ROBLA CREEK TO ARCADE CREEK
The NEMDC East Levee between Robla Creek and Arcade Creek was evaluated by Kleinfelder (NEMDCEL Station 3056+00 to 3192+25). Kleinfelder assessed seepage conditions of the subject levee by reviewing prior seepage evaluations, which met criteria, and comparing them to the DWSE and HTOL water levels.

Kleinfelder concluded the analysis was performed at critical sections and met analysis criteria. Levee crest profiles and levee cross sections used previously for seepage analyses are consistent with recent surveys (Psomas, 2024) and reevaluation of critical sections is not necessary. Kleinfelder also compared the DWSE used in prior analysis with the current DWSE and determined that the WSE was equal to or lower than values used in prior evaluations. In addition, based on a review of available construction records, geotechnical data, construction materials, construction quality control and quality assurance testing, historic performance, and the post-construction seepage analyses referenced in the due diligence report prepared by Kleinfelder (Appendix E), the NEMDC East Levee between Robla Creek and Arcade Creek meets underseepage requirements.

Therefore, the NEMDC East Levee between Robla Creek and Arcade Creek meets the requirements for ULDC 7.5 Underseepage for Intermittently Loaded Levees.

ARCADE CREEK NORTH LEVEE
AECOM and Kleinfelder assessed seepage conditions of the subject levee by reviewing prior seepage evaluations, which met criteria, and comparing them to the DWSE and HTOL water levels and concluded the analysis was performed at critical sections and met analysis criteria. Levee crest profiles and levee cross sections used previously for seepage analyses are consistent with recent surveys (Psomas, 2024) and reevaluation of critical sections is not necessary. In addition, based on a review of available construction records, geotechnical data, construction materials, construction quality control and quality assurance URBAN LEVEL OF FLOOD PROTECTION ENGINEER’S REPORT

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19 testing, historic performance, and the post-construction seepage analyses referenced in the due diligence reports prepared by AECOM (Appendix D) and Kleinfelder (Appendix E), the Arcade Creek North Levee meets underseepage requirements.

Therefore, the Arcade Creek North Levee meets the requirements for ULDC 7.5 Underseepage for Intermittently Loaded Levees.

ULDC 7.6: FREQUENTLY LOADED LEVEES
ULDC 7.6 clarifies that frequently loaded levees are subject to more stringent requirements. Frequently loaded levees are those levees that experience a WSE of 1 foot or higher above the elevation of the landside levee toe at least once a day for more than 36 days per year on average.

As part of the ULE Program, DWR determined that the Robla-Arcade levee system is intermittently loaded (URS, 2015b). The SAFCA certification team reviewed DWR’s conclusion and concurs. ULDC 7.6 requirements for frequently loaded levees is not applicable.

ULDC 7.7: SEISMIC VULNERABILITY
ULDC 7.7 requires an analysis of seismic vulnerability of the levee system for the 200-year return period ground motions. ULDC 7.7.1 indicates that if seismic damage from the 200-year return period ground motion is expected, a post-earthquake remediation plan is required as part of a flood safety plan developed in coordination with pertinent local, State, and Federal agencies.

Seismic vulnerability analyses were performed by Kleinfelder to evaluate liquefaction potential and pseudo static stability. This evaluation is summarized in the 2024 Kleinfelder Seismic Performance Summary Report included as an appendix to the Due Diligence report provided in Appendix E.

This evaluation determined that all levee segments are rated as “Low” Seismic Vulnerability. These findings are consistent with analyses that were performed previously in 2015 (URS, 2015b).

Due to these findings, a post-earthquake remediation plan is not required.

Therefore, the entire Robla-Arcade Levee System meets the requirements for ULDC 7.7 for Seismic Vulnerability.

ULDC 7.8: LEVEE GEOMETRY
ULDC 7.8 requires that for new levees or levees with extensive reconstruction situated along major waterways, a minimum 20-foot-wide crown width for Major Streams (mainstreams) or 12-foot crown width for Minor Streams (tributaries to mainstream) and 3:1 horizontal-to-vertical ratio (H:V) waterside and landside slopes are required. Landside slopes can remain 2H:1V for existing levees where this was the authorized slope configuration, performance has been good, and slope stability and seepage criteria are met. As outlined in the 1953 MOU, the Arcade Creek North Levee, NEMDC East Levee, and Robla Creek South Levee are considered minor stream levees.

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20 ULDC 7.8.1 allows levees wider than the minimum requirement to have steeper slopes if the minimum required dimensions would fit entirely within the actual levee, and if seepage and slope stability criteria are met (for both deep and shallow failure surfaces).

ULDC 7.8.2 requires a patrol road along the crest of the levee for inspection, maintenance, and floodfighting. The patrol road must be designed, constructed, and maintained to provide “all-weather” support of maintenance and patrolling vehicles.

ROBLA CREEK SOUTH LEVEE
The Robla Creek South Levee is classified as minor stream levee. The ULDC requires that minor stream levees have the following geometry (minimum theoretical prism):
• 2H:1V landside slope (allowed as discussed above)
• 12-foot-wide levee crown
• 3H:1V waterside slope
Construction projects have modified the original levee, including geometry corrections. These corrections are consistent with ULDC requirements and as-builts of these projects and recent survey data verify these criteria were met. Psomas obtained recent ground survey data (Psomas, 2024) to compare existing geometry to criteria. Cross sections and a discussion of this review are included in the Due Diligence Report prepared by Kleinfelder (Appendix E). These cross sections confirm the prior as-built cross sections still exist, which indicate the Robla Creek South Levee meets current geometry criteria.

Therefore, the Robla Creek South Levee meets requirements for ULDC 7.8 Levee Geometry.

NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE – ROBLA CREEK TO ARCADE CREEK
The NEMDC East Levee between Robla Creek and Arcade Creek is classified as a minor stream levee. The ULDC requires that minor stream levees have the following geometry (minimum theoretical prism):
• 2H:1V landside slope (allowed as discussed above)
• 12-foot-wide levee crown
• 3H:1V waterside slope
Construction projects have modified the original levee, including geometry corrections. These corrections are consistent with ULDC requirements and as-builts of these projects and recent survey data verify these criteria were met. Psomas obtained recent ground survey data (Psomas, 2024) to compare existing geometry to criteria. Cross sections and a discussion of this review are included in the Due Diligence Report prepared by Kleinfelder (Appendix E). These cross sections confirm the prior as-built cross sections still exist, which indicate the NEMDC East Levee meets current geometry criteria.

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21 Therefore, the NEMDC East Levee between Robla Creek and Arcade Creek meets requirements for ULDC

7.8 Levee Geometry.

ARCADE CREEK NORTH LEVEE
The Arcade Creek North Levee is classified as a minor stream levee. The ULDC requires that minor stream levees have the following geometry (minimum theoretical prism):
• 2H:1V landside slope (allowed as discussed above)
• 12-foot-wide levee crown
• 3H:1V waterside slope
Construction projects have modified the original levee, including geometry corrections. These corrections are consistent with ULDC requirements and as-builts of these projects and recent survey data verify these criteria were met. Psomas obtained recent ground survey data (Psomas, 2024) to compare existing geometry to criteria. Cross sections and a discussion of this review are included in the Due Diligence Reports prepared by AECOM and Kleinfelder (Appendices D and E, respectively). These cross sections confirm the prior as-built cross sections still exist.

Therefore, the Arcade Creek North Levee meets requirements for ULDC 7.8 Levee Geometry.

ULDC 7.9: INTERFACES AND TRANSITIONS
This section describes the levee documentation and general requirements for ULDC 7.9 Interfaces and Transitions.
“The civil engineer must consider, evaluate, and explicitly design for interfaces and transitions between different types of levee sections and features along a levee system. Appropriate overlaps, transitions, and connections between features must be evaluated and designed to ensure that the levee system functions holistically, such that no levee reach is more susceptible to problems than an adjacent reach due to gaps in features, loading/demand concentrations, or other three-dimensional effects. Such interfaces, transitions, and connections commonly occur at the ends of seepage berms, seepage cutoff walls, revetments, and floodwalls.”
ULDC 7.9 highlights the need to ensure that the levee system functions holistically, such that no levee reach is more susceptible to problems than an adjacent reach, due to gaps in features, loading/demand concentrations, or other three-dimensional effects when designing interfaces, transitions, and connections that commonly occur at the ends of seepage berms, seepage cutoff walls, and revetments.

Boundary conditions at each of the intersections of the levee segments were evaluated to consider the most critical loading scenario with respect to underseepage and stability. These evaluations were performed by AECOM and Kleinfelder, with conclusions provided in the individual due diligence reports.

Evaluation of structures discussed in this section are included under ULDC 7.14 and were evaluated by Mead & Hunt.

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22 A summary of the transitions and interfaces present in this levee system are outlined below.

ROBLA CREEK SOUTH LEVEE (RCSL)
A summary of the interface and transitions reviewed along the Robla Creek South Levee is provided below. Additional documentation can be found in the due diligence report prepared by Kleinfelder provided in Appendix E.
1) RCSL Station 6003+00: Transition of RCSL embankment to UPRR stop log structure which includes a concrete retaining structure on either side of the tracks and below the ballast section. This transition was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025).
2) RCSL Station 6012+00: Interface of detention basin to RCSL embankment. Detention basin includes an unlined ditch at the landside toe extending approximately 10 feet below grade, located approximately 70 feet from the levee toe. This interface was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025). 3) RCSL Station 6031+00 to 6032+00: Interface of City Pump Station No. 140 to RCSL embankment.

Pump Station includes 3 pipes crossing through the levee and retaining wall at the landside toe.

This interface was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025).
4) RCSL Station 6078+00 to 6079+00: Interface of Rio Linda Boulevard Bridge and RCSL embankment. This bridge was constructed in 1988. This interface was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025). 5) RCSL Station 6090+50: Interface of Sacramento Northern Bike Trail to RCSL embankment. This interface was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025).
6) RCSL Station 6118+20: Transition of RCSL embankment to high ground at Dry Creek Road. This interface was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025).

These overlaps and transitions are considered appropriate as discussed above for the Robla Creek South Levee.

Therefore, the Robla Creek South Levee meets requirements for ULDC 7.9 Interfaces and Transitions.

NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE – ROBLA CREEK TO ARCADE CREEK
A summary of the interfaces and transitions reviewed along the NEMDC East Levee between Robla Creek and Arcade Creek is provided below. Additional documentation can be found in the due diligence reports prepared by Kleinfelder provided in Appendix E.

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23 1) NEMDCEL Station 3056+00 to 3192+25: Interface of NEMDCEL embankment to UPRR embankment along the entire length of NEMDC. The UPRR embankment was constructed prior to levee construction. This transition was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025).
2) NEMDCEL Station 3057+75: Transition of newly constructed drained stability berm to existing levee. A berm was constructed at the intersection of the NEMDCEL and Arcade Creek North Levee (ACNL) in 2025 to remediate seepage exiting the UPRR embankment toe. The transition from the berm to the levee was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025).
3) NEMDCEL Station 3090+00 to 3091+00: Interface of San Juan Road/Silver Eagle Road Bridge Foundation and NEMDCEL embankment. CVFPB provided inspection during bridge construction in 1984 to 1985. This interface was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025).
4) NEMDCEL Station 3132+00 to 3134+00: Interface of Interstate 80 Bridge Foundation and NEMDCEL embankment. CVFPB provided inspection during original bridge construction in 1968.

The bridge was widened in 2010. This interface was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025).
5) NEMDCEL Station 3313+50: Interface of City Sump 157 to NEMDCEL embankment. The Pump Stations include a total of three pipes that pass through the levee and four box culverts that pass through the levee foundation. This interface was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025).
6) NEMDCEL Station 3184+00 to 3185+00: Interface of Del Paso/Main Avenue Bridge to NEMDCEL embankment. This interface was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025).

These overlaps and transitions are considered appropriate as discussed above for the NEMDC East Levee between Robla Creek and Arcade Creek.

Therefore, the NEMDC East Levee between Robla Creek and Arcade Creek meets requirements for ULDC

7.9 Interfaces and Transitions.

ARCADE CREEK NORTH LEVEE
A summary of the interface and transitions reviewed along the Arcade Creek North Levee are provided below. Additional documentation can be found in the due diligence reports prepared by AECOM and Kleinfelder provided in Appendices D and E, respectively. 1) ACNL Station 5000+40: Transition of ACNL embankment to UPRR stop log structure which includes a concrete retaining structure on either side of the tracks and below the ballast section.

This transition was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025).

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24 2) ACNL Station 5001+50: Transition of newly constructed drained stability berm to existing levee. A berm was constructed at the intersection of the NEMDCEL and ACNL in 2025 to remediate seepage exiting the UPRR embankment toe. The transition from the berm to the levee was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025). 3) ACNL Station 5023+00 to 5031+40: Transition of ACNL levee embankment and shallow landside ditch to landside toe relief wells and deeper ditch. Twelve relief wells are present at the landside levee toe between ARNL Station 5023+00 and 5031+40. Relief wells discharge into a lined ditch which conveys water to a pump station upstream of the wells. The transition from the upstream and downstream ACNL embankment to the wells was reviewed and meets the geotechnical requirements of this criteria (Kleinfelder, 2025 and AECOM, 2024). 4) ACNL Station 5038+00 to 5075+00: Transitions between cutoff wall types and location occurred within this levee segment. The cutoff wall tied into the existing embankment at Station 5039+50.

The wall type transitions between an SB and SCCB wall between Stations 5064+50 and 5071+00.

The SB cutoff wall transitioned from the levee crest to the waterside toe between Station 5071+47 and 5076+50. A culvert crosses through the levee foundation near Station 5065+35, where the cutoff wall stepped up and over the pipe. These transitions from wall to levee embankment, and between wall variations was reviewed and meets the geotechnical requirements of this criteria (AECOM, 2024).
5) ACNL Station 5070+40 to 5111+40: Transitions of floodwall located along the levee crest. The levee embankment transitions to floodwall near Stations 5070+40, 5071+47, and between Stations 5107+90 and 5111+40. This transition from floodwall to levee embankment was reviewed and meets the geotechnical requirements of this criteria (AECOM, 2024). 6) ACNL Station 5100+00: Transition of cutoff wall to levee embankment. This transition from wall to levee embankment was reviewed and meets the geotechnical requirements of this criteria (AECOM, 2024).
7) ACNL Station 5112+43: Transition of floodwall to high ground at Marysville Boulevard interface.

The interface includes levee embankment against concrete retaining wall at the bridge abutment.

This transition/interface from levee embankment to wall was reviewed and meets the geotechnical requirements of this criteria (AECOM, 2024).

These overlaps and transitions are considered appropriate as discussed above for the Arcade Creek North Levee.

Therefore, the Arcade Creek North Levee meets requirements for ULDC 7.9 Interfaces and Transitions.

ULDC 7.10: EROSION
Levees that pose an immediate erosional breaching hazard during either a flood or normal flow conditions need to be repaired to ensure levee integrity is maintained. Similarly, levees that are likely to be significantly damaged during either a flood or normal flow condition should be protected with appropriate revetment. Erosion hazards are evaluated for the following conditions: 1) high-velocity flows coupled with erosive levee materials and/or poor hydraulic conditions; 2) large waves developed by wind URBAN LEVEL OF FLOOD PROTECTION ENGINEER’S REPORT

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25 over large, open bodies of water; and 3) boat wakes. MBK performed an evaluation of the levees and considered potential factors such as existing erosion, geomorphologic trends, streamflow velocity and inundation depths during high-water, wind-wave shear stress, levee materials, encroachments and anomalies, bank protection, and vegetation.

The Local Maintaining Agency (LMA) performs routine inspections along the waterside bank of RoblaArcade levee system. The levee embankment has performed against erosion as intended during all highwater events since its construction in 1996. MBK performed erosion evaluations of the Robla-Arcade Levee System based on site inspections and analysis of results from hydraulic modeling. These results were documented in an Erosion Report (MBK, 2024c). MBK Engineers performed a levee inspection to observe multiple topics related to Operation and Maintenance, including erosion on July 10, 2024 (MBK, 2024b). MBK evaluated the erosion conditions of the levees in the Robla-Arcade Levee System and the report is referred herein as “SAFCA Levee Certification, Robla-Arcade Levee System Erosion Report, August 2024” (MBK, 2024c).

ROBLA CREEK SOUTH LEVEE
Robla Creek is comprised of flows emanating from the foothill areas and receives flow from Magpie Creek.

Review of the hydraulic modeling shows the velocity for the 200-year flow along the left waterside slope of the Robla Creek South Levee varies between 5.8 fps at the upstream end at Dry Creek Road and less than 1 fps near the confluence with NEMDC. The calculated velocities are within the permissible range for clay embankment soil types and vegetated channel conditions, which is up to 6 fps (USACE EM 1110-2- 1601). The low fetch length for wind setup and wave runup reduces the likelihood of significant erosion occurring along the waterside slope during high-water events. Non-existent boating activity along Robla Creek further diminishes the likelihood of erosion from potentially occurring from boat wakes. Along the upper reaches of the levee, where the Robla Creek is nearest to the levee, the adjacent levee bank consists of erosion resistant materials and adequate vegetative cover which have prevented erosion from occurring during high-water events.

The Robla Creek South Levee meets the requirements for ULDC 7.10 for Erosion.

NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE – ROBLA CREEK TO ARCADE CREEK
The NEMDC conveys flows from several minor tributaries originating from foothill areas. However, a majority of the NEMDC experiences backwater conditions when stages in the American River increase. As a result, flood velocities along the NEMDC East Levee are below the threshold of concern and the maximum velocity was determined to be under 3.5 fps for the modeled event. The channel along NEMDC is very narrow and significant waves are not expected to develop. Non-existent boating activity within NEMDC further diminishes the likelihood of erosion from potentially occurring from boat wakes. The calculated water velocities are equal or less than the maximum permissible velocities for either bare-earth or vegetated flow channels, which is 6 to 7 fps (USACE EM 1110-2-1601). The embankment material, primarily silty clay, has a relatively low susceptibility to erosion. The condition of the existing levee is free of significant erosion. There are no major meanders, constrictions, or a fetch length for wind setup and wave runup within the NEMDC that would cause concerns for erosion to potentially occur. Recent encampments have collected large amounts of debris within the channel which collect and cause URBAN LEVEL OF FLOOD PROTECTION ENGINEER’S REPORT

ROBLA-ARCADE LEVEE SYSTEM
26 blockage in the channel. It is unclear what impact this may have long term on the direction of flow of water and contribution to erosive conditions. ARFCD has an active program to monitor, clear out encampments, and repair damaged levee segments as needed.

The NEMDC East Levee between Robla Creek and Arcade Creek meets the requirements for ULDC 7.10 for Erosion.

ARCADE CREEK NORTH LEVEE
Arcade Creek conveys flows from open water channels in the upstream foothill areas through the leveed portion from Marysville Blvd to its confluence with NEMDC. The downstream portion of the Arcade Creek is directly influenced by the stage along NEMDC which experiences backwater conditions as stages in the American River increase. The maximum velocity was determined to be up to 3.7 fps for the modeled event and are less than the maximum permissible velocities for either bare-earth or vegetated flow channels, which is 6 to 7 fps (USACE EM 1110-2-1601). The embankment material, primarily silty clay, has a relatively low susceptibility to erosion. As a result, flood velocities along the Arcade Creek North Levee are generally below the threshold of concern for erosion to occur during high-water conditions. The floodway for Arcade Creek along the leveed portion is very narrow and significant waves from wind setup are not expected to develop. Non-existent boating activity within Arcade Creek further diminishes the likelihood of erosion from potentially occurring from boat wakes. There are no major meanders, constrictions, or confluences in Arcade Creek. Recent encampments have collected large amounts of debris within the channel which collect and cause blockage in the channel. It is unclear what impact this may have long term on the direction of flow of water and contribution to erosive conditions. ARFCD has an active program to monitor, clear out encampments, and repair damaged levee segments as needed.

The Arcade Creek North Levee meets the requirements for ULDC 7.10 for Erosion.

ULDC 7.11: RIGHT-OF-WAY
As per ULDC, right-of-way criteria for levees and floodwalls in urban and urbanizing areas need to allow adequate room for maintenance, inspection, patrolling during high-water, and flood-fighting; allow additional room to expand facilities in the future; and prohibit excavations and land modifications that would endanger the integrity of the levee or floodwall.

Specifically, the ULDC requires fee title or an easement for the entire levee prism extending to a minimum of 20 feet beyond the landside toe of the flood protection system for access and inspection. ULDC also allows for two alternatives where adjacent lands are developed: 1) rights for a minimum 10-foot-wide landside clear zone, or 2) a 20-foot-wide landside visibility zone. Furthermore, waterward of the levee prism, where there is sufficient area to do so without resulting in the loss of sensitive riparian habitat, consideration should be given to acquiring a 15-foot-wide zone.

In addition to the minimums required by the ULDC for access and inspection, the ULDC recommends acquiring right-of-way that has a width equal to at least four times the levee height or 50 feet, whichever is greater, on the landside of the 20-foot clear zone for longer-term flood protection.

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27 Lastly, the ULDC recommends that the city or county adopt restrictions on excavations within 200 to 400 feet, depending on the levee height.

As part of its levee improvement program, SAFCA has worked to acquire land associated with the levee embankment, Operation & Maintenance (O&M) corridors, and/or other flood control features.

In general, future waterside development is not allowed and landside development within 50 feet of the levee is limited per a local grading ordinance which also restricts construction of swimming pools. In 2013, the City adopted a grading ordinance (Ordinance 2013-0020 Section 1; Ordinance 2013-0007 Section 1) outlined in Title 17, Division II, Article III (17.200.340 F zone - Setbacks) that restricts any grading activity within 50 feet of the levee. Sacramento County has adopted a similar ordinance found in Sacramento County Zoning Code Section 4.7.3 Development Standards, specifically for Lots Protected by Levees (Section 4.7.3.A) which restricts construction of structures to no closer than 25 feet from the landside levee toe. Where swimming pools are located in close proximity to the landside levee toe, the geotechnical engineering review has assessed the condition, and a discussion is provided in the supporting documentation included in Appendices D and/or E. Additionally, DWR reviews the presence of pools at the landside levee toe as part of the fall and spring inspections.

The entire Robla-Arcade Levee System meets ULDC for right-of-way. However, there are some portions of the levees where 20-foot fee title right-of-way landward of the levee was not possible, and in these areas, right-of-way is met through either a reduced landside right-of-way in fee or easement and/or the presence of a 20 foot “free and clear” zone. Figures provided in Appendix G show the right-of-way acquired in fee-title and easement right-of-way for the levees. Despite the levee system meeting ULDC for right-of-way, the goal is to acquire long-term rights (i.e., fee-title or easement) in locations where there is not currently 20-feet at the landside toe. These locations are identified in the recommended Robla-Arcade levee system Right-of-Way Plan in Appendix I. The land use agency will need to adopt this plan or revise based on their planning needs and create a Right-of-Way Implementation Plan. In 2013, the City of Sacramento adopted a grading ordinance (Ordinance 2013-0020 Section 1; Ordinance 2013-0007 Section 1) outlined in Title 17, Division II, Article III (17.200.340 F zone - Setbacks) that restricts any grading activity within 50 feet of the levee.

ROBLA CREEK SOUTH LEVEE
ARFCD and SAFCA do not presently own or have easement to all the lands encompassing the levee embankment, or the area 10 feet landward of the landside toe. Because existing rights and access meet the intent of the ULDC, portions of the Robla Creek South Levee meet ULDC 7.11 for right-of-way.

However, there are some portions where a 10-foot access zone or 20-foot visibility zone is not present, and therefore, those portions of the levee do not meet ULDC 7.11 for right-of-way. Where fee or easement is not present for the 20-foot landside corridor, and either a reduced landside right-of-way corridor and/or 20 foot “free and clear” zone are not present, as shown on figures provided in Appendix G, a Right of Way Plan has been prepared and is provided in Appendix I. The figures from this Plan illustrate the existing right of way. The “free and clear” zone allows visibility, but the goal is to acquire long-term rights (i.e., fee-title or easement) in locations where there is not currently 20-feet at the landside toe. These locations are identified in the Robla-Arcade Right-of-Way Plan included in Appendix I.

Therefore, because full 20-feet is not present in fee-title or easement, the levee system meets ULDC for right-of-way by exception through implementation of the prepared Right-of-Way Plan.

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28 The Robla Creek South Levee meets the requirements for ULDC 7.11 Right-Of-Way, by exception.

NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE – ROBLA CREEK TO ARCADE CREEK
The NEMDC East Levee and O&M corridors are located within lands owned by City of Sacramento, County of Sacramento, Reclamation District 1000, Western Pacific Railroad Co., Union Pacific Railroad Co., ARFCD, and private owners. Where fee or easement is not present for the 20-foot landside corridor, either a reduced landside right-of-way corridor and/or 20 foot “free and clear” zone are present, as shown on figures provided in Appendix G, a Right of Way Plan has been prepared and is provided in Appendix I. The figures from this Plan illustrate the existing right of way. The “free and clear” zone allows visibility, but the goal is to acquire long-term rights (i.e., fee-title or easement) in locations where there is not currently 20- feet at the landside toe. These locations are identified in the Robla-Arcade Right-of-Way Plan included in Appendix I. Therefore, because full 20-feet is not present in fee-title or easement, the levee system meets ULDC for right-of-way by exception through implementation of the prepared Right-of-Way Plan.

The NEMDC East Levee between Robla Creek and Arcade Creek meets the requirements for ULDC 7.11 Right-Of-Way, by exception.

ARCADE CREEK NORTH LEVEE
ARFCD and SAFCA do not presently own or have easement to all the lands encompassing the levee embankment, or the area 10 feet landward of the landside toe. This is especially true upstream of Rio Linda Boulevard where very little to no landside toe access is present due to private properties located very close to the landside toe. Downstream of Rio Linda Boulevard, a landside toe access road is present within property owned by City of Sacramento, Sacramento San Joaquin Drainage District, and SAFCA.

Because existing rights and access meet the intent of the ULDC, portions of the Arcade Creek North Levee meet ULDC 7.11 for right-of-way. However, there are some portions where a 10-foot access zone or 20- foot visibility zone is not present, and therefore, those portions of the levee do not meet ULDC 7.11 for right-of-way. Where fee or easement is not present for the 20-foot landside corridor, and either a reduced landside right-of-way corridor and/or 20 foot “free and clear” zone are not present, as shown on figures provided in Appendix G, a Right of Way Plan has been prepared and is provided in Appendix I. The figures from this Plan illustrate the existing right of way. The “free and clear” zone allows visibility, but the goal is to acquire long-term rights (i.e., fee-title or easement) in locations where there is not currently 20-feet at the landside toe. These locations are identified in the Robla-Arcade Right-of-Way Plan included in Appendix I. Therefore, because full 20-feet is not present in fee-title or easement, the levee system meets ULDC for right-of-way by exception through implementation of the prepared Right-of-Way Plan.

The Arcade Creek North Levee meets the requirements for ULDC 7.11 Right-Of-Way, by exception.

ULDC 7.12: ENCROACHMENTS
ULDC 7.12 requires an assessment of each existing encroachment, permitted or not, to determine the encroachment’s impact on the reliability of levee performance. The evaluation of encroachments URBAN LEVEL OF FLOOD PROTECTION ENGINEER’S REPORT

ROBLA-ARCADE LEVEE SYSTEM
29 considers the following: age, type, condition, performance history, impacts on the levee structural integrity, impacts on the hydraulic effect of the channel, and impacts on the O&M of the levee.

A summary of Encroachments along with the methodology used, which follows USACE, ULDC, and CVFPB guidelines is included in Appendix H (Mead & Hunt, 2024c). Additionally, MBK Engineers performed a site visit to observe general conditions related to Operation and Maintenance, including encroachments, on Jul 10, 2024. Observations from this visit are summarized in a letter provided in Appendix F (MBK, 2024b) and all observed encroachments were consistent with prior evaluations with none being considered highrisk.

There are 119 encroachments summarized in Appendix H. None of these pose a risk to levee integrity or reliability of the levee to perform under the full loading condition up to the HTOL. No high-risk encroachments were identified within this levee system. It should be noted that the high number of encroachments is due to adjacent urban development in near proximity to the landside levee toe. A framework for an encroachment remediation plan is included in Appendix I to address the low and moderate risk items identified by being non-compliant and non-permitted, as required by ULDC. The land use agency will need to use this framework to create and adopt an encroachment remediation plan.

Therefore, the Robla-Arcade Levee System meets the requirements for ULDC 7.12 Encroachments.

ULDC 7.13: PENETRATIONS
ULDC 7.13 requires a hazard assessment of each existing penetration, permitted or not, to determine the penetration’s impact on the reliability of levee performance. If penetrations are considered high-hazard, additional evaluation and action are required. For other existing penetrations that are not considered to be high-hazard, but have not been permitted, the City or County is required to have a remediation plan in place, or reference such a plan, for the entire length of levee that the finding is to cover.

A summary of Penetrations along with the methodology used is included in Appendix H (Mead & Hunt, 2024b).

There are 50 penetrations summarized in Appendix H, which include 16 gravity drain penetrations. These gravity drain penetrations all have compliant closure structures. A few of these require an exception due to structural evaluation (1 penetration), age of pipes (12 penetrations), and permits not found (4 penetrations). In addition, up to 46 penetrations are being tracked as requiring submittal of inspection documentation, although many of these penetrations are reported as having recent inspections. None of these pose a risk to levee integrity or reliability of the levee to perform under the full loading condition up to the HTOL. No high-hazard penetrations were identified within this levee system. A framework for a penetration remediation plan is included in Appendix I to address the penetration identified above, as required by ULDC. The land use agency will need to use this framework to create and adopt a penetration remediation implementation plan.

Therefore, the Robla-Arcade Levee System meets the requirements for ULDC 7.13 Penetrations through exception.

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30 ULDC 7.14: FLOODWALLS, RETAINING WALLS, AND CLOSURE

STRUCTURES
This section describes the levee documentation and general requirements for ULDC 7.14 Floodwalls, Retaining Walls, and Closure Structures.
“Current USACE design guidance for special features such as floodwalls, retaining walls, and closure structures is to be followed. This information is included in EM 1110-2-1913, EM 1110-2-2502, EC 1110-2-6067, and ETL 1110-2-571. Because design considerations for floodwalls and closure structures are still evolving since the 2005 New Orleans flood, caution should be used when designing and assessing these structures. All global slope stability and embankment throughseepage and underseepage safety criteria requirements are applicable for floodwalls, retaining walls, and closure structures on levees.

For closure structures, the civil engineer needs to provide the following information: maintaining entity, levee mile, Global Positioning System coordinates, Board permit number (if applicable), structure details, length of time to close structure, location and type of materials for closure, structure dimensions, age, and performance history.

Closure structures need to be tested at least once a year before the flood season so that crews responsible for implementing the structures are familiar with their operation and to provide assurance that all parts are present and in working order.”

ROBLA CREEK SOUTH LEVEE
Floodwalls are located at the following locations (Mead & Hunt, 2024c and Kleinfelder, 2025):
• Upstream and downstream of Rio Linda Boulevard Bridge (Station 6079+00) Retaining walls are located at the following locations (Mead & Hunt, 2024c and Kleinfelder, 2025):
• At City Sump 140 (Station 6032+00)
Closure structures are located at the following locations (Mead & Hunt, 2024c and Kleinfelder, 2025):
• UPRR crossing stoplog structure (Station 6000+00)
A structural review of the floodwall and retaining walls was performed by Mead & Hunt (2024b) and they were found to be well maintained and in a serviceable condition for their intended use. These features are discussed as part of ULDC 7.14 Floodwall, Retaining Walls, and Closure Structures, provided by Mead & Hunt (2024b).

A structural review of this closure structure was performed by Mead & Hunt (2024b) and concluded it is in good working order and there are no anticipated impacts to the reliability of the levee performance under the HTOL loading condition. However, the operation frequency for activating the UPRR stoplog structures is currently being performed at 5-year increments in order to minimize impacts to UPRR. The ULDC criteria states that closure structures need to be tested at least once a year before each flood season to URBAN LEVEL OF FLOOD PROTECTION ENGINEER’S REPORT

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31 ensure the responsible parties are familiar with the operation and material required for proper implementation. Upon review of the City of Sacramento Emergency Response Plan, prior installation/activation reports, and inventoried items, an exception is requested to extend the testing period of 5 years maximum. The City shall continue to perform annual reviews of materials, procedures, and inspections. Additionally, the prior trial closures have been performed without incident. Additional documentation for this exception may be found in Appendix H (Mead & Hunt, 2024c).

Therefore, these structures on the Robla Creek South Levee meet the requirements for ULDC 7.14 Floodwalls, Retaining Walls, and Closure Structures through exception.

NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE – ROBLA CREEK TO ARCADE CREEK
Retaining walls are located at the following locations (Mead & Hunt, 2024c and Kleinfelder, 2025):
• 3 retaining walls downstream of Interstate 80 adjacent to City Sump 157 Outfall (Station 3131+00 to 3132+00)
There are no closure structures or floodwalls along the NEMDC East Levee between Robla Creek and Arcade Creek.

There are retaining walls on the waterside slope of the levee near Magpie Creek Diversion Canal for the City’s Sump 157 outfall structure. A structural review of the retaining walls was performed by Mead & Hunt (2024b) and they were found to be well maintained and in a serviceable condition for their intended use. These features are discussed as part of ULDC 7.14 Floodwall, Retaining Walls, and Closure Structures, provided by Mead & Hunt (2024b).

Therefore, these structures on the NEMDC East Levee between Robla Creek and Arcade Creek meet the requirements for ULDC 7.14 Floodwalls, Retaining Walls, and Closure Structures.

ARCADE CREEK NORTH LEVEE
Closure structures are located at the following locations (Mead & Hunt, 2024c and Kleinfelder, 2025):
• UPRR crossing stoplog structure (Station 5000+75)
Floodwalls are located at the following locations (Mead & Hunt, 2024c and AECOM, 2024):
• Upstream and downstream of Rio Linda Boulevard (Station 5070+00) • Station 5074+50 to 5106+00
• Station 5107+90 to 5111+20
Retaining walls are located at the following locations (Mead & Hunt, 2024c and AECOM, 2024):
• Sump 158 (Station 5032+00)
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32 • Residential retaining wall – landside toe (Station 5081+00) There are floodwalls on the levee crest, and retaining walls on the levee near Rio Linda Boulevard and on the landside of the levee at the City’s Sump 158. A structural review of the floodwalls and retaining walls was performed by Mead & Hunt (2024b) and they were found to be well maintained and in a serviceable condition for their intended use. These features are discussed as part of ULDC 7.14 Floodwall, Retaining Walls, and Closure Structures, provided by Mead & Hunt (2024b).

Additionally, Mead & Hunt (2024b) evaluated the structural adequacy of the UPRR closure structure and concluded it is in good working order and there are no anticipated impacts to the reliability of the levee performance under the HTOL loading condition. However, the operation frequency for activating the UPRR stoplog structures is currently being performed at 5-year increments in order to minimize impacts to UPRR. The ULDC criteria states that closure structures need to be tested at least once a year before each flood season to ensure the responsible parties are familiar with the operation and material required for proper implementation. Upon review of the City of Sacramento Emergency Response Plan, prior installation/activation reports, and inventoried items, an exception is requested to extend the testing period of 5 years maximum. The City shall continue to perform annual reviews of materials, procedures, and inspections. Additionally, the prior trial closures have been performed without incident. Additional documentation for this exception may be found in Appendix H (Mead & Hunt, 2024c).

Therefore, these structures on the Arcade Creek North Levee meet the requirements for ULDC 7.14 Floodwalls, Retaining Walls, and Closure Structures through exception.

ULDC 7.15: ANIMAL BURROWS
Borrowing animals can present a significant threat to levee integrity and, therefore, proactive animal control and damage repair are required as part of levee maintenance.

ARFCD follows a rodent control and abatement program (ARFCD, 2017) to maintain constant observation and deterrence of burrowing animals which are present in the Robla-Arcade levee system. The rodent control and abatement program tracks active burrows as well as the monthly abatement activity. ARFCD is vigilant in inspecting for burrowing animals and reacting quickly to repair any damage to the levees. MBK Engineers performed a site visit to observe general conditions related to Operation and Maintenance, including animal burrows, on July 10, 2024. Observations from this visit are summarized in a letter provided in Appendix F (MBK, 2024b) and no indications of burrowing rodent activity were observed in that inspection. Additionally, the USACE Routine Inspection Report (USACE, 2010) provided a review of animal control and rated the system Minimally Acceptable (M). We understand a more recent Routine Inspection was performed, but the report has not been finalized for circulation at the time of publication of this report.

The rodent control and abatement program tracks active burrows as well as the monthly abatement activity; therefore, the entire Robla-Arcade Levee System meets the requirements for ULDC 7.15 Animal Burrows.

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33 ULDC 7.16: LEVEE VEGETATION
ULDC 7.16.1 requires an engineering inspection and evaluation to identify trees and other woody vegetation on the levee and within 15 feet of the levee toe that pose an unacceptable threat to the integrity of the levee. Those posing an unacceptable threat are to be removed; those not posing an unacceptable threat need not be removed. Non-hazardous vegetation is allowed to remain because they do not pose an unacceptable threat but must be trimmed and thinned for access and visibility. The USACE Periodic Inspection Report (USACE, 2010) provided a review of unwanted vegetation growth and rated the system Unacceptable (U) along Robla Creek South Levee NEMDC East Levee, and Arcade Creek North Levee. We understand a more recent Routine Inspection was performed, but the report has not been finalized for circulation at the time of publication of this report. Conversations with ARFCD indicate they have worked diligently to remove and address the unacceptable vegetation identified in the 2010 USACE inspection and expect a higher rating to be published in the upcoming inspection report. This information is consistent with observations from MBK Engineers site visit on July 10, 2024, to view general conditions related to Operation and Maintenance, including vegetation. Observations from this visit are summarized in a letter provided in Appendix F (MBK, 2024b). Some woody vegetation is present in the upstream segment of Arcade Creek North Levee; however, this is considered acceptable as the trees are randomly spaced and do not affect visibility and/or flood fighting.

Therefore, the entire Robla-Arcade Levee System meets the requirements for ULDC 7.16 Levee Vegetation.

ULDC 7.17: WIND SETUP AND WAVE RUNUP
ULDC 7.17 requires a wind-wave analysis. The wind setup and wave runup distances must be computed, and when added to the median 200-year still WSE the resultant shall be no more than the MTOL.

Additionally, wind setup and wave runup must also be considered for analysis of erosion and overtopping impacts.

The formation and magnitude of wind-generated waves against shoreline structures is controlled by the physical conditions present on and near the shore such as slope and roughness of the structure, wind speed, and distance over which wind blows (fetch length). The Wind Wave Analysis determined the wind setup and the runup for the 2 percent exceedance wave (wave runup which is exceeded by 2 percent of waves on average). These analyses were performed at the location on the levees expected to generate the largest wind setup and wave runup.

ROBLA CREEK SOUTH LEVEE
The Robla Creek South Levee was evaluated for wind setup and wave runup with expected ranges of approximately 1.7 to 2.3 feet (Mead & Hunt, 2024a). There is more than 3 feet of freeboard available along this levee.

The wind-wave analysis for the Robla Creek South Levee meets the requirements for ULDC 7.17 Wind Setup and Wave Runup.

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34 NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE – ROBLA CREEK TO ARCADE CREEK
The NEMDC East Levee between Robla Creek and Arcade Creek was evaluated for wind setup and wave runup of approximately 1.7 feet (Mead & Hunt, 2024a). There is more than 3 feet of freeboard available along this levee.

The wind-wave analysis for the NEMDC East Levee between Robla Creek and Arcade Creek meets the requirements for ULDC 7.17 Wind Setup and Wave Runup.

ARCADE CREEK NORTH LEVEE
The Arcade Creek North Levee was evaluated for wind setup and wave runup with expected ranges of approximately 0.9 to 1.4 feet (Mead & Hunt, 2024a). There is more than 3 feet of freeboard available along this levee.

The wind-wave analysis for the Arcade Creek North Levee meets the requirements for ULDC 7.17 Wind Setup and Wave Runup.

ULDC 7.18: SECURITY
ULDC 7.18 requires a security plan to protect urban and urbanizing area levee systems from acts of terrorism and other malicious or negligent acts. The security plan is to identify security personnel, responsibilities, resources, and measures. In developing the security plan, the agency/agencies responsible for levee maintenance must consider and prioritize vulnerabilities and employ an array of security measures from four basic categories to address vulnerabilities: networked detection (criterion 7.18.1); deterrence (criterion 7.18.2); physical security (criterion 7.18.3); and intrusion interdiction (criterion 7.18.4) during high-threat periods.

American River Flood Control District utilizes a Security Plan (ARFCD, 2024) in addition to a Flood Safety Plan and an Emergency Action Plan. The Security Plan describes security personnel, their responsibilities, the resources available to cope with various emergencies, and measures applicable to each type of emergency or security threat. This plan is closely coordinated with the City of Sacramento Police Department to help prevent unauthorized access, and to remove and arrest those who are observed in vandalizing the levees and security measures. It is also closely coordinated with the local firefighting agency to assist in addressing the several instances of fires which occur in the dry valley conditions during the summer. Locked gates, security fences, signage, advanced alarm systems, and CCTV systems, armed security if necessary, and outlined patrol frequency are also outlined in the Security Plan. The levee system specific security plan is provided in Appendix I.

Therefore, the Robla-Arcade Levee System has adequate plans and features to address the security of the levee system and meets the requirements for ULDC 7.18 Security.

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35 ULDC 7.19: SEA LEVEL RISE
ULDC 7.19 requires that the effects of sea level rise be estimated and addressed for the duration during which a ULOP Criteria Finding may be valid. The sea level rise projection estimated by the State of California Department of Water Resources (DWR) in the 2022 Central Valley Flood Protection Plan (CVFPP) Update (DWR, 2022), which was based on the State of California Sea-Level Rise Guidance 2018 Update (OPC, 2018), was used for the analysis.

The 2022 Central Valley Flood Protection Plan (CVFPP) (DWR, 2022) used a 50-year sea level rise projection of 3.68 feet at San Francisco. DWR computed the effects of this sea level rise throughout the Sacramento-San Joaquin Delta with the RMA Bay-Delta model. Stage hydrographs computed by the RMA Bay-Delta model were used as downstream boundaries in the ULDC hydraulic analysis. The duration of the ULOP Finding is 20-years, therefore the use of a 50-year sea level rise projection is a conservative application. The hydraulic modeling shows that the assumed sea level rise has no effect on the DWSE for the Robla-Arcade Levee System.

The Robla-Arcade Levee System meets the requirements for ULDC 7.19 Sea Level Rise.

ULDC 7.20: EMERGENCY ACTIONS AND FLOOD SAFETY
PLANS
ULDC 7.20 includes requirements for preparing flood safety plans, as it is important that local maintaining agencies and communities understand the responsibilities of flood risk management within their jurisdictions. Specifically, the ULDC requires each public agency with the responsibility for public safety for residents protected by levees and floodwalls to have a plan for flood events and other natural or manmade, flood-related, incidents that could result in human casualties, property destruction, and economic losses.

Several agencies, including ARFCD, City of Sacramento, and County of Sacramento, have the responsibility for the public safety of residents protected by the Robla-Arcade levee system. ARFCD, with primary responsibility for the levee system, has a Flood Safety Plan (ARFCD, 2018), Appendix I, that outlines their planned response to flood emergencies affecting their levee systems. This plan meets the requirements of California Water Code, Section 9650; and relies on the similar plans adopted by the City (City of Sacramento, 2018 and 2020) and County (Sacramento County, 2022). No changes to the 2018 plan have been made and this is considered the most current version of the Flood Safety Plan.

The Robla-Arcade levee system’s performance during a 200-year flood event relies on the operation of flap gates and positive closure valves at drainage crossings, installation of the stoplog structure at the UPRR, and operation of the emergency isolation gates at NEMDC stormwater pumping plants, in addition to the performance of the levee. These features are identified in the O&M Manual for the levee system.

The City and County of Sacramento are responsible for operation and maintenance of these features, which are documented in their respective Emergency Operations Plans.

The Robla-Arcade Levee System meets the requirements for ULDC 7.20 Emergency Actions and Flood Safety Plans.

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36 ULDC 8.0 OPERATIONS & MAINTENANCE
The ULDC 8.0 includes requirements related to operations and maintenance. Specifically, ULDC requires:
 The levee system must have an operation and maintenance manual consistent with USACE requirements, including inspection requirements, except as may be appropriate to deviate from those requirements to comply with the ULDC.
 The facilities providing the urban level of flood protection be operated and maintained by a public agency with the authority and resources to do so.  Damage and maintenance inadequacies identified from inspections should be prioritized and addressed in a timely manner, not awaiting the periodic review process.  Monitoring during high-water needs to provide for a thorough visual inspection of both the waterside and landside levee slope (and landside berm toe area) at intervals of no more than 1 hour.
 Plans required under ULDC 7.18 for security, and ULDC 7.20 for a flood safety; other plans, such as a right-of- way plan, encroachment remediation plan, penetration remediation plan, or flood fight plan be in-place, as applicable.

This levee system is included in USACE Supplement to Standard Operation and Maintenance Manual (O&M Manual), Sacramento River Flood Control Project, Unit No. 118 – Part No. 2. North Levee of American River, East Levee of Natomas Canal, Both Levees of Arcade Creek, South Levee of Linda Creek and Magpie Creek Diversion Channel, revised date 28 Jan 2023. As previously indicated, this levee system is maintained by the ARFCD, and the City of Sacramento maintains and operates the UPRR stoplog structures. The City of Sacramento maintains and operates the various pump stations and drainage culverts within the Robla-Arcade levee system. The manuals for these pump stations were reviewed and found to be consistent with the facility operations and maintenance needs. ARFCD performs inspections and patrols as outlined in the levee O&M Manual and addresses damage and maintenance issues as they arise. A security plan and flood safety plan are in place as described in relevant sections above. Mead & Hunt (2024b) provided a review of the referenced manuals and includes a discussion in Appendix H.

Additionally, MBK Engineers performed a site visit on July 10, 2024, to view general conditions related to Operation and Maintenance. Observations from this visit are summarized in a letter provided in Appendix F (MBK, 2024b).

The Robla-Arcade Levee System meets the requirements for ULDC 8.0 Operations and Maintenance.

6.0 BIBLIOGRAPHY
As mentioned in Chapter 1, this Engineer’s Report relies on dozens of other documents, reports, analyses, and evaluations. Many of these are listed in the following bibliography; however, this bibliography is mostly limited to presenting the substantial evidence required to demonstrate that an urban level of flood protection exists. Items shown BOLD are included as appendices to this report. (AECOM, 2024). Urban Levee Design Criteria, Geotechnical Findings Report Arcade Creek North Levee Stations 5023+00 to 5112+43, Robla-Arcade Levee System. August 13, 2024. (Appendix D).

URBAN LEVEL OF FLOOD PROTECTION ENGINEER’S REPORT

ROBLA-ARCADE LEVEE SYSTEM
37 (ARFCD, 2017). American River Flood Control District Rodent Control & Abatement Program.

Revised October 2017. (Appendix I4).
(ARFCD, 2018). American River Flood Control District Flood Safety Plan, as required by California Water Code 9650. January 2018. (Appendix I6).
(ARFCD, 2024). American River Flood Control District Security Plan – American River North Levee System. May 2024. (Appendix I5).
(Kleinfelder, 2013a). Geotechnical Data Report, North Area Streams, SAFCA FEMA Levee Accreditation (North Area Streams, American River, Sacramento River Downstream of American River, and Beach Lake Levee). Sacramento County. May 31, 2013.
(Kleinfelder, 2013b). Problem Identification Report, North Area Streams, SAFCA FEMA Levee Accreditation (North Area Streams, American River, Sacramento River Downstream Of American River, and Beach Lake Levee). Sacramento County, California. September 18, 2013. (Kleinfelder, 2015). Draft ULDC Geotechnical Results Summary, North Area Streams, SAFCA FEMA Levee Accreditation (North Area Streams, American River, Sacramento River Downstream of American River, and Beach Lake Levee). Sacramento County, California. December 18, 2015. (Kleinfelder, 2024). Seismic Performance Summary Report, North Area Streams Levee Areas, ULDC & FEMA Levee Certification Project, Sacramento Area Flood Control Agency Levee Systems, Sacramento County, California. February 12, 2024, Revised Date September 10, 2024. (Appendix E, sub-Appendix C).
(Kleinfelder, 2025). ULDC Geotechnical Finding – Robla Creek South Levee Stations 6000+00 to 6118+20; NEMDC East Levee Station 3056+00 to 3192+25; Arcade Creek North Levee Stations 5000+00 to 5023+00; ULDC Finding and FEMA Levee Certification Program. August 25, 2025. (Appendix E).
(MBK, 2014). SAFCA Levee Certification Erosion Report. Sacramento, California. 2014. (MBK, 2016a). Technical Memorandum. Overview of High Hazard Encroachments to Support Adequate Progress Towards an Urban Level of Flood Protection. Sacramento, California. April 15, 2016. (MBK, 2016b). Technical Memorandum. Overview of High Hazard Vegetation to Support Adequate Progress Towards an Urban Level of Flood Protection. Sacramento, California. April 15, 2016. (MBK, 2024a). Technical Memorandum Robla-Arcade Levee System- Determination of the Urban Levee Design Criteria Design Water Surface Elevation, Minimum Top of Levee, and Hydraulic Top of Levee. July 15, 2024. (Appendix C).
(MBK, 2024b). SAFCA Robla-Arcade Levee System, Levee O&M Review in Support of FEMA and ULDC Certification. August 3, 2024. (Appendix F).
(MBK, 2024c). SAFCA Certification, Robla-Arcade Levee System, Erosion Report. October 2024.

URBAN LEVEL OF FLOOD PROTECTION ENGINEER’S REPORT

ROBLA-ARCADE LEVEE SYSTEM
38 (MBK, 2024d). Robla-Arcade Levee System Framework for Encroachment Remediation Plan.

September 27, 2024. (Appendix I2).
(MBK, 2025a). Arcade NEMDC Berm Construction Documentation Report. August 2025. (MBK, 2025b). City of Sacramento Recommended Right-of-Way Plan to Comply with ULDC Criteria

7.11 Robla-Arcade Levee System. August 2025. (Appendix I1). (Mead & Hunt, 2024a). Wind-Wave Analysis for American River North and Robla-Arcade Levee Systems. July 9, 2024. (Appendix H, sub-Appendix D).
(Mead & Hunt, 2024b). Penetration Exceptions Work Plan, Robla-Arcade Levee System (ASLS) SAFCA Due Diligence Review for Urban Levee Design Criteria Section 7.13. August 27, 2024. (Appendix I3).
(Mead & Hunt, 2024c). Robla-Arcade Levee System, Due Diligence Review for ULDC & FEMA Certification. November 15, 2024. (Appendix H).
(Psomas, 2024). O&M Right of Way Map, Robla-Arcade Levee System. September 2024. (Appendix G).
(SAFCA, 2015). Sacramento Federal Emergency Management Agency Certification White Paper for Addressing Encroachments. August 6, 2015.
(SAFCA, 2023). Urban Level of Flood Protection Annual Report. August 2023. (URS, 2008). Levee Seismic Vulnerability Assessment Methodology Report. 2008. (URS, 2009). Geotechnical Levee Practice Standard Operating Procedures. [USACE Sacramento Districts].

Sacramento, California. 2009.
(URS, 2010). Modified Supplemental Geotechnical Data Report (MSGDR), Natomas East Main Drainage Canal (NEMDC) West Study, Urban Levee Geotechnical Evaluations Program Contract 4600007418 and 4600008101. [Department of Water Resources]. November 2010. (URS, 2015a). Geotechnical Evaluation Report, Volume 1, Existing Conditions, Natomas East Main Drainage Canal, West Study Area, Urban Levee Evaluations Project, Contract 4600008101. [Department of Water Resources]. January 2015.
(URS, 2015b). Geotechnical Evaluation Report (Existing Conditions and Seismic Assessment), Natomas North Study Area, Urban Levee Evaluations Project, Contract 4600008101. [Department of Water Resources]. March 2015.
(USACE, 2023). Supplement to Standard Operation and Maintenance Manual (O&M Manual), Sacramento River Flood Control Project, Unit No. 118 – Part No. 2. North Levee of American River, East Levee of Natomas Canal, Both Levees of Arcade Creek, South Levee of Linda Creek and Magpie Creek Diversion Channel. Revised 28 Jan 2023.

Appendix A.

Robla-Arcade Levee System
Consultant Certification Statements
ENGINEER’S OPINION
ULDC 7.1: DESIGN WATER SURFACE ELEVATION
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM - ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  Robla-Arcade Levee System – Determination of the Urban Levee Design Criteria Design Water Surface Elevation, Minimum Top of Levee, and Hydraulic Top of Levee, prepared by MBK Engineers, dated November 18, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.1 Design Water Surface Elevation, as described in the above referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Don Trieu, PE
MBK Engineers
455 University Avenue, Suite 100
Sacramento, CA 95825-6579
_________________________________________________8/22/2025 Signature Date
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.2: MINIMUM TOP OF LEVEE
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  Robla-Arcade Levee System - Determination of the Urban Levee Design Criteria Design Water Surface Elevation, Minimum Top of Levee, and Hydraulic Top of Levee, prepared by MBK Engineers, dated November 18, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.2 Minimum Top of Levee, by exception, as described in the above referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Don Trieu, PE
MBK Engineers
455 University Avenue, Suite 100
Sacramento, CA 95825-6579
_______________________________________________8/22/2025 Signature Date Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.3: SOIL SAMPLING, TESTING, AND LOGGING
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE NORTH LEVEE STATIONS 5023+00 TO 5112+43
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  ULDC Geotechnical Findings Report Arcade Creek North Levee Stations 5023+00 to 5112+43 Robla-Arcade Levee System, prepared by AECOM, dated November 15, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC 7.3 Soil Sampling, Testing and Logging, by exception, as described in the above referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Richard Millet, PE
AECOM
2020 L Street
Sacramento, CA 95811
___________________________________________________________________ Signature Date
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.3: SOIL SAMPLING, TESTING, AND LOGGING
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE: ROBLA CREEK SOUTH LEVEE STATIONS 6000+00 TO 6118+20 ; NEMDC EAST LEVEE STATIONS 3056+00 TO 3192+25; ARCADE CREEK NORTH LEVEE STATIONS 5000+00 TO 5023+00
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  ULDC Geotechnical Finding – Robla Creek South Levee Stations 6000+00 to 6118+20 ; NEMDC East Levee Stations 3056+00 to 3192+25; Arcade Creek North Levee Stations 5000+00 to 5023+00 ULDC Finding and FEMA Levee Certification Program Sacramento Area Flood Control Agency; Sacramento County, California, prepared by Kleinfelder, dated August 2025.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business and Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.3 Soil Sampling, Testing and Logging, by exception, as described in the above referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Timothy Williams, PE
Kleinfelder
3130 Kilgore Road, Suite 200
Rancho Cordova, CA 95670
___________________________________________________________________ Signature Date Not Valid Unless Stamped
August 25, 2025
ENGINEER’S OPINION
ULDC 7.4: SLOPE STABILITY FOR INTERMITTENTLY

LOADED LEVEES
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE NORTH LEVEE STATIONS 5023+00 TO 5112+43
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  ULDC Geotechnical Findings Report Arcade Creek North Levee Stations 5023+00 to 5112+43 RoblaArcade Levee System, prepared by AECOM, dated November 15, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.4 Slope Stability for Intermittently Loaded Levees as described in the above referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Richard Millet, PE
AECOM
2020 L Street
Sacramento, CA 95811
___________________________________________________________________ Signature Date
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.4: SLOPE STABILITY FOR INTERMITTENTLY

LOADED LEVEES
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE: ROBLA CREEK SOUTH LEVEE STATIONS 6000+00 TO 6118+20; NEMDC EAST LEVEE STATIONS 3056+00 TO 3192+25; ARCADE CREEK NORTH LEVEE STATIONS 5000+00 TO 5023+00
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  ULDC Geotechnical Finding – Robla Creek South Levee Stations 6000+00 to 6118+20 ; NEMDC East Levee Stations 3056+00 to 3192+25; Arcade Creek North Levee Stations 5000+00 to 5023+00 ULDC Finding and FEMA Levee Certification Program Sacramento Area Flood Control Agency; Sacramento County, California, prepared by Kleinfelder, dated August 2025.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business and Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.4 Slope Stability for Intermittently Loaded Levees as described in the above referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Timothy Williams, PE, GE
Kleinfelder
3130 Kilgore Road, Suite 200
Rancho Cordova, CA 95670
________________________________________________________ Signature Date Not Valid Unless Stamped
August 25, 2025
ENGINEER’S OPINION
ULDC 7.5: UNDERSEEPAGE FOR INTERMITTENTLY

LOADED LEVEES
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE CREEK NORTH LEVEE STATIONS 5023+00 TO 5112+43 All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or reference in the following document forms the basis of this opinion.  ULDC Geotechnical Findings Report Arcade Creek North Levee Stations 5023+00 to 5112+43 RoblaArcade Levee System, prepared by AECOM, dated November 15, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.5 Underseepage for Intermittently Loaded Levees, as described in the above referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Richard Millet, PE
AECOM
2020 L Street
Sacramento, CA 95811
___________________________________________________________________ Signature Date
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.5: UNDERSEEPAGE FOR INTERMITTENTLY

LOADED LEVEES
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE: ROBLA CREEK SOUTH LEVEE STATIONS 6000+00 TO 6118+20 ; NEMDC EAST LEVEE STATIONS 3056+00 TO 3192+25; ARCADE CREEK NORTH LEVEE STATIONS 5000+00 TO 5023+00
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  ULDC Geotechnical Finding – Robla Creek South Levee Stations 6000+00 to 6118+20 ; NEMDC East Levee Stations 3056+00 to 3192+25; Arcade Creek North Levee Stations 5000+00 to 5023+00 ULDC Finding and FEMA Levee Certification Program Sacramento Area Flood Control Agency; Sacramento County, California, prepared by Kleinfelder, dated August 2025.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levees will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business and Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.5 Underseepage for Intermittently Loaded Levees as described in the above referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Timothy Williams, PE, GE
Kleinfelder
3130 Kilgore Road, Suite 200
Rancho Cordova, CA 95670
___________________________________________________________________ Signature Date
Not Valid Unless Stamped
August 25, 2025
ENGINEER’S OPINION
ULDC 7.6: FREQUENTLY LOADED LEVEES
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  Sacramento Area Flood Control Agency; Urban Level of Flood Protection Engineer’s Report for the Robla-Arcade Levee System, prepared by SAFCA, dated July 2025.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions a the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.6 Frequently Loaded Levees, as described in the above referenced document;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Tom Engler, PE, CFM
MBK Engineers
455 University Avenue, Suite 100
Sacramento, CA 95825-6579
__________________________________________________8/22/2025_____________ Signature Date
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.7: SEISMIC VULNERABILITY
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE NORTH LEVEE STATIONS 5023+00 TO 5112+43
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  ULDC Geotechnical Findings Report Arcade Creek North Levee Stations 5023+00 to 5112+43 RoblaArcade Levee System, prepared by AECOM, dated November 15, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levees will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.7 Seismic Vulnerability as described in the above referenced document;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Richard Millet, PE
AECOM
2020 L Street
Sacramento, CA 95811
___________________________________________________________________ Signature Date
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.7: SEISMIC VULNERABILITY
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE: ROBLA CREEK SOUTH LEVEE STATIONS 6000+00 TO 6118+20 ; NEMDC EAST LEVEE STATIONS 3056+00 TO 3192+25; ARCADE CREEK NORTH LEVEE STATIONS 5000+00 TO 5023+00
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  ULDC Geotechnical Finding – Robla Creek South Levee Stations 6000+00 to 6118+20 ; NEMDC East Levee Stations 3056+00 to 3192+25; Arcade Creek North Levee Stations 5000+00 to 5023+00 ULDC Finding and FEMA Levee Certification Program Sacramento Area Flood Control Agency; Sacramento County, California, prepared by Kleinfelder, dated August 2025.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levees will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business and Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.7 Seismic Vulnerability as described in the above referenced document;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Timothy Williams, PE, GE
Kleinfelder
3130 Kilgore Road, Suite 200
Rancho Cordova, CA 95670
___________________________________________________________________ Signature Date Not Valid Unless Stamped
August 25, 2025
ENGINEER’S OPINION
ULDC 7.8: LEVEE GEOMETRY (GEOTECHNICAL)
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE CREEK NORTH LEVEE STATIONS 5023+00 TO 5112+43 All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  ULDC Geotechnical Findings Report Arcade Creek North Levee Stations 5023+00 to 5112+43 RoblaArcade Levee System, prepared by AECOM, dated November 15, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC 7.8 Levee Geometry from a geotechnical standpoint, as described in the above referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Richard Millet, PE
AECOM
2020 L Street
Sacramento, CA 95811
___________________________________________________________________ Signature Date
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.8: LEVEE GEOMETRY (GEOTECHNICAL)
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE: ROBLA CREEK SOUTH LEVEE STATIONS 6000+00 TO 6118+20; NEMDC EAST LEVEE STATIONS 3056+00 TO 3192+25; ARCADE CREEK NORTH LEVEE STATIONS 5000+00 TO 5023+00
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  ULDC Geotechnical Finding – Robla Creek South Levee Stations 6000+00 to 6118+20 ; NEMDC East Levee Stations 3056+00 to 3192+25; Arcade Creek North Levee Stations 5000+00 to 5023+00 ULDC Finding and FEMA Levee Certification Program Sacramento Area Flood Control Agency; Sacramento County, California, prepared by Kleinfelder, dated August 2025.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business and Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC 7.8 Levee Geometry from a geotechnical standpoint, as described in the above referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Timothy Williams, PE
Kleinfelder
3130 Kilgore Road, Suite 200
Rancho Cordova, CA 95670
___________________________________________________________________ Signature Date
August 25, 2025
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.9: INTERFACES AND TRANSITIONS (GEOTECHNICAL)
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE CREEK NORTH LEVEE STATIONS 5023+00 TO 5112+43 All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  ULDC Geotechnical Findings Report Arcade Creek North Levee Stations 5023+00 to 5112+43 RoblaArcade Levee System, prepared by AECOM, dated November 15, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.9 Interfaces and Transitions from a geotechnical standpoint, as described in the above referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Richard Millet, PE, GE
AECOM
2020 L Street
Sacramento, CA 95811
___________________________________________________________________ Signature Date
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.9: INTERFACES AND TRANSITIONS (GEOTECHNICAL)
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE: SOUTH LEVEE STATIONS 6000+00 TO 6118+20 ; NEMDC EAST LEVEE STATIONS 3056+00 TO 3192+25; ARCADE CREEK NORTH LEVEE STATIONS 5000+00 TO 5023+00
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  ULDC Geotechnical Finding – Robla Creek South Levee Stations 6000+00 to 6118+20 ; NEMDC East Levee Stations 3056+00 to 3192+25; Arcade Creek North Levee Stations 5000+00 to 5023+00 ULDC Finding and FEMA Levee Certification Program Sacramento Area Flood Control Agency; Sacramento County, California, prepared by Kleinfelder, dated August 2025.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.9 Interfaces and Transitions from a geotechnical standpoint, as described in the above referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Timothy Williams, PE
Kleinfelder
3130 Kilgore Road, Suite 200
Rancho Cordova, CA 95670
___________________________________________________________________ Signature Date Not Valid Unless Stamped
August 25, 2025
ENGINEER’S OPINION
ULDC 7.10: EROSION
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE CREEK NORTH LEVEE STATIONS 5023+00 TO 5112+43 All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or evaluated in the following document forms the basis of this opinion.  ULDC Geotechnical Findings Report Arcade Creek North Levee Stations 5023+00 to 5112+43 RoblaArcade Levee System, prepared by AECOM, dated November 15, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.10 Erosion as described in the above referenced document;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Richard Millet, PE
AECOM
2020 L Street
Sacramento, CA 95811
_________________________________________________________________ Signature Date
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.10: EROSION
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or evaluated in the following document forms the basis of this opinion.  SAFCA Robla Arcade Levee System; Levee O&M Review in Support of FEMA and ULDC Certification, prepared by MBK Engineers, dated August 15, 2025.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.10 Erosion as described in the above referenced document;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Tom Engler, PE, CFM
MBK Engineers
455 University Avenue, Suite 100
Sacramento, CA 95825-6579
___________________________________________________8/22/2025______________ Signature Date
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.11: RIGHT-OF-WAY
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  O&M Right of Way Map; Robla Arcade Basin, prepared by Psomas, dated September 11, 2023.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.11 Right-of-Way through exception as described in the above referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Tom Engler, PE, CFM
MBK Engineers
455 University Avenue, Suite 100
Sacramento, CA 95825-6579
______________________________________________8/22/2025____________ Signature Date Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.12: ENCROACHMENTS
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or evaluated in the following document forms the basis of this opinion.  SAFCA Robla Arcade Levee System; Levee O&M Review in Support of FEMA and ULDC Certification, prepared by MBK Engineers, dated August 15, 2025.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.12 Encroachments as described in the above referenced document;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Tom Engler, PE, CFM
MBK Engineers
455 University Avenue, Suite 100
Sacramento, CA 95825-6579
_______________________________________________8/22/2025________ Signature Date Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.12: ENCROACHMENTS
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in and evaluated in the following document forms the basis of this opinion.  Robla-Arcade Levee System; Due Diligence Review for ULDC & FEMA Certification, prepared by Mead & Hunt, dated November 15, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.12 Encroachments as described in the above-referenced document;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Stephen R. Sullivan, PE
Mead & Hunt
180 Promenade Circle, Suite 240
Sacramento, CA 95834
___________________________________________________________________ Signature Date Not Valid Unless Stamped
August 21, 2025
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ENGINEER’S OPINION
ULDC 7.13: PENETRATIONS
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE CREEK NORTH LEVEE STATIONS 5023+00 TO 5112+43 All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or evaluated in the following document forms the basis of this opinion.  ULDC Geotechnical Findings Report Arcade Creek North Levee Stations 5023+00 to 5112+43 RoblaArcade Levee System, prepared by AECOM, dated November 15, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.13 Penetrations through exception, as described in the above referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge;
 the analyses supporting this opinion have been performed in accordance with DWR’s ULDC and/or sound engineering practices;
 the structural works are in place and function as intended for the 200-year ULDC event.

Richard Millet, PE
AECOM
2020 L Street
Sacramento, CA 95811
______________________________________________________________ Signature Date
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.13: PENETRATIONS
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or evaluated in the following document forms the basis of this opinion.  Robla-Arcade Levee System; Due Diligence Review for ULDC & FEMA Certification, prepared by Mead & Hunt, dated November 15, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time of the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.13 Penetrations through exception, as described in the above-referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge;
 the analyses supporting this opinion have been performed in accordance with DWR’s ULDC and/or sound engineering practices; and
 the structural works are in place and function as intended for the 200-year ULDC event.

Stephen R. Sullivan, PE
Mead & Hunt
180 Promenade Circle, Suite 240
Sacramento, CA 95834
______________________________________________________________ Signature Date
Not Valid Unless Stamped
August 21, 2025
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ENGINEER’S OPINION
ULDC 7.14: FLOODWALLS, RETAINING WALLS, AND CLOSURE STRUCTURES (GEOTECHNICAL)
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA- ARCADE CREEK NORTH LEVEE STATIONS 5023+00 TO 5112+43 All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or evaluated in the following document forms the basis of this opinion.  ULDC Geotechnical Findings Report Arcade Creek North Levee Stations 5023+00 to 5112+43 RoblaArcade Levee System, prepared by AECOM, dated November 15, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system for interface and transitions only meets the requirements of the ULDC for Section 7.14 Floodwalls, Retaining Walls, and Closure as described in the above referenced document;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge;
 the analyses supporting this opinion have been performed in accordance with DWR’s ULDC and/or sound engineering practices; and
 the structural works are in place and function as intended for the 200-year ULDC.

Richard Millet, PE
AECOM
2020 L Street
Sacramento, CA 95811
___________________________________________________________________ Signature Date
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.14: FLOODWALLS, RETAINING WALLS, AND

CLOSURE STRUCTURES (GEOTECHNICAL)
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA ARCADE: ROBLA CREEK SOUTH LEVEE STATIONS 6000+00 TO 6118+20 ; NEMDC EAST LEVEE STATIONS 3056+00 TO 3192+25; ARCADE CREEK NORTH LEVEE STATIONS 5000+00 TO 5023+00
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  ULDC Geotechnical Finding – Robla Creek South Levee Stations 6000+00 to 6118+20 ; NEMDC East Levee Stations 3056+00 to 3192+25; Arcade Creek North Levee Stations 5000+00 to 5023+00 ULDC Finding and FEMA Levee Certification Program Sacramento Area Flood Control Agency; Sacramento County, California, prepared by Kleinfelder, dated August 2025.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business and Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.14 Floodwalls, Retaining Walls, and Closure Structures for geotechnical requirements as described in the above referenced document;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge;
 the analyses supporting this opinion have been performed in accordance with DWR’s ULDC and/or sound engineering practices; and
 the structural works are in place and function as intended for the 200-year ULDC event.

Timothy Williams, PE
Kleinfelder
3130 Kilgore Road, Suite 200
Rancho Cordova, CA 95670
___________________________________________________________________ Signature Date Not Valid Unless Stamped
August 25, 2025
ENGINEER’S OPINION
ULDC 7.14: FLOODWALLS, RETAINING WALLS, AND CLOSURE STRUCTURES (CIVIL) This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or evaluated in the following document forms the basis of this opinion.  Robla-Arcade Levee System; Due Diligence Review for ULDC & FEMA Certification, prepared by Mead & Hunt, dated November 15, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of ULDC 14 Floodwalls, Retaining Walls, and Closure Structures (Civil) as described in the above-referenced document.  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge;
 the analyses supporting this opinion have been performed in accordance with DWR’s ULDC and/or sound engineering practices; and
 the structural works are in place and function as intended for the 200-year ULDC.

Steve R. Sullivan, PE
Mead & Hunt
180 Promenade Circle, Suite 240
Sacramento, CA 95834
___________________________________________________________________ Signature Date Not Valid Unless Stamped
August 21, 2025
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ULDC 7.15: ANIMAL BURROWS
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or evaluated in the following documents form the basis of this opinion.  SAFCA Robla Arcade Levee System; Levee O&M Review in Support of FEMA and ULDC Certification, prepared by MBK Engineers, dated August 15, 2025.
 Rodent Control & Abatement Program, prepared by American River Flood Control District, dated October 2017.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumed the levees will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.15 Animal Burrows as described in the above referenced documents;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Tom Engler, PE, CFM
MBK Engineers
455 University Avenue, Suite 100
Sacramento, CA 95825-6579
____________________________________________8/22/2025_______________ Signature Date Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.16: LEVEE VEGETATION
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or evaluated in the following documents form the basis of this opinion.  SAFCA Robla Arcade Levee System; Levee O&M Review in Support of FEMA and ULDC Certification, prepared by MBK Engineers, dated August 15, 2025.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.16 Levee Vegetation as described in the above referenced document;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Tom Engler, PE, CFM
MBK Engineers
455 University Avenue, Suite 100
Sacramento, CA 95825-6579
_____________________________________________8/22/2025_____________ Signature Date Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.17: WIND SETUP AND WAVE RUNUP
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or evaluated in the following documents form the basis of this opinion.  Robla-Arcade Levee System; Due Diligence Review for ULDC & FEMA Certification, Appendix H, subAppendix D; Wind-Wave Analysis for American River North and Robla-Arcade Levee Systems, prepared by Mead & Hunt, dated July 9, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.17 Wind Setup and Wave Runup as described in the above-referenced document;  data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Stephen R. Sullivan, PE
Mead & Hunt
180 Promenade Circle, Suite 240
Sacramento, CA 95834
___________________________________________________________________ Signature Date Not Valid Unless Stamped
August 21, 2025
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ULDC 7.18: SECURITY
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or evaluated in the following document forms the basis of this opinion.  Security Plan - American River North Levee System, prepared by American River Flood Control District, dated May 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.18 Security as described in the above referenced document;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Tom Engler, PE, CFM
MBK Engineers
455 University Avenue, Suite 100
Sacramento, CA 95825-6579
_______________________________________________8/22/2025________ Signature Date Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.19: SEA LEVEL RISE
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or evaluated in the following documents form the basis of this opinion.  Robla-Arcade Levee System – Determination of the Urban Levee Design Criteria Design Water Surface Elevation, Minimum Top of Levee, and Hydraulic Top of Levee, prepared by MBK Engineers, dated November 18, 2024.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.19 Sea Level Rise as described in the above referenced document;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Don Trieu, PE
MBK Engineers
455 University Avenue, Suite 100
Sacramento, CA 95825-6579
______________________________________________8/22/2025 Signature Date
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 7.20: EMERGENCY ACTIONS AND FLOOD SAFETY PLANS
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or referenced in the following document forms the basis of this opinion.  American River Flood Control District Flood Safety Plan, as required by California Water Code 9650, January 2018.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.20 Emergency Actions as described in the above referenced document;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and
 the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Tom Engler, PE, CFM
MBK Engineers
455 University Avenue, Suite 100
Sacramento, CA 95825-6579
________________________________________________8/22/2025_________ Signature Date
Not Valid Unless Stamped
ENGINEER’S OPINION
ULDC 8.0 OPERATIONS AND MAINTENANCE
This opinion is made to assist the Sacramento Area Flood Control Agency (SAFCA) in complying with the requirements, definitions, and descriptions in the California Department of Water Resources’ (DWR) Urban Levee Design Criteria (ULDC) (May 2012) and to support SAFCA’s certification of the Urban Levee System of:

ROBLA-ARCADE LEVEE SYSTEM: ALL
All information, calculations, definitions, descriptions, restrictions, limitations, or other pertinent data contained in or evaluated in the following document forms the basis of this opinion.  Sacramento Area Flood Control Agency; Urban Level of Flood Protection Engineer’s Report for the Robla-Arcade Levee System, prepared by SAFCA, dated August 2025.
 SAFCA Robla Arcade Levee System; Levee O&M Review in Support of FEMA and ULDC Certification, prepared by MBK Engineers, dated August 15, 2025.

LIMITATIONS OF ENGINEER’S OPINION
Consistent with current practice, this opinion of expected flood control system performance is valid for 20 years from the date of the SAFCA certification and assumes the levee will be properly maintained during the certification period.

It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions at the time the work was performed.

The use of the term certification in this document is based on the following:

Per California Business And Professions Code, Division 3, Chapter 7, Article 3, 6735.5. The use of the word “certify” or “certification” by a registered professional engineer in the practice of professional engineering or land surveying constitutes an expression of professional opinion regarding those facts or findings which are the subject of the certification, and does not constitute a warranty or guarantee, either expressed or implied.

OPINION
This Engineer’s Opinion attests that:
 the subject levee system meets the requirements of the ULDC for Section 7.18 Security as described in the above referenced documents;
 data used in the evaluations and analyses supporting this opinion are accurate to the best of my knowledge; and  the analyses have been performed in accordance with DWR’s ULDC and/or sound engineering practices.

Tom Engler, PE, CFM
MBK Engineers
455 University Avenue, Suite 100
Sacramento, CA 95825-6579
_______________________________________________8/22/2025________ Signature Date
Not Valid Unless Stamped
Appendix B.

Robla-Arcade Levee System
Independent Panel of Experts
Report and Comment Closeout
September 08, 2025
Mr. Tom Engler, PE
MBK Engineers
455 University Ave, Suite 100
Sacramento, CA 95825
Dear Mr. Engler:

Subject: Urban Level of Flood Protection Engineer’s Report for the Robla-Arcade Levee System
Independent Panel of Experts’ Concurrence with Engineer’s Report City of Sacramento and Sacramento County
At your request, the Independent Panel of Experts (IPE) (Dr. David Williams, P.E., PH, CFM, BC.WRE, Mr. Michael Hughes, PE, and Mr. Darren Mack, PE, GE) has conducted an independent quality assurance review of the Urban Level of Flood Protection (ULOP) Engineers’ Report for the RoblaArcade Levee System that provides flood protection within the jurisdiction of the City of Sacramento and Sacramento County. The Robla-Arcade Levee System consists of Robla Creek South Levee; Natomas East Main Drainage Canal East Levee, between Robla Creek and Arcade Creek; and Arcade Creek North Levee.

The Engineer’s Report and its supporting documents are intended to provide substantial evidence that the Robla-Arcade Levee System meets the Department of Water Resources’ (DWR’s) ULOP Criteria for a 200-year flood event (1-in-200 annual chance of exceedance) in accordance with the DWRs’ Urban Levee Design Criteria (ULDC) issued in May 2012.

IPE Charge and Scope of Work
The IPE has been tasked to provide independent, expert opinion regarding certification. Tasks include, but are not limited to, the following:
• Preparation and attendance of IPE meetings;
• Review and comment on Due Diligence reports supporting ULOP certifications; • Review and comment on the Engineer’s Reports supporting the certifications; and • Preparation of IPE’s report documenting opinion on whether the flood system meets ULOP certification standards.

Materials provided to the IPE for review included the draft Engineer’s Report for the Robla-Arcade Levee System, dated August 2025, and the following supporting documents:
• Appendix C: Robla-Arcade Levee System - Determination of the Urban Levee Design Criteria Design Water Surface Elevation, Minimum Top of Levee, and Hydraulic Top of Levee, November 18, 2024.
• Appendix D: Urban Levee Design Criteria Geotechnical Findings Report, Arcade Creek North Levee Stations 5023+00 to 5112+43, Robla-Arcade Levee System, November 15, 2024. • Appendix E: ULDC GEOTECHNICAL FINDING – ROBLA CREEK SOUTH LEVEE STATIONS 6000+00 TO 6118+20, NEMDC EAST LEVEE STATIONS 3056+00 TO 3192+25, ARCADE CREEK NORTH LEVEE STATIONS 5000+00 TO 5023+00, ULDC FINDING AND FEMA LEVEE CERTIFICATION PROGRAM,

SACRAMENTO AREA FLOOD CONTROL AGENCY LEVEE SYSTEMS, SACRAMENTO COUNTY, CALIFORNIA, Kleinfelder Inc., June 18, 2024, revised August 25, 2025. • Appendix F: SAFCA Robla Arcade Levee System, Levee O&M Review in Support of FEMA Certification and ULDC Evaluation, August 15, 2025.
• Appendix H: ROBLA-ARCADE LEVEE SYSTEM Due Diligence Review for ULDC & FEMA Certification, Mead & Hunt, November 15, 2024.

Other information was provided for context but are not presented in this letter.

DWR Urban Level of Flood Protection Criterion EVD-1:

Section 2.0 of the ULOP provides the following criterion that is considered by DWR to be necessary for reasonable and responsible decision making.

EVD-1: Substantial evidence in the record to support a finding related to an urban level of flood protection based on flood management facilities providing the required level of flood protection shall include the following, at a minimum:
• A report prepared by a Professional Civil Engineer registered in California to document the data and analyses for demonstrating that the property, development project, or subdivision has an urban level of flood protection.
• A report by an Independent Panel of Experts on the review of the report prepared by the Professional Civil Engineer.
• A response by the Professional Civil Engineer to the comments from the Independent Panel of Experts.
• Any additional data and information that cities or counties use to make the finding.

DWR’s ULDC document presents mainly procedural criteria associated with making a finding consistent with legislative requirements. DWR considers that an urban level of flood protection could be achieved by structural and nonstructural means, or a combination of both. Therefore, DWR’s ULDC, as described below, are incorporated by reference in the ULOP Criteria.

DWR’s ULDC document provides the engineering criteria and guidance for the design, evaluation, operation, and maintenance of levees and floodwalls that provide a 200-year ULOP and outlines 20 technical areas associated with levee integrity and the evaluations needed for compliance, these being:
• Section 7.1 - Design Water Surface Elevation
• Section 7.2 - Minimum Top of Levee
• Section 7.3 - Soil Sampling, Testing, and Logging
• Section 7.4 - Slope Stability for Intermittently Loaded Levees • Section 7.5 - Underseepage for Intermittently Loaded Levees • Section 7.6 - Frequently Loaded Levees
• Section 7.7 - Seismic Vulnerability
• Section 7.8 - Levee Geometry
• Section 7.9 - Interfaces and Transitions
• Section 7.10 - Erosion
• Section 7.11 - Right-of-Way
• Section 7.12 - Encroachments
• Section 7.13 - Penetrations
• Section 7.14 - Floodwalls, Retaining Walls, and Closure Structures • Section 7.15 - Animal Burrows
• Section 7.16 - Levee Vegetation
• Section 7.17 - Wind Setup and Wave Runup
• Section 7.18 - Security
• Section 7.19 - Sea Level Rise
• Section 7.20 - Emergency Actions
The above listed sections were referenced during the IPE review to verify that the completed levee system certification meets the ULDC standards.

Independent Panel of Experts Review and Findings
The IPE reviewed the Engineer’s Report and supporting documents (Appendix C, D, E, F, and H), attended meetings with the certification team, visited the levee sites, and provided review comments and “backcheck” replies to Engineer’s team responses. A spreadsheet that documents the IPE comments, Engineer’s team responses, and comment closures is attached to this letter.

Changes, clarifications, and improvements to the Engineer’s Report, and supporting documents, were made where needed.

Based on its review, the IPE provides the following findings:
• The certification team, in our opinion, had followed the standards of engineering required for certifying the levees included in the Robla-Arcade Levee System. • Adequate and appropriate information has been gathered and presented to the IPE to perform the review needed to support the certification package. • The engineering documentation provided were appropriate to accurately provide compliance with the ULDC to address the technical areas listed above. • The references cited in the Engineer’s Report (including the Due Diligence and Engineer’s Opinions reports), provide the appropriate and adequate information to support those Opinions.
• Exceptions to ULDC criteria requested by the certification team are reasonable and adequately supported.
• In the IPE’s judgment, the documentation, evaluations, and management approaches were completed in accordance with sound engineering practices1to provide protection up to the 200-year flood event, and support ULOP and ULDC certifications of the Robla-Arcade Levee System.

The Engineer’s Report is a requirement to obtain ULOP Certification for a levee system. The ULOP Criteria, Sub-Section EVD-1, requires a report by the IPE documenting its review of the Engineer’s Report and its supporting documents. This letter and its attachment serve as documentation of the IPE’s review and concurrence that the completed levee system provides the required Urban Level of Flood Protection.

Respectfully submitted,
Sacramento Area Levee Certification Project
Independent Panel of Experts
_____________________________ ____________________________ Michael Hughes, P.E. Darren Mack, P.E., G.E.

Independent Expert Panel Member Independent Expert Panel Member _______________________________________
Dr. David T. Williams, P.E., PH, CFM, BC.WRE
Independent Expert Panel Member
1 It is assumed that “sound engineering practices” are practices that are performed in a manner consistent with the degree of skill and care ordinarily exercised by members of the profession currently practicing in the same locality under similar conditions.

No. DOCUMENT LOCATION IN DOCUMENT

IPE'S COMMENT
(10/30/2024) Significance Rating ENGINEER'S RESPONSE (11/27/24) IPE's COMMENT (01/08/25) ENGINEER'S RESPONSE (Date) IPE's FINAL COMMENT / CLOSURE (Date) 1 URBAN LEVEL OF FLOOD PROTECTIONENGINEER’S REPORT FOR THE ROBLAARCADE LEVEE SYSTEM, OCT 2024 General Figure 1 should be imbedded in report Figure added to report after Section 2. accepted, closed 2 General
Check that acronyms used in the report are defined before their use, for example WSE on pg 4 of the text isn't defined until pg 6. Also, once defined they are used consistently thereafter (e.g. 'water surface elevation' last paragraph page 10) Corrected and all acronyms were checked. accepted, closed 3 General Many report references have an 'a' or 'b' after the year in Section 5.0 Bibliography, but in the report text this is missing. Please check and update all references. References corrected.

A quick check still shows some inconsistencies. Should the reference to MBK, 2024b, on the fifth line of the second paragraph on page 24 be MBK, 2024c? Also, pages 29 and 30 reference Kleinfelder, 2024 without an 'a' or 'b' to distinguish correct report in the Bibliography.

Editorial comment only. Comment closed.
4 General
Lower case has been used in the mainstream for referencing levee location - 'south levee', 'east levee, and 'north levee'. However in some places capitals have been used. Make consistent.

Cases corrected. accepted, closed.
567 Introduction, top of page 2 Should the document October 2023 Adequate Progress Finding (APF), as well as the other reports cited in the first paragraph be included in the references? Added reference accepted, closed 8 Introduction, last paragraph, page 2
There is a comment in the text that caveats "does not require structural improvements" and comments in the notes states "Also assumes no work is needed for upstream Robla Creek." It is unclear what upstream Robla Creek work is being referenced. Does it have a potential impact on Certification? The comment in the report was referring to the stability berm to be constructed at the intersection of NEMDC and Arcade. There is no impact on certification. Work is anticipated to be done in Spring 2025. Report comment deleted. The final version of this report will not be published until after construction of this feature. accepted, closed
9 3.0 PHYSICAL DESCRIPTION, General The presence of homeless people along the waterside slopes is significant in certain sections of the levee system and should be mentioned as appropriate in the text. The presence of homeless encampments is included under Section 7.11 Erosion. We do not feel it is appropriate to discuss in this section of the report. accepted, closed 10 3.0 PHYSICAL DESCRIPTION, ROBLA CREEK SOUTH LEVEE, 2nd para Who is responsible to put it the stoplogs during floods? City of Sacramento Department of Public Works is responsible for stop log installation. accepted, closed 11 NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE – ROBLA CREEK TO ARCADE CREEK, page 3 Stated Stationing and miles do not match up. Please check and make consistent. Stationing corrected. accepted, closed 12 NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE – ROBLA CREEK TO ARCADE CREEK, page 4 First paragraph discusses work completed along Arcade Creek north levee. Why is being discussed under NEMDC east levee? Sentence deleted. accepted, closed 13 NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE – ROBLA CREEK TO ARCADE CREEK, page 4 Do not see sump 158 in Figure 1. Figure corrected. accepted, closed 14 NATOMAS EAST MAIN DRAINAGE CANAL EAST LEVEE – ROBLA CREEK TO ARCADE CREEK, page 4 Are the bridges at Silver Eagle Road, Interstate 80, and Del Paso Road/Main Avenue higher than the 200 year event? Yes they extend above the levee and above the 200-year event.

Suggest stating this in the document
accepted, closed,
15 Arcade Creek North Levee Are the bridges on the Northen levee higher than the 200 year event? Yes they extend above the levee and above the 200-year event.

Suggest stating this in the document
accepted, closed,
16 Arcade Creek North Levee, 2nd para Who is responsible to put it the stoplogs during floods? City of Sacramento Department of Public Works is responsible for stop log installation. accepted, closed 17 Arcade Creek North Levee, 3rd para What were the frequencies associated with the 1986 or 1997 high water events? Based upon a flow-frequency analysis for Arcade Creek by the USACE in American River Common Features Project General Reevaluation Report Appendix B, Dry and Arcade Creeks Flow Frequency Curves and Synthetic 8-Flood Series Hydrographs Upstream of Steelhead Creek , January 2010, 1986 was about a 4% annual-chance flood (25-year), and 1997 was about a 25% annual-chance flood (4-year).

Suggest stating this in the document
accepted, closed,
18 Arcade Creek North Levee, 3rd para
"This deficiency led to the overtopping in 1986." Was there any actions to remedy this in the future? We see that this is addressed in the Performance section but suggest referring to that section here.

This paragraph was moved to Section 4.0 Past Performance. Yes, the Norwood Avenue bridge was raised to remediate the overtopping condition. Text was added to the 3rd paragraph. accepted, closed
19 Arcade Creek North Levee, 3rd para
Suggest moving this paragraph/combining with information presented in Performance History section, as there is no similar write up in either the Robla Creek south levee or NEMDC east lee write ups and so the text seems out of place.

Move paragraph to Arcade Creek North Levee under Performance 4.0. Deleted from History 3.0 accepted, closed 20 3.0 PERFORMANCE HISTORY Based on the sequencing this should be Section 4.0, not 3.0. Also impacts numbering of subsequent sections. Section numbering corrected. accepted, closed 21 3.0 PERFORMANCE HISTORY, 4th para "A drained seepage berm was constructed in this area in 2024." Reference a report on this? This berm will be constructed in 2025 and a construction completion report will be prepared at that time. This ULDC report will not be submitted until after construction occurs. Construction was delayed due to obtaining permission from railroad so moved work until after flood season. The construction completion report will be referenced when complete. accepted, closed
22 3.0 PERFORMANCE HISTORY, Robla
Creek South Levee, 1st para Who owns and maintains the gage? Sacramento County owns the gage as stated in the second paragraph. accepted, closed 23 3.0 PERFORMANCE HISTORY Please include the datum on the elevations cited. Elevation datum information added to report. accepted, closed 24 3.0 PERFORMANCE HISTORY, Robla
Creek South Levee, 2nd para Have any of the observed WSEL exceeded the design WSEL? No, text was added to this paragraph to clarify. accepted, closed 25 ULDC 7.2 - Minimum Top of Levee Based on cross sections comparing 2024 surveyed levee profile the MTOL is below the ULDC required geometry at Station 6117+50 (KLF, 2024, Appendix B). The second paragraph of Section 7.2 describes this condition. No changes to text needed. accepted, closed 26 ULDC 7.3 - Soil Sampling HEM (helicopter-based electromagnetic surveys)' is introduced in the Robla Creek section, after which HEM can be used without further explanation. Text revised. accepted, closed 27 ULDC 7.4 - Slope Stability, pg 10
An abbreviation for NEMDC east levee is introduced under the NEMDC write-up, and used in defining station limits. Seems odd to introduce this abbreviation so late in the report and it isn't always used in conjunction with Station limits. Suggest deleting.

Text revised to remove odd abbreviation. accepted, closed 28 ULDC 7.4 - Slope Stability, NEMDC east
levee, pg 10
Suggest revising the text in the second to last sentence of the first paragraph to read 'Kleinfelder concluded the analysis was performed at critical sections and results of the evaluated WSE, which is higher than the current DWSE, met analysis criteria.' Text revised. accepted, closed
29 ULDC 7.8 - Levee Geometry May need to comment on Robla Creek Station 6117+50 (see comment on Kleinfelder Report, Appendix E), which appear to be outside the design levee prism. The upper end of Robla Creek is discussed in Section 7.2 MTOL. Geometry can still meet criteria independent of the MTOL. No need to revised Section 7.8. accepted, closed 30 ULDC 7.8 - Levee Geometry, ACNL,
page 14.

Move the word 'respectively' at the end of the second paragraph to after Appendices D and E - (AECOM and Kleinfelder (Appendices D and E respectively). Text revised. accepted, closed 31 ULDC 7.9, Interfaces and Transitions, page 15, btm of third paragraph. delete the word 'by additionally' in the last line. Text revised. accepted, closed

SAFCA CERTIFICATION
Robla-Arcade Levee Basin

REVIEW BY INDEPENDENT PANEL OF EXPERTS (IPC)
1 No. DOCUMENT LOCATION IN DOCUMENT

IPE'S COMMENT
(10/30/2024) Significance Rating ENGINEER'S RESPONSE (11/27/24) IPE's COMMENT (01/08/25) ENGINEER'S RESPONSE (Date) IPE's FINAL COMMENT / CLOSURE (Date) 32 ULDC 7.9, Interfaces and Transitions,
NEMDCEL, Item #5
Sump 157 references three pipes and four box culverts. However, other documents reference 4, 48-inch and 3-54-inch WSP. This should be conformed. Also, see comments on missing evaluation of 48-inch WSP in Mead & Hunt (Appendix H), which could propagate to this report.

Three 54' WSP (north) and quad 54'X54'cast-in-place reinforced concrete box culverts with positive closure gates (south sump). Engineer's report is correct. Kleinfelder and Mead & Hunt to conform reports accordingly. accepted, closed
33 ULDC 7.9, Interfaces and Transitions,
ACNL
Cross check items #3 through #7 against AECOM's Geotechnical Findings Report, Sept. 2024, Section 8, Table 8-1, page 12, as there appear to be differences and these should be consistent. Suggest making these portions of the report identical for ease of reference and cross checking.

Section 7.9 for Arcade Creek North Levee was updated to match AECOM's list. We are not capturing all of the road crossings, so not all of their items are included in the Engineer's Report. accepted, closed
34 ULDC 7.10: EROSION fps should be included in abbreviations section. Added feet per second to Acronyms section. accepted, closed35 ULDC 7.10: EROSION maximum permissible velocities cited should be referenced properly Reference added as suggested. accepted, closed36 ULDC 7.10: EROSION, RCSL, pg 18 The paragraph indicates an upperbound velocity of 5.8 fps and states that this is within the permissible limits for clay embankment soil types and vegetated channel conditions. This is at odds with text for NEMDCEL on the next page that states the maximum permissible velocities for bare earth or vegetated channels is 4 fps. Please explain why or revise text accordingly.

Text revised. accepted, closed
37 ULDC 7.10: EROSION, NEMDCEL, page
19 The last two sentences discuss debris in the channel from homeless activity and states that the impact on erosive conditions is unclear. This wording doesn't seem appropriate for this type of certification document and needs to be rationalized/explained better. For example, 'The impacts to date of this debris on erosion within the channel does not appear to have been significant, and is monitored by ???? as part of routine maintenance inspections and therefore is not considered a major problem' - if this is indeed the case. A similar explanation should be considered for the other two creeks where homeless activity was also observed.

Text revised. accepted, closed
38 ULDC 7.10: Erosion, ARCADE CREEK

NORTH LEVEE
It is mentioned that debris from encampments may collect and block the channel. The report should state, if true, that although "It is unclear what impact this may have on the direction of flow of water and contribution to erosive conditions" the impacts, based upon engineering judgement, would be minimal.

We don't know the long term impacts during a high water event and don't want to give a false impression that everything will be fine. We are choosing to leave the text as is and not include language of what the impact may be. accepted, closed
39 ULDC 7.11 - Right of Way See comment in Kleinfelder (Appendix E) - does the pool with non-compliant gradients in the dewatered condition need to be accepted by Exception? Pools are reviewed as part of DWR's inspection program. High gradients under pools is not called out in ULDC specifically and we don't feel an exception is warranted. Instead, the LMA is aware of the risk of empty pools and DWR is alerted to this condition also. No revisions to the text were made.

It is important that inspection to confirm that pools are 'maintained per permit conditions' includes the need for pools to be maintained in a full condition during the flood season and we strongly recommend that there is a continuing effort by land use agencies and local maintaining agencies to inform residents and inspection staff of the importance of keeping pools full during the winter.

Comment closed.
40 ULDC 7.13, Penetrations Third paragraph references Appendix J, but none is contained within the report. Appendix reference updated. Remediation will be included in final report. IPE does not need to review the plan. accepted, closed 41 ULDC 7.14: FLOODWALLS, RETAINING WALLS, AND CLOSURE STRUCTURES, ARCADE CREEK NORTH LEVEE, last sentence It should be noted that the 5-year testing frequency for the closure structure is also accepted by Exception. Text revised. accepted, closed 42 ULDC 7.14: FLOODWALLS, RETAINING WALLS, AND CLOSURE STRUCTURES, ARCADE CREEK NORTH LEVEE, last sentence "The rodent control and abatement program tracks active burrows as well as the monthly abatement activity structures through exception." Not a complete sentence. Should this be included in Section 7.15? Text revised. accepted, closed
43 ULDC 7.17 WindSetup Does the word 'still' in the second line of the first paragraph need deleting? Yes, it means there is no wave and is defined in ULDC. accepted, closed44 ULDC 7.19: SEA LEVEL RISE, 2nd para It is of interest to note that the hydraulic modeling shows that the assumed sea level rise has no effect on the DWSE for the Robla-Arcade levee system." Suggest just stating that the hydraulic modeling showed there was no effect on the DWSE for the Robla-Arcade levee system due to sea level rise.

Text revised. accepted, closed
45 ULDC 8.0 OPERATIONS & MAINTENANCE, 2nd para
"USACE Supplement to Standard Operation and Maintenance Manual (O&M Manual), Sacramento River Flood Control Project, Unit No. 118 – Part No. 2. North Levee of American River, East Levee of Natomas Canal, Both Levees of Arcade Creek, South Levee of Linda Creek and Magpie Creek Diversion Channel, revised date 28 Jan 2023" should be in the references Reference added. accepted, closed
46 ULDC 8.0 OPERATIONS & MAINTENANCE, last sentence
"The American River north levee system meets the requirements for ULDC 8.0 Operations and Maintenance." To be consistent with other sections, shouldn’t it specifically state the Robla-Arcade system meets ULDC 8.0 instead of ARN levee system? Text revised. accepted, closed
47 5.0 Bibliography References need re-ordering to be sequential alphabetically and then numerically Reference section cleaned up. accepted, closed 1 No. DOCUMENT

LOCATION IN

DOCUMENT
IPE Reviewer IPE'S COMMENT
(10/30/2024)
Significance
Rating

ENGINEER'S RESPONSE
(11/27/24)

IPE'S COMMENT
(01/08/25)

ENGINEER'S RESPONSE
(09/04/25)

IPE'S FINAL COMMENT / CLOSURE
(09/08/25)
1 Appendix C - Robla-Arcade Levee System - Determination of the Urban Levee Design Criteria Design Water Surface Elevation, Minimum Top of Levee, and Hydraulic Top of Levee - DRAFT, by MBK, dated July 15, 2024 Figure 3 and 4 Please expand on the descriptions of the lower right legend. Units? Elevation in NGDV88? Units and datum information for legend values added to report. accepted, closed 2 Figure 3 and 4 Since no cross sections up Robla Creek, assume it is 2-D - if so please state in text.

Second paragraph of Section 3.0 already states "Reaches with small low flow channels and wide floodways, such as Dry Creek, Robla Creek and Magpie Creek, were replaced with 2-D flow areas." accepted, closed
3 3. Hydraulic Model, page
6 National Land Cover Database should be properly cited A reference for the National Land Cover Database has been added to the report. accepted, closed 4 3. Hydraulic Model, page
6 "Manning’s n-values were initially assigned for the various land classifications based on recommendations in the HEC-RAS 2D User’s Manual (USACE, 2023b), and refined as necessary through the calibration process" Suggest in Table 4 to put in the suggested "n" values and the final values used.

Suggested n-values have been added to Table 4. accepted, closed 5 3. Hydraulic Model, end
of page 7 What were the associated frequencies of the 2006 flood? Based upon a flow-frequency analysis for the Arcade Creek and Dry Creek by the USACE in American River Common Features Project General Reevaluation Report Appendix B, Dry and Arcade Creeks Flow Frequency Curves and Synthetic 8-Flood Series Hydrographs Upstream of Steelhead Creek , January 2010, the 2006 flood event is about a 6% annual-chance flood (16-year). This has been added to the report. accepted, closed
6 Table 5 Should explain some of the abbreviations used in the table. 10yr_C=99.5? 10yr_C=RIOLINDA_MAGPIE ? 10yr_C=ARC
Definitions of abbreviations added to Table 5. accepted, closed 7 5.2 Debris Loading, 2nd
para
Please properly cite July 2014 letter A reference has been added for the July 2014 letter. accepted, closed 8 5.7 Sea Level Rise Should explicitly state that there was no effect on the DWSE due to sea level rise.

Disagree. We did not determine the effect of sea level rise on the DWSE. To do that would require hydraulic simulation without sea level rise. Since the ULDC requires accounting for sea level rise in the determination of the DWSE, a simulation without sea level rise was not made.

Because the check was performed with sea level rise and was acceptable, this comment can be closed.
9 Figures 6, 7 and 8 Please cite source of the top of levee/floodwall elevations. Source of top of levee data added to report. accepted, closed 10 Figure 8.

Please explain the reason the top of levee is below the DWSE at the far right and how it does not violate the requirements for the DWSE. It is described in section 6.2, but suggest repeating here or reference section 6.2.

Reference to Section 6.2 added to report. accepted, closed 11 6.2 Minimum Top of
Levee (MTOL), 2nd para
"That is, where there is insufficient freeboard, the levee is dry at the DWSE." Is it better to say the DWSE does not reach the levee at this location? Report revised as recommended. accepted, closed 12 6.3. Hydraulic Top of
Levee (HTOL), Figure 14
In section 6.3, suggest referring the reader to see section 6.2 for explanation of the far right end of Figure 14. Reference to Section 6.2 added to report. accepted, closed 1 Appendix D, Urban Levee Design Criteria Geotechnical Findings Report, Arcade Creek North Levee Station 5023+00 to 5112+43, Robla-Arcade Levee System, prepared by AECOM, September 13, 2024 General Check that references in the report text match and/or are contained in Section 13 References. For example, Spink, 1997 is not in Section 13. Correlated with text and reference added. Note there are several broken links to references in the PDF that will need to be corrected for the final report. 2 Updated November 15, 2024 Section 1.1, North Area Stream Background First paragraph references north and south banks of Dry/Robla Creek and Arcade Creek, but this study covers only Robla Creek south levee and Arcade Creek north levee. Suggest revising to avoid confusion to the reader. Text revised and footnote added to clarify that only Arcade Creek northlevee is covered by AECOM's report. accepted, closed 3 Section 2.1 Data
Reviewed
Suggest revising the second sentence to include the words 'by exception' after the word 'adequate', to be consistent with Section 3.0 ULDC Section 7.3. Revised as suggested accepted, closed 4 Section 2.7 DWSE Suggest adding '(0.16 feet)' after the word 'minor' in the third paragraph show the reading knows how minor the difference is or just state the difference itself. Revised as suggested accepted, closed5 Section 3.1, 4th paragraph, last sentence
This report, and several others, reference a history of good performance during previous wet seasons as an indicator of future performance. However, I have not found a summary of past hydrologic events, including actual WSEs, to provide context to these statements. It would be helpful if one of the documents had such a summary to make the statements more meaningful. This may be best added to Appendix C.

AECOM’s geotechnical analysis firmly supports the premise that the levees shall adequately perform at the ULDC DWSE provided by MBK. The report provides sufficient detail on the seepage and slope stability analyses using current USACE methodology and criteria. AECOM stands behind our assessment that the levees meet ULDC and shall continue to do so on the condition that O&M practices and routine inspections are performed by the LMA, any performance issues during a high-water event are documented, a 200-year event occurs, or when the levees are re-evaluated again for ULDC. Since the time when the last levee improvement project was completed in 2017, there has not been a high-water event that matches the conditions to which the levee was designed and evaluated (i.e. 200-year), nor there have been any performance issues or concerns that would alter our opinion. Therefore, a summary of hydrologic events with specific WSE’s would not be relevant in the context and/or intent of the report for which its primary purpose is to demonstrate that the levees meet current ULDC criteria. accepted, closed
6 Section 5.0, Table 5.0 The second sentence of Note 2 below the table is incomplete. Notes and table have been corrected and expanded to further clarify ULDC requirements. accepted, closed 7 Section 5.2 Conclusions
There doesn't appear to be mention of seepage above the landside toe in previous sections and so the comment in the third sentence about minimal seepage at the landside toe appears out of context. It is suggested to remove this sentence.

Disagree. Section 5.1 mentions landside levee seepage above the toe and references Section 8.6 that addresses the issue in more detail. accepted, closed
8 Section 8.2 and 8.3 When describing results of AECOMS PIR analysis change 'does not meet' to 'did not meet', as the deficiency has since been addressed. Text revises as suggested, including Section 8.1 as well. accepted, closed 9 Section 8.5.1 Floodwalls
The second paragraph on page 17 references a 'metal closure assembly' for a small gap 'between the end of the wall and the abutment'. I don't recall this being mentioned in the Engineers Report prepared by MBK. Is this structure considered a true closure structure? I think a clearer definition of the purpose and operation of this structure is required.

The feature is a wave protection splash plate 1-foot wide in the freeboard zone that connects the end of the wall with the bridge dech railing. It is not a closure structure meant to hold flood water. To address the question, we have eliminated any reference to a closure feature and referred to it a a splash plate as defined on the record drawing with some additional description. Do not believe it requires any special treatment in the MBK report. accepted, closed
10 Section 8.5.1 Floodwalls The fourth paragraph on page 17 references PIR, Addendum1. Please cite a reference for this report and include in the reference section. Reference cited in text. Was cited previously and is already in the reference section (URS, 2015b). accepted, closed 11 Section 9.0 ULDC
Section 7.13
Penetrations
Cite the Mead and Hunt report and include in the reference section. Addition made accepted, closed 12 Section 9.0 ULDC
Section 7.13
Penetrations
The fourth paragraph discusses an AT&T duct bank. Is the duct bank truly encased in the SCCB at the toe of the waterside slope and there is no window below? Yes, the duct bank was near surface after preparatory excavations in the area. The slurry trench excavation exposed the top, sides, and excavated out under the bottom so the duct bank is fully encased with no window. accepted, closed
13 Section 13.0 References Update to cover all references in the report text and check order/sequencing of references is correct. For example, where is URS Corporation 2014a or should URS Corporation 2014b be 2014a? References list updated to be specific to this report, several removed that are not cited. accepted, closed 1 Appendix E, ULDC Geotechnical Finding - Robla Creek South Levee Stations 6000+00 to 6118+20, NEMDC East Levee Stations 3056+00 to 3192+25, Arcade Creek North Levee Stations 5000+00 to 5023+00, prepared by Kleinfelder, September 13, 2024 General Check that acronyms used in the report are defined before their use, for example CVFBP is used on pg 26 of the text isn't defined until pg 29. Also, once defined they are used consistently thereafter.

Corrected and all acronyms were checked.
accepted, closed

SUPPORTING REPORTS

REVIEW BY INDEPENDENT PANEL OF EXPERTS (IPC)
1 No. DOCUMENT

LOCATION IN

DOCUMENT
IPE Reviewer IPE'S COMMENT
(10/30/2024)
Significance
Rating

ENGINEER'S RESPONSE
(11/27/24)

IPE'S COMMENT
(01/08/25)

ENGINEER'S RESPONSE
(09/04/25)

IPE'S FINAL COMMENT / CLOSURE
(09/08/25)
2 General Check that cited references are provided in the Reference Section. For example KLF, 1997 appears in the text but isn't in the reference section. The Kleinfelder 1997 reference from Section 1.5 was added to the Reference section. Other Section 1.5 references were confirmed to be included in Reference Section.
accepted, closed
3 Section 1.1 Project
Introduction
Station limits for NEMDCEL presented on the third line of the first paragraph are different from those presented in the Engineers Report (MBK, 2024). Comment also applies to the remaining sections of the report.

Kleinfelder discussed with MBK and confirmed the NEMDCEL Stationing of 3056+00 to 3192+25. MBK updated the Engineering report to match. accepted, closed 4 Section 1.2 and
elsewhere in the
document
The terms keyway, key trench and inspection trench are used throughout the report and it isn't clear to the reader if they are the same thing or different. Recommend standardizing terminology as much as possible. It seems keyway relates to new fill placed at the levee toe and inspection trench/key trench relate to the centerline of the levee. It would be useful to make this clear in the report and where information is available state width of excavation in addition to depth.

Section 1.2 was revised to keyways and inspection ditches to be consistent to how they are reference on the as-built drawing and to be consistent throughout the text. Keyway trench - refers to a trench along the landside or waterside levee toe. Inspection trench - refers to a trench excavated beneath the orginal levee embankment. accepted, closed
5 Section 1.2, Page 3, 2nd
paragraph
There are several references throughout the document to the drained stability berm for the UPRR embankment. Some say it is to be constructed and some say it is complete. The document references to this work should be conformed to the current status of the work and consistently described. Also, the location of seepage and subsequent remediation work should be stated in the report text.

The construction has been pushed to Spring 2025. The text was review to reflect the delay.

This report will not be finalized until construction of the drained stability berm is complete and the quality control testing is final. At that time, details of the construction will be included in the report.

Response is reasonable. Closure pending receipt of final report after construction of the seepage berm is complete.

Construction is complete, reference to project and Construction Completion Report are included in the Engineer's Report.

Moved to Section 1.2.2 and updated for 2025
Construction. Accepted, closed.
6 Section 1.2, Page 4, 1st
paragraph The last sentence is a repeat of what was stated at the bottom of page 3 and is redundant. Agree, revised. accepted, closed 7 Section 1.4, page 5, 2nd
para. 2nd to last
sentence
This section states that prior analyses "substantially met project criteria", but later sections show criteria were met. This sentence should be clarified as to what parts of the prior analyses did not meet project criteria, if any. word 'substantially' was removed to avoid confusion.
accepted, closed
8 Section 1.4, page 5, last
paragraph.

It is noted in Table 1.1 and from the 2024 WSE analysis presented in Appendix A that the 2024 200-year WSE is equal to or above the previous highest WSE upstream of approximately Station 6113+00. As such, the IPE would like to check that KLF has taken this into account when performing their check on seepage and stability analysis for RCSL and that 2024 200-year WSE in this section of levee does not cause a certification problem.

The 2024 HTOL (with USACE Magpie Project) at Station 6117+00 is 44.86 and increases to 46.25 at Station 6118+19. The 2024 200-Year is 44.40 to 45.64 at the same stations.The previous HTOL analyzed for the entire length of RCSL is 44.48 to 45.23 which is higher than 2024 WSEs except for Station 6118+19. At Station 6118+19 the RSCL landside toe and surrounding ground surface elevation rises to approximately 46.4 feet [LiDAR topography profiles from ULE SGDR (URS, 2011)], which is above the 2024 HTOL WSE at this location. Table 1.1 was revised and a footnote added. The added footnote was included in Section 1.4.Additionally in Tables 2.4 and 2.5 display the previously analyzed WSE vs the 2024 WSE. The previous WSE is higher for at each critical cross section.
accepted, closed
9 Section 1.7, pg. 7, first
sentence first para. Typo - the word 'above' isn't needed. removed accepted, closed 10 Section 2.1, Tables 2.1 to

2.3 and first sentence
after Table 2.3
Since many explorations did not meet SPK SOP 2022 criteria, it's not clear what the relevance of "all explorations" is. It might be simpler to not include this data and focus on the non-boring data that fills in the gaps, which is sufficient to justify the Exception.

SPK SOP 2022 requirements include depth of exploration, sampling, blow counts, and laboratory testing. However, the exploration not meeting all of these requirements were still included on the plan and profile sheets and are used simliarly to the geology and geophysical data to help fill in gaps such as levee embankment and blanket composition and continuity. The following sentence was added on Page 13, last paragraph of Section 2.1, "While explorations not meeting the SPK SOP requirements where not solely relied upon for analysis, the data was reviewed in conjunction with adjacent explorations meeting SPK SOP in addition to geology and geomorphology, geophysical HEM (helicopter-based electromagnetics surveys), past performance information, historical records, and construction records (including inspection and keyway trench observations). " accepted, closed
11 Table 2.4
For the Through Seepage column, "meets" is not very descriptive when describing analyses performed elsewhere. It implies there were no locations for which seepage exited the face above the toe and/or if it did, the materials are erosion resistant. But it would be better to conclusively state that in the text or note where seepage exiting above the toe was evaluated and justified. Why is through seepage not applicable at Station RCSL 6016+00?Note 2 at the bottom of the table on page 17 doesn't appear in the table. Please review and correct as needed.

Section 2.2, Page 16, 1st paragraph, "Through seepage occurs where the phreatic seepage surface exits above the levee toe on the landside levee slope. For through seepage, reaches where the phreatic seepage surface exited on a levee slope that is composed of erodible material (sands and non-plastic silts and silty sands) were generally considered to not meet criteria." This sentence was added as Note 1 to Table 2.4. The analysis cross sections for Station RCSL 6016+00 were evaluated and the through seepage assessment was revised to 'Meets' since the embankment material is consistent with other RCSL analysis sections and the phreatic surface is not shown exiting the landside slope face. Note 3 (was 2) is shown on NEMDCEL 3133+00 with ditch and drain trench. The Note 2 in the text is revised to, "2.“NEMDCEL 3133+00 with ditch and drain trench” Analysis was performed by URS and included in 2014 technical memorandum “Drain Trench System Design along Reach NAS-NE-3 (City of Sacramento Sump No. 157 at Magpie Creek).” Regarding "meets", the IPE agrees with the definition of "meets" and "does not meet" used. However, as presented, there is no way for the IPE to assess the evaluation performed. The IPE suggest that future reports include a breakout distance above the toe (if any) and material classification to provide more transparency in the evaluation, which is similar to including factors of safety for slope stability.

The other two responses are acceptable.

Comment closed.
12 Table 2.4 and 2.5 In reference to comment 8 above regarding the 2024 200-year WSE along RCSL, check to make sure that changes to the tables are not required. Table was reviewed and the previously analyzed WSE are consistent with the published analysis included in the Kleinfelder 2016 PIR and ULDC Reports. accepted, closed 13 Table 2.4, NEMDCEL
3080+00
The highest previous WSE is noted as 42.1, but the current HTOL is 43.17, which suggests the difference column should be positive 1.07 feet, not negative. This entry should be checked and the additional 1-foot of head commented on, if necessary.

The 2024 WSE were entered incorrectly for the 2024 200-yr and 2024 HTOL. For NEMDCEL STA 3080+00, the 2024 200-yr is 37.63 ft and the 2024 HTOL is 40.63 ft. For NEMDCEL STA 3080+00, the previosly analyzed WSE was 42.1 ft. The differences between the 2024 and previous WSE are -1.93 feet and -1.47 feet. Table 2.4 has been revised.

Response acceptable, although WSE are noted to be -4.47 and -1.47 feet, as shown in Table 2.4. Comment closed.
14 First bullet at the top of
page 22
Section 2.3 is addressing underseepage. The bullet references slope stability. Revise to reference underseepage.

to 5023+00) at critical locations. "
accepted, closed
15 Section 2.5.1, page 25 The third sentence seems incorrect as written as Psomas performed survey work in 2024. Delete or revise sentence. Sentence revised to, "Prior to 2024 no surveys of the levee were performed since there has been no construction activity since the improvements in the 1990's and early 2000's. "
accepted, closed
16 Section 2.6.2
Please confirm if the base of the foundation, and any integral extension thereof, for the stop log structure extends into the impermeable levee material beneath the railway ballast and that this transition is modelled correctly in the seepage analysis. Same comment applies to the other stop log structure along NEMDCEL (Section 2.6.13).

Section 2.6.2 is to address the transition between the stop log structure and the levee embankment. 2.6.2 was revised to discuss more of the retaining wall construction and reference was added to Section 2.7.3 of the report regarding more details of the stop log structure. accepted, closed
17 Section 2.6.3 The word 'between' in the heading and the text needs to be replaced as only once Station is referenced. revised accepted, closed 18 Section 2.6.7, page 28 "intersection or NEMDCEL" should be "intersection of NEMDCEL". revised accepted, closed 19 Section 2.6.9 This paragraph bounces around chronologically and by CVFPB permit and is difficult to follow. Suggest reorganizing chronologically for clarity. This section has been revised to be more clear. accepted, closed 20 Section 2.6.10, first para. Recommend including the word 'through the levee' after 'installed' in the second to last sentence, 'installed through the levee', if this is indeed the case. revised accepted, closed21 Section 2.6.12 The final statement notes that the seepage berm will be constructed in the summer/fall of 2024 and additional QC/QC testing details need to be added. This should be added prior to final review of the report by the IPE.

Concur, see response to comment 5
accepted, closed
1 No. DOCUMENT

LOCATION IN

DOCUMENT
IPE Reviewer IPE'S COMMENT
(10/30/2024)
Significance
Rating

ENGINEER'S RESPONSE
(11/27/24)

IPE'S COMMENT
(01/08/25)

ENGINEER'S RESPONSE
(09/04/25)

IPE'S FINAL COMMENT / CLOSURE
(09/08/25)
22 Section 2.6.15
High gradients are noted for empty pools analyses at STA 6027+00 for both the DWSE and HTOL analyses. Have the proposed additions to the O&M manual discussed at the end of the section been incorporated? Given the non-conforming analysis results, does this require an Exception that is justified by the O&M Manual changes? Swimming pools observed and evaluated for this study are located outside of the landside levee easement. This limits the ability of the LMA to perform enforcement since this is an area where they have no jurisdiction. The DWR pre and post flood season inspection checklist includes swimming pools. Last paragraph in this section was revised as follows. "Based on review of the RCSL swimming pools, the swimming pools evaluated meet allowable gradient criteria if the swimming pools were full and four of the five swimming pools met criteria if they were empty. One swimming pool, RCSL-1 located 32 feet from the landside levee toe, does not meet criteria if it is empty. The Department of Water Resources pre and post flood season inspection checklist includes evaluation of residential pools. It is recommended that swimming pools be noted as features of interest during levee inspections and levee patrols." It is important that inspection to confirm that pools are 'maintained per permit conditions' includes the need for pools to be maintained in a full condition during the flood season and we strongly recommend that there is a continuing effort by land use agencies and local maintaining agencies to inform residents and inspection staff of the importance of keeping pools full during the winter.

Comment closed.
22 Section 2.7, General
Comment
It is noted that AECOM dealt with this section in a different way by stating the geotechnical aspects of the review were covered under ULDC 7.9 Interfaces, Transitions and Gaps and that structural aspects were covered by Mead and Hunt. Suggest to follow the same approach for consistency.

The report sections are intended to be standalone and to address each aspect of the ULDC section being evaluated.The second introductory paragraph was revised to reference Mead and Hunt's evaluation of the structural integrity of the floodwalls, retaining walls, and closure structures. accepted, closed
23 Section 2.7
Additional comments in case approach identified in comment 22 isn't followed.Opening paragraph states there are no floodwalls along the project alignment. However the Engineers Report (MBK, 2024) references floodwalls. Reports need to be consistent. Should sumps be include? Are they considered to be a floodwall, retaining wall or closure structure under ULDC 7.14? The conclusions statements only reference settlement . Is that all that is needed under 7.14? The floodwalls at Rio Linda Boulevard Bridge abutment was included as Section 2.7.4 and Section 2.6.4 was included to discuss the walls. Retaining walls and/or flood walls associated with sumps are included in Section 2.7. Since sumps are located at or offset form the landside levee toe, we have not considered sumps as closure structures. The last sentences of Section 2.7.1 through 2.7.4 discuss settlement is no longer a concern due to construction occurring over 10 years ago. accepted, closed
24 Section 2.7
This report, and several others, makes multiple references to a history of good performance during previous wet seasons as an indicator of future performance. However, I have not found a summary of past hydrologic events, including actual WSEs, to provide context to these statements. It would be helpful if one of the documents had such a summary to make the statements more meaningful. This may be best added to Appendix C.

Past performance is summmarized in the MBK engineering report. accepted, closed
25 Section 2.7.3, 5th
Sentence
This references Mead & Hunt 2018. Should this be Mead & Hunt 2024? Revised to Mead and Hunt 2024. accepted, closed 26 Section 2.7.3
This paragraph states both that there is a 8-inch-wide cutoff extending 3 feet below the ballast as a cut off and that seepage is expected through the thin layer of ballast not cut off by the concrete pad or cutoff wall. These statements should be conformed. Also, it seems appropriate to present this information in the relevance sections of ULDC 7.9 Interfaces, Transitions and Gaps.

This section was revised to include the closure structure at RSCL. See comment response #16. accepted, closed
27 Appendix B, Cross
Sections, Robla Creek
6117+50
This cross sections shows the crest of the levee per Psomas 2024 is below the ULDC profile.This should be discussed in the text and also the Engineers Report needs to address this in terms of ULDC 7.2 MTOL.

Section 2.5.1 was revised to include the following," Cross section Station RSCL 6117+50 was noted to have a higher minimum top of levee (MTOL) elevation of 47.92 than the surveyed elevation of 46.6 feet. However, the geotechnical evaluation 200-year WSE is 45.02 feet and HTOL is 45.56 feet, both of which are below the levee crown and landside toe. This is an area of high ground, where the channel is incised and the levee is for freeboard. Therefore, from a geotechnical standpoint, stability is considered to meet criteria at Station 6117+50. Levee freeboard is addressed in the MBK Engineers Report. " MTOL and geometry concerns are addressed in the MBK report. accepted, closed
1 Appendix F, MBK, September 2024, SAFCA Robla Arcade Levee System, Levee O&M Review in Support of FEMA Certification and ULDC Evaluation Third page, second to
last paragraph
Text states that the PI did not identify any critical issues, but the Engineers Report notes that the USACE 2010 PI report rated that unwanted vegetation was Unacceptable. Was this not considered a critical issue? This is not a critical issue. ARFCD has cleared the rating and works to control vegetation all year long. A sentence was added to provide this insight.

Please include USACE Attachments 1 and 2 to the document in Appendix F as and when available.

Comment Closed
Attachments included in final backcheck copy. Accecpted, closed 2 Appendix F2, MBK, October 2024, SAFCA Levee Certification, Robla-Arcade Levee System, Erosion Report General No comments. Acknowledged.
1 Appendix H - ROBLA-ARCADE LEVEE SYSTEMDue Diligence Review for ULDC &FEMA Certification, by Mead& Hunt, September 13, 2024 Section 2.2.4, 1st
paragraph LMA is used as an acronym but hasn't been previously defined. Editorial Corrected accepted, closed 2 Section 2.5, 1st para. Cite MBK 2016 report and include in references. Included Please confirm reference. This appears to be listed as a SAFCA document, rather than and MBK document, in the references. This is a SAFCA document. References updated to clarify. Accecpted, closed 3 Section 2.5, 3rd
paragraph, 2nd sentence Should this read "…will address non-compliance and non-permitted encroachments"? Editorial Corrected accepted, closed 4 Section 4.4 Results, 3rd
para., pg 10
Please include additional details regarding the closure structure (8-inch wide cutoff wall extending a minimum 3 feet below the ballast between retaining walls) as presented by KLF in their ULDC Geotechnical Finding Report.

The language is updated to include a description of the two phases of construction for the grade beam (cutoff) at the UPRR closure structures, and the original City of Sacramento drawings have been added to the Appendix E. accepted, closed
5 5. ULDC Section 7.17,
Wind Setup and Wave
Runup
no comments Acknowledged.
6 7. 1.4 Wind Setup and
Wave Runup
no comments Acknowledged.
1 Appendix H - ROBLA-ARCADE LEVEE SYSTEMDue Diligence Review for ULDC &FEMA Certification, by Mead& Hunt, September 13, 2024Appendix A - Penetration Evaluation Technical Memorandum, Attachment 1 Reach AR02B, City Sump
157
This section only discusses the 3, 54-inch WSP in the north sump, which pass through the crest in the siphon breaker. It does not discuss the 4, 48-inch WSP penetrations for the south sump, which are described by Kleinfelder (Appendix E, Section 2.6.10) as passing through the levee. The NEMDC Phase 3A plans do not show a siphon breaker corresponding to these pipes, and the penetration may be a significant distance below the DWSE. Potential issues with these pipes, in particular, the potential for piping, should be discussed, including the potential for piping around the gate control structure and potential mitigating effects of the structure.

High
The south sump outlet is through the quad 54-inch by 54-inch cast-in-place reinforced concrete gravity culverts with positive closure slide gates and outfall flap gates, constructed for the Magpie Creek Closure by the USACE during 1954 levee construction.. Culvert has waterstop joints at 12 to 15 foot spacing and joints are encased by reinforced concrete collars. The screening effort did not flag this structure for further review at it complies with criteria set forth, and hence not included in this further evaluation TM. See 2.1, 3rd paragraph Footnote 1.There is come confusion in the record keeping indicating that 48" WSP's were installed inside of culverts, but the original box culvert arrangement has been confirmed by the City via pipe entry. accepted, closed
1 Appendix H - ROBLA-ARCADE LEVEE SYSTEMDue Diligence Review for ULDC &FEMA Certification, by Mead& Hunt, September 13, 2024Appendix D - RALS Wind Setup and Wave Runup Analysis

2.3 Wind Speed Data Suggest stating (in a Table?) the period of record for each airport as well as the periods NOT used in the analyses. Added table to Section 2.3 to summarize the dates of wind speed data available at each airport, the years for which data was used, the years for which data was not used, and the reason data was not used. accepted, closed 1 No. DOCUMENT

LOCATION IN

DOCUMENT
IPE Reviewer IPE'S COMMENT
(10/30/2024)
Significance
Rating

ENGINEER'S RESPONSE
(11/27/24)

IPE'S COMMENT
(01/08/25)

ENGINEER'S RESPONSE
(09/04/25)

IPE'S FINAL COMMENT / CLOSURE
(09/08/25)
2 2.4 Fetch length and
Critical Wind
Should state somewhere in this section that the net wind velocity did not take into consideration the water velocity and orientation to the wind direction.

Added this statement. accepted, closed
3 2.4 Fetch length and
Critical Wind, equation 1
and 2
U is not in equation 1 or 2. U is in mph? What is F in equation 1 - not defined for 1st equation. Subscript of F in equation 1 and 2 is not the same as described for equation 2. Updated equation 1 and definition of terms. accepted, closed 4 3.1 Stationarity and
Detrending
Good to see the test for stationarity. Did splitting the record leave enough data in each partition to be statistically significant? Yes, the minimum sample size after splitting was 23 (for MCC airport), and guidance from USACE indicates the K-S test can be calculated for sample sizes greater than 12. The calculated significance level takes the sample size into account. accepted, closed
5 3.3. Analysis Procedure,
equation 3 Suggest adding that k not equal to zero and ky > -1 Added. accepted, closed 6 3.3. Analysis Procedure Is the GEV method recommended by ULDC or was this decided by the author of this document? The GEV distribution was selected for this analysis by Mead & Hunt. No statistical distribution for analysis of annual maxima is recommended in ULDC. The GEV distribution is commonly used for extreme value analysis, including wind speed. Previously-published 50-year fastest-mile wind speed data included in the USACE Coastal Engineering Manual (EM 1110-2-1100) was based on the Fisher-Tippett Type-I (or Gumbel) distribution, which is a subset of the GEV distribution.

The document should include the justification to use GEV. Justification for the selection of the GEV distribution for annual peak wind speed analysis has been incorporated into the document. Accecpted, closed 7 7.1 Acceptance Criteria,
page 21
The penultimate sentence of the first paragraph states 'Additionally, the interior drainage system must be assessed to determine satisfactory drainage to handle any predicted overtopping flows.' No changes are required to the report text, but the IPE notes that any interior drainage assessments should use the latest available information/standards, unless it is not considered appropriate at that time, in which case a justification for deviation should be stated.

Informational / no change. accepted, closed
8 7.2 Overtopping rate,
page 21, last sentence
Suggest "No overtopping locations were identified due to combinations of windsetup and wave runup in this study." Revised. accepted, closed
9 Table 2 Suggest some wording on locations at or near 3 feet saying all assumptions to obtain these values are conservative and have confidence these values would not be exceeded for the design event.

Engineer is not comfortable with the suggested wording. While no assumptions are known to be unconservative and some assumptions are considered conservative, others are neutral and there is some uncertainty due to the empirical nature of the analysis methods. However, the results have been determined in accordance with ULDC and other best practices. accepted, closed
1 Appendix C.

Robla-Arcade Levee System
ULDC Water Surface Elevation
Profiles - MBK Engineers
Water Resources Flood Control Water Rights

TECHNICAL MEMORANDUM
DATE: November 18, 2024
PREPARED FOR: SAFCA
PREPARED BY: Michael Archer, P.E.

REVIEWED BY: Don Trieu, P.E.

SUBJECT: Robla-Arcade Levee System - Determination of the Urban Levee Design Criteria Design Water Surface Elevation, Minimum Top of Levee, and Hydraulic Top of Levee
SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 2

Acronyms and Abbreviations
1-D one dimensional
2-D two dimensional
AEP annual exceedance probability
ARN American River north
cfs cubic feet per second
CVFED Central Valley Floodplain Evaluation and Delineation CVFPP Central Valley Flood Protection Plan
CVHS Central Valley Hydrology Study
DWR California Department of Water Resources
DWSE Design Water Surface Elevation
FEMA Federal Emergency Management Agency
HTOL Hydraulic Top of Levee
LAR Lower American River
MBK MBK Engineers
MTOL Minimum Top of Levee
NAS North Area Streams
NAVD88 North American Vertical Datum of 1988
NEMDC Natomas East Main Drainage Canal
RM River Mile
SAFCA Sacramento Area Flood Control Agency
SNRR Sacramento Northern Railroad
SVRP Seismic Vulnerability Restoration Profile
ULDC Urban Levee Design Criteria
ULOP Urban Level of Flood Protection
UPRR Union Pacific Railroad
USACE U.S. Army Corps of Engineers
WSE water surface elevation

1. Purpose
The Sacramento Area Flood Control Agency (SAFCA) is in the process of evaluating the levees within its jurisdictional boundaries for compliance with the State of California’s Urban Levee Design Criteria (ULDC) (DWR, 2012). This technical memorandum provides documentation of the determination of the hydraulic parameters listed in Table 1, which are necessary for the ULDC compliance evaluation of the Robla-Arcade levee system.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 3 Table 1. ULDC Hydraulic Parameters
Parameter ULDC Definition
Design Water Surface Elevation (DWSE) Median 200-year water surface elevation (WSE) Minimum Top of Levee (MTOL)
DWSE plus the higher of
• 3 feet, or
• wind setup and wave runup
Hydraulic Top of Levee (HTOL)
The lower of
• DWSE plus 3 feet, or
• Median 500-year WSE
Seismic Vulnerability Restoration Profile (SVRP)
10-year water surface elevation plus the higher of
• 3 feet, or
• wind setup and wave runup

2. Study Area
The Robla-Arcade levee system protects the floodplain bounded on the south by Arcade Creek, on the west by the Natomas East Main Drainage Canal (NEMDC), on the north by Robla Creek, and on the east by high ground (see Figure 1). The levee system is made up of the three levee segments summarized in Table 2.

Table 2. Robla-Arcade Levee System
Levee Segment Length (feet) Upstream Limit Downstream Limit Arcade Creek north levee 11,200 Marysville Blvd. NEMDC east levee NEMDC east levee 13,637 Robla Creek south levee Arcade Creek north levee Robla Creek south levee 11,820 Dry Creek Road NEMDC east levee SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 4 Figure 1. Robla-Arcade Levee System

3. Hydraulic Model
A HEC-RAS 6.4.1 hydraulic model was developed for this analysis. HEC-RAS is software developed by the USACE Hydrologic Engineering Center for the purpose of performing one-dimensional (1-D) and twodimensional (2-D) hydraulic calculations for a full network of natural and constructed channels (USACE, 2023).

The hydraulic model, referred to as the Sacramento north area streams, or NAS, model is made up of both 1-D elements and 2-D flow areas. The model was developed from an existing 1-D model. Reaches with small low flow channels and wide floodways, such as Dry Creek, Robla Creek and Magpie Creek, were replaced with 2-D flow areas. A schematic of the model is shown in Figure 2. The streams within the model study area are summarized in Table 3. The downstream boundary of the model is the NEMDC at the American River north levee.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 5 Table 3. Streams Within the Model Study Area
Stream Upstream Boundary Downstream Boundary Model
Element
Length
(miles)
Dry Creek Below Q Street NEMDC 2-D 3.5
Robla Creek Above 16th Street NEMDC 2-D 3.3
Magpie Creek Patrol Road Robla Creek 2-D 1.8
Don Julio Creek Patrol Road Magpie Creek 2-D 1.3
Arcade Creek Auburn Blvd. NEMDC 1-D 6.6
NEMDC D-15 Pump Station American R. north levee 1-D 4.3 Figure 2. North Area Stream HEC-RAS Model Schematic
HEC-RAS 2-D flow areas require a terrain model for the establishment of its geometric and hydraulic properties. The primary terrain used for the NAS model was developed by USACE for use in their hydraulic analysis of the Magpie Creek project (USACE, 2021). The USACE terrain did not provide coverage of the entire NAS model study area, as shown in Figure 3. Terrain developed for the California Department of Water Resources (DWR) Central Valley Floodplain Evaluation and Delineation (CVFED) program (Wood SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 6 Rodgers, 2014) was used to extend coverage to the entire NAS model study area, as shown in Figure 4.

The vertical and horizontal accuracy and resolution of the USACE terrain is not provided in the referenced documentation. The CVFED terrain has a vertical accuracy of 0.6 feet, a horizontal accuracy of 3.5 feet, and an average point spacing of 3.28 feet.

Figure 3. USACE Terrain Coverage (elevations are Figure 4. Final Terrain Coverage (elevations are in In feet NAVD88) feet NAVD88)
Manning’s n roughness coefficient values within the 2-D flow areas were defined using land classification mapping from the National Land Cover Database (USGS, n.d.), as shown in Figure 5. Manning’s n-values were initially assigned for the various land classifications based on suggestions in the HEC-RAS 2D User’s Manual (USACE, 2023b), and refined as necessary through the calibration process. The land classifications, suggested n-values, and final calibrated n-values are listed in Table 4.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 7 Figure 5. Land Classification Map
SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 8 Table 4. Land Classifications and Assigned Manning’s n-values Land Classification
Manning’s n-value
Suggested
Range
Model Calibrated
Value
Barren Land Rock-Sand-Clay 0.023 – 0.030 0.035
Cultivated Crops 0.02 – 0.05 0.038
Deciduous Forest 0.10 – 0.20 0.08
Developed, High Intensity 0.12 – 0.20 0.10
Developed, Low Intensity 0.06 – 0.12 0.05
Developed, Medium Intensity 0.08 – 0.16 0.07
Developed, Open Space 0.03 – 0.05 0.04
Emergent Herbaceous Wetlands 0.05 – 0.085 0.06
Evergreen Forest 0.08 – 0.16 0.08
Grassland-Herbaceous 0.025 – 0.05 0.035
Open Water 0.025 – 0.05 0.03
Pasture-Hay 0.025 – 0.05 0.042
Shrub-Scrub 0.07 – 0.16 0.08
Woody Wetlands 0.045 – 0.15 0.07
The model was calibrated to the high flow event that occurred during the end of December 2005 and the beginning of January 2006 (the “2006 flood”). Based on a flow-frequency analysis by USACE for the American River Common Features Project General Reevaluation Report (USACE, 2010), the 2006 flood is about the 6% annual-chance flood. Calibration results are provided and summarized in Appendix B.

4. Hydrology
Central Valley Hydrology Study (CVHS) procedures and hydrologic data were used in this analysis. The CVHS was commissioned by the California Department of Water Resources (DWR) and prepared by the USACE (USACE, 2015). For the Sacramento River and San Joaquin River basins, the CVHS defines a procedure in which a scaled flood event with a pattern based on a historical flood event is selected to represent the flood of a specific frequency at a specific location, or centering. The CVHS also developed hydrologic data for several smaller ungaged watersheds, including the Natomas-Area Stream Group, which includes Dry Creek, Robla Creek and Arcade Creek (USACE, 2013). The hydrologic data for the Natomas-Area Stream Group was developed for discrete N-year flood frequencies with centerings defined by contributing area (C) parameters. The Natomas-Area Stream Group hydrologic data was updated by USACE in 2019. There are four CVHS defined flood centerings that influence the NAS model study area:
• Natomas-Area Stream Group: Dry Creek
• Natomas-Area Stream Group: Robla and Magpie Creeks
• Natomas-Area Stream Group: Arcade Creek
• Sacramento River Basin: American River at Fair Oaks and Latitude of Sacramento The ULDC requires the computation of water surface elevations for the 10-year, 200-year, and 500-year flood events. The Sacramento River Basin scaled flood events and Natomas-Area Stream Group C parameters for these flood frequencies and flood centerings are summarized in Table 5. The final computed maximum WSE is the composite maximum of the maximum WSE’s computed for the four flood centerings.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 9 Table 5. CVHS Flood Events
Flood Centering
Flood
Frequency
(Recurrence
Interval)
Watershed
North Area Streams Sacramento River
Dry Creek 10-year 10yr_C=99.5 1
1995-60% 2, 3
200-year 200yr_C=99.5 1
1995-105% 2
500-year 500yr_C=99.5 1
1995-120% 2
Robla-Magpie Creeks 10-year 10yr_C=RIOLINDA_MAGPIE 1
1995-60% 2, 3
200-year 200yr_C=RIOLINDA_MAGPIE 1
1995-105% 2
500-year 500yr_C=RIOLINDA_MAGPIE 1
1995-120% 2
Arcade Creek 10-year 10yr_C=ARC 1
1995-60% 2, 3
200-year 200yr_C=ARC 1
1995-105% 2
500-year 500yr_C=ARC 1
1995-120% 2
Fair Oaks-latitude of
Sacramento
10-year 1986-55% 2 1986-55% with 40% on American
R. 1, 2
200-year 1986-110% 2 1986-110% with 125% on
American R. 2
500-year 1986-100% 4 1986-100% with 176% on
American R. 4
1 Data ID from USACE 2019 updated hydrologic data set, consisting of recurrence interval (Nyr) and contributing area (C=99.5) or centering (C=RIOLINDA_MAGPIE, C=ARC).
2 Event selection by USACE (USACE, 2019). “1995-60%” = 1995 flood pattern with a 60% scale factor. 3 CVHS hydrologic data does not include the 1995-60% flood event. The closest available flood event data, 1995-75%, was used in the analysis. The 1995-75% data approximately represents the 20-year flood event. 4 Event selection by USACE (USACE, 2020).

The County of Sacramento’s D-15 pump station, at the upstream end of the modeled NEMDC reach, is an inline pump station with gates (County of Sacramento, 2007). During large flood events the gates close automatically when the water surface elevation at the pump station reaches a pre-defined trigger elevation, preventing backwater due to high flows in Dry and Robla creeks from affecting flood stages north of the pump station. After the gates close, the pumps will automatically turn on to ensure positive flow from north to south. The station has three 333 cfs capacity pumps. The operation criteria specify a firm capacity based on use of two of the three pumps, keeping one for a backup. However, all three pumps may be operated concurrently if required. For the ULDC analysis, the conservative assumption of a three-pump operation, with a total flow of 999 cfs, was used.

5. Urban Levee Design Criteria (ULDC)
Section 7.1 of the ULDC allows for two options for the determination of the DWSE. The first option is the Federal Emergency Management Agency (FEMA) Approach, in which the DWSE is computed deterministically with a hydraulic model. The second option is the U.S. Army Corps of Engineers Approach, which incorporates uncertainty into the determination of the DWSE. The approach selected for this analysis was the FEMA Approach, due to its application and results being more straightforward and economical.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 10 The ULDC defines the DWSE as the “200-year stage or water level used to design a levee or floodwall”.

Section 7.1.1 of the ULDC specifies that the hydraulic modeling used to determine the DWSE must consider the following:
• Upstream, downstream, and nearby levees and floodwalls protecting urban areas are assumed to be raised to the median 200-year water surface elevation plus 3 feet and not allowed to breach, even if overtopped. Overtopping flows are assumed to leave the channel and remain in the 200- year floodplain.
• All project levees and floodwalls are to be modeled to incorporate a minimum crown elevation equal to the authorized (usually the 1955/1957) USACE design profiles – this affects nonurbanized areas for the most part – all such levees and floodwalls are to be allowed to overtop, act as weirs, and not breach for floods up to and including the median 500-year flood.

Overtopping flows are assumed to leave the channel and remain in the 200-year floodplain. • Non-project levees and floodwalls in non-urbanized areas in the region, to the extent they may affect the DWSE, are to be modeled at their existing or authorized height, whichever is higher, and to act as weirs without breaching if overtopped.
• Debris loading on bridges must be considered. Bridges with less than 3 feet of clearance above the DWSE may experience extraordinary debris loading that must be evaluated in addition to typical pier/bent debris loading. The evaluation should include historic and potential debris transport in the stream, an analysis of loading on the bridge, and analysis of backwater impacts on the DWSE in the vicinity of the bridge.

Section 7.1.3 of the ULDC requires adjustments to the DWSE for the effects of superelevation, when applicable. Superelevation is a tilting of the water surface, which may occur as water flows through a bend in the channel. Computational methods for determining superelevation adjustments are in the USACE Engineering Manual 1110-2-1601.

Section 7.1.3 of the ULDC also states that the “…the civil engineer should consider increasing the DWSE to account for the potential increases in water surface associated with climate change, updated hydrology, updated hydraulic models, and sea level rise”. This statement implies that adjustment for sea level rise is optional; however, Section 7.19 of the ULDC states, “the effects of sea level rise are to be estimated and addressed for the duration during which a Finding that the urban level of flood protection exists may be valid”. Based on the second statement, sea level rise adjustment appears to be mandatory.

Additionally, Section 7.1.3 of the ULDC states:
“[T]he civil engineer also needs to address two other situations: (1) whether upstream levee or floodwall breaches could produce overland flows that would reach the area protected by the levee system or increase the water surface elevation along the levee system, and (2) whether flooding in a nearby leveed area could fill that area and breach a nearby levee or floodwall, returning flow to the stream and increasing the DWSE for a portion of the levee system".

Neither of these conditions are applicable to the Study Area, and therefore were not evaluated.

The following sections address the requirements in the ULDC and discuss the application of each requirement for the American River North levee system.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 11

5.1 Levees
As per the ULDC, all urban levees were assumed to have a minimum top elevation of the median 200-year water surface elevation plus 3 feet. All non-urban State-Federal Project levees were assumed to have a minimum crown elevation equal to the authorized USACE design profiles.

5.2 Debris Loading
The ULDC specifies that debris loading on bridges must be considered, and that “bridges with less than 3 feet of clearance above the DWSE may experience extraordinary debris loading that must be evaluated in addition to typical pier/bent debris loading”.

Bridge pier debris are applied in accordance with guidelines provided in a July 2014 letter (USACE, 2014), sent by USACE to the California Central Valley Flood Protection Board in order to clarify the level of screening and analysis that should be included on encroachment permit applications that are sent to the USACE for review. A copy of the letter is provided in Appendix C. Included in the letter was guidance for modeling debris build-up. Based on this guidance, under the ULDC “typical” debris loading condition, the hydraulic analysis included floating debris with a width equal to double the pier width, and a depth of 2 feet below the water surface. Under the ULDC “extraordinary” debris loading condition, floating debris with a depth of 2 feet below the water surface were modeled for the full width with the “extraordinary” condition.

Debris were not applied to bridges in the model upstream of the levee reaches, as debris on these bridges would have no effect on the water surface elevation in the levee reaches.

A summary of the bridge pier debris conditions included in the hydraulic analysis is provided in Table 6.

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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 12 Table 6. Bridge Pier Debris Loading
River River
Station1
Bridge
Debris Loading Condition2
200-yr 500-yr
Dry Creek West Branch 1,340 ft Rio Linda Blvd. E E
Dry Creek East Branch 3,910 ft SNRR Bike Trail t t
640 ft Rio Linda Blvd. E E
Dry Creek (lower) 6,120 ft private bridge E E
110 ft UPRR (near mouth) E E
Robla Creek 9,680 ft SNRR Bike Trail E E
8,290 ft Rio Linda Blvd. E E
90 ft UPRR (near mouth) E E
Magpie Creek 6,120 ft Raley Blvd. E E
4,010 ft Vinci Ave. E E
1,130 ft Dry Creek Rd. E E
Arcade Creek 1.344 mi Rio Linda Blvd. E E

1.26 mi SNRR Bike Trail E E

0.722 mi Norwood Avenue E E

0.045 mi UPRR (near mouth) E E
NEMDC 6.139 mi Main Avenue t t

5.168 mi Interstate 80 t t

4.347 mi Silver Eagle Road t t

3.03 mi West El Camino Avenue mix E

2.653 mi Arden-Garden Connector t t
American River 13.46 mi Bike Trail bridge t E

9.31 mi Watt Ave t E

7.748 mi Howe Ave t E

7.065 mi Guy West t E

6.588 mi H St t E

3.989 mi Cap City Fwy t t

3.715 mi RR t E

2.333 mi RR t E

2.235 mi Bike Trail t E

2.068 mi CA-160 E t mix

2.046 mi CA-160 W t mix

0.355 mi I-5 t mix

0.242 mi Jibboom St mix E
1 River station in miles for 1-D reaches and in feet for 2-D flow areas. 2 t = typical; E = extraordinary; mix = combination of t and E.

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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 13

5.3 Superelevation
Superelevation is a tilting of the water surface that occurs on the outside of a river bend. The ULDC notes that, “on the outside of a bend, the superelevation needs to be added to the DWSE”. The superelevation adjustment, per USACE Engineer Manual 1110-2-1416, River Hydraulics, is specific to 1-D hydraulic modeling. There are no locations in the Robla-Arcade levee system subject to superelevation.

5.4 Climate Change
The effects of climate change on extreme precipitation events in the Central Valley are being studied, but there is no indication of what the outcome of that work will be. Therefore, the hydrology used in this analysis has not been adjusted for the effects of climate change.

5.5 Updated Hydrology
This analysis makes use of the most recent accepted hydrologic data for the Study Area, which was developed as part of the Central Valley Hydrology Study, as noted in Section 4 of this report.

5.6 Updated Hydraulic Model
The hydraulic model used for this analysis was developed from the most current available data. Due to the calibration process, an updated hydraulic model would not be expected to have a substantial effect on the computed results unless significant physical changes have occurred in the modeled system. Since no significant physical changes have occurred since the data used for the model development was collected, no adjustment for updated hydraulic model has been included.

5.7 Sea Level Rise
The ULDC notes that, “the effects of sea level rise are to be estimated and addressed for the duration during which a Finding that the urban level of flood protection exists may be valid”. The duration of finding proposed for the subject project is 20 years.

The analysis assumed a sea level rise of 3.68 feet at San Francisco. This is the 50-year sea level rise projection determined by the California Department of Water Resources (DWR) for the 2022 update of the Central Valley Flood Protection Plan (CVFPP) (DWR, 2022). Being that the duration of the Urban Level of Protection finding is 20 years, the use of a 50-year projection is a conservative assumption. The effects of this sea level rise were applied at the downstream boundaries of the Sacramento River systemwide hydraulic model simulations, which were used to determine the downstream boundary conditions for the LAR model.

6. Computed ULDC Hydraulic Parameters
The following sections present the computed ULDC hydraulic parameters that were described in Section 1 of this technical memorandum:
• Design Water Surface Elevation (DWSE)
• Minimum Top of Levee (MTOL)
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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 14 • Hydraulic Top of Levee (HTOL)
• Seismic Vulnerability Restoration Profile

6.1 Design Water Surface Elevation (DWSE)
The ULDC defines the DWSE as “[the] median 200-year water surface elevation”, with adjustments for the following factors:
• Bridge pier debris loading
• Superelevation
• Sea level rise
Debris loading and sea level rise are accounted for in the hydraulic model simulations, as described in Sections 5.2 and 5.7. As noted in Section 5.3, the superelevation adjustment is not applicable to the Robla-Arcade levee system.

Profile plots of the computed DWSE for each of the levee segments in the Robla-Arcade levee system are provided in Figures 6, 7 and 8. The levee crest profiles are included on the profile plots. The Robla Creek south levee (Figure 8) shows at the upstream end of the levee, at Dry Creek Road, that the DWSE appears to exceed the top of levee elevation. The implications of this are describe in detail in Section 6.2.

Tabulations of the DWSE profiles are provided in Appendix D.

Figure 6. ULDC DWSE Profile, Arcade Creek North Levee
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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 15 Figure 7. ULDC DWSE Profile, NEMDC East Levee
Figure 8. ULDC DWSE Profile, Robla Creek South Levee
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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 16

6.2 Minimum Top of Levee (MTOL)
The ULDC defines the MTOL as the higher of the DWSE plus 3 feet, or the DWSE plus the computed wind setup and wave runup. Wind setup and wave runup for the Robla-Arcade levee system has been computed by Mead & Hunt (Mead & Hunt, 2024). The maximum computed wind setup and wave runup for each of the Robla-Arcade levee segments is shown in Table 7. Since they are all less than 3.0 feet, the MTOL for each of the Robla-Arcade levee segments is the DWSE plus 3 feet. Profile plots of the MTOL for each of the levee segments in the Robla-Arcade levee system are provided in Figures 9, 10 and 11.

Tabulation of the MTOL profiles are provided in Appendix D.

Table 7. Wind Setup and Wave Runup
Levee Segment
Maximum Wind Setup
and Wave Runup (feet)
Arcade Creek north levee 1.4
NEMDC east levee 1.7
Robla Creek south levee 2.3
The Arcade Creek north levee and NEMDC east levee elevations exceed the MTOL. The Robla Creek south levee exceeds the MTOL except at its upstream end, immediately downstream of Dry Creek Road. A detailed look (Figure 12) shows that where the MTOL elevation is not met, between stations 6114+00 and 6118+00, the DWSE is below the landside toe of the levee. That is, where there is insufficient freeboard, the DWSE does not reach the levee.

Figure 9. ULDC MTOL Profile, Arcade Creek North Levee
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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 17 Figure 10. ULDC MTOL Profile, NEMDC East Levee
Figure 11. ULDC MTOL Profile, Robla Creek South Levee
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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 18 Figure 12. Detail of Profiles at Upstream End of Robla Creek South Levee

6.3. Hydraulic Top of Levee (HTOL)
The ULDC defines the HTOL as the lower of the DWSE plus 3 feet, or the median 500-year WSE. Profile plots of the HTOL for each of the levee segments in the Robla-Arcade levee system are provided in Figures 12, 13 and 14. For reference, the DWSE plus 3 feet and 500-year WSE profiles are also shown.

Refer to Section 6.2 for discussion regarding the upstream end of the Robla Creek south levee (Figure 14).

Tabulations of the HTOL profiles are provided in Appendix D.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 19 Figure 12. ULDC HTOL Profile, Arcade Creek North Levee
Figure 13. ULDC HTOL Profile, NEMDC East Levee
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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 20 Figure 14. ULDC HTOL Profile, Robla Creek South Levee

6.4 Seismic Vulnerability Restoration Profile (SVRP)
The ULDC specifies that if there is the potential for levee damage due to a seismic event, a plan needs to be in place to “restore grade and dimensions for at least 10-year WSE plus 3 feet of freeboard or higher for wind setup and wave runup within 8 weeks”. An evaluation of seismic performance by Kleinfelder (Kleinfelder, 2024) determined that the levee segments in the Robla-Arcade levee system have low seismic vulnerability, as defined in the DWR Urban Levee Evaluation (ULE) program, making seismic vulnerability restoration profiles for the Robla-Arcade levee system unnecessary.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 21 References
County of Sacramento. (2007). D-15 NEMDC Drainage Pump Station Summary of Operations and Procedures Manual. May 2007.

DWR. (2012). Urban Levee Design Criteria. May 2012.

DWR. (2022). 2022 CVFPP Update - Technical Analyses Summary Report, Public Draft. May 2022.

Kleinfelder. (2024). Seismic Performance Summary Report, North Area Streams Levee Areas. February 12, 2024.

MBK Engineers. (2019). Technical Memorandum - Sacramento Weir Widening Project, Initial Hydraulic Impact Analysis. October 31, 2019.

Mead & Hunt. (2024). Wind-Wave Analysis for American River North and Robla-Arcade Levee Systems.

January 16, 2024.

USACE. (2013). Central Valley Hydrology Study: Natomas-area Stream Group - Pleasant Grove Creek, Dry Creek, and Arcade Creek Watersheds Hydrologic Analysis. March 26, 2013.

USACE. (2015). Central Valley Hydrology Study. November 29, 2015.

USACE. (2019). Memorandum for Record, Subject: CVHS Hydrograph Package for HEC-RAS Model Inputs.

February 20, 2019.

USACE. (2020). Hydrology Technical Memorandum for Developing WRDA 2016 Water Surface Profiles. April 10, 2020.

USACE. (2021). Hydraulic Model Summary Magpie Creek Canal For American River Common Features Project. USACE - Vicksburg District. April 2021.

USACE. (2023a). HEC-RAS User's Manual. Retrieved from
https://www.hec.usace.army.mil/confluence/rasdocs/rasum/6.4 USACE. (2023b). HEC-RAS 2D User's Manual. Retrieved from https://www.hec.usace.army.mil/confluence/rasdocs/r2dum/latest Wood Rodgers. (2014). Central Valley Floodplain Evaluation and Delineation, Lower Sacramento River Technical Memorandum. January 17, 2014.

APPENDIX A
Lower American River
Hydraulic Model Calibration
Lower American River November 18, 2024
Hydraulic Model Calibration Page A-1
Simulation Event Peak American River flow
Calibration January 1997 flow 117,000 cfs
Verification February 10, 2017 ~85,000 cfs
Figure A-1. Calibration, January 1997, Maximum Water Surface Elevation Profile with Surveyed High Water Marks, American River river miles 10 to 23 (Mayhew Drain to Nimbus Dam) Figure A-2. Calibration, January 1997, Maximum Water Surface Elevation Profile with Surveyed High Water Marks, American River river miles 0 to 11 (Sacramento River to Mayhew Drain) Figure A-3. Verification, February 10, 2017, Maximum Water Surface Elevation Profile with Surveyed Water Surface Elevation, American River river miles 10 to 23 (Mayhew Drain to Nimbus Dam)
Figure A-4. Verification, February 10, 2017, Maximum Water Surface Elevation Profile with Surveyed Water Surface Elevation, American River river miles 0 to 11 (Sacramento River to Mayhew Drain)

Lower American River November 18, 2024
Hydraulic Model Calibration Page A-2
Figure A-1. Calibration, January 1997, Maximum Water Surface Elevation Profile with Surveyed High Water Marks, American River, river miles 10 to 23 (Mayhew Drain to Nimbus Dam) Figure A-2. Calibration, January 1997, Maximum Water Surface Elevation Profile with Surveyed High Water Marks, American River, river miles 0 to 11 (Sacramento River to Mayhew Drain) Lower American River November 18, 2024
Hydraulic Model Calibration Page A-3
Figure A-3. Verification, February 10, 2017, Maximum Water Surface Elevation Profile with Surveyed Water Surface Elevations, American River, river miles 10 to 23 (Mayhew Drain to Nimbus Dam) Figure A-4. Verification, February 10, 2017, Maximum Water Surface Elevation Profile with Surveyed Water Surface Elevations, American River, river miles 0 to 11 (Sacramento River to Mayhew Drain)

APPENDIX B
North Area Streams
Hydraulic Model Calibration
North Area Streams November 18, 2024
Hydraulic Model Calibration Page B-1
Calibration flood event: December 2005-January 2006
The stream gages listed in Table B-1 provided the available observed data used for calibration of the Dry Creek and Robla Creek watershed area. All the gages are part of the Sacramento County ALERT system (https://www.sacflood.org/). The gage data was provided by Sacramento County. The gage locations are shown in Figure B-1.

Table B-1. Stream Gages with Observed Data Available for Calibration Gage Agency Sensor ID
Dry Creek West Branch at SNRR Bike Trail Sacramento County ALERT 2230 Dry Creek West Branch at Elkhorn Blvd. Sacramento County ALERT 1661 Dry Creek Bypass at Elkhorn Blvd. Sacramento County ALERT 1662 Dry Creek East Branch at Elkhorn Blvd. Sacramento County ALERT 2782 Robla Creek at SNRR Bike Trail Sacramento County ALERT 2753 D15/NEMDC Downstream Sacramento County ALERT 2772
Figure B-1. Stream Gage Location Map
A comparison of the observed and computed peak stages at the gage locations is provided in Table B-2.

Profile plots of the computed maximum water surface elevations with available observed gage peaks are North Area Streams November 18, 2024
Hydraulic Model Calibration Page B-2
provided in Figures B-2 through B-6.

Table B-2. Calibration Results, Comparison of Observed and Computed Peak Stages Gage Maximum Stage (feet NAVD88) Difference
Observed Computed (feet)
Dry Creek West Branch at SNRR Bike Trail 47.62 48.06 +0.44 Dry Creek West Branch at Elkhorn Blvd. 46.06 46.17 +0.11 Dry Creek Bypass at Elkhorn Blvd. 46.95 46.58 -0.37
Dry Creek East Branch at Elkhorn Blvd. 46.88 49.33 +2.45 a Robla Creek at SNRR Bike Trail 40.59 40.78 +0.19
D15/NEMDC Downstream 36.44 36.69 +0.25
a The Sacramento County ALERT website for this gage notes that “when the east branch reaches 49.9’ +/- the stage at the west branch is approximately 46.5’ +/-“. The computed peak stage difference for these locations of 3.2’ is similar to the reported difference of 3.6’. Therefore, it can be concluded that the reported peak stage of 46.88’ at the Dry Creek East Branch at Elkhorn Blvd gage is suspect.

Figure B-2. Calibration Analysis Maximum Water Surface Elevation Profile, Dry Creek West Branch North Area Streams November 18, 2024
Hydraulic Model Calibration Page B-3
Figure B-3. Calibration Analysis Maximum Water Surface Elevation Profile, Dry Creek East Branch Figure B-4. Calibration Analysis Maximum Water Surface Elevation Profile, Dry Creek (lower) North Area Streams November 18, 2024
Hydraulic Model Calibration Page B-4
Figure B-5. Calibration Analysis Maximum Water Surface Elevation Profile, Dry Creek Bypass Channel Figure B-6. Calibration Analysis Maximum Water Surface Elevation Profile, Robla Creek Appendix C
USACE Letter with Debris Loading Guidance
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-1
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-2
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-3
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-4
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-5
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-6
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-7
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-8
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-9

APPENDIX D

Tabulation of ULDC Hydraulic Parameter Profiles
for the Robla-Arcade Levee System
Tabulation of ULDC Hydraulic Parameter Profiles November 18, 2024 for the Robla-Arcade Levee System Page D-1
Table D-1. ULDC Hydraulic Parameter Profiles, Arcade Creek North Levee Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
5000+00 37.10 40.10 40.10 5038+00 37.77 40.77 40.77 5076+00 38.50 41.50 41.50 5001+00 37.44 40.44 40.44 5039+00 37.78 40.78 40.78 5077+00 38.52 41.52 41.52 5002+00 37.54 40.54 40.54 5040+00 37.78 40.78 40.78 5078+00 38.54 41.54 41.54 5003+00 37.63 40.63 40.63 5041+00 37.78 40.78 40.78 5079+00 38.56 41.56 41.56 5004+00 37.64 40.64 40.64 5042+00 37.78 40.78 40.78 5080+00 38.58 41.58 41.58 5005+00 37.65 40.65 40.65 5043+00 37.78 40.78 40.78 5081+00 38.61 41.61 41.61 5006+00 37.65 40.65 40.65 5044+00 37.79 40.79 40.79 5082+00 38.64 41.64 41.64 5007+00 37.66 40.66 40.66 5045+00 37.79 40.79 40.79 5083+00 38.68 41.68 41.68 5008+00 37.66 40.66 40.66 5046+00 37.79 40.79 40.79 5084+00 38.71 41.71 41.71 5009+00 37.66 40.66 40.66 5047+00 37.79 40.79 40.79 5085+00 38.74 41.74 41.74 5010+00 37.67 40.67 40.67 5048+00 37.80 40.80 40.80 5086+00 38.80 41.80 41.80 5011+00 37.67 40.67 40.67 5049+00 37.80 40.80 40.80 5087+00 38.87 41.87 41.87 5012+00 37.67 40.67 40.67 5050+00 37.80 40.80 40.80 5088+00 38.94 41.94 41.94 5013+00 37.67 40.67 40.67 5051+00 37.81 40.81 40.81 5089+00 39.01 42.01 42.01 5014+00 37.67 40.67 40.67 5052+00 37.81 40.81 40.81 5090+00 39.08 42.08 42.08 5015+00 37.68 40.68 40.68 5053+00 37.82 40.82 40.82 5091+00 39.15 42.15 42.15 5016+00 37.68 40.68 40.68 5054+00 37.83 40.83 40.83 5092+00 39.20 42.20 42.20 5017+00 37.68 40.68 40.68 5055+00 37.83 40.83 40.83 5093+00 39.26 42.26 42.26 5018+00 37.68 40.68 40.68 5056+00 37.85 40.85 40.85 5094+00 39.31 42.31 42.31 5019+00 37.68 40.68 40.68 5057+00 37.86 40.86 40.86 5095+00 39.36 42.36 42.36 5020+00 37.69 40.69 40.69 5058+00 37.88 40.88 40.88 5096+00 39.41 42.41 42.38 5021+00 37.69 40.69 40.69 5059+00 37.89 40.89 40.89 5097+00 39.44 42.44 42.38 5022+00 37.69 40.69 40.69 5060+00 37.91 40.91 40.91 5098+00 39.47 42.47 42.38 5023+00 37.69 40.69 40.69 5061+00 37.91 40.91 40.91 5099+00 39.49 42.49 42.38 5024+00 37.70 40.70 40.70 5062+00 37.92 40.92 40.92 5100+00 39.52 42.52 42.39 5025+00 37.70 40.70 40.70 5063+00 37.93 40.93 40.93 5101+00 39.55 42.55 42.39 5026+00 37.71 40.71 40.71 5064+00 37.93 40.93 40.93 5102+00 39.76 42.76 42.41 5027+00 37.71 40.71 40.71 5065+00 37.92 40.92 40.92 5103+00 40.00 43.00 42.44 5028+00 37.71 40.71 40.71 5066+00 38.05 41.05 41.05 5104+00 40.25 43.25 42.48 5029+00 37.72 40.72 40.72 5067+00 38.11 41.11 41.11 5105+00 40.49 43.49 42.51 5030+00 37.73 40.73 40.73 5068+00 38.13 41.13 41.13 5106+00 40.73 43.73 42.54 5031+00 37.74 40.74 40.74 5069+00 38.14 41.14 41.14 5107+00 40.95 43.95 42.57 5032+00 37.74 40.74 40.74 5070+00 38.30 41.30 41.30 5108+00 41.12 44.12 42.60 5033+00 37.74 40.74 40.74 5071+00 38.36 41.36 41.36 5109+00 41.30 44.30 42.63 5034+00 37.74 40.74 40.74 5072+00 38.39 41.39 41.39 5110+00 41.47 44.47 42.66 5035+00 37.74 40.74 40.74 5073+00 38.42 41.42 41.42 5111+00 41.65 44.65 42.69 5036+00 37.73 40.73 40.73 5074+00 38.45 41.45 41.45 5112+00 41.82 44.82 42.73 5037+00 37.77 40.77 40.77 5075+00 38.48 41.48 41.48

Tabulation of ULDC Hydraulic Parameter Profiles November 18, 2024 for the Robla-Arcade Levee System Page D-2
Table D-2. ULDC Hydraulic Parameter Profiles, NEMDC East Levee Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
3055+86 37.10 40.10 40.10 3102+00 38.29 41.29 41.29 3149+00 39.33 42.33 42.33 3056+00 37.10 40.10 40.10 3103+00 38.31 41.31 41.31 3150+00 39.36 42.36 42.33 3057+00 37.13 40.13 40.13 3104+00 38.33 41.33 41.33 3151+00 39.38 42.38 42.34 3058+00 37.15 40.15 40.15 3105+00 38.35 41.35 41.35 3152+00 39.41 42.41 42.34 3059+00 37.17 40.17 40.17 3106+00 38.37 41.37 41.37 3153+00 39.43 42.43 42.34 3060+00 37.20 40.20 40.20 3107+00 38.39 41.39 41.39 3154+00 39.45 42.45 42.35 3061+00 37.22 40.22 40.22 3108+00 38.41 41.41 41.41 3155+00 39.48 42.48 42.35 3062+00 37.24 40.24 40.24 3109+00 38.43 41.43 41.43 3156+00 39.50 42.50 42.35 3063+00 37.27 40.27 40.27 3110+00 38.45 41.45 41.45 3157+00 39.53 42.53 42.36 3064+00 37.29 40.29 40.29 3111+00 38.47 41.47 41.47 3158+00 39.55 42.55 42.36 3065+00 37.31 40.31 40.31 3112+00 38.49 41.49 41.49 3159+00 39.57 42.57 42.36 3066+00 37.34 40.34 40.34 3113+00 38.52 41.52 41.52 3160+00 39.60 42.60 42.37 3067+00 37.36 40.36 40.36 3114+00 38.54 41.54 41.54 3161+00 39.62 42.62 42.37 3068+00 37.38 40.38 40.38 3115+00 38.56 41.56 41.56 3162+00 39.65 42.65 42.37 3069+00 37.40 40.40 40.40 3116+00 38.59 41.59 41.59 3163+00 39.68 42.68 42.38 3070+00 37.43 40.43 40.43 3117+00 38.61 41.61 41.61 3164+00 39.71 42.71 42.38 3071+00 37.45 40.45 40.45 3118+00 38.64 41.64 41.64 3165+00 39.75 42.75 42.39 3072+00 37.47 40.47 40.47 3119+00 38.66 41.66 41.66 3166+00 39.78 42.78 42.39 3073+00 37.49 40.49 40.49 3120+00 38.68 41.68 41.68 3167+00 39.81 42.81 42.40 3074+00 37.51 40.51 40.51 3121+00 38.70 41.70 41.70 3168+00 39.84 42.84 42.40 3075+00 37.53 40.53 40.53 3122+00 38.72 41.72 41.72 3169+00 39.87 42.87 42.41 3076+00 37.55 40.55 40.55 3123+00 38.74 41.74 41.74 3170+00 39.90 42.90 42.41 3077+00 37.57 40.57 40.57 3124+00 38.77 41.77 41.77 3171+00 39.93 42.93 42.42 3078+00 37.59 40.59 40.59 3125+00 38.79 41.79 41.79 3172+00 39.96 42.96 42.42 3079+00 37.61 40.61 40.61 3126+00 38.81 41.81 41.81 3173+00 39.99 42.99 42.43 3080+00 37.63 40.63 40.63 3127+00 38.83 41.83 41.83 3174+00 40.02 43.02 42.43 3081+00 37.65 40.65 40.65 3128+00 38.85 41.85 41.85 3175+00 40.05 43.05 42.43 3082+00 37.68 40.68 40.68 3129+00 38.87 41.87 41.87 3176+00 40.08 43.08 42.44 3083+00 37.70 40.70 40.70 3130+00 38.90 41.90 41.90 3177+00 40.10 43.10 42.44 3084+00 37.72 40.72 40.72 3131+00 38.91 41.91 41.91 3178+00 40.12 43.12 42.45 3085+00 37.73 40.73 40.73 3132+00 38.90 41.90 41.90 3179+00 40.15 43.15 42.45 3086+00 37.75 40.75 40.75 3133+00 38.93 41.93 41.93 3180+00 40.17 43.17 42.45 3087+00 37.77 40.77 40.77 3134+00 38.97 41.97 41.97 3181+00 40.19 43.19 42.46 3088+00 37.79 40.79 40.79 3135+00 39.02 42.02 42.02 3182+00 40.22 43.22 42.46 3089+00 37.79 40.79 40.79 3136+00 39.04 42.04 42.04 3183+00 40.24 43.24 42.46 3090+00 37.75 40.75 40.75 3137+00 39.06 42.06 42.06 3184+00 40.31 43.31 42.48 3091+00 37.77 40.77 40.77 3138+00 39.07 42.07 42.07 3185+00 40.44 43.44 42.50 3092+00 37.83 40.83 40.83 3139+00 39.09 42.09 42.09 3186+00 40.48 43.48 42.50 3093+00 37.89 40.89 40.89 3140+00 39.11 42.11 42.11 3187+00 40.53 43.53 42.51 3094+00 37.95 40.95 40.95 3141+00 39.13 42.13 42.13 3188+00 40.64 43.64 42.55 3095+00 38.00 41.00 41.00 3142+00 39.15 42.15 42.15 3189+00 40.75 43.75 42.59 3096+00 38.06 41.06 41.06 3143+00 39.18 42.18 42.18 3190+00 40.86 43.86 42.62 3097+00 38.11 41.11 41.11 3144+00 39.20 42.20 42.20 3191+00 40.97 43.97 42.66 3098+00 38.16 41.16 41.16 3145+00 39.23 42.23 42.23 3192+00 41.07 44.07 42.69 3099+00 38.22 41.22 41.22 3146+00 39.26 42.26 42.26 3192+23 41.10 44.10 42.70 3100+00 38.25 41.25 41.25 3147+00 39.28 42.28 42.28
3101+00 38.27 41.27 41.27 3148+00 39.31 42.31 42.31
Tabulation of ULDC Hydraulic Parameter Profiles November 18, 2024 for the Robla-Arcade Levee System Page D-3
Table D-3. ULDC Hydraulic Parameter Profiles, Robla Creek South Levee Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
6000+00 41.19 44.19 42.78 6040+00 41.31 44.31 42.89 6080+00 42.30 45.30 43.45 6001+00 41.25 44.25 42.83 6041+00 41.31 44.31 42.89 6081+00 42.46 45.46 43.54 6002+00 41.25 44.25 42.84 6042+00 41.32 44.32 42.89 6082+00 42.50 45.50 43.56 6003+00 41.26 44.26 42.84 6043+00 41.32 44.32 42.90 6083+00 42.54 45.54 43.59 6004+00 41.26 44.26 42.84 6044+00 41.32 44.32 42.90 6084+00 42.58 45.58 43.61 6005+00 41.26 44.26 42.85 6045+00 41.33 44.33 42.90 6085+00 42.62 45.62 43.63 6006+00 41.26 44.26 42.85 6046+00 41.33 44.33 42.90 6086+00 42.65 45.65 43.65 6007+00 41.27 44.27 42.85 6047+00 41.33 44.33 42.91 6087+00 42.67 45.67 43.67 6008+00 41.27 44.27 42.85 6048+00 41.34 44.34 42.91 6088+00 42.69 45.69 43.68 6009+00 41.27 44.27 42.85 6049+00 41.34 44.34 42.91 6089+00 42.70 45.70 43.69 6010+00 41.27 44.27 42.85 6050+00 41.35 44.35 42.92 6090+00 42.71 45.71 43.69 6011+00 41.27 44.27 42.85 6051+00 41.35 44.35 42.92 6091+00 42.72 45.72 43.70 6012+00 41.27 44.27 42.85 6052+00 41.36 44.36 42.93 6092+00 43.04 46.04 43.83 6013+00 41.27 44.27 42.85 6053+00 41.37 44.37 42.93 6093+00 43.17 46.17 43.89 6014+00 41.27 44.27 42.86 6054+00 41.38 44.38 42.94 6094+00 43.19 46.19 43.90 6015+00 41.27 44.27 42.86 6055+00 41.39 44.39 42.95 6095+00 43.22 46.22 43.91 6016+00 41.27 44.27 42.86 6056+00 41.40 44.40 42.96 6096+00 43.28 46.28 43.94 6017+00 41.27 44.27 42.86 6057+00 41.41 44.41 42.96 6097+00 43.33 46.33 43.97 6018+00 41.27 44.27 42.86 6058+00 41.42 44.42 42.97 6098+00 43.37 46.37 43.99 6019+00 41.27 44.27 42.86 6059+00 41.42 44.42 42.97 6099+00 43.41 46.41 44.03 6020+00 41.28 44.28 42.86 6060+00 41.43 44.43 42.98 6100+00 43.47 46.47 44.06 6021+00 41.28 44.28 42.86 6061+00 41.45 44.45 42.99 6101+00 43.52 46.52 44.09 6022+00 41.28 44.28 42.86 6062+00 41.45 44.45 42.99 6102+00 43.56 46.56 44.12 6023+00 41.28 44.28 42.86 6063+00 41.46 44.46 43.00 6103+00 43.60 46.60 44.15 6024+00 41.28 44.28 42.86 6064+00 41.48 44.48 43.01 6104+00 43.62 46.62 44.17 6025+00 41.28 44.28 42.87 6065+00 41.50 44.50 43.02 6105+00 43.65 46.65 44.18 6026+00 41.28 44.28 42.87 6066+00 41.52 44.52 43.03 6106+00 43.67 46.67 44.20 6027+00 41.28 44.28 42.87 6067+00 41.54 44.54 43.05 6107+00 43.71 46.71 44.23 6028+00 41.29 44.29 42.87 6068+00 41.56 44.56 43.06 6108+00 43.75 46.75 44.25 6029+00 41.29 44.29 42.87 6069+00 41.57 44.57 43.07 6109+00 43.78 46.78 44.28 6030+00 41.29 44.29 42.87 6070+00 41.59 44.59 43.08 6110+00 43.80 46.80 44.30 6031+00 41.29 44.29 42.87 6071+00 41.60 44.60 43.08 6111+00 43.82 46.82 44.31 6032+00 41.29 44.29 42.88 6072+00 41.61 44.61 43.09 6112+00 43.84 46.84 44.33 6033+00 41.30 44.30 42.88 6073+00 41.64 44.64 43.11 6113+00 43.86 46.86 44.35 6034+00 41.30 44.30 42.88 6074+00 41.67 44.67 43.13 6114+00 43.92 46.92 44.40 6035+00 41.30 44.30 42.88 6075+00 41.71 44.71 43.15 6115+00 44.00 47.00 44.47 6036+00 41.30 44.30 42.88 6076+00 41.75 44.75 43.17 6116+00 44.14 47.14 44.60 6037+00 41.30 44.30 42.88 6077+00 41.80 44.80 43.19 6117+00 44.41 47.41 44.97 6038+00 41.31 44.31 42.89 6078+00 41.85 44.85 43.22 6118+19 46.32 49.32 46.72 6039+00 41.31 44.31 42.89 6079+00 42.12 45.12 43.36
Appendix D.

Robla-Arcade Levee System
ULDC Due Diligence, Geotech -
AECOM
Urban Levee Design Criteria
Geotechnical Findings Report
Arcade Creek North Levee
Stations 5023+00 to 5112+43
Robla-Arcade Levee System
November 15, 2024
Prepared For
Sacramento Area Flood Control Agency
Only the Client or its Designated Representatives May Use this Document and Only for the Specific Project for Which
This Geotechnical Findings Report is Prepared
November 15, 2024
Mr. Dan Tibbitts, PE
Director of Engineering
Sacramento Area Flood Control Agency
1325 J Street, Suite 1700
Sacramento, CA 95814
Subject: Robla-Arcade Levee System
Geotechnical Findings Report
Urban Levee Design Criteria Compliance
Arcade Creek North Levee - Stations 5023+00 to 5112+43
Dear Mr. Tibbitts:

Enclosed please find AECOM’s Geotechnical Findings Report containing conclusions regarding compliance of the Arcade Creek north levee, a part of the Arcade-Robla Streams Levee System, with the geotechnical-related criteria contained in the following sections of the State of California, Department of Water Resources, Urban Levee Design Criteria (ULDC) (DWR, 2012), which is required for certification:

Section 7.3, Soil Sampling, Testing, and Logging
Section 7.4, Slope Stability for Intermittently Loaded Levees Section 7.5, Underseepage for Intermittently Loaded Levees Section 7.7, Seismic Vulnerability
Section 7.8, Levee Geometry
Section 7.9, Interfaces and Transitions
Section 7.10, Erosion
Section 7.13, Penetrations
Section 7.14, Floodwalls, Retaining Walls, and Closure Structures AECOM completed the geotechnical evaluation for the Sacramento Area Flood Control Agency (SAFCA). The evaluation relies upon available subsurface and soil characterization data, reports, design evaluations, record drawings, and other relevant documentation for the project prepared by AECOM (formerly URS) and other consultants to SAFCA. No new investigations or geotechnical analyses were performed.

Geotechnical analysis methods, safety factors and results were compared against current standards of practice for levees established in the ULDC as well as in U. S. Army Corps of Engineers, and other agency standards.

If you have questions regarding this report, please contact the undersigned.

Sincerely,
Richard Millet, PE, GE
Senior Geotechnical Engineer
Cc: Mr. Pro Mitra, PE/MBK Engineers ([email protected]) Ms. Becky Money, PE/GE/MBK Engineers ([email protected]) ULDC Geotechnical Findings i 11/15/2024
Arcade Creek North Levee IPC Backcheck

TABLE OF CONTENTS

1.0 Introduction ............................................................................................................. 1

1.1 North Area Streams Background .................................................................... 1

1.2 In-Ground Pools ............................................................................................. 2

2.0 Data, Criteria, and Methods .................................................................................... 3

2.1 Data Reviewed ............................................................................................... 3

2.2 Stationing and Reaches ................................................................................. 3

2.3 Documents Reviewed .................................................................................... 3

2.4 Applicable Criteria .......................................................................................... 4

2.5 Critical Levee Cross Sections ......................................................................... 4

2.6 Levee Height and Hydraulic Head .................................................................. 5

2.7 Design Water Surface Elevations ................................................................... 5

3.0 ULDC Section 7.3 Soil Sampling, Testing, and Logging ......................................... 7

3.1 Subsurface investigations ............................................................................... 8

3.1.1 Conclusion ......................................................................................... 9

3.2 Sampling and Testing ..................................................................................... 9

3.2.1 Conclusion ......................................................................................... 9

4.0 ULDC Section 7.4 Slope Stability for Intermittently Loaded Levees ..................... 10

4.1 Conclusion .....................................................................................................11

5.0 ULDC Section 7.5 Underseepage ......................................................................... 12

5.1 Landside Levee Toe Seepage and Erosion .................................................. 12

5.2 Conclusion .................................................................................................... 13

6.0 ULDC Section 7.7 Seismic Vulnerability ............................................................... 14

6.1 Conclusion .................................................................................................... 14

7.0 ULDC Section 7.8 Levee Geometry ...................................................................... 15

7.1 Conclusion .................................................................................................... 15

8.0 ULDC Section 7.9 Interfaces, Transitions, GAps .................................................. 16

8.1 Levee Reach Stations 5023+00 to 5033+00 (ARN-1) .................................. 16

8.1.1 Downstream Interface at Station 5023+00 ....................................... 17

8.1.2 Interface at Station 5031+40 ............................................................ 17

8.1.3 Conclusion ....................................................................................... 17

8.2 Levee Reach Stations 5038+00 to 5075+00 (ARN-3) .................................. 17

8.2.1 Interface at Station 5039+50 ............................................................ 18

8.2.2 Transitions SB to SCCB Slurry Cutoff Walls .................................... 18

8.2.3 Transition Centerline to Toe Cutoff Wall. .......................................... 18

8.2.4 Slurry Wall Gap Stations 5065+30 to 5065+70 ................................ 18

8.2.5 Conclusion ....................................................................................... 19

8.3 LEvee Reach Station 5075+00 to Station 5100+00 (ARN-4)........................ 19

8.3.1 Transition Centerline to Toe Slurry Cutoff Walls ............................... 20

8.3.2 Interface End of Toe Slurry Cutoff Wall Station 5100+00 ................. 20

8.3.3 Conclusion ....................................................................................... 20 ULDC Geotechnical Findings ii 11/15/2024
Arcade Creek North Levee IPC Backcheck

8.4 Slurry Cutoff Wall Transitions at Road Crossings ......................................... 20

8.4.1 Conclusion ....................................................................................... 21

8.5 Station 5070+40 to Station 5112+43 ............................................................ 21

8.5.1 Floodwalls ........................................................................................ 21

8.5.2 Interface at Marysville Boulevard ..................................................... 22

8.5.3 Conclusion ....................................................................................... 22

8.6 ULDC Section 7.10 Erosion .......................................................................... 22

8.7 Conclusion .................................................................................................... 22

9.0 ULDC Section 7.13 Penetrations .......................................................................... 23

9.1 Conclusion .................................................................................................... 24

10.0 ULDC Section 7.14 Floodwalls, Retaining Walls, and Closure Structures ............ 25

11.0 Arcade Creek North Levee Study Area Summary of Results ................................ 26

12.0 Limitations ............................................................................................................. 27

13.0 References ........................................................................................................... 28 TABLES
Table 2-1 Arcade Creek North Levee Reach and Station Limits ................................ 3 Table 2-2 Critical Levee Cross Section Locations...................................................... 5 Table 3-1 Subsurface Explorations ACNL ................................................................. 8 Table 4-1 Minimum ULDC Safety Factors for Slope Stability ................................... 10 Table 5-1 Allowable Exit Gradients .......................................................................... 12 Table 8-1 Interfaces, Transitions, and Gaps ............................................................ 16 Table 11-1 Summary of Results................................................................................. 26

FIGURES
Figure 1 Arcade Creek North Levee

APPENDICES
A ULDC 200-Year Design Water Surface Elevations
B Geotechnical Evaluation Results Summary
C Levee Geometry Cross Section Evaluation

ACRONYMS AND ABBREVIATIONS
AAR Alternative Analysis Report
AECOM AECOM Technical Services, Inc.

ACNL Arcade Creek North Levee
CPT Cone Penetrometer
DWR California Department of Water Resources
DWSE Design Water Surface Elevation
ft feet
GDR Geotechnical Data Report
GERPD Geotechnical Engineering Report for Project Design HTOL hydraulic top of levee
ULDC Geotechnical Findings iii 11/15/2024
Arcade Creek North Levee IPC Backcheck
MBK MBK Engineers
NEMDC Natomas East Main Drainage Canal
pcf pounds per cubic feet
PIRs Problem Identification Reports
SCCB slag cement-cement-bentonite
SAFCA Sacramento Area Flood Control Agency
SRFCP Sacramento River Flood Control Project
ULDC Urban Levee Design Criteria
USACE U.S. Army Corps of Engineers
WSE Water Surface Elevation
ULDC Geotechnical Findings 1 11/15/2024
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1.0 INTRODUCTION
This geotechnical finding report documents AECOM’s evaluation of approximately

1.7 miles of the Arcade Creek north levee (ACNL) shown on Figure 1 between Stations 5023+00 and 5112+43Error! Reference source not found.. ACNL is part of the RoblaArcade Levee System. AECOM was formally URS. Both names are synonymous, and both may appear in this report and other documents referenced herein.

AECOM’s evaluation was conducted at the request of the Sacramento Area Flood Control Agency (SAFCA) to ascertain levee compliance with the geotechnical criteria specified in the following nine sections of the California Department of Water Resources (DWR) Urban Levee Design Criteria (ULDC) (DWR, 2012):
 Section 7.3 Soil Sampling, Testing, Logging
 Section 7.4 Slope Stability for Intermittently Loaded Levees  Section 7.5 Underseepage for Intermittently Loaded Levees  Section 7.7 Seismic Vulnerability
 Section 7.8 Levee Geometry
 Section 7.9 Interfaces and Transitions
 Section 7.10 Erosion
 Section 7.13 Penetrations
 Section 7.14 Floodwalls, Retaining Walls, and Closure Structures There are floodwall segments along the waterside crest of ACNL between Stations 5023+00 and 5111+40. The structural evaluation of the floodwalls for ULDC compliance is being addressed by other consultants. However, included in this report is AECOM’s geotechnical evaluation of floodwall-levee interfaces and transitions required under ULDC Section 7.9.

AECOM’s conclusions regarding ACNL compliance with the ULDC criteria are based on comparisons of available data and levee analysis findings found in the existing project documentation with the criteria. Conclusions may change if the current (2012) ULDC criteria changes.

1.1 NORTH AREA STREAMS BACKGROUND
The Robla-Arcade levee system includes about 12 miles of levee along the east bank of the Natomas East Main Drainage Canal (NEMDC), the north and south banks of Dry/Robla Creek, and the north bank of Arcade Creek1. These levees were originally constructed in the 1930s and 1950s as components of the Sacramento River Flood Control Project (SRFCP) by the U.S. Army Corps of Engineers (USACE) as authorized by Congress under the Flood Control Act of 1917 including amendments.

After completing upgrades to conform these levees to SRFCP requirements, levee operation and maintenance responsibility was transferred to the State of California. The Central Valley Flood Protection Board is the non-Federal project sponsor; the American 1 Only the Arcade Creek north levee ULDC evaluation is covered in this report.

ULDC Geotechnical Findings 2 11/15/2024
Arcade Creek North Levee IPC Backcheck
River Flood Control District is responsible for maintaining the levees; and SAFCA is responsible for implementing levee improvement projects as the managing agency for these levees.

Beginning in the 1990’s SAFCA implemented various improvement projects within the Robla-Arcade levee system that included levee raises, landside and/or waterside widening, and the addition of crest walls and floodwalls. In addition to these types of improvements, the most recent ACNL improvements completed in 2019 included constructing centerline slurry cutoff walls, toe slurry cutoff walls combined with waterside slope reconstruction, and other related work meant to remediate seepage and stability deficiencies identified in analyses documented in Problem Identification Reports (PIRs). More detailed descriptions for completed levee improvement projects including record drawings, supporting site investigation and testing data, engineering analyses, and other information referenced in this report will be found in the documents listed in Section 2.3.

1.2 IN-GROUND POOLS
In-ground pools on the landside of the levee can present a seepage-related failure risk, particularly if they are located close to the levee toe. From site reconnaissance, topographic surveys, and aerial photography, there are no known in-ground pools requiring seepage evaluation for ACNL.

ULDC Geotechnical Findings 3 11/15/2024
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2.0 DATA, CRITERIA, AND METHODS

2.1 DATA REVIEWED
To establish compliance with ULDC Section 7.3, Soil Sampling, Testing, and Logging, AECOM reviewed all the geotechnical data contained in the reports cited in Section 2.3.

Based on this review, AECOM concludes the available information is adequate by exception to arrive at conclusions regarding ULDC compliance and further site investigations or engineering analyses are not considered necessary. Section 3.1 (subsurface investigations) and Section 3.2 (sampling and testing) compare the extent of available geotechnical data with the ULDC requirements and provide conclusions.

2.2 STATIONING AND REACHES
In this report and in the referenced documents, the location for site investigations, geotechnical analyses, interfaces and transitions, and other information is typically given as the centerline ACNL station and/or a reach designation. Table 2-1 shows the reach identifier names used herein and in the referenced documents with the corresponding ACNL station limits for the reach. Figure 1Error! Reference source not found. also includes the reach limit stations. Selecting reach limits and describing how critical analytical sections were selected within each reach for analysis is described further in Section 2.5.

Table 2-1 Arcade Creek North Levee Reach and Station Limits Station Limits
(feet) Reach Component Features
5023+00 to 5033+00 ARN-1 Embankment Levee
5033+00 to 5038+00 ARN-2 Embankment Levee
5038+00 to 5075+00 ARN-3 Embankment Levee with Crest
Floodwall
5075+00 to 5100+00 ARN-4 Embankment Levee with Crest
Floodwall
5100+00 to 5112+43 ARN-5 Embankment Levees and Floodwalls

2.3 DOCUMENTS REVIEWED
To assess ULDC compliance, AECOM reviewed the following reports containing descriptions, data, and geotechnical analyses for ACNL:
 AECOM, 2016 - SAFCA North Area Streams Levee Improvement Project, Final Geotechnical Engineering Report for Project Design (GERPD).  AECOM, 2020 - SAFCA North Area Streams Levee Improvement Project, Record Drawings, NEMDC and Arcade Creek Levees, Project Plans for Construction, Volume 2 of 3, October 2020.
 Spink, 1997 - Arcade Creek Unit 1B Levee Improvement, As-built Drawings.
 URS, 2014a - Problem Identification Report (PIR).
 URS, 2014b - Geotechnical Data Report (GDR).

ULDC Geotechnical Findings 4 11/15/2024
Arcade Creek North Levee IPC Backcheck
 URS, 2014c - Alternatives Analysis Report (AAR).
 URS, 2015a - Geotechnical Data Report, Addendum 1.
 URS, 2015b - Problem Identification Report, Addendum 1.  URS, 2015c - Geotechnical Data Report, Addendum 2.
 URS, 2016a - Geotechnical Data Report, Addendum 3.
 USACE, 2023 - Supplement to the Standard Operations and Maintenance Manual, Sacramento River Flood Control Project, Unit No. 118-Part No. 2.

2.4 APPLICABLE CRITERIA
AECOM’s evaluation compared geotechnical analysis methods and calculated safety factors in the record documents with recommended current practice methods and safety factors given in the following guidance documents:
 USACE EM 1110-2-1913 - Design and Construction of Levees, April 30, 2000 (USACE, 2000).
 USACE ETL 1110-2-569 - Design Guidance for Levee Underseepage, May 1, 2005 (USACE, 2005).
 USACE EM 1110-2-1902 - Engineering and Design, Slope Stability, October 2003 (USACE, 2003).
 USACE EM 1110-2-1901 - Engineering and Design, Seepage Analysis and Control for Dams, April 1993 (USACE, 1993).
 USACE SOP SPK EDG-03 - Standard Operating Procedure 3, Geotechnical Levee Practice, May 2022 (USACE, 2022).
 State of California Department of Water Resources. 2012. Urban Levee Design Criteria (ULDC). May 2012 (DWR, 2012).

2.5 CRITICAL LEVEE CROSS SECTIONS
Table 2-2 lists the locations where critical levee sections were evaluated for ULDC compliance in each levee reach as documented in the GERPD, PIR, and AAR documents. Levee reaches were selected so the physical and geotechnical characteristics of the levee within the reach are reasonably consistent based on stratigraphy, soil characteristics, topography, levee geometry, hydraulic head, and previous performance history. One or more critical analytical sections were identified within each reach. These sections represent worst case conditions in the reach and were used for seepage, stability, settlement, and other analyses. The GERPD and PIR documents provide additional background on selecting critical analytical sections.

Table 2-2 also includes a comparison of levee crest elevations and design water surface elevations (DWSE) used for levee analyses in the record documents with corresponding information from hydraulic study updates for the DWSE completed in 2024 and ground survey updates completed in 2024. The comparisons are discussed further in Section 2.6 and Section 2.7.

ULDC Geotechnical Findings 5 11/15/2024
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Table 2-2 Critical Levee Cross Section Locations
Evaluation
Section Location
Landside
Toe El.2
(feet)
Hydraulic
Head1
(feet)
Crest El.

Comparisons
(feet)2,3
Design Water Surface El. Comparison
(feet)2
Used For
Analyses
2024
Survey
Check
200-Year
(MBK, 2014)
200-Year
(MBK, 2024)
Difference
(feet)
Station 5031+00
Station 5036+00
Station 5049+00
Station 5065+27
Station 5097+00
Station 5100+00
Station 5110+464

26.3 32.0

31.9 33.8

35.6 37.4

39.6 12.7

7.0 8.2

6.3 5.4

2.7 1.8

46.3 45.0

44.5 44.7

42.1 42.5

46.5 46.01

44.61 44.87

45.18 42.44

42.71 46.40

39.0 39.0

40.1 40.1

41.0 40.1

41.4 37.74

37.73 37.80

37.96 39.44

39.52 41.56
-1.26
-1.27
-2.30
-2.14
-1.56
-0.58
+0.16

1. 200-year design water surface elevation hydraulic head relative to the landside toe.

2. All elevations (feet) based on North American Vertical Datum 1988.

3. Top of levee embankment excluding flood or freeboard walls unless noted otherwise.

4. Data at Station 5110+46 is for an existing floodwall.

2.6 LEVEE HEIGHT AND HYDRAULIC HEAD
Table 2-2, summarized from information in Appendix B, provides levee design characteristics for the critical sections evaluated, including crest elevations, landside toe elevations, and hydraulic head measured above the landside toe for the 200-year DWSE (refer to Section 2.7). These characteristics are representative of the levee in the reach they represent.

To confirm that the levee crest elevations for the critical sections analyzed have not changed since the analyses were performed, SAFCA authorized Psomas to survey elevations along the levee crown at approximately 100-foot intervals, and survey cross sections at selected locations (Psomas, 2024). Table 2-2 provides a comparison of the 2024 crest elevation survey results with the elevations used at critical sections analyzed in the record documents. The elevation differences are not large enough to warrant reevaluating seepage, stability, or settlement analyses or reevaluating ULDC compliance at interfaces, transitions, gaps, or closure structures.

Also, where the crest was degraded and reconstructed for the most recent slurry cutoff wall construction work, AECOM compared the levee centerline profile used for design from the record drawings (AECOM, 2020) with the 2024 Psomas centerline survey check. Results showed that the reconstructed crest varied from 4 inches to 6 inches higher than the design profile. AECOM concludes the reconstructed crest satisfies flood protection and freeboard requirements and height increases are not significant enough to warrant any seepage or stability reevaluations at the critical sections.

2.7 DESIGN WATER SURFACE ELEVATIONS
The DWSE profile was developed by MBK Engineers (MBK, 2014). The geotechnical evaluation of the levees in the record documents used the 200-year DWSE profile as well as the hydraulic top of levee (HTOL) profile that was set three feet above the DWSE.

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To support the ULDC compliance reviews, MBK updated the DWSE and HTOL profile information (MBK, 2024). Appendix A provides the updated information by levee station in tabular form.

Table 2-2 provides a comparison of the 2024 DWSE update with the DWSEs used for the geotechnical analyses at critical sections. In all but one case, the MBK 2024 updated water surface elevations are lower than the earlier MBK 2014 elevations used for analysis. For the one, higher case, the difference is minor (only approximately

0.16 feet). Based on data in Table 2-2, there is no need to reevaluate geotechnical analyses for seepage, stability, and settlement in the record documents, or to reevaluate the adequacy of interfaces, transitions, gaps, or closure structures.

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3.0 ULDC SECTION 7.3 SOIL SAMPLING, TESTING, AND LOGGING AECOM evaluated the geotechnical field investigations and laboratory testing for ACNL to reach conclusions regarding compliance with guidance provided in ULDC Section 7.3, Soil Sampling, Testing, and Logging, which is reproduced below:

ULDC (DWR, 2012) 7.3 requires soil sampling, testing, and logging per standard procedures prescribed in guidance documents, including the USACE Sacramento District’s Geotechnical Levee Practice Standard Operating Procedures (SPK SOP) (USACE, 2022) and DWR’s Division of Flood Management Soil and Rock Logging, Classification, Description and Presentation Manual (2009). This includes an evaluation of soil exploration quantity and location as outlined in the SPK SOP (USACE, 2022). Based on this document, explorations for a feasibility levee evaluation should be obtained at a spacing of approximately 1,000 feet along the levee crest. For preconstruction and design studies a spacing of approximately 500 feet along the waterside toe, levee crown, landside toe. Exploration depths should be a minimum of four times the levee height and extending to an appropriate stratum. Additional borings may be performed landward and waterward of the levee (100 to 500 ft away from the levee) to evaluate the distal seepage conditions. Explorations that did not meet the requirements outlined (e.g., explorations that were not drilled deep enough) above were not included.

The SPK SOP recommends a thorough evaluation of existing information as part of a levee evaluation program. This includes a review of original construction (if available), improvements, performance history, existing subsurface information, and regional and local geomorphology. The standard also recommends the use of cone penetrometers (CPTs) and geophysics to supplement borings, where appropriate.

In addition, where available, the as-built plans, conformance laboratory tests, and in-place compaction tests for the construction and improvements of each levee were retained as part of the ULDC (DWR, 2012) evaluation. This information was used to evaluate the levee geometry and material properties within the newly constructed and improved levee sections.

Sources of information for AECOM’s review include the following:
 The GDRs, PIRs, and GERPD for information on surficial geologic mapping and geomorphic assessments from various consultant reports, including (URS/AMEC Geomatrix 2009 and 2011), (Fugro-William Lettis and Associates, 2008 and 2011), and Kleinfelder (2013b).  The GDRs for information on electric resistivity imaging surveys along the waterside toe of the Arcade Creek levees.
 GDRs, PIRs and GERPD for boring logs used to develop subsurface profiles, and laboratory testing on borehole samples used to characterize soil layers for analysis. Borings, sampling, and testing data is based on URS/AECOM site investigations as well as historic reports listed in Section 13.0 prepared by (USACE, 1954), (Caltrans, 1967), (Wahler Associates, 1987), (Kleinfelder, 1994a, 1995, 2002, 2013a, 2013b).  GDR for off-site borrow area Site 2K (URS, 2015d).
 GDRs for groundwater information developed from piezometers installed in separate boreholes adjacent to investigation boreholes. Depths ranged from 20 to 66 feet.

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3.1 SUBSURFACE INVESTIGATIONS
Table 3-1 summarize bore hole drilling statistics for ACNL. Boring logs and location maps are included in the GERPD and GDR documents. Logs and subsurface profiles are also included in the record drawings (AECOM, 2020).

Table 3-1 Subsurface Explorations ACNL
Exploration
Location
Number of
Explorations
Average Spacing
(feet)
Levee Crown 27 357
Landside Toe 4 2,000
Total 31
The boring count includes borings ranging from 35 to 80 feet below crest or toe.

Shallower borings used to investigate levee slopes and waterside near surface conditions are not included. Note that locating and drilling bore holes off the levee along ACNL was inhibited by factors that included lack of access to landside toe areas for investigations due to private property constraints, building encroachments, ponding conditions that limited access on the waterside in some locations, and environmental restrictions preventing access on the waterside due to the presence of delineated wetlands along Arcade Creek.

While boring locations and spacings by themselves may not meet ULDC guidelines, a significant amount of other information is available that verifies the borings, fills in gaps, and confirms there is an adequate understanding of levee and foundation conditions to support analyses and arrive at conclusions regarding ULDC compliance. Most notably, deep centerline and toe slurry cutoff walls were installed along significant portions of ACNL as part of the most recent remediation work completed by AECOM (reference record drawings [AECOM, 2020]). During slurry cutoff wall installation, excavation was monitored and trench logs were prepared on average every ten feet along the slurry wall by AECOM and the contractor. Trench logs were used by AECOM as the wall construction work was progressing to verify actual conditions against soil profiles developed from available borings and soil sampling data. Correlation was good. Where variations in soil conditions were noted at the planned bottom of the slurry wall, the slurry wall depth was varied as needed in real time by the responsible geotechnical engineers as work progressed to ensure the bottom of the slurry wall penetrated into suitably dense, low permeability material.

Based on historic performance, there are no known seepage or stability issues that have not been satisfactorily remediated by modification projects implemented by USACE and SAFCA. The levee has performed well during the most recent high-water events occurring during the 2023 and 2024 wet seasons.

An independent consulting board for SAFCA reviewed the historic background geotechnical data and the planned explorations to support the most recent levee remediation work. The board conclude the existing and new information taken together was adequate to define site geotechnical conditions.

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3.1.1 Conclusion
Geotechnical data supporting levee analyses includes levee and foundation drilling, soil sampling and testing, surficial geologic mapping and geomorphic assessments, resistivity surveys, observations during recent deep slurry cutoff wall and slope reconstruction work, other historic construction records, and past performance evaluations. While the extent of drilling may not meet SPK SOP (USACE, 2022) guidelines, AECOM concludes subsurface investigations are adequate to meet ULDC criteria by exception considering all the information available from the different investigations and construction observations made over time. Additional investigations are not warranted. The SAFCA board of consultants concurred.

3.2 SAMPLING AND TESTING
Borings were sampled and logged in accordance with ASTM D1586, and soils were classified in accordance with ASTM specification D2488 and the Unified Soil Classification System, ASTM D2487. Undisturbed samples were also obtained at selected locations from offset borings located adjacent to borings with logs to obtain representative samples for laboratory testing to support seepage, stability, and settlement analyses.

The GDR documents describe sampling and testing programs and the use of the results to define soil layering and soil layer characterizations for the critical sections that were used in design analyses. Results are summarized in tables in the GDRs and GERPD.

3.2.1 Conclusion
Based on AECOM’s review of the sampling and testing program, and reviews by SAFCA’s independent consulting board, AECOM concludes sampling and testing is adequate to meet ULDC criteria by exception considering all the information available from the different investigations and construction observations over time.

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4.0 ULDC SECTION 7.4 SLOPE STABILITY FOR INTERMITTENTLY LOADED LEVEES
This section provides a summary of AECOM’s review of existing geotechnical stability analyses for ACNL and AECOM’s conclusions regarding compliance with ULDC Section 7.4, Slope Stability.

The ULDC provides the following definition for intermittently loaded levees:
“Intermittently loaded levee means a levee that does not experience a water surface elevation of one foot or higher above the elevation of the levee toe at least once a day for more than 36 days per year on average.”
ACNL levees meet the intermittently loaded definition because historical flood hydrographs confirm short-term peak flood flow events. ULDC requirements and criteria for stability for intermittently loaded levees is as follows:

ULDC Section 7.4, Slope Stability for Intermittently Loaded Levees: Requires slope stability analysis for the design water surface elevation (DWSE) and at the Hydraulic Top of Levee (HTOL) WSE. “Engineers should use sound engineering judgment and guidance from EM 1110-2-1902 to decide what constitutes a minor, insignificant slip surface versus a sliding surface that threatens the integrity of the levee. These determinations should be based on performance history, levee geometry, type of levee fill material, stratigraphy of the levee embankment and foundation soils, seepage conditions (including pore water pressures calculated for the seepage analysis), soil strength characteristics, and potential for erosion. Those surfaces which significantly threaten the integrity of the levee must meet minimum slope stability criteria.” Steady-state landside stability and rapid drawdown waterside stability should be evaluated using the minimum factors of safety summarized in Table 4-1.

Table 4-1 Minimum ULDC Safety Factors for Slope Stability Stability Analysis ULDC Minimum Factor of Safety1
Steady-State DWSE, Landside Slope 1.4
Steady-State HTOL WSE, Landside Slope 1.2
Rapid Drawdown DWSE, Waterside Slope 1.0-1.2
End of Construction2 1.3

1. Critical failure surface should intersect the levee crown and exceed a minimum of 3-foot depth into the level slope.

2. End of construction case does not apply due to the levee age, including most recent repairs completed in 2019.

AECOM reviewed the slope stability analyses for the critical sections listed in Table 2-2 to verify compliance with the ULDC safety factors given in Table 4-1. The analyses included applicable underseepage and through seepage pressure gradients from the seepage analyses discussed in Section 5.0. Analysis results are summarized in tables in Appendix B. Required safety factors equal or exceed what is required for each design case listed in Table 4-1. As discussed previously in Section 2.7, the ULDC Geotechnical Findings 11 11/15/2024
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updated MBK 2024 water levels confirm that the stability analyses using the MBK 2014 DWSE and HTOL water levels are still applicable.

4.1 CONCLUSION
ACNL has been evaluated and found to meet slope stability criteria using the 200-year DWSE and HTOL water levels. Underseepage and through seepage evaluations for the DWSE condition are reflected in the analyses. Levee crest profiles and levee cross sections used previously for slope stability analyses are consistent with recent surveys (Psomas, 2024) and reevaluation at critical sections is not necessary. AECOM concludes that ACNL meets the ULDC requirements of Section 7.4, Slope Stability, for intermittently loaded levees based on a review of available construction records, geotechnical data, construction materials, construction quality control and quality assurance testing, historic performance, and the slope stability analysis referenced in this report.

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5.0 ULDC SECTION 7.5 UNDERSEEPAGE
This section provides a summary of AECOM’s review of existing geotechnical seepage analyses for ACNL and provides conclusions regarding compliance with ULDC Section 7.5, Underseepage. The general requirements of ULDC Section 7.5 for intermittently loaded levees are as follows:

ULDC Section 7.5, Underseepage: Requires seepage analysis performed for the design water surface elevation (DWSE) and the hydraulic top of levee (HTOL) WSE. Exit gradients measured at the landside levee toe, seepage berm toe, ditches, canals, depressions, or areas of thin blanket. The allowable maximum exit gradients are summarized in Table 5-1.

Table 5-1 Allowable Exit Gradients
Seepage Analysis Location Allowable Maximum Exit Gradient Steady-State DWSE
Landside Levee Toe 0.5
Seepage Berm/Blanket
Layer

0.5 at levee toe and 0.8 at seepage
berm toe1
Ditches, canals,
depressions 0.5-0.82
Steady-State HTOL WSE
Landside Levee Toe 0.6
Seepage Berm/Blanket
Layer 0.6-0.83
Ditches, canals,
depressions 0.6 at levee toe4

1. The allowable underseepage exit gradient through the combined seepage berm/blanket layer between the levee toe and the seepage berm toe for a water surface set at the DWSE is determined by interpolation, using 0.5 at the levee toe and 0.8 at the seepage berm toe (for seepage berms less than 300 feet wide).

2. Maximum allowable exit gradient in ditch, canal, or depression is 0.5 at the landside levee toe and up to 0.8 at 150 feet from the levee toe (and beyond), using linear interpolation for distances in between.

3. ULDC (DWR, 2012) allows for higher exit gradients at the seepage berm toe provided sound engineer judgement is used. If the berm is less than 100-ft wide, the maximum exit gradient may increase by up to 20 percent of the DWSE maximum exit gradient.

4. Gradients beyond the toe are allowed up to 20 percent higher than the maximum allowable exit gradients specified above for the DWSE for the same distance from the levee toe.

Table 5-1 is applicable to conditions where existing blanket layer soils have a saturated unit weight of 112 pcf or more. When saturate unit weight is lower, refer to additional ULDC requirements pertaining to allowable exit gradient adjustments.

AECOM reviewed the seepage evaluations for the critical sections listed in Table 2-2 to verify compliance with the ULDC exit gradients given in Table 5-1. Analysis results are provided in tables in Appendix B. Exit gradients at critical section locations meet allowable values specified in Table 5-1. As discussed previously in Section 2.7, the updated MBK 2024 water levels confirm that the seepage analyses in the record documents using the MBK 2014 DWSE and HTOL water levels are still applicable.

5.1 LANDSIDE LEVEE TOE SEEPAGE AND EROSION
Several sections evaluated for seepage show the potential for phreatic surface breakout just above the landside levee toe based on the seepage results provided in Appendix B.

Section 8.6 addresses this seepage and the potential for local toe erosion. AECOM ULDC Geotechnical Findings 13 11/15/2024
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concludes that this seepage does not present a risk to the levee as described in Section 8.6.

5.2 CONCLUSION
The ACNL has been evaluated and found to meet seepage criteria using the 200-year DWSE and HTOL water levels. Levee crest profiles and levee cross sections used previously for seepage analyses are consistent with recent verification surveys (Psomas, 2024) and reevaluations of critical sections is not necessary. Any minimal seepage at the landside toe of the levee is not a risk to the levee. AECOM concludes that the ACNL meets the requirements of ULDC Section 7.5, Underseepage, for intermittently loaded levees.

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6.0 ULDC SECTION 7.7 SEISMIC VULNERABILITY
A seismic vulnerability analysis was performed by Kleinfelder to evaluate liquefaction potential and pseudo-static stability. This evaluation is summarized in the 2024 Kleinfelder Seismic Performance Summary Report included with Kleinfelder’s due diligence report. That report can be found in Appendix E in MBK’s Engineer’s Report.

The seismic vulnerability analysis concluded that the ACNL has low seismic vulnerability based on acceptable factors of safety against liquefaction. Therefore, a post-earthquake remediation plan required under ULDC 7.7.1 is not required.

6.1 CONCLUSION
Based on the above information, AECOM concludes that seismic vulnerability has been adequately addressed for ACNL, and the geotechnical requirements of ULDC Section

7.7, Seismic Vulnerability, have been met.

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7.0 ULDC SECTION 7.8 LEVEE GEOMETRY
ACNL is classified as a minor stream levee, and the following minimum geometric requirements are provided in ULDC Section 7.8:
 2H:1V landside slope
 12-foot-wide levee crown
 3H:1V waterside slope
Psomas obtained representative levee cross sections (Psomas, 2024) to evaluate the existing geometry against the ULDC criteria. Cross sections for ACNL prepared by MBK are included in Appendix C. Each section shows two profiles, the required ULDC geometry and the surveyed cross section. The crest elevation for the required geometry section is the design water surface elevation plus an additional three feet for freeboard; the centerline is the historic centerline. The cross sections show the levee is typically overbuilt.

Since originally constructed, remediation projects have modified the original levee, including geometry. However, record drawing sections for past remediations as well as the recent Psomas survey data verify ACNL complies with the ULDC geometry criteria.

7.1 CONCLUSION
Based on the record drawings (AECOM, 2020) and the recent Psomas cross section surveys, AECOM concludes the ACNL meets the requirements for ULDC Section 7.8, Levee Geometry.

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8.0 ULDC SECTION 7.9 INTERFACES, TRANSITIONS, GAPS
This section addresses ACNL compliance with the requirements of ULDC Section 7.9, Interfaces, Transitions, and Gaps. Conclusions regarding compliance are based on AECOM’S review of existing information contained in the record documents listed in Section 2.3. ULDC Section 7.9 contains the following requirements:

The civil engineer must consider, evaluate, and explicitly design for interfaces and transitions between different types of levee sections and features along a levee system.

Appropriate overlaps, transitions, and connections between features must be evaluated and designed to ensure that the levee system functions holistically, such that no levee reach is more susceptible to problems than an adjacent reach due to gaps in features, loading/demand concentrations, or other three-dimensional effects. Such interfaces, transitions, and connections commonly occur at the ends of seepage berms, seepage cutoff walls, revetments, and floodwalls.

Table 8-1 lists the interfaces, transitions, and gaps evaluated for the ACNL.

Table 8-1 Interfaces, Transitions, and Gaps
Condition Locations
Station 5023+00 to Station 5033+00 (ARN-1)
Interfaces – Relief Wells with Upstream and
Downstream Embankment Levees Station 5023+00 and Station 5031+40 Station 5038+00 to Station 5075+00 (ARN-3)
Interface - SB Centerline Slurry Cutoff Wall with
Downstream Embankment Levee Station 5039+50
Transitions - SB to SCCB Slurry Cutoff Walls Station 5064+50 and Station 5071+00 Gap - bottom of slurry cutoff wall to avoid 66”
sewage transmission main Station 5065+30 to 5065+70
Station 5075+00 to Station 5100+00 (ARN-4)
Transition - Centerline to Toe Slurry Cutoff Wall Station 5071+47 to 5076+50 Interface - End of Toe Slurry Cutoff Wall Station 5100+00 Transitions at Road Crossings
Transition – Sacramento Norther Bike Trail
Crossing Station 5037+80
5070+40 to Station 5112+43
Interfaces - Floodwalls Station 5070+40 and Station 5071+47 Stations 5107+90 to 5111+40
Interface – Levee with Marysville Boulevard Station 5112+43

8.1 LEVEE REACH STATIONS 5023+00 TO 5033+00 (ARN-1)
ACNL between Stations 5023+00 and 5033+00 (Reach ARN-1) was originally constructed in 1957 by USACE. Construction included an inspection trench keyed into the foundation a minimum of 6 feet. City of Sacramento Sump 158 is located at Station 5032+00. A concrete-lined ditch at the landside toe of the levee conveys landside runoff ULDC Geotechnical Findings 17 11/15/2024
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to the Sump. In 1996 the levee was raised on the waterside by about 1 to 3 feet. Refer to the GERPD for addition levee details and generalized subsurface conditions.

The PIR (URS, 2014a) analysis indicates this levee segment did not meet ULDC criteria for stability and underseepage prior to implementation of the relief well improvements described herein. The AAR (URS, 2014c) concluded the preferred improvement to address instability and seepage was to install 12 relief wells in the concrete lined ditch between Stations 5023+00 and 5031+40 (reference record drawings (AECOM, 2020) for locations, spacing, and details). As described in the GERPD, exploratory borings were drilled at each well location and the collected data used to set the required well depth, and for designing the filter pack, slot size, and screened interval. Analysis results indicate the wells would produce a limited flow with the water level in the creek at or near the DWSE and with the concrete channel dewatered. Based on review of construction record and AECOM field inspections during installation, wells were successfully installed. The following paragraphs address the interfaces between the segment with the wells and the upstream and downstream embankment levees.

8.1.1 Downstream Interface at Station 5023+00
The first relief well was located at the beginning of the levee reach at Station 5023+00.

Downstream from this well, the levee was found to meets ULDC seepage and stability criteria based on evaluations by other consultants (Kleinfelder) as described in their reports. Based on evaluations provided in AECOM’s GERPD and PIR documents using all available data, there is no potential for adverse levee settlement, instability, or endaround seepage at the interface at Station 5023+00.

8.1.2 Interface at Station 5031+40
Upstream from Station 5031+40, the existing levee was found to meet ULDC criteria for stability and seepage as described in the PIR analysis (URS, 2014a). As indicated in the GERPD, the furthest upstream well was selectively positioned to intercept any potential seepage originating from the interface with the upstream levee segment. Based on geotechnical site data, levee construction materials, construction documentation, field inspection data, and other findings in AECOM’s GERPD and PIR documents, there is no need to extend the wells upstream to control seepage, and there is no potential for adverse levee settlement, instability, or end-around seepage at the interface at Station 5031+40.

8.1.3 Conclusion
Based on the above information, AECOM concludes that the relief well interfaces with adjacent levee reaches at ACNL Station 5023+00 and 5031+40 meets the geotechnical requirements of ULDC Section 7.9, Interfaces and Transitions.

8.2 LEVEE REACH STATIONS 5038+00 TO 5075+00 (ARN-3)
ACNL between Stations 5038+00 and 5075+00 (reach ARN-3) was originally constructed in 1957 by USACE. Construction included an inspection trench keyed into the foundation a minimum of 6 feet. In 1996, there was a 2- to 3-foot-high levee raise.

The levee raise was on the waterside from Station 5038+00 to 5065+50 and from ULDC Geotechnical Findings 18 11/15/2024
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Station 5071+00 to 5075+00. There was also a levee raise on both the landside and waterside between Station 5065+50 and 5069+00.

AECOM’s PIR analysis (URS, 2014a) indicates ACNL between Stations 5039+50 and 5075+00 did not meet ULDC criteria for underseepage, through seepage, and landside stability prior to implementation of the slurry cutoff wall improvements described herein.

From the AAR (URS, 2014c), the improvement to remediate underseepage, through seepage, and landside stability was construction of a soil-bentonite (SB) slurry cutoff wall along the centerline of the levee for the full length of the reach.

Subsequently, it was decided to substitute slag cement-cement-bentonite (SCCB) for the SB cutoff wall crossing of the Sacramento Norther Bike Trail between approximate Stations 5064+50 and 5071+00. This was done to reduce bike trail road closure times to construct the cutoff wall at the crossings and to allow the wall to be routed down slope on the waterside to pass under the Rio Linda Boulevard bridge (refer to the record drawings [AECOM, 2020]). Based on review of construction records and AECOM periodic site visits, the cutoff walls were successfully installed. The following paragraphs address the various interfaces at the upstream and downstream ends of the SB cutoff wall, and where the SB and SCCB cutoff wall overlap.

8.2.1 Interface at Station 5039+50
The existing levee segments downstream from Station 5039+50 was found to meet ULDC criteria for stability and seepage as described in the PIR (URS, 2014a). As described in the GERPD, based on geologic conditions near the end of the slurry cutoff wall, end-around seepage conditions are not considered likely. Geotechnical site data, levee construction materials and construction documentation indicate no potential for adverse levee settlement at the interface at Station 5039+50.

8.2.2 Transitions SB to SCCB Slurry Cutoff Walls
As shown in the record drawings (AECOM, 2020), transitions between the SB and SCCB slurry cutoff wall occur at approximate Stations 5064+50 and 5071+00. The SCCB wall was constructed first, followed by construction of the SB wall after the SCCB wall gained strength. As indicated on the record drawings (AECOM, 2020), the SB wall was constructed in direct contact with the vertical face of the completed SCCB wall with the two walls overlapping longitudinally a minimum of 25 feet to avoid a gap.

8.2.3 Transition Centerline to Toe Cutoff Wall.

As shown on the record drawings (AECOM, 2020), the centerline SB cutoff wall transitions down the waterside slope of the levee approximately between Stations 5071+47 and 5076+50 to interface with the toe cutoff wall required upstream of Station 5076+50. The interface detail is discussed in Section 8.3.1.

8.2.4 Slurry Wall Gap Stations 5065+30 to 5065+70
There is an existing 66-inch diameter reinforced concrete pipe sewer main at Station 5065+35 that runs in the levee foundation. Underseepage treatment at this location is an SCCB slurry cutoff wall. The invert of the sewer main and bottom of the cutoff wall are at the same approximate elevation and removal and replacement of the sewer main ULDC Geotechnical Findings 19 11/15/2024
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is not feasible. To avoid damaging the main, the SCCB wall was stepped up and over the main leaving a window in the cutoff wall between Stations 6065+30 and 5065+70.

AECOM completed a seepage analysis of the gap that is documented in the GERPD.

The analysis indicated seepage was not an issue, but AECOM determined that a relief well should be installed on the landside to serve as a monitoring and relief well. As shown in the record drawings (AECOM, 2020), the well was installed at a location adjacent to the sewer main at the SUMP 103 pump station. The relief well is piped to discharge to the pump station sump. Details of the design of the well are provided in the GERPD. A boring was drilled at the well location to support relief well design. No relief well seepage has been noted to date.

8.2.5 Conclusion
Based on geotechnical site data, levee construction materials, construction documentation, field inspection data, and other findings in AECOM’s GERPD and PIR documents, there is no potential for adverse levee settlement or end-around seepage at the interface at Station 5039+50 or at the overlap between cutoff wall types at approximate Stations 5064+50 and 5071+00. Likewise, potential seepage at the slurry cutoff wall gap at Station 5065+35 is not an issue and a monitoring well is installed for verification. Based on the above information, AECOM concludes that the interface at ACNL Station 5038+00 with the downstream ULDC compliant levee, the two slurry cutoff wall overlaps at Stations 5064+50 and 5071+00, and the window gap in the SCCB slurry cutoff wall at Station 5065+35 meet the geotechnical requirements of ULDC Section 7.9, Interfaces, Transitions, and Gaps.

8.3 LEVEE REACH STATION 5075+00 TO STATION 5100+00 (ARN-4) ACNL between Stations 5075+00 and 5100+00 (Reach ARN-4) was originally constructed in 1957 by USACE. Construction included an inspection trench keyed into the foundation a minimum of 6 feet. A 1996 levee raise increased freeboard with floodwall segments and waterside or landside slope reconstruction. The floodwall segments range from 1.5 to 6 feet tall and were constructed along the waterside hinge point from Station 5075+00 to 5111+40. Floodwall interfaces are discussed in Section 8.5.

AECOM’s PIR analysis (URS, 2014a) indicates ACNL between Stations 5075+00 and 5100+00 did not meet ULDC criteria for underseepage and through seepage prior to implementation of the slurry cutoff wall and slope repair improvements described herein.

Based on AECOM’s AAR (URS, 2014c) for the reach, the reach improvement for underseepage and through seepage was a SCCB slurry cutoff wall constructed along the waterside toe of the levee combined with waterside slope reconstruction using levee fill material. Based on review of completed construction records and field inspections by AECOM, the toe wall and slope reconstruction were successfully completed.

Note that the existing floodwalls located along the waterside crest of the levee were protected in place and not disturbed or modified by the toe slurry wall installation or slope reconstruction work described in this section. The structural evaluation and ULDC Geotechnical Findings 20 11/15/2024
Arcade Creek North Levee IPC Backcheck
stability of the existing floodwalls was evaluated by other consultants to SAFCA, and their findings and conclusions relative to ULDC compliance are provided in their reports.

8.3.1 Transition Centerline to Toe Slurry Cutoff Walls
At the downstream end of levee reach ARN-4, the toe cutoff wall and slope reconstruction interface with the centerline cutoff wall installed in downstream reach ARN-3. As shown on the record drawings (AECOM, 2020), the centerline cutoff wall (ARN-3) was transitioned down the slope and joined with the toe wall (ARN-4) approximately between Stations 5071+47 and 5076+50. In addition, to ensure waterside slope through seepage was addressed in the transition, the waterside slope reconstruction was carried downstream from Station 5076+50 and under the Rio Linda Bridge abutment to approximate Station 5068+00. This extension encompasses the stationing where downslope and upslope cutoff wall transition were made. Select levee fill for slope reconstruction encases the top of the cutoff walls for a complete seepage barrier.

8.3.2 Interface End of Toe Slurry Cutoff Wall Station 5100+00 The existing levee reach ARN-5 upstream from Station 5100+00 meets ULDC geotechnical criteria for seepage as described in the PIR analysis (URS, 2014a), (URS, 2015b). Based on geotechnical site data, levee construction materials, construction documentation, field inspection data, and other findings in AECOM’s GERPD and PIR documents, there is no potential for adverse levee settlement or end-around seepage at the end of the toe slurry cutoff wall and slope reconstruction for Reach ARN-4 at the interface with upstream Reach ARN-5 at Station 5100+00 (PIR, URS, 2015b).

8.3.3 Conclusion
Based on the above information, AECOM concludes that the above-described transition between centerline and toe slurry cutoff walls (Stations 5071+47 to 5076+50), and toe slurry cutoff wall interface and slope reconstruction at ACNL Station 5100+00 meets the geotechnical requirements of ULDC Section 7.9 for Interfaces and Transitions.

8.4 SLURRY CUTOFF WALL TRANSITIONS AT ROAD CROSSINGS
As can be seen on Figure 1, the only location where a slurry cutoff wall crosses a road or trail is at the Sacramento Northern Bile Trail located at approximate ACNL Station 5037+80. There is no cutoff wall crossing of Norwood Avenue since the levee in this area meets ULDC criteria. At Rio Linda Boulevard, the slurry cutoff wall is routed under the bridge (refer to Section 8.2 for addition details).

As discussed previously and shown on the record drawings (AECOM, 2020), the centerline SB slurry cutoff wall was transition to an SCCB wall with the same depth at the crossing to address seepage and minimized bike trail closure time. The SCCB wall was constructed first followed by construction of the downstream SB wall with a direct contact overlap of the wall a minimum of 25 feet long.

As indicated in the GDR documents, the levee was investigated to develop geotechnical data needed for seepage and stability analyses. These investigations include a cone penetrometer hole and nearby bore hole at the bike trail crossing. Results of the ULDC Geotechnical Findings 21 11/15/2024
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analyses in the GERPD show compliance with ULDC criteria after slurry cutoff wall construction as summarized in Appendix B. Analysis of subsurface data and performance history indicate settlement at or adjacent to road crossings are not a concern.

8.4.1 Conclusion
Based on the above review, AECOM concludes that the Sacramento Norther Bike Trail road crossing described in this section meet the geotechnical requirements of ULDC Section 7.9, Interfaces and Transitions.

8.5 STATION 5070+40 TO STATION 5112+43

8.5.1 Floodwalls
Reinforced concrete floodwalls are present along the waterside crest of ACNL. A short section (approximately 100 feet long) is located between the Rio Linda bridge at Station 5070+40 and Station 5071+47. This wall has an average height of three feet and only provides freeboard protection along an access ramp from Marysville Boulevard to the ACNL levee crest. The longest flood wall section (approximately 3,680 feet long) begins at Station 5074+50 and runs east terminating just before Marysville Boulevard at approximate Station 5111+40. Except for one section located near Marysville Boulevard, the average wall height is approximately 3.5 feet and mostly provide freeboard protection. The walls were constructed in the mid-1990’s and details are shown on record drawings prepared by Spink Engineering (SPINK, 1997). These drawings were reviewed by AECOM as part of its ULDC compliance review. Also, Psomas surveys for recent remediation designs confirm wall locations, alignments, and elevations.

The beginning of the short section of freeboard floodwall interfaces with the Rio Linda Bridge abutment at Station 5070+40. A metal splash plate assembly provides freeboard zone wave action protection for the small gap (maximum 1 foot) between the end of the wall and the existing bridge deck guardrail. Refer to the record drawings (Spink, 1997) for the splash plate detail. There are no reports of poor splash plate performance. At the upstream end, the top of wall is level with the levee crest and extends six feet longitudinally into the crest. Recent remediations reconstructed the waterside slope with levee fill to control through seepage in the levee and, by extension, underseepage for the wall and end-around seepage at the end.

The long section of the wall begins at Station 5074+50 level with the levee crest and extending approximately ten feet into the ULDC-compliant downstream levee fill. Recent remediations reconstructed the waterside slope with levee fill to control through seepage in the levee and, by extension, underseepage for the wall and end-around seepage at the end.

Between Stations 5107+90 and 5112+43, there are three gaps in the wall. The gaps are filled with levee fill to raise grade or form a levee section with top elevations equal to the adjacent top-of-wall elevation on either side. This levee reach was evaluated by AECOM and found to meet seepage and stability criteria as described in PIR, Addendum 1(URS, 2015b). Since the ends of the walls extend into suitable fill or native ULDC Geotechnical Findings 22 11/15/2024
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materials and seepage and stability criteria are met, underseepage and end-around seepage for the walls and interfaces is not a concern.

8.5.2 Interface at Marysville Boulevard
A short section of freeboard levee (approximately 100 feet long) exists between the end of the last floodwall segment at Station 5111+40 and Marysville Boulevard at Station 5112+43. At Marysville Boulevard, the fill terminates against a retaining wall running parallel to Marysville Boulevard that is part of the bridge abutment. Per the record drawings (Spink, 1997), the retaining wall includes a vertical cutoff key for the full height of the levee that extends two feet into the levee fill in line with the center of the levee.

There have been no indications of past performance issues at the interface. Since the levee is primarily for freeboard and the interface detail is considered adequate, endaround seepage at the Marysville Boulevard levee interface is not considered a concern.

8.5.3 Conclusion
Based on the above review, AECOM concludes that the existing floodwall interfaces and levee closure at Marysville Boulevard as described above meet the geotechnical requirements of ULDC Section 7.9, Interfaces and Transitions.

8.6 ULDC SECTION 7.10 EROSION
This section addresses the potential for surface or internal erosion developing where seepage analyses indicate through seepage could exit the landside slope at or above the levee toe. Erosion evaluation for the waterside levee slope for ULDC compliance is addressed in reports prepared by other consultants.

Based on the phreatic surface profiles derived from the seepage evaluations at critical sections, seepage breakout could occur at the landside toe of levee for three sections analyzed. These sections are identified in the seepage results provided in Appendix B.

However, as seen in the appendix, the breakout height above the landside toe is estimated to be 2-feet or less for the 200-year DWSE case. Soils in the breakout area are sand clay (SC) that are not considered susceptible to significant erosion, particularly under the low hydraulic heads at breakout and the short duration of the flooding events.

No evidence of such seepage has been observed during past flooding events.

8.7 CONCLUSION
Based on the findings described above, AECOM concludes that landside toe erosion due to potential seepage breakout at the landside toe is not a risk to the levee and the criteria in ULDC Section 7.9, Erosion, is met relative to landside toe erosion.

ULDC Geotechnical Findings 23 11/15/2024
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9.0 ULDC SECTION 7.13 PENETRATIONS
The evaluation of penetrations for ULDC compliance for the Robla-Arcade levee system that includes ACNL is being performed by Mead & Hunt. However, as part of AECOM’s evaluation of ACNL, the tabulation of known penetrations in Mead & Hunt’s report (Mead & Hunt, 2024) was compared with penetrations shown on the record drawings (AECOM, 2020). Any inconsistencies were noted and resolved. Also, wherever possible, AECOM confirmed acceptable abandonment (capping, plugging) of culverts and other utilities shown as abandoned in Mead & Hunts penetration tabulations that are located within the limits of the most recent levee remediation work.

There are small diameter active gas and electric penetrations remaining in the levee that can be found on the record drawings (AECOM, 2020). These were reviewed by AECOM on a case-by-case basis. AECOM determined that the penetrations do not present a seepage hazard to the levee from the geotechnical perspective.

AECOM has evaluated the potential for seepage associated with a gap in the slurry cutoff wall at the 66-inch sewage transmission main penetration located in the levee foundation at approximate Station 5065+40. This evaluation is described in Section 8.2.4.

As shown in the record drawings (AECOM, 2020), there is also a multi-conduit concrete encased AT&T duct bank that crosses under the levee crown at approximate Station 5069+31. The duct bank then runs down under the waterside slope crossing under Arcade Creek. Potholing confirmed that the invert elevation of the duct bank at the levee crest is at elevation 39.0 feet. The 200-year DWSE provided by MBK at Station 5069+31 is elevation 38.2 feet. With the invert located just above the DWSE, seepage along the duct bank under the levee crown would not occur. In addition, the duct bank is encased in the SCCB toe slurry cutoff wall where the wall and duct bank cross and the slope over the duct bank is cover with select levee fill placed when the slope was reconstructed following slurry wall construction.

Five gravity drainage pipes (24-inch and 36-inch) pass through the levee between Stations 5077+61 and 5096+67 as shown on the record drawings (AECOM, 2020).

Each has a flap gate at the waterside end and a gate valve for closure at the levee crest. These culverts are located along the levee where a toe slurry cutoff wall was constructed, and the waterside slope was excavated and replace with select levee material to remediate through seepage and underseepage. To construct the cutoff wall and slope reconstruction, the pipes were cut and reconstructed. Reconstruction details are provided in the record drawings (AECOM, 2020). The reconstructed sections of pipes are encased in CLSM and covered with levee fill material placed to reconstruct the waterside slope. The levee fill is integral with the top of the toe cutoff wall. The fill and CLSM pipe encasement provide the barrier against through seepage at these penetrations. Flap gates at the waterside end of the pipes were reconstructed.

At the Sump 103 pump station located at Station 5065+00, the pump discharge pipes have been raised above the 200-year DWSE to eliminate seepage concerns. Shutoff valve vaults have been added. Pipes were encased in controlled low strength material (CLSM) and the encasement covered with select levee fill to complete reconstructing ULDC Geotechnical Findings 24 11/15/2024
Arcade Creek North Levee IPC Backcheck
the levee slopes. The 54-inch gravity drainage pipe was also removed and replaced and includes a new shutoff valve vault. The SCCB slurry cutoff wall constructed in the area encases the gravity drainage pipe. The record drawings (AECOM, 2020) provide details for the pipe relocations/replacements, including new shutoff valve vaults.

9.1 CONCLUSION
Based on the above review, AECOM concludes that the known penetrations in or under the levee pose no seepage, stability, or settlement risk to the levee from the geotechnical perspective.

ULDC Geotechnical Findings 25 11/15/2024
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10.0 ULDC SECTION 7.14 FLOODWALLS, RETAINING WALLS, AND CLOSURE

STRUCTURES
There are no retaining walls or closure structures along ACNL. There are floodwalls, however, and structural analyses of these walls for ULDC compliance is being performed by other consultants. AECOM has evaluated interfaces and transitions for these walls, which is presented in Section 8.5.1.

ULDC Geotechnical Findings 26 11/15/2024
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11.0 ARCADE CREEK NORTH LEVEE STUDY AREA SUMMARY OF RESULTS Based on the evaluations described in this report, Table 11-1 summarizes AECOM’s conclusions regarding levee compliance with the criteria contained in the ULDC (DWR, 2012):

Table 11-1Summary of Results
Project Levee Stationing Meets All
Criteria
Does Not
Meet All
Criteria
ULDC Criteria Selection
Arcade
Creek North
Levee
Stations 5023+00
to 5100+00
X
By Exception

7.3 Soil Sampling, Testing,
and Logging. (Refer to
Report Section 3.1 and
Section 3.2 for discussion
of bore hole data and
sampling.

X

7.4 Slope Stability. (Refer
to Report Section 4.0).

X

7.5 Underseepage. (Refer
to Report Section 5.0).

X

7.7 Seismic Vulnerability.
(Refer to Report Section

6.0)
X

7.9 Interfaces, Transitions,
and Gaps. (Refer to
Report Section 8.0.

X

7.14 Floodwalls, Retaining
Walls, and Closure
Structures. (Refer to
Report Section 9.0).

Based on the summary of results in Table 11-1, AECOM concludes that the ACNL levees meet the geotechnical-related requirements of the ULDC.

ULDC Geotechnical Findings 27 11/15/2024
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12.0 LIMITATIONS
This Report, along with the associated data collection and preparation, has been conducted in adherence to the standard of care commonly practiced in the due diligence profession. The standard of care is defined as the ordinary diligence exercised by professionals in this field performing similar services under comparable circumstances during the same period.

Summaries of pertinent information referenced and provided in this report are based on due diligence review of available information.

No warranty, whether express or implied, is made in the provision of this report, which is the outcome of due diligence evaluation services. There is no guarantee, whether express or implied, that actual conditions on-site will precisely match the conditions described herein.

The accuracy, completeness, or reliability of data collected by third parties and referenced in this report, including, but not limited to, geotechnical borings and subsurface data, is not attested by AECOM. In the creation of this report, reliance is placed on data and information provided by external sources, without the ability for independent validation or verification.

Data presented in this report are time-sensitive and are applicable only to the locations and conditions that existed at the time of data collection. Such data should not be extrapolated to other projects in the vicinity or applied at a future date without appropriate verification.

This Geotechnical Findings Report is intended for the use and benefit of SAFCA or its designated representatives only. Any use by other parties is at their own discretion and risk.

ULDC Geotechnical Findings 28 11/15/2024
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13.0 REFERENCES
AECOM, 2016 - SAFCA North Area Streams Levee Improvement Project, Final Geotechnical Engineering Report for Project Design (GERPD).

AECOM, 2020 - SAFCA North Area Streams Levee Improvement Project, Record Drawings, NEMDC and Arcade Creek Levees, Project Plans for Construction, Volume 2 of 3, October 2020.

Caltrans. 1967. Natomas East Canal Bridge and Overhead Study.

DWR, 2012. State of California, Department of Water Resources. Urban Levee Design Criteria.

May.

Fugro-William Lettis & Associates, Inc. 2008. Summary of Surficial Geologic Mapping, Natomas Basin, California Department of Water Resources Urban Levee Program, Sacramento County, California. April.

Fugro-William Lettis & Associates, Inc. 2011. Surficial geologic mapping and geomorphic assessment, California Department of Water Resources Urban Levees Evaluation Project, Natomas East Main Drainage Canal East Study Area, Sacramento County, California. February.

Kleinfelder, 2013a. Kleinfelder, Inc., Consulting Engineers. Geotechnical Data Report, North Area Streams, SAFCA FEMA Accreditation, American River, Sacramento River downstream of American River, and Beach Lake Levee, Sacramento County, California.

May.

Kleinfelder, 2013b. Kleinfelder, Inc., Consulting Engineers. Problem Identification Report, North Area Streams, SAFCA FEMA Accreditation, American River, Sacramento River downstream of American River, and Beach Lake Levee, Sacramento County, California.

September.

Kleinfelder, 1994a. Kleinfelder, Inc. Consulting Engineers. Geotechnical Evaluation of Proposed Levee Improvements Arcade Creek Levees. May.

Kleinfelder, 1995. Kleinfelder, Inc. Geotechnical Investigation Along the East Bank of NEMDC.

Kleinfelder, 2002. Kleinfelder, Inc. Consulting Engineers. Reclamation Board Permit No. 17468, PG&E. Geotechnical Engineering Report, Pacific Gas and Electric Pipeline 119A Replacement, Sacramento County, California. January.

MBK, 2014. Draft Technical Memorandum, 1/10, 1/200, 1/500 AEP Water Surface Elevations for SAFCA Levee Certification Reaches. April.

MBK, 2024. Robla-Arcade Levee System - Determination of the Urban Levee Design Criteria Design Water Surface Elevation, Minimum Top of Levee, and Hydraulic Top of Levee.

November.

Mead & Hunt, 2024 Robla-Arcade Levee System Due Diligence Review for ULDC Certification.

September 13, 2024.

Psomas, 2024. Updated levee crown and Cross Section Surveys for FEMA and ULDC compliance Reviews, Arcade-Robla System. May.

Spink, 1997. Arcade Creek Unit 1B Levee Improvement, Record Drawings.

USACE, 1954. United States Army Corps of Engineers. 1954. Sacramento River, California, Flood Control Project, American River, Natomas Canal, Arcade Creek, and Linda Creek, Levee Construction (including field boring logs.

ULDC Geotechnical Findings 29 11/15/2024
Arcade Creek North Levee IPC Backcheck
USACE, 2005. Engineer Technical Letter 1110-2-569, Engineering and Design: Design Guidance for Levee Underseepage. May.

USACE, 2003. Engineer Manual 1110-2-1902, Engineering and Design: Slope Stability. October.

USACE, 2000. Engineer Manual 1110-2-1913, Engineering and Design: Design and Construction of Levees. April.

USACE, 1993. Engineer Manual 1110-2-1901, Engineering and Design: Seepage Analysis and Control for Dams. April.

USACE 2022. SOP SPK EDG-03, Standard Operating Procedure 3, Geotechnical Levee Practice, May 2022.

USACE, 2023 Supplement to the Standard Operations and Maintenance Manual, Sacramento River Flood Control Project, Unit No. 118-Part No. 2, North Levee of American River, East Levee of Natomas Canal, Both Levees of Arcade Creek, South Levee of Linda Creek, and Magpie Creek Diversion Channel. October.

URS, 2014a. Problem Identification Report, Sacramento Flood Control Agency, North Area Streams Improvement Project. August.

URS, 2014b. Geotechnical Data Report, Sacramento Flood Control Agency, North Area Streams Improvement Project. May.

URS, 2014c. Alternatives Analysis Report, Sacramento Area Flood Control Agency, North Area Streams Levee Improvement Project. August.

URS, 2015a. Geotechnical Data Report, Addendum 1, Sacramento Area Flood Control Agency, North Area Streams Levee Improvement Project. February.

URS, 2015b. Problem Identification Report, Addendum 1, Sacramento Area Flood Control Agency, North Area Streams Levee Improvement Project. February.

URS, 2015c. Geotechnical Data Report, Addendum 2, Sacramento Area Flood Control Agency, North Area Streams Levee Improvement Project. June.

URS, 2015d. North Area Streams (NAS) Levee Improvement Project Geotechnical Data Report for Borrow Site 2K. October.

URS, 2016a. Addendum No. 3 to Geotechnical Data Report, North Area Streams Levee Improvement Project. August.

URS/AMEC Geomatrix. 2009. Phase 1 Geotechnical Data Report for Natomas East Main Drainage Canal (NEMDC) East Study Area, Urban Levee Evaluations Project. March.

URS/AMEC Geomatrix. 2011. Supplemental Geotechnical Data Report (SGDR), Natomas East Main Drainage Canal (NEMDC) East Study Area, Urban Levee Evaluations Project.

November.

Wahler Associates. 1987. Levee Investigation: American River Flood Control District and Maintenance Areas 10 and 11, Dry Creek, Arcade Creek, Natomas East Main Drainage Canal, American River, and Sacramento River, Sacramento County, California.

FIGURES
FIGURE 1 - ARCADE CREEK NORTH LEVEE
Appendix A
ULDC 200-Year Design Water Surface Elevations
Arcade Creek North Levee
Water Surface Profile Data
Source: MBK Engineers (2023) 2024
Appendix B
Geotechnical Evaluation Results Summary
SECTION 7.0 GEOTECHNICAL EVALUATION RESULTS SUMMARY
20150226_SAFCA_PIR-Addendum1.docx 7-3 Issue Date: 02-2015 Table 7-1 Seepage and Stability Analysis Results.

Reach and
Station for
Analysis
Section
Top of Levee
Elevation
(NAVD88,
approx.
feet)
Landside
Toe
Elevation
(NAVD88,
approx. f
eet)
Levee or
Floodwall
Height
(feet)
Hydraulic
Head (feet)
Flood
Level
Analyzed
Water
Surface
Elevation
(NAVD88,
feet)
Steady State Seepage Analysis Results Landside Slope Stability Analysis Results Average Vertical
Exit Gradient, i [Location, Blanket
Thickness]
Breakout
Above
Landside
Toe (feet)
Comments Minimum
Factor
of Safety
Comments
Reach NAS-ARN-5 (Station 5100+00 to 5112+43, 1243 feet)Station 5100+00 42.5 (Top of the Levee) 45.2 (Top of Floodwall)

37.4 5.1 (From the
top of the levee) 7.8 (From top of floodwall)

2.0 100-year 39.4 0.12 [Toe, blanket = 9 feet] 0.5 (SC) Meets underseepage and through seepage criteria for 100-year, 200-year, and HTOL WSEs.

2.92 Meets criteria for 200-year and
HTOL WSEs

2.7 200-year 40.1 0.17 [Toe, blanket = 9 feet] 0.9 (SC) 2.81 5.7 HTOL 43.1 0.34 [Toe, blanket = 9 feet] 1.5 (SC) 2.37 Station 5110+46 NA (No Levee)

46.5 (Top of Floodwall)

39.6 (Base of Flood Wall)

6.9 (From top of floodwall)

1.3 100-year 40.9 0.18 [Toe, blanket = 7.2 feet] NA (No Levee)
Meets underseepage and through seepage criteria for 100-year, 200-year WSE, and HTOL WSEs. The calculated gradient at the HTOL WSE is only 0.01 higher than the criteria of 0.6. Also, a sensitivity analysis using site-specific hydraulic conductivity testing results indicate this section meets criteria for the HTOL WSE.

NA (No Levee) Not applicable (No levee).

1.8 200-year 41.4 0.24 [Toe, blanket = 7.2 feet] NA (No Levee)
NA (No Levee)

4.8 HTOL 44.4 0.61 [Toe, blanket = 7.2 feet]

0.53 [Toe, blanket = 7.2 feet, Sensitivity with measured Kv=5.3E-05 cm/sec in layer 2 (aquifer)] NA (No Levee)
NA (No Levee)
Reach NAS-ARS-5 (Station 4083+21 to 4110+00, 2679 feet) Station 4090+00 43.1 (Top of the Levee) 44.7 (Top of Floodwall)

35.6 7.5 (From the
top of the levee) 9.1 (From top of floodwall)

3.5 100-year 39.1 0.21 [Toe, blanket = 5.3 feet]

0.24 [4 feet from toe, blanket = 5.1 feet]

1.2 (SC) Meets underseepage and through seepage criteria for 100-year, 200-year, and HTOL WSEs. Sensitivity Analysis Sensitivity: Landside blanket (Layer 2) thickness decreased 0.5 feet by raising the interface of Layers 2 and 3. 100yr, i=0.23 at toe, i=0.26 at 4 feet from toe 200yr, i=0.29 at toe, i=0.30 at 4 feet from toe HTOL, i=0.46 at toe, i=0.46 at 4 feet from toe Sensitivity results meet criteria.

2.10 Meets criteria for 200-year and
HTOL WSEs Sensitivity Analysis: Sensitivity #1: Determine factor of safety using combination circular/non-circular failure mode for 200-yr WSE. 200yr, FOS=2.02 Sensitivity meets criteria. Sensitivity #2: Determine factor of safety using non-circular failure mode for 200-yr WSE. 200yr, FOS=2.24 Sensitivity meets criteria.

4.2 200-year 39.8 0.25 [Toe, blanket = 5.3 feet]

0.27 [4 feet from toe, blanket = 5.1 feet]

1.5 (SC) 2.04

7.2 HTOL 42.8 0.42 [Toe, blanket = 5.3 feet]

0.41 [4 feet from toe, blanket = 5.1 feet]

2.5 (SC) 1.79
Station 4094+00 43.5 (Top of
the Levee) 45.0 (Top of Floodwall)

36.3 7.2 (From the
top of the levee) 8.7 (From top of floodwall)

3.0 100-year 39.3 0.29 [Toe, blanket = 7.8 feet] 1.3 (SC) Meets underseepage and through seepage criteria for 100-year, 200-year, and HTOL WSEs.

2.23 Meets criteria for 200-year and
HTOL WSEs

3.7 200-year 40.0 0.35 [Toe, blanket = 7.8 feet] 1.3 (SC) 2.14 6.7 HTOL 43.0 0.60 [Toe, blanket = 7.8 feet] 3.2 (SC) 1.74 Station 4102+30 43.7 (Top of
the Levee) 45.7 (Top of Floodwall)

39.5 4.2 (From the
top of the levee) 6.2 (From top of floodwall)

0.5 100-year 40.0 0.03 [Toe, blanket = 9.3 feet]

0.01 [20 feet from toe, blanket = 7.2 feet]

0.0 (SC) Meets underseepage and through seepage criteria for 100-year, 200-year, and HTOL WSEs.

3.20 Meets criteria for 200-year and
HTOL WSEs

1.1 200-year 40.6 0.08 [Toe, blanket = 9.3 feet]

0.06 [20 feet from toe, blanket = 7.2 feet]

0.3 (SC) 3.08

4.1 HTOL 43.6 0.26 [Toe, blanket = 9.3 feet]

0.25 [4 feet from toe, blanket = 7.2 feet]

1.1 (SC) 2.56
Table taken from the PIR Addendum 1.Analysis results are for existing levees meeting criteria without requiring remediation.

SECTION 8.0 GEOTECHNICAL EVALUATION RESULTS SUMMARY
SAFCA_GERPD-Final.docx 8-3 Issue Date: 08-2016
Table 8-1. Seepage and Stability Analysis Results.

Reach and
Station for
Analysis
Section
Top of Levee
Elevation
(NAVD88,
approx.
feet)
Landside
Toe
Elevation
(NAVD88,
approx.
feet)
Levee or
Floodwall
Height
(feet)
Hydraulic
Head
(feet)
Flood
Level
Analyzed
Water
Surface
Elevation
(NAVD88,
feet)
Steady State Seepage Analysis Results Landside Slope Stability Analysis Results
Waterside Rapid Drawdown
Slope Stability Analysis
Results
Average Vertical
Exit Gradient, i [Location, Blanket
Thickness]
Breakout
Above
Landside
Toe (feet)
Comments Minimum
Factor
of Safety
Comments Minimum
Factor
of Safety
Comments
Station 4063+57
Centerline
SCCB Cutoff
Wall Closure
(66-inch sewer
crossing)

45.0 34.1 10.9 6.0 200-year
DWSE

40.1 0. 29 [Toe, blanket = 14.0 feet] 1.1 (SC) Meets underseepage and through seepage criteria for 200-
year DWSE and HTOL WSE.

2.15 Meets criteria for 200-year
DWSE and HTOL WSE
NA

9.0 HTOL
WSE

43.1 0.42 [Toe, blanket = 14.0 feet] 1.5 (SC) 2.03
Reach NAS-ARS-4 (Station 4068+45 to 4083+21, 1,476 feet) Station 4079+00
Waterside SCCB
Cutoff Wall with
Waterside Slope
Replacement

43.6 (Top of
levee)

44.9 (Top of
floodwall)

34.3 9.3 (From
top of
levee)

10.6 (From
top of
floodwall)

6.2 200-year
DWSE

40.5 0.02 [Toe, blanket = 32.7 feet] Below
levee toe
Meets underseepage and
through seepage criteria for 200-
year DWSE and HTOL WSE.

1.46 Meets criteria for 200-year
DWSE and HTOL WSE.

1.88 Meets criteria for
200-year DWSE with
a 12 foot drop 9.2 HTOL
WSE

43.5 0.04 [Toe, blanket = 32.7 feet] Below
levee toe

1.46 Reach NAS-ARN-3 (Station 5038+00 to 5075+00, 3,700 feet) Station 5049+00
Centerline SB
Cutoff Wall

44.5 31.9 12.4 8.2 200-year
DWSE

40.1 NA [Toe, blanket = 8.3 feet]

0.13 [17 feet from toe, blanket = 6.8 feet]

0.0 Meets underseepage and
through seepage criteria for 200-
year DWSE and HTOL WSE.

1.85 Meets criteria for 200-year
DWSE and HTOL WSE.

NA

11.2 HTOL
WSE

43.1 0.01 [Toe, blanket = 8.3 feet]

0.18 [17 feet from toe, blanket = 6.8 feet]

0.0 1.80
Station 5065+27
Centerline
SCCB Cutoff
Wall Closure
(66-inch sewer
crossing)

44.7 33.8 10.9 6.3 200-year
DWSE

40.1 0.31 [Toe, blanket = 11.1 feet] 0.0 Meets underseepage and through seepage criteria for 200-
year DWSE and HTOL WSE.

1.89 Meets criteria for 200-year
DWSE and HTOL WSE
NA

9.3 HTOL
WSE

43.1 0.45 [Toe, blanket = 11.1 feet] 0.0 1.79
Reach NAS-ARN-4 (Station 5075+00 to 5110+00, 2,500 feet) Station 5097+00
Waterside SCCB
Cutoff Wall with
Waterside Slope
Replacement

42.1 (Top of
levee)

44.0 (Top of
floodwall)

35.6 6.5 (From
top of
levee)

8.4 (From
top of
floodwall)

5.4 200-year
DWSE

41.0 0.03 [Toe, blanket = 14.7 feet] 0.0 Meets underseepage and through seepage criteria for 200-
year DWSE and HTOL WSE.

1.92 Meets criteria for 200-year
DWSE and HTOL WSE.

NA

8.4 HTOL
WSE

44.0 0.05 [Toe, blanket = 14.7 feet] 0.2 (SM) 1.88
*An increase of 20 percent was applied to two-dimensional average exit gradients to account for three-dimensional effects in Reaches NE-2 and ARS-1.

Table taken from the final GERPD.

Analysis results are for remediated levees.

Meets Criteria After Installation of
12 relief wells. See GERPD.

Appendix C
Levee Geometry Cross Section Evaluation
Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 12 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 13 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 14 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 15 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 16 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 17 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Appendix E.

American River South ULDC
Due Diligence, Geotech - Kleinfelder
24001006.001A/SAC24R169107_R2 Page i of v June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025
Copyright 2025 Kleinfelder
All Rights Reserved

ONLY THE CLIENT OR ITS DESIGNATED REPRESENTATIVES MAY USE THIS DOCUMENT AND ONLY FOR THE SPECIFIC PROJECT FOR WHICH THIS DATA REPORT WAS PREPARED.

ULDC GEOTECHNICAL FINDING –
ROBLA CREEK SOUTH LEVEE STATIONS 6000+00 TO 6118+20
NEMDC EAST LEVEE STATIONS 3056+00 TO 3192+25
ARCADE CREEK NORTH LEVEE STATIONS 5000+00 TO 5023+00

ULDC FINDING AND FEMA LEVEE CERTIFICATION PROGRAM

SACRAMENTO AREA FLOOD CONTROL AGENCY LEVEE SYSTEMS

SACRAMENTO COUNTY, CALIFORNIA
KLEINFELDER PROJECT # 24001006.001A
24001006.001A/SAC24R169107_R2 Page i of v June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025
24001006.001A/SAC24R169107_R2 Page ii of v June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025
August 25, 2025
File No.: 24001006.001A
Mr. Dan Tibbitts, PE
Principal Engineer
Sacramento Area Flood Control Agency
1325 J Street, Suite 1700
Sacramento, CA 95814
SUBJECT: ULDC Geotechnical Finding –
Robla Creek South Levee (Stations 6000+00 to 6118+20)
NEMDC East Levee (Stations 3056+00 to 3192+25)
Arcade Creek North Levee (Stations 5000+00 to 5023+00)
ULDC Finding and FEMA Levee Certification Program
Sacramento Area Flood Control Agency Levee Systems
Sacramento County, California
Dear Mr. Tibbitts:

This report presents Kleinfelder’s geotechnical evaluation of portions of the existing Robla Arcade (RA) study area. Specifically, Robla Creek South Levee (RCSL) Stations 6000+00 to 6118+20, NEMDC East Levee (NEMDCEL) from Stations 3056+00 to 3192+25, and Arcade Creek North Levee (ACNL) Stations 5000+00 to 5023+00 in Sacramento County, California were evaluated.

This evaluation was performed for Sacramento Area Flood Control Agency (SAFCA) to provide a geotechnical engineering finding as to whether the RCSL, NEMDCEL, and ACNL study area can be certified from a geotechnical perspective to meet State of California Department of Water Resources Urban Levee Design Criteria (ULDC) (DWR, 2012). This report contains Kleinfelder’s review and an opinion regarding whether these levees meet the geotechnical aspects of ULDC (DWR, 2012) (soil sampling, testing, and logging; slope stability; underseepage; seismic vulnerability; levee geometry; interfaces and transitions; and floodwalls, retaining walls, and closure structures). Other sections of ULDC (DWR, 2012) are not addressed in this report and are being addressed by other consultants.
24001006.001A/SAC24R169107_R2 Page iii of v June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025
If you have questions regarding this report or if we may be of further assistance, please contact the undersigned.

Sincerely,
KLEINFELDER, INC.

Edrei Espinosa, EIT Meredith Beswick, PE, PG
Staff Engineer Principal Engineer
Reviewed By:

Timothy A. Williams, PE, GE
Sr. Principal Geotechnical Engineer
cc: Mr. Pro Mitra, PE/MBK Engineers ([email protected]) Ms. Becky Money, PE/MBK Engineers ([email protected]) 24001006.001A/SAC24R169107_R2 Page iv of v June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025

TABLE OF CONTENTS

SECTION PAGE
1 INTRODUCTION ........................................................................................................................1

1.1 PROJECT INTRODUCTION....................................................................................................1

1.2 BACKGROUND AND CONSTRUCTION HISTORY...................................................................1

1.2.1 RCSL Stations 6000+00 to 6118+20 .......................................................................2

1.2.2 NEMDCEL Stations 3056+00 to 3192+25 ...............................................................3

1.2.3 ACNL Stations 5000+00 to 5023+00 ......................................................................4

1.3 PROJECT STATIONING AND DATUMS .................................................................................4

1.4 METHODOLOGY ..................................................................................................................5

1.5 REFERENCED REPORTS........................................................................................................6

1.6 CRITERIA..............................................................................................................................7

1.7 WATER SURFACE ELEVATIONS............................................................................................7 2 ULDC GEOTECHNICAL CRITERIA REVIEW ...................................................................................9

2.1 ULDC Section 7.3 Soil Sampling, Testing, and Logging........................................................9

2.1.1 Conclusion............................................................................................................14

2.2 ULDC Section 7.4 Slope Stability for intermittently loaded levees ...................................14

2.2.1 Conclusion............................................................................................................19

2.3 ULDC Section 7.5 Underseepage ......................................................................................19

2.3.1 Conclusion............................................................................................................23

2.4 ULDC Section 7.7 Seismic Vulnerability ............................................................................23

2.4.1 Conclusion............................................................................................................24

2.5 ULDC Section 7.8 Levee Geometry ...................................................................................24

2.5.1 Current Levee Geometry .....................................................................................26

2.5.2 Conclusion............................................................................................................26

2.6 ULDC Section 7.9 Interfaces and Transitions ....................................................................27

2.6.1 Interface of a Detention Basin at RCSL Landside Toe Near Station 6012+00 ......27

2.6.2 Transition of UPRR Stop log Structure at approximate RCSL Station 6000+50....27

2.6.3 Interface of Sump Station No. 140 at Approximate RCSL Station 6032+00.........28

2.6.4 Interface of Rio Linda Boulevard Bridge and Floodwalls approximately between RCSL Stations 6078+00 to 6079+00 .....................................................................29

2.6.5 Interface of a Sacramento Northern Bike Trail Near RCSL Station 6090+50 .......29

2.6.6 Transition of a Dry Creek Road at RCSL Station 6118+20 to High Ground...........30

2.6.7 Interface of UPRR Embankment along the landside slope of NEMDCEL .............30

2.6.8 Interface of San Juan Road/Silver Eagle Road Bridge Foundation at NEMDCEL Stations 3090+00 to 3091+00 ..............................................................................31

2.6.9 Interface of Interstate 80 Bridge Foundations at Approximately Between NEMDCEL Stations 3132+00 and 3134+00 ..........................................................31

2.6.10 Interface of Sump Station No 157 at NEMDCEL Station 3132+00 .......................32

2.6.11 Interface of Del Paso Road /Main Avenue Bridge at NEMDCEL Stations 3184+00 to 3185+00...........................................................................................................33

2.6.12 Interface of ACNL and NEMDCEL Drained Stability Berm....................................33

2.6.13 Transition of UPRR Stop log Structure at ACNL Station 5000+40 ........................34

2.6.14 Transition of ACNL Landside Toe Relief Wells to ACNL Station 5023+00 ............34

2.6.15 Geotechnical Evaluation of Swimming Pools at or Near the Landside Toe .........35

2.6.16 Conclusion............................................................................................................39 24001006.001A/SAC24R169107_R2 Page v of v June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025

2.7 ULDC SECTION 7.14 FLOODWALLS, RETAINING WALLS, AND CLOSURE STRUCTURES .....39

2.7.1 Sump Station No 157 at NEMDCEL Station 3132+00...........................................39

2.7.2 Sump Station No. 140 at RCSL Approximately Between Station 6032+00 ..........41

2.7.3 UPRR Closure Structures (RCSL at Station 6000+00 and ACNL Station 5000+40)41

2.7.4 Floodwalls at Rio Linda Boulevard Bridge Abutment...........................................42

2.7.5 Conclusion............................................................................................................43 3 ROBLA-ARCADE LEVEE STUDY AREA SUMMARY OF RESULTS ..................................................44 4 LIMITATIONS ..........................................................................................................................46 5 REFERENCES ...........................................................................................................................48

EMBEDDED TABLES

1.1 Water Surface Elevation Reference Summary

2.1 Summary of RCSL Exploration Locations and Approximate Spacing

2.2 Summary of NEMDCEL Exploration Locations and Approximate Spacing

2.3 Summary of ACNL Exploration Locations and Approximate Spacing

2.4 Stability Analyses Comparison Summary

2.5 Seepage Analyses Comparison Summary

2.6 Seismic Vulnerability Classifications for North Area Streams Levees

2.7 Swimming Pool Geotechnical Review Summary - 2024 200-Year DWSE

2.8 Swimming Pool Geotechnical Review Summary - 2024 HTOL DWSE

3.1 Levee Reaches That Meet Geotechnical Aspects of ULDC Criteria

FIGURES
1 Robla Creek South Levee, Arcade Creek North Levee, NEMDC East Levee Site Vicinity Map 2 Robla Creek South Levee, Arcade Creek North Levee, NEMDC East Levee Location Map

APPENDICES
A MBK Engineers, 2024a. “Technical Memorandum - Robla-Arcade Levee System - Determination of the Urban Levee Design Criteria Design Water Surface Elevation, Minimum Top of Levee, and Hydraulic Top of Levee.” Dated November 18, 2024.

B MBK, Engineers (MBK), 2024b. “Robla-Arcade Levee System: Geometry Analysis (ULDC)." Sheets 1 through 13. Dated June 2024.

C Kleinfelder, 2024. “Seismic Performance Summary Report North Area Streams Levee Areas, ULDC & FEMA Levee Certification Project, Sacramento Area Flood Control Agency Levee Systems, Sacramento County, California.” Dated September 10, 2024. 24001006.001A/SAC24R169107_R2 Page 1 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025
1 INTRODUCTION
____________________________________________________________________________________

1.1 PROJECT INTRODUCTION
This report presents Kleinfelder’s geotechnical evaluation of the Robla-Arcade Levee System (RA) that includes Robla Creek South Levee (RCSL) Stations 6000+00 to 6118+20, NEMDC East Levee (NEMDCEL) from Stations 3056+00 to 3192+25, and Arcade Creek North Levee (ACNL) Stations 5000+00 to 5023+00 in Sacramento County, California. This evaluation was performed for Sacramento Area Flood Control Agency (SAFCA) to provide a geotechnical engineering finding as to whether these levees meet the geotechnical criteria within the State of California Department of Water Resources Urban Levee Design Criteria (ULDC) (DWR, 2012).

This report contains Kleinfelder’s review and an opinion regarding whether RCSL, NEMDCEL, and ACNL meet the geotechnical aspects of ULDC (DWR, 2012) (soil sampling, testing, and logging; slope stability; underseepage; seismic vulnerability; levee geometry; interfaces and transitions; and floodwalls, retaining walls, and closure structures). Other sections of ULDC (DWR, 2012) are not addressed in this report and are being addressed by other consultants.

This report should be considered a “snapshot” of the condition of the levee system at this time. Additional study and work may be needed due to the passage of time and if ULDC (DWR, 2012) requirements change.

This report includes conclusions related to the geotechnical aspects of the levee. Conclusions are subject to the LIMITATIONS section of this report.

1.2 BACKGROUND AND CONSTRUCTION HISTORY
RCSL Stations 6000+00 to 6118+20, NEMDCEL Stations 3056+00 to 3192+25, and ACNL Stations 5000+00 to 5023+00 are a part of the North Area Streams (NAS) levees comprised of NEMDC, Arcade Creek, Dry Creek and Robla Creek levees. The project location relative to cities, rivers, and existing roadways is shown on Figures 1 and 2. The American River Flood Control District (ARFCD) is the local maintaining agency and is responsible for operations and maintenance.
24001006.001A/SAC24R169107_R2 Page 2 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025

1.2.1 RCSL Stations 6000+00 to 6118+20
The total length of RCSL (Stations 6000+00 to 6118+20) is 2.24-miles (11,820 feet) long. The downstream portion of RCSL (Stations 6000+00 to 6052+00) was constructed around 1957 under a USACE contract.

Based on as built drawings, construction included an inspection trench a minimum of 6-feet deep into the foundation under the levee embankment.

Levee improvements were constructed under a SAFCA contract (1995 and 1997) between Stations 6000+00 and 6052+00. Because authorization for raising the levee crest had not yet been approved, the 1995 improvements only included landside levee widening in preparation for a future raise. The 1997 improvements included levee crown raising, which in some cases required an additional slight widening of the embankment toward the landside or waterside. Levee widening typically occurred on the landside from Stations 6000+00 to 6027+00 and on the waterside from Stations 6027+00 to 6052+00. Levee raises ranged from 3 to 4 feet. The levee raise and widening included a keyway trench along the levee waterside or landside toe. Typical keyway trenches were approximately 2-feet deep beneath the levee toe on the same side as the widening associated with the levee raise. Kleinfelder prepared the geotechnical engineering report for the project and Kleinfelder representatives observed construction (including material conformance and compaction testing) of this levee and confirmed the keyway trench was extended up to 11 feet to penetrate into underlying fine-grained and/or cemented soils. Construction also included an unlined, 1-foot-deep V-ditch approximately 10 feet from the landside levee toe extending the length of the project. The stop log structure at the intersection of RCSL and NEMDCEL that was originally constructed in 1986/1987 was increased in height and length during the 1997 SAFCA levee improvements.

As part of the 1997 improvements, RCSL was extended from Stations 6052+00 to 6106+66, at which point the levee ties into high ground at Dry Creek Road. This levee was constructed with a 12-foot-wide inspection trench below the levee centerline. Depths were specified at a minimum of 6 feet deep where levee heights are greater or equal to 6 feet, or a depth equal to the levee height when the levee is less than 6 feet tall (but in no case less than 3 feet). Kleinfelder prepared the geotechnical engineering report for the project, and Kleinfelder representatives observed construction (including material conformance and compaction testing) of this levee and confirmed the inspection trench was extended to penetrate into underlying fine-grained and/or cemented soils.
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1.2.2 NEMDCEL Stations 3056+00 to 3192+25
The length of NEMDCEL (Stations 3056+00 to 3192+25) evaluated by Kleinfelder is 2.58 miles (13,625 feet) long and extends from Arcade Creek to Robla Creek. NEMDCEL north of ACNL was originally constructed under a USACE contract in the 1950s along the waterside of an existing Union Pacific Railroad (UPRR) embankment. Based on review of historical aerial photographs, the railroad embankment was constructed prior to 1950. As-built construction documents indicate the 1950s construction included an inspection trench ranging from 5 to 11 feet deep into the foundation. The inspection trench was deepened to between 8 and 11 feet where the historical Magpie Creek crossed beneath the levee alignment, approximate Stations 3120+00 to 3140+00. It appears this deepening was performed to remove water, brush, grass, and tree roots mixed with some mud which was described in boring log 2F-4 included on the drawings.

Levee embankment improvements were completed along the entire NEMDCEL in two phases under a SAFCA contract. The upstream Phase 2B/3B project was constructed between August and November 1996. Work included raising the crown elevation which widened the embankment toward the landside and/or water side. Upstream of Arcade Creek (Stations 3055+00 to 3181+00), levee raises were approximately 3.5 feet, and widening was performed on both the waterside and landside above the UPRR embankment. Upstream of Main Avenue, levee raises were approximately 4 to 5 feet, and the levee widening was performed along both the waterside (Stations 3181+00 to 3192+00) and landside above the UPRR embankment. Due to replacement of the Main Avenue Bridge in 2005 with a taller structure, the stop log structure at this location was no longer needed and was removed. The levee raise and widening included a keyway trench along the levee waterside or landside toe. Typical keyway trenches were 10- feet wide and 1 to 2-feet deep on the landside and 2 to 4-feet deep on the waterside. Kleinfelder prepared the geotechnical engineering report for the project, and Kleinfelder representatives observed construction of the levee modifications (including material conformance and compaction testing).

Kleinfelder engineers also confirmed the keyway trenches were extended to penetrate into underlying fine-grained and/or cemented soils.

In 2017 through 2023, seepage was noted exiting from the UPRR embankment toe. Kleinfelder performed multiple investigations to identify the source of the seepage; however, the source was not definitively identified. A drained stability berm was constructed in 2025 to provide a filtered exit for the seepage and to reinforce ACNL and NEMDCEL (Kleinfelder, 2025). Prior to construction, Kleinfelder prepared a Geotechnical Basis of Design Report with analysis at the DWSE (Kleinfelder, 2024a). 24001006.001A/SAC24R169107_R2 Page 4 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025

1.2.3 ACNL Stations 5000+00 to 5023+00
The length of ACNL (Stations 5000+00 to 5023+00) evaluated by Kleinfelder is 0.43-miles (2,300 feet) long.

ACNL was constructed around 1957 under a USACE contract. Based on USACE as-built construction documents, an inspection trench was constructed a minimum of 6 feet deep into the foundation prior to embankment construction.

During the 1986 flood event, low points in the ACNL at the Norwood Avenue Bridge (upstream of the study area) and at the UPRR railroad (Station 5003+00, adjacent to NEMDCEL) were filled with sandbags.

After the initial peak flow passed, the sandbags at the Norwood Avenue bridge were partially removed and a second peak flow resulted in flooding of the residential area behind the ACNL. As a result, concrete stop log structures were installed in 1986/1987 along NAS levees at railroad and bridge/road crossings where the rail or bridge was lower than the levee crest. The log structure at NEMDCEL included in this evaluation was initially constructed at this time. There were no other past performance issues that have been reported along this reach of the ACNL study area.

Levee improvements were constructed along the entire ACNL under a SAFCA contract between June and November 1996. Improvements included levee crown raising and widening of the embankment toward the waterside (Stations 5001+00 to 5065+60). The levee raise ranged from 2 to 3 feet to increase available freeboard. Waterside slope reconstruction and levee raise included a keyway trench constructed to hardpan to cutoff levee embankment and near surface permeable lenses. Typical keyway trenches were 10 feet wide and 2 feet deep. Kleinfelder field representatives confirmed the keyway trench was extended to penetrate into underlying fine-grained and/or cemented soils up to about 4 feet deep between approximate Stations 5002+00 and 5020+00. Kleinfelder prepared the geotechnical engineering reports for ACNL improvements, and Kleinfelder field representatives observed construction (including material conformance and compaction testing) of the levee embankment. The stop log structure at the intersection of ACNL and NEMDCEL originally constructed in 1986/1987 was increased in height and length during the SAFCA project.

1.3 PROJECT STATIONING AND DATUMS
Project stationing used in this report is based on Department of Water Resources stationing developed for the Urban Levee Evaluation (ULE) project. Elevation references in this report are in feet and are based on the North American Vertical Datum of 1988 (NAVD88). Other project-related documents may reference elevations that are based on the National Geodetic Vertical Datum of 1929 (NGVD29). Based on information provided by Psomas for the North Area Streams Geotechnical Data Report (Kleinfelder, 24001006.001A/SAC24R169107_R2 Page 5 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025
2013), a conversion factor of 2.2 feet may be applied to convert from NGVD29 to NAVD88, provided Psomas project control points are used (0.00 feet NGVD29 = 2.2 feet NAVD88). Elevations from documents that referenced an NGVD29 elevation were converted to NAVD88 using this conversion.

Where elevations are reported from reference documents that use a different elevation datum, that elevation datum is referenced.

1.4 METHODOLOGY
Kleinfelder performed seepage and slope stability analyses in previous reports for RCSL at Stations 6003+00, 6012+00, 6016+00, 6057+00, and 6098+00; for NEMDCEL at Stations 3080+00, 3126+00, 3133+00, 3137+50, 3167+00, and 3185+00; and for ACNL at Station 5003+00. The results of these analyses were included in the Problem Identification Report (PIR) and ULDC Geotechnical Results Summary (ULDC GRS) reports (Kleinfelder, 2016a and 2016b, respectively). The analyses were prepared using the 100-year design water surface elevation (DWSE) for the PIR (Kleinfelder 2016a) and the 200-year DWSE and Hydraulic Top of Levee (HTOL) for the ULDC GRS that were in use at the time each report was prepared.

MBK prepared a new 200-year DWSE and HTOL (MBK, 2024a) for the current ULDC evaluation, which are designated the 2024 200-year DWSE and 2024 HTOL. The reports containing the previous analyses are summarized in Section 1.5.

The cross sections analyzed were considered the critical locations based on stratigraphy and levee geometry at the time the PIR and ULDC GRS reports (Kleinfelder, 2016a and 2016b, respectively). were prepared. Based on our review for this study, the analyzed cross sections are still considered the critical cross sections. For RCSL the highest WSE previously analyzed was Elevation 45.23 feet and the highest 2024 HTOL is 46.72 feet. The maximum WSE previously analyzed for RSCL was 45.23 feet at Station 6107+00. The 2024 HTOL from Station 6107+00 to 6117+00 is 44.23 to 44.97 feet. The 2024 HTOL is 1.00 to 0.26 feet below the highest previous RSCL between Stations 6107+00 and 6117+00. The 2024 HTOL increases to 46.72 feet at Station 6118+19, which is 1.49 feet above the maximum analyzed WSE. The RSCL landside toe at Station 6118+19 rises to approximately 46.4 feet [LiDAR topography profiles from ULE SGDR (URS, 2011)] which is 0.32 feet below the 2024 HTOL at this location.

For NEMDCEL the highest WSE previously analyzed was an elevation of 44.24 feet (NAVD88) and the highest 2024 HTOL is 44.10 feet. For ACNL the highest WSE previously analyzed was an elevation of 41.98 feet and the highest 2024 HTOL is 40.69 feet.

Therefore, this summary was developed by comparing analysis results at the previous WSEs with the 2024 200-year DWSE and HTOL (MBK, 2024a) to estimate an analysis result at each model location for the 2024 24001006.001A/SAC24R169107_R2 Page 6 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025
WSEs. Since the existing analyses met project criteria, the analyses with the new lower 2024 200-year DWSE and HTOL (MBK, 2024a) are also considered to meet criteria. This procedure is described in Section 2 of this report.

1.5 REFERENCED REPORTS
This report includes results from previous studies performed by Kleinfelder and URS for the North Area Streams (NAS) which encompasses for RCSL, NEMDCEL, and ACNL study areas. Kleinfelder reviewed and used existing analyses from the following reports.
• Kleinfelder, 1994, “Geotechnical Evaluation of Proposed Levee Improvements Dry Creek Levees.” Dated June 1994.
• Kleinfelder, 1997. “Final Report, Final Compaction Test Results, Pump Station, NEMDC – Units 2A/3C, and Robla Units 1B/1C, Sacramento, California.” Dated March 3, 1997. • Kleinfelder, 2003. “Compaction Test Results and Geotechnical Evaluation, Robla Creek and NEMDC West Levee Improvements, Rio Linda, California.” Dated March 14, 2003. • Kleinfelder, 2013. “Geotechnical Data Report, North Area Streams, SAFCA FEMA Levee Accreditation (North Area Streams, American River, Sacramento River Downstream of American River, and Beach Lake Levee).” Dated May 31, 2013.
• Kleinfelder, 2016a. “Problem Identification Report, North Area Streams, SAFCA FEMA Levee Accreditation (North Area Streams, American River, Sacramento River Downstream of American River, and Beach Lake Levee).” Dated September 18, 2013. Revised April 29, 2016. • Kleinfelder, 2016b. “ULDC Geotechnical Results Summary, North Area Streams, SAFCA FEMA Levee Accreditation (North Area Streams, American River, Sacramento River Downstream of American River, and Beach Lake Levee).” Dated April 26, 2016. • URS, 2009. “Phase 1 Geotechnical Data Report (P1GDR), Natomas East Main Drainage Canal (NEMDC) East Study Area, Urban Levee Geotechnical Evaluations Program, Contract 4600007418.” Dated March 2009.
• URS, 2011. “Supplemental Geotechnical Data Report (SGDR), Natomas East Main Drainage Canal (NEMDC) East Study Area, Urban Levee Geotechnical Evaluations Program, Contract 4600007418.” Dated November 2011.
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• URS, 2014. “Technical Memorandum, Drain Trench System Design along Reach NAS-NE-3 (City of Sacramento Sump No. 157 at Magpie Creek).” Dated November 11, 2014.

In addition to the reports referenced above, Kleinfelder reviewed the design and construction documents related to the Robla-Arcade study area. These documents are contained in the list of references, which are included in Section 5 of this report.

1.6 CRITERIA
The purpose of this study was to review existing geotechnical information available for RCSL (Stations 6000+00 to 6118+20), NEMDCEL (Stations 3056+00 to 3192+25), and ACNL (Stations 5000+00 to 5023+00) in order to perform an evaluation as to whether these levees currently meet the geotechnical requirements of ULDC (DWR, 2012). This information is contained in the reports referenced in Section

1.5. These reports were prepared based on the following references:
• USACE EM 1110-2-1913 “Design and Construction of Levees,” dated April 30, 2000 • USACE ETL 1110-2-569 “Design Guidance for Levee Underseepage,” dated May 1, 2005 • USACE SOP SPK EDG-03 “Standard Operating Procedure 3, Geotechnical Levee Practice, US Army Corps of Engineers, Sacramento District, Geotechnical Engineering Branch” dated May 20221 • US Title 44 Code of Federal Regulations 65.10: Mapping of Areas Protected by Levee Systems, dated October 1, 2011
• Urban Levee Design Criteria (ULDC), State of California Department of Water Resources, dated May 2012

1.7 WATER SURFACE ELEVATIONS
Previous water surface elevations (WSE) were provided to Kleinfelder for the reports referenced in Section

1.5. The 2024 200-year DWSE and HTOL (MBK, 2024a) used for the current ULDC evaluation were provided in tabular form at 100-foot intervals along the listed NAS levees. The 2024 200-year DWSE and HTOL (MBK, 2024a) are included in Appendix A. The following table lists these WSEs. 1 This is the date of the current USACE SPK Standard Operating Procedure 3, Geotechnical Levee Practice, which is periodically updated. Reports referenced in this report were prepared using the Standard Operating Procedure 3, Geotechnical Levee Practice in effect at the time the report was prepared. 24001006.001A/SAC24R169107_R2 Page 8 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025
Table 1.1
Water Surface Elevation Reference Summary
Levee WSE
Elevation
Range
(NAVD88, ft)
Source Date
Previous RCSL Reports
100-Year 40.14 – 43.49
200-Year 41.48 – 43.83
HTOL 44.48 – 45.231
MBK Engineers Table entitled
“NAS WSE data - transmitted to Kleinfelder
02-18-14-160000CFS.xls”
February
18, 2014
ULDC Geotechnical Finding, 2024
200-Year 41.19 – 46.32
RSCL
HTOL 42.78 – 46.721
MBK Engineers, Technical Memorandum -
Robla-Arcade Levee System - Determination
of the Urban Levee Design Criteria Design
Water Surface Elevation, Minimum Top of
Levee, and Hydraulic Top of Levee
November
18, 2024
Previous NEMDCEL Reports
100-Year 37.74 – 39.91
200-Year 38.78 – 41.24
HTOL 41.78 – 44.24
MBK Engineers Table entitled
“NAS WSE data - transmitted to Kleinfelder
02-18-14-160000CFS.xls”
February
18, 2014
ULDC Geotechnical Finding, 2024
200-Year 37.10 – 41.10

NEMDCEL
HTOL 40.10 – 42.70
MBK Engineers, Technical Memorandum -
Robla-Arcade Levee System - Determination
of the Urban Levee Design Criteria Design
Water Surface Elevation, Minimum Top of
Levee, and Hydraulic Top of Levee
November
18, 2024
Previous ACNL Reports
100-Year 38.03 - 38.07
200-Year 38.94 - 38.98
HTOL 41.94 - 41.98
MBK Engineers Table entitled
“NAS WSE data - transmitted to Kleinfelder
02-18-14-160000CFS.xls”
February
18, 2014
ULDC Geotechnical Finding, 2024
200-Year
WSE 37.10 – 37.69
ACNL
HTOL 40.10 – 40.69
MBK Engineers, Technical Memorandum -
Robla-Arcade Levee System - Determination
of the Urban Levee Design Criteria Design
Water Surface Elevation, Minimum Top of
Levee, and Hydraulic Top of Levee
November
18, 2024

1. The maximum WSE previously analyzed for RSCL is 45.23 feet at Station 6107+00. The 2024 HTOL from Station 6107+00 to 6117+00 is 44.23 to 44.97 feet. The 2024 HTOL is 1.00 to 0.26 feet below the highest previous RSCL between Stations 6107+00 and 6117+00. The 2024 HTOL increases to 46.72 feet at Station 6118+19, which is 1.49 feet above the maximum analyzed WSE. The RSCL landside toe at Station 6118+19 rises to approximately 46.4 feet which is 0.32 feet below the 2024 HTOL at this location.
24001006.001A/SAC24R169107_R2 Page 9 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025
2 ULDC GEOTECHNICAL CRITERIA REVIEW
____________________________________________________________________________________ Kleinfelder performed a review of existing reports and analyses contained in those reports referenced in Section 1.5, above. This review was performed to determine whether the listed NAS levees meet ULDC (DWR, 2012) from a geotechnical perspective for the following sections:
• 7.3 Soil Sampling, Testing, and Logging
• 7.4 Slope Stability
• 7.5 Underseepage
• 7.7 Seismic Vulnerability
• 7.8 Levee Geometry
• 7.9 Interfaces and Transitions
• 7.14 Floodwalls, Retaining Walls, and Closure Structures This evaluation includes a review of existing information referenced in this report and has not included performance of new analyses or field investigation. Where available, construction inspection records have also been reviewed.

The following sections of this report contain a summary of our analysis.

2.1 ULDC SECTION 7.3 SOIL SAMPLING, TESTING, AND LOGGING This section contains a summary of the review of existing information for RCSL (Stations 6000+00 to 6118+20), NEMDCEL (Stations 3056+00 to 3192+25), and ACNL (Stations 5000+00 to 5023+00) with regards to ULDC (DWR, 2012) Section 7.3 Soil Sampling, Testing, and Logging. The general requirements of this section are outlined below.

ULDC 7.3 requires soil sampling, testing, and logging per standard procedures prescribed in guidance documents, including the USACE Sacramento District’s (CESPK) Geotechnical Levee Practice Standard Operating Procedures (SOP) (USACE, 2022) and DWR’s Division of Flood Management Soil and Rock Logging, Classification, Description and Presentation Manual (2009). This includes an evaluation of soil exploration quantity and location as outlined in the CESPK SOP (USACE, 2022). Based on this document, explorations for a feasibility levee evaluation should be obtained at a spacing of approximately 1,000 feet along the levee crest. For preconstruction and design studies a spacing of approximately 500 feet along the waterside toe, levee crown, landside toe. Exploration depths should be a minimum of 4 24001006.001A/SAC24R169107_R2 Page 10 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025
times the levee height and extending to an appropriate stratum. Explorations that did not meet the requirements outlined (e.g., explorations that were not drilled deep enough) above were not included.

The CESPK 2022 SOP (USACE, 2022) recommends a thorough evaluation of existing information as part of a levee evaluation program. This includes a review of original construction (if available), improvements, performance history, existing subsurface information, and regional and local geomorphology. The standard also recommends the use of cone penetrometers (CPTs) and geophysics to supplement borings, where appropriate.

Based on the paraphrased requirements above, Kleinfelder interpreted the geotechnical guidance from the ULDC and SOP as the following:
• One exploration taken from the levee crown for every 500 feet of levee. • One exploration taken from the levee landside toe for every 500 feet of levee. • One exploration taken from the levee waterside toe for every 500 feet of levee. Waterside explorations may be omitted if site conditions prevent explorations from being conducted (site access is not possible, environmental issues, etc.)
• Landside field explorations are not included in the frequency specified by the ULDC Section 7.3 and CESPK 2022 SOP guidance. Kleinfelder included landside field borings in Tables 2.1 through

2.3 to illustrate relative spacing of explorations that were performed outside of the levee prism.

Additionally, each exploration was reviewed for laboratory testing performed on samples. Boring logs from as early as the late 1960s to as late as the early 2020s were considered to meet guidelines if they contained results for plasticity, dry unit weight, permeability, or other testing results that adequately characterized the logged material. Explorations were also evaluated for logging procedures. Although logging methods varied across borings (such as USACE and DWR methods), the methods used in the reviewed explorations were generally in accordance with ASTM D2488, which aligns with the appropriate field logging manual identified in the ULDC Section 7.3 guidance. Where available, the as-built plans, conformance laboratory tests, and in-place compaction tests for the construction and improvements of each levee were reviewed as part of the ULDC evaluation. This information was used to evaluate the levee geometry and material properties within the newly constructed and improved levee sections.

RCSL from Stations 6000+00 to 6118+20 is approximately 2.24-miles (11,820 feet) long, NEMDCEL from Stations 3056+00 to 3192+25 is approximately 2.58 miles (13,625 feet) long, and ACNL from Stations 5000+00 to 5023+00 is approximately 0.43-miles (2,300 feet) long.

The approximate number of explorations for each levee segment should be spaced apart on average by 500 feet for levee design. This applies to explorations taken from the waterside toe, levee crown, and 24001006.001A/SAC24R169107_R2 Page 11 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025
landside toe individually (i.e., one levee crown exploration at Station 6000+00, then one levee crown exploration at Station 6005+00, then at 6010+00, etc.). Following this guideline, each segment should generally have the following quantities of valid explorations (approximately 33 explorations per mile):

1. RCSL (2.24 miles): 24 explorations of each type (waterside toe, levee crown, landside toe) – 72 total explorations

2. NEMDCEL (2.58 miles): 28 explorations of each type - 84 total explorations

3. ACNL (0.43 miles): 5 explorations of each type - 15 total explorations RCSL, NEMDCEL, and ACNL have been explored by Kleinfelder and others for levee evaluations and improvement projects. Explorations include drilled borings and cone penetrometer soundings (CPTs). The explorations reviewed by Kleinfelder included those advanced for the SAFCA FEMA Levee Accreditation program, the DWR Urban Levee Evaluation (ULE) program, and previous studies by others. To be included in the summary, the explorations were evaluated for depth (generally a minimum of 4 times the levee height for crest explorations), sampling frequency, laboratory testing, and classification. For example, shallow borings that only assess the levee embankment were not included in the “Meets SPK SOP 2022” exploration count summaries.

Tables 2.1 through 2.3 below summarize the total number of explorations performed, total number of explorations that meet the exploration requirement described in SPK SOP (USACE, 2022), and total number of explorations required to meet ULDC Section 7.3 for each levee location. 24001006.001A/SAC24R169107_R2 Page 12 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025
Table 2.1
Summary of Exploration Locations and Spacing for RCSL (Stations 6000+00 to 6118+20) Explorations that Meet CESPK
2022 SOP All Explorations ULDC Requirements
Exploration
Location Number of
Explorations
Average
Spacing of
Explorations
(ft)
Number of
Explorations
Average
Spacing of
Explorations
(ft)
Explorations
Required to
Meet ULDC
Section 7.3
and CESPK
2022 SOP
Spacing
Required to
Meet CESPK
2022 SOP (ft)
Waterside
Toe* 0 - 0 - 24 500
Levee
Crown 18 723 33 368 24 500
Landside
Toe 5 1,837 8 1,531 24 500
Landside
Field 1 5,479 5 994 - -
Total 24 46 72
Average Per
Mile 11 21 33
*Waterside explorations may be omitted due to environmental issues, site access, or other conditions preventing investigation.

Table 2.2
Summary of Exploration Locations and Spacing for NEMDCEL (Stations 3056+00 to 3192+25) Explorations that Meet CESPK
2022 SOP All Explorations ULDC Requirements
Exploration
Location Number of
Explorations
Average
Spacing of
Explorations
(ft)
Number of
Explorations
Average
Spacing of
Explorations
(ft)
Explorations
Required to
Meet ULDC
Section 7.3
and CESPK
2022 SOP
Spacing
Required to
Meet CESPK
2022 SOP (ft)
Waterside
Toe* 1 12,834 5 2,562 28 500
Levee
Crown 20 703 31 407 28 500
Landside
Toe 4 2,095 4 1,645 28 500
Landside
Field 3 5,965 5 3,844 - -
Total 28 45 84
Average Per
Mile 11 17 33
*Waterside explorations may be omitted due to environmental issues, site access, or other conditions preventing investigation. 24001006.001A/SAC24R169107_R2 Page 13 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025
Table 2.3
Summary of Exploration Locations and Spacing for ACNL (Stations 5000+00 to 5023+00) Explorations that Meet CESPK
2022 SOP All Explorations ULDC Requirements
Exploration
Location Number of
Explorations
Average
Spacing of
Explorations
(ft)
Number of
Explorations
Average
Spacing of
Explorations
(ft)
Explorations
Required to
Meet ULDC
Section 7.3
and CESPK
2022 SOP
Spacing
Required to
Meet CESPK
2022 SOP (ft)
Waterside
Toe* 0 - 0 - 5 500
Levee
Crown 4 575 6 400 5 500
Landside
Toe 2 1,150 2 1,150 5 500
Landside
Field 0 - 0 - - -
Total 6 8 15
Average Per
Mile 14 18 33
*Waterside explorations may be omitted due to environmental issues, site access, or other conditions preventing investigation.

It is noted that the total number of explorations is not within the recommended range of explorations in the CESPK 2022 SOP for levee crown, waterside toe, and landside toe borings (no quantity and spacing guidelines were noted for landside field borings, which lie outside the levee prism). While explorations not meeting the CESPK 2022 SOP requirements were not relied upon for analysis, the data was reviewed in conjunction with adjacent explorations that meet CESPK 2022 SOP requirements and were included as part of the “All Explorations” summary.

In addition, geology and geomorphology, geophysical HEM (helicopter-based electromagnetics surveys), past performance information, historical records, and construction records (including inspection trench and keyway trench observations) were also used to assess geotechnical conditions. The geophysical HEM provides a continuous record of the subsurface conditions along the levee.

Construction as-builts and records were reviewed for the levee improvements since the 1990s. The RoblaArcade levees were constructed in the late 1950s by USACE and improved in the late 1990’s to early 2000’s as part of a SAFCA flood control improvement project. The SAFCA levee construction was observed and tested by Kleinfelder. USACE and SAFCA levee construction included excavation of inspection and keyway trenches to between 2 and 11 feet in depth to confirm the levee rested on firm, low permeability soils.

Levee embankment fill was tested to confirm that it met USACE requirements for levee construction. 24001006.001A/SAC24R169107_R2 Page 14 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025

2.1.1 Conclusion
Based on the above information, it is Kleinfelder’s opinion that sufficient and appropriate information was collected and reviewed to provide an adequate assessment of the subsurface conditions as outlined in the SPK SOP for design of levee improvements. Therefore, it is Kleinfelder’s opinion that the RCSL (Stations 6000+00 to 6118+20), NEMDCEL (Stations 3056+00 to 3192+25), and ACNL (Stations 5000+00 to 5023+00) geotechnical investigations were generally performed following the guidance outlined above and meet the requirements of ULDC (DWR, 2012) 7.3 for Soil Sampling, Testing, and Logging through Exception.

2.2 ULDC SECTION 7.4 SLOPE STABILITY FOR INTERMITTENTLY LOADED LEVEES This section contains a summary of the review of the existing reports and analyses performed for RCSL (Stations 6000+00 to 6118+20), NEMDCEL (Stations 3056+00 to 3192+25), and ACNL (Stations 5000+00 to 5023+00) as it applies to ULDC (DWR, 2012) Section 7.4 Slope Stability for Intermittently Loaded Levees.

ULDC (DWR, 2012) defines an intermittently loaded levee as:
“Intermittently loaded levee means a levee that does not experience a water surface elevation of one foot or higher above the elevation of the levee toe at least once a day for more than 36 days per year on average.”
The general requirements of ULDC (DWR, 2012) Section 7.4 Slope Stability for Intermittently Loaded Levees are outlined below.

ULDC (DWR, 2012) 7.4 requires slope stability analysis for the design water surface elevation (DWSE) and at the Hydraulic Top of Levee (HTOL) WSE. “Engineers should use sound engineering judgment and guidance from EM 1110-2-1902 to decide what constitutes a minor, insignificant slip surface versus a sliding surface that threatens the integrity of the levee. These determinations should be based on performance history, levee geometry, type of levee fill material, stratigraphy of the levee embankment and foundation soils, seepage conditions (including pore water pressures calculated for the seepage analysis), soil strength characteristics, and potential for erosion. Those surfaces which significantly threaten the integrity of the levee must meet minimum slope stability criteria.” Steady-state landside stability and rapid drawdown waterside stability should be evaluated using the minimum factors of safety summarized in Table 1.

Stability Analysis ULDC Minimum Factor of Safety1
Steady-State DWSE, Landside Slope 1.4
Steady-State HTOL WSE, Landside Slope 1.2
Rapid Drawdown DWSE, Waterside Slope 1.0-1.22
End of Construction 1.33
24001006.001A/SAC24R169107_R2 Page 15 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 25, 2025

1. Critical failure surface should intersect the levee crown and exceed a minimum of 3- foot depth into the level slope.

2. Minimum factor of safety dependent on time extent DWSE may have saturated the waterside levee slope.

3. End of Construction is performed for newly constructed levees. Since the RCSL, NEMDCEL, and ACNL were improved/constructed nearly 30 years ago, this loading case was not analyzed for this current study.

Through seepage occurs where the phreatic seepage surface exits above the levee toe on the landside levee slope. For through seepage, reaches where the phreatic seepage surface exited on a levee slope that is composed of erodible material (sands and non-plastic silts and silty sands) were generally considered to not meet criteria.

Detailed discussions of the slope analyses previously performed are discussed in the reports listed in Section 1.5 and included in the reference list. These analyses results were compared with the current 2024 200-year DWSE and HTOL (MBK, 2024a). Since the previously performed analyses were analyzed with a WSE that is generally higher than the current 2024 200-year DWSE and HTOL and met slope stability criteria and soil and geometry conditions have not changed, the analyses are considered to meet criteria for the current, lower WSEs. Between RSCL Stations 6117+00 to 6118+19, the 2024 HTOL increases from Elevation 44.97 to 46.72 feet, which is 1.49 feet above the maximum previously analyzed WSE. The RSCL landside toe at Station 6118+19 rises to approximately 46.4 feet [LiDAR topography profiles from ULE SGDR (URS, 2011)] which is 0.32 feet below the 2024 HTOL at this location. This area is considered to meet ULDC 7.4 Through Seepage since there is less than half a foot of water above the landside toe for the 2024 HTOL WSE.
24001006.001A/SAC24R169107_R2 Page 16 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
Table 2.4
Stability Analyses Comparison Summary
Reference Report Summary (Kleinfelder, 2016b) 2024 ULDC Summary Meets/Does Not Meet Meets/Does Not Meet
Approximate
Station
Highest
Previously
Modeled
WSE
Through
Seepage
Steady -
State
Landside
Stability
FOS
Rapid
Drawdown
Waterside
Stability FOS
2024 WSE
Difference
2024
WSE –
Highest
Previously
Modeled
WSE
Through1
Seepage
Steady-State
Landside
Stability
Rapid
Drawdown
Waterside
Stability

41.26 200-yr -3.24 Meets Meets Meets RCSL 6003+00 44.5 Meets Meets,

1.43 1.62 42.84 HTOL -1.66 Meets Meets Meets

41.27 200-yr
-3.23
(HTOL)
-0.23 (200-
Yr)
Meets Meets Not Analyzed
RCSL 6012+00

44.5 (HTOL)

41.5 (200-
yr)
Meets
Meets,

1.2 (HTOL)

1.4 (200-
Yr)
Not Analyzed

42.85 HTOL -1.65
(HTOL) Meets Meets Not Analyzed

41.27 200-yr -3.23 Meets Meets Meets
RCSL 6016+00 44.5 Meets Meets,

1.82 1.72 42.86 HTOL -1.64 Meets Meets Meets

41.41 200-yr -3.19 Meets Meets Meets
RCSL 6057+00 44.6 Meets Meets,

1.73 1.89

42.96 HTOL -1.64 Meets Meets Meets

43.37 200-yr -1.83 Meets Meets Meets RCSL 6098+00 45.2 Meets Meets,

1.85 2.19

43.99 HTOL -1.21 Meets Meets Meets
24001006.001A/SAC24R169107_R2 Page 17 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
Table 2.4 (cont.)
Stability Analyses Comparison Summary
Reference Report Summary (Kleinfelder, 2016b) 2024 ULDC Summary Meets/Does Not Meet Meets/Does Not Meet
Approximate
Station
Highest
Previously
Modeled
WSE
Through
Seepage
Steady -State
Landside
Stability FOS
Rapid Drawdown
Waterside
Stability FOS
2024 WSE
Difference
2024WSE –
Highest
Previously
Modeled WSE
Through1
Seepage
SteadyState
Landside
Stability
Rapid
Drawdown
Waterside
Stability

37.13 200-yr -2.77 Meets Meets Not
Analyzed

NEMDCEL
3057+182
With Drained
Stability
Berm

39.9 Meets
Meets,

2.16 (Berm)

1.82 (Global)
Not Analyzed

40.13 HTOL +0.23 Meets Meets Not
Analyzed

37.63 200-yr -4.47 Meets Meets Meets NEMDCEL
3080+00 42.1 Meets Meets, 1.74 Meets, 2.27

40.63 HTOL -1.47 Meets Meets Meets

38.81 200-yr -4.09 Meets Meets Meets NEMDCEL
3126+00 42.9 Meets Meets, 1.88 Meets, 1.28 41.81 HTOL -1.09 Meets Meets Meets NEMDCEL 38.93 200-yr -4.07 Meets Meets Meets
3133+00
without ditch

43.0 Meets Meets, 2.82 Meets, 1.21

41.93 HTOL -1.07 Meets Meets Meets

38.93 200-yr -4.07 Meets Meets Meets NEMDCEL
3133+003
with ditch
and drain
trench

43.0 Meets Meets, 1.76 Not Evaluated

41.93 HTOL -1.07 Meets Meets Meets

39.07 200-yr -4.43 Meets Meets Meets NEMDCEL
3137+50 43.5 Meets Meets, 1.59 Meets, 1.40

42.07 HTOL -1.43 Meets Meets Meets
24001006.001A/SAC24R169107_R2 Page 18 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
Table 2.4 (cont.)
Stability Analyses Comparison Summary
Reference Report Summary 2024 ULDC Summary
Meets/Does Not Meet Meets/Does Not Meet
Approximate
Station
Highest
Previously
Modeled WSE
Through
Seepage
Steady-State
Landside
Stability FOS
Rapid Drawdown
Waterside Stability
FOS
2024
WSE
Difference 2024
WSE – Highest
Previously
Modeled WSE
Through1
Seepage
SteadyState
Landside
Stability
Rapid
Drawdown
Waterside
Stability

39.81 200-yr -3.19 Meets Meets Meets NEMDCEL
3167+00 43.6 Meets Meets, 1.81 Meets, 1.57 42.40
HTOL -1.20 Meets Meets Meets

40.44 200-yr -5.56 Meets Meets Meets NEMDCEL
3185+00 46.0 Meets Meets, 1.97 Meets, 1.51 42.50
HTOL -3.50 Meets Meets Meets

37.44 200-yr -2.46 Meets Meets Not Analyzed ACNL 5000+602 With Drained
Stability
Berm

39.9 Meets
Meets,

3.06 (Berm)

2.29 (Global)
Not Analyzed 40.44
HTOL +0.54 Meets Meets Not Analyzed

37.63 200-yr -4.27 Meets Meets Meets ACNL
5003+00 41.9 Meets Meets, 1.59 1.50 40.63
HTOL -1.27 Meets Meets Meets

1. Through seepage occurs where the phreatic seepage surface exits above the levee toe on the landside levee slope. For through seepage, reaches where the phreatic seepage surface exited on a levee slope that is composed of erodible material (sands and non-plastic silts and silty sands) were generally considered to not meet criteria.

2. Analysis performed by Kleinfelder and included the 2024 Geotechnical Basis of Design Report, “Drained Stability Berm Seepage Repair, Arcade Creek North Levee and NEMDC East Levee, Sacramento County, California.” Original analysis was performed at a slightly lower previous WSE than the 2024 HTOL; however, the analysis is considered to meet underseepage criteria since the 2024 200-yr WSE is below the previous HTOL, the 2024 HTOL is less than 0.6 feet above the previous WSE, the previous analysis yielded high slope stability FOS, and no slope stability past performance issues were noted.

3. “NEMDCEL 3133+00 with ditch and drain trench” Analysis was performed by URS and included in 2014 technical memorandum “Drain Trench System Design along Reach NAS-NE-3 (City of Sacramento Sump No. 157 at Magpie Creek).” 24001006.001A/SAC24R169107_R2 Page 19 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
Based on this review the following conclusions can be made:
• Analysis cross sections model slope stability along RCSL (Stations 6000+00 to 6118+20), NEMDCEL (Stations 3056+00 to 3192+25), and ACNL (Stations 5000+00 to 5023+00) at critical locations. • The 2024 200-year DWSE and HTOL are lower than the WSEs modeled in the existing analyses. • The modeled improvements at the analysis cross section were the same or less conservative than the constructed improvements and met criteria at the analyzed locations.

2.2.1 Conclusion
Based on the above review, it is Kleinfelder’s opinion RCSL (Stations 6000+00 to 6118+20), NEMDCEL (Stations 3056+00 to 3192+25), and ACNL (Stations 5000+00 to 5023+00) meet the requirements of ULDC (DWR, 2012) 7.4 Slope Stability for Intermittently Loaded Levees.

2.3 ULDC SECTION 7.5 UNDERSEEPAGE
This section contains a summary of the review of the existing reports and analyses performed for RCSL (Stations 6000+00 to 6118+20), NEMDCEL (Stations 3056+00 to 3192+25), and ACNL (Stations 5000+00 to 5023+00) as it applies to ULDC (DWR, 2012) Section 7.5 Underseepage for Intermittently Loaded Levees.

The general requirements of ULDC (DWR, 2012) Section 7.5 Underseepage for Intermittently Loaded Levees are outlined below.

ULDC (DWR, 2012) 7.5 requires seepage analysis performed for the design water surface elevation (DWSE) and the hydraulic top of levee (HTOL) WSE. Exit gradients measured at the landside levee toe, seepage berm toe, ditches, canals, depressions, or areas of thin blanket. The allowable maximum exit gradient is summarized in the table below.

Seepage Analysis Location Allowable Maximum Exit
Gradient
Landside Levee Toe 0.51
Steady-State DWSE Ditches, canals,
depressions, berms 0.5-0.82
Landside Levee Toe 0.6
Steady-State HTOL WSE Ditches, canals,
depressions, berms 0.6-0.92

1. The allowable underseepage exit gradient through the combined seepage berm/blanket layer between the levee toe and the seepage berm toe for a water 24001006.001A/SAC24R169107_R2 Page 20 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
surface set at the DWSE is determined by interpolation, using 0.5 at the levee toe and 0.8 at the seepage berm toe.

2. Maximum allowable exit gradient at the landside levee toe is 0.5 and up to 0.8 at 150 feet from the levee toe, using linear interpolation for distances in between.

ULDC (DWR, 2012) does allow for higher exit gradients at the seepage berm toe provided sound engineer judgement, and additional analysis. For the HTOL, “In general if the berm is less than 100-ft wide, the maximum exit gradient may increase by up to 20 percent of the DWSE maximum exit gradient.“ ULDC (DWR, 2012) 7.5 provides criteria for blanket layer soils with saturated unit weights of 112 pcf or less. Robla-Arcade levee stratigraphy blanket layers did not require this analysis because saturated unit weights were greater than the minimum specified.

Detailed discussions of the analyses previously performed are discussed in the reports listed in Section

1.5 and included in the reference list. These analyses results were compared with the current 2024 200- year DWSE and HTOL (MBK, 2024a). Since the previously performed analyses were analyzed with a WSE that is generally higher than the current the 2024 200-year DWSE and HTOL and met seepage criteria, the analyses are considered to meet criteria for the current lower WSEs. Table 2.5 contains the previously performed analysis results with the previously used design WSEs and the current 2024 WSEs. The 2016 Kleinfelder ULDC report includes analysis of three-dimensional effects of levee intersections including from ACNL to NEMDCEL and NEMDCEL to RCSL. The estimated three dimensional effects met criteria at the previously used WSEs that were higher than the 2024 WSEs. 24001006.001A/SAC24R169107_R2 Page 21 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
Table 2.5
Seepage Analyses Comparison Summary
ULDC Report Summary (Kleinfelder, 2016b) 2024 ULDC Summary Approximate Meets/Does Not Meet Meets/Does Not Meet
ULE Station
Highest
Previously
Modeled WSE Underseepage 2024 WSE Difference 2024 WSE – Highest Previously Modeled WSE Underseepage

41.26 200-yr -3.24 Meets
RCSL 6003+00
With Swale 44.5
Meets,
No positive gradient at landside toe

0.51 (SC/CL, ML) 40 feet from landside
toe

42.84 HTOL -1.66 Meets

41.27 200-yr -3.23 Meets
RCSL 6012+00 44.5
Meets,

0.23 (CL) at landside toe

0.12 (SC/CL) 70 feet from landside toe 42.85 HTOL -1.65 Meets

41.27 200-yr -3.23 Meets
RCSL 6016+00 44.5
Meets,
<0.10 (SC) at landside toe

0.34 (ML/CL) 30 feet from landside toe 42.86 HTOL -1.64 Meets

41.41 200-yr -3.19 Meets
RCSL 6057+00 44.6
Meets,

0.13 (CL) at landside toe

0.42 (CL) 30 feet from landside toe 42.96 HTOL -1.64 Meets

43.37 200-yr -1.83 Meets
RCSL 6098+00 45.2
Meets,
No positive gradient at landside toe

0.31 (CL) 20 feet from landside toe 43.99 HTOL -1.21 Meets

37.13 200-yr -2.77 Meets NEMDCEL
3057+181
With Drained
Stability Berm

39.9 Meets
Berm toe: < 0.10 (CL and
sand filter)
Ditch Toe: 0.19 (CL) and < 0.10 (CL &
ML/CL Hardpan layer)

40.13 HTOL +0.23 Meets2

37.63 200-yr -4.47 Meets NEMDCEL
3080+00 42.1
Meets,
No gradient at toe

0.36 (CL) at 100 feet from landside toe 40.63 HTOL -1.47 Meets

38.81 200-yr -4.09 Meets NEMDCEL
3126+00 42.9
Meets,
No gradient at toe

0.49 (CL) at 50 feet from landside toe 41.81 HTOL -1.09 Meets 24001006.001A/SAC24R169107_R2 Page 22 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
Table 2.5 (cont.)
Seepage Analyses Comparison Summary
ULDC Report Summary (Kleinfelder, 2016b) 2024 ULDC Summary Approximate Meets/Does Not Meet Meets/Does Not Meet
ULE Station
Highest
Previously
Modeled WSE Underseepage 2024 WSE Difference 2024 WSE – Highest Previously Modeled WSE Underseepage
NEMDCEL 38.93 200-yr -4.07 Meets
3133+00
(without ditch)

43.0 Meets,
No gradient at toe

0.20 (CL) at 80 feet from landside toe 41.93 HTOL -1.07 Meets

38.93 200-yr -4.07 Meets NEMDCEL
3133+003 (with
ditch and drain
trench)

43.0 Meets,
0 at levee toe (ML)
<0.10 UPRR Embankment Toe (CL)

0.49 Ditch Toe (SM)

0.48 Drain Trench (SM)

41.93 HTOL -1.07 Meets

39.07 200-yr -4.43 Meets NEMDCEL
3137+50 43.5
Meets,
No gradient at toe

0.64 (CL) at 150 feet from landside toe 42.07 HTOL -1.43 Meets

39.81 200-yr -3.79 Meets NEMDCEL
3167+00 43.6
Meets,

0.12 (CL) at landside toe

0.46 (CL) at 110 feet from landside toe 42.40 HTOL -1.20 Meets

40.44 200-yr -5.56 Meets NEMDCEL
3185+00 46.0
Meets,
No gradient at toe

0.6443 (CL) at 110 feet from landside toe 42.50 HTOL -3.50 Meets ACNL 37.44 200-yr -2.46 Meets
5000+601,2
With Drained
Stability Berm

39.9 Meets,
No positive gradient at landside toe 40.44 HTOL +0.54 Meets

37.63 200-yr -4.27 Meets
ACNL 5003+00 41.9
Meets,
<0.10 at landside toe

0.51 (CL) 40 feet from landside toe 40.63 HTOL -1.27 Meets

1. Analysis performed by Kleinfelder and included the 2024 Geotechnical Basis of Design Report, “Drained Stability Berm Seepage Repair, Arcade Creek North Levee and NEMDC East Levee, Sacramento County, California.”

2. Original analysis was performed at a lower WSE than the 2024 HTOL, however the analysis is considered to meet underseepage criteria due to the slightly higher WSE, no positive exit gradient measured at the toe, and no past performance issues.

3. Analysis performed by URS and included in 2014 technical memorandum “Drain Trench System Design along Reach NAS-NE-3 (City of Sacramento Sump No. 157 at Magpie Creek).”
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Based on this review the following conclusions can be made:
• Analysis cross sections model steady-state underseepage conditions along RCSL (Stations 6000+00 to 6118+20), NEMDCEL (Stations 3056+00 to 3192+25), and ACNL (Stations 5000+00 to 5023+00) at critical locations.
• The 2024 200-year DWSE and HTOL are generally lower than the WSE modeled in the existing analyses.
• The modeled improvements at the analysis cross section were the same or less conservative than the constructed improvements and met criteria at the analyzed locations.

2.3.1 Conclusion
Based on the above review, it is Kleinfelder’s opinion RCSL (Stations 6000+00 to 6118+20), NEMDCEL (Stations 3056+00 to 3192+25), and ACNL (Stations 5000+00 to 5023+00) meet the requirements of ULDC (DWR, 2012) 7.5 Underseepage for Intermittently Loaded Levees.

2.4 ULDC SECTION 7.7 SEISMIC VULNERABILITY
This section contains a summary of the review of the existing reports and analyses performed for RCSL (Stations 6000+00 to 6118+20), NEMDCEL (Stations 3056+00 to 3192+25), and ACNL (Stations 5000+00 to 5023+00) as it applies to ULDC Section 7.7 - Seismic Vulnerability for Intermittently Loaded Levees.

The objective of the seismic vulnerability evaluation was to develop information to characterize the potential vulnerability of levee segments during the postulated 200-year return period seismic event. This information can then be used as a basis to classify the levees in terms of its ability to provide post-seismic flood protection in accordance with the requirements of ULDC. For intermittently loaded levees (or floodwalls), ULDC states the following requirement:
“If seismic damage from 200-year-return-period ground motions is expected after the urban level of flood protection is achieved, a post-earthquake remediation plan is required as part of a flood safety plan that is developed in coordination with pertinent local, State, and federal agencies.”
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In accordance with ULDC, post-seismic flood protection requires maintaining a levee crown sufficient for protection against the 10-year flood with 3 feet of freeboard within 8 weeks of the seismic event with a full level of protection required by the next flood season.

Kleinfelder has been tasked by SAFCA with evaluating the seismic vulnerability of the SAFCA Sacramento area levees located in Sacramento and Sutter Counties, California in support of ULDC levee certification.

As part of that project, Kleinfelder prepared a Seismic Performance Summary Report (Kleinfelder, 2024b) that addresses the seismic vulnerability of the North Area Streams study area, which includes the subject portions of the ACNL, NEMDCEL, and RCSL. This report is included in Appendix C of this report.

2.4.1 Conclusion
Based upon the Seismic Performance Summary Report (Kleinfelder, 2024b), ULDC seismic vulnerability classification for RCSL (Stations 6000+00 to 6118+20), NEMDCEL (Stations 3056+00 to 3192+25), and ACNL (Stations 5000+00 to 5023+00) is shown in Table 2.6, below.

Table 2.6
Seismic Vulnerability Classifications for North Area Streams Levees Levee Station Start Station End 2023 Seismic
Vulnerability
RCSL 6000+00 6118+20 Low
ACNL 5000+00 5023+00 Low
NEMDCEL 3056+00 3192+25 Low
It is Kleinfelder’s opinion that the subject RCSL, NEMDCEL, and ACNL outlined above meets the geotechnical aspects of the Section 7.7 Seismic Vulnerability. The Seismic Performance Summary Report (Kleinfelder, 2024) is included in Appendix C.

2.5 ULDC SECTION 7.8 LEVEE GEOMETRY
This section contains a summary of the review of existing information for RCSL (Stations 6000+00 to 6118+20), NEMDCEL (Stations 3056+00 to 3192+25), and ACNL (Stations 5000+00 to 5023+00) with regards to ULDC (DWR, 2012) Section 7.8 Levee Geometry. ULDC (DWR, 2012) Section 7.8 Levee Geometry is as follows.
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“Minimum levee geometry criteria have previously been specified by various USACE and State guidance documents. The guidance for various minimum levee geometry and their references are as follows in Table 7-1.
“For new levees, or levees with extensive reconstruction, situated along major waterways, a minimum 20-foot-wide crown width and 3h:1v waterside and landside slopes (4h:1v waterside slope for bypass levees) is required. Exceptions may be allowed for reconstruction of existing levees where the authorized geometry provides for a steeper slope or narrower crown, the levee has performed well, and it meets stability and seepage criteria. These geometry requirements represent minimum requirements, and wider levee crowns and/or flatter slopes may be necessary in some areas, depending upon geologic and geotechnical considerations. At the same time, however, minimum requirements should be associated with generally uniform, levee materials and homogeneous embankments. Steeper slopes may be allowed in certain circumstances where there is limited space available, and where levees are demonstrated to meet minimum seepage and stability criteria. Steeper waterside levee slopes may be acceptable where stability criteria are met and either slope protection is provided or it is determined that wavewash erosion for a water surface at or below the DWSE could not result in breaching of the levee. For example, levees with slopes steeper than new minimum requirements may be acceptable with elements such as central clay cores, seepage cutoff walls, landside filters or drains, or soil reinforcement that substantially decrease seepage hazards and increase slope stability.

The levee prism should be considered to continue underground based on projection of the above-ground levee slopes. The projected levee slopes are useful for evaluating erosion, excavations, and encroachments near the levee.” 24001006.001A/SAC24R169107_R2 Page 26 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
Kleinfelder provided continuous geotechnical observation, inspection, and testing during construction of the SAFCA improvements to the subject RCSL, NEMDCEL, and ACNL including continuous logging by a geotechnical engineer of the keyway trench that was locally deepened up to 11 feet to cutoff shallow sand or soft layers. There was no reported distress from the 1997 high water event or more recent high-water events from 2002, 2004, 2005, 2006, or 2017. Generally, the levees were constructed with landside and waterside slopes at 2H:1V and 3H:1V inclinations, respectively, and a crown width varying between 12 feet and 30 feet.

2.5.1 Current Levee Geometry
Psomas provided levee cross sections at select locations along the Robla-Arcade Levees that correspond to previous analysis locations. MBK projected the project levee template on to the select cross sections to confirm the levee geometry. The figures of the levee geometry analysis are included in Appendix B.

Prior to 2024, no surveys of the levee were performed since there has been no construction activity since the improvements in the 1990's and early 2000's. Kleinfelder visited RCSL (Stations 6000+00 to 6118+20), NEMDCEL (Stations 3056+00 to 3192+25), and ACNL (Stations 5000+00 to 5023+00) and no significant changes to the levee geometry (slope failures, erosion, etc.,) from the previous evaluations were noted.

The 2024 levee cross section slopes were compared to the analyzed geometry and the 2024 landside levee slopes were generally the same or flatter than the existing analysis models. Therefore, existing analysis models are considered applicable to the current geometry and met stability for a generally higher WSE than the 2024 WSE.

Cross section Station RSCL 6117+50 was noted to have a higher minimum top of levee (MTOL) elevation of 47.92 than the surveyed elevation of 46.6 feet. However, the geotechnical evaluation 200-year WSE is

45.02 feet and HTOL is 45.56 feet, both of which are below the levee crown and landside toe. This is an area of high ground, where the channel is incised and the levee is for freeboard. Therefore, from a geotechnical standpoint, stability is considered to meet criteria at Station 6117+50. Levee freeboard is addressed in the MBK Engineers Report.

2.5.2 Conclusion
From a geotechnical perspective, the above information is considered applicable and appropriate to provide an adequate assessment of levee geometry for meeting the guidance outlined above for ULDC Section 7.8 Levee Geometry. Therefore, from a geotechnical standpoint (seepage and slope stability), the subject levees are considered to meet ULDC Section 7.8 Levee Geometry. 24001006.001A/SAC24R169107_R2 Page 27 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025

2.6 ULDC SECTION 7.9 INTERFACES AND TRANSITIONS
This section contains a summary of the review of existing information for RCSL (Stations 6000+00 to 6118+20), NEMDCEL (Stations 3056+00 to 3192+25), and ACNL (Stations 5000+00 to 5023+00) with regards to ULDC (DWR, 2012) Section 7.9 Interfaces and Transitions. ULDC (DWR, 2012) Section 7.9 Interfaces and Transitions is as follows.

The civil engineer must consider, evaluate, and explicitly design for interfaces and transitions between different types of levee sections and features along a levee system. Appropriate overlaps, transitions, and connections between features must be evaluated and designed to ensure that the levee system functions holistically, such that no levee reach is more susceptible to problems than an adjacent reach due to gaps in features, loading/demand concentrations, or other threedimensional effects. Such interfaces, transitions, and connections commonly occur at the ends of seepage berms, seepage cutoff walls, revetments, and floodwalls.

Each transition or interface along the subject levees is discussed below.

2.6.1 Interface of a Detention Basin at RCSL Landside Toe Near Station 6012+00 An unlined detention basin was located approximately 70 feet from the landside RCSL toe near Station 6012+00 with an invert elevation of 26 feet or approximately 10 feet below the adjacent ground surface.

Kleinfelder performed seepage and stability analyses at RCSL Station 6012+00 (Kleinfelder, 2016b) that met criteria at a higher WSE than the 2024 WSE. No past performance issues were documented in this area.

Based on review of the RCSL compaction testing, the interface of the landside detention basin does not present a gap or other three-dimensional effects. Therefore, it is Kleinfelder’s opinion that the RCSL at the detention basin meets the geotechnical requirements of ULDC 7.9 Interfaces and Transitions.

2.6.2 Transition of UPRR Stop log Structure at approximate RCSL Station 6000+50 The stop log structure across the UPRR tracks located at the intersection of NEMDCEL and RCSL was originally constructed under Central Valley Flood Protection Board (CVFPB) Permit #14477 after it was reported ACNL was overtopped at a sandbag closure during a highwater event in 1986. The stop log structure was retrofitted and raised to accommodate a levee raise in 1995 (Spink, 1995b). The stop log structure is comprised of two retaining walls parallel to the UPRR tracks that are connected by a concrete 24001006.001A/SAC24R169107_R2 Page 28 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
grade beam across the tracks. Compacted embankment fill was used below and behind the retaining walls at both stop log structures (Kleinfelder, 1997a, b).

The construction of this closure structure was evaluated for geotechnical considerations related to slope stability and seepage at the transition from the levee to the UPRR closure structure and retaining walls (both sides) during a flood event. Kleinfelder visited the site and reviewed the UPRR stop log structure drawings (Spink, 1995b). Evaluation of the structural properties of the closure structure was performed by Mead and Hunt (Mead & Hunt, 2024). As-built drawings show that the requirement for pervious backfill behind the retaining walls was removed from the project plans during construction. We understand compacted embankment fill was placed against the retaining walls. Further discussion of the stop log structure is discussed in Section 2.7.3.

Kleinfelder performed seepage and stability analyses of the embankment adjacent to the stop log structure near RCSL Station 6003+00 (Kleinfelder, 2016b) that met criteria at a higher WSE than the 2024 WSE. No past performance issues were documented in this area.

Based on review of the existing site conditions, past performance history, and seepage and stability analyses, the transition between RCSL and the UPRR stop log structure do not present gaps or other threedimensional effects. Therefore, it is Kleinfelder’s opinion that the transitions between RCSL and the UPRR stop log structure walls meet the geotechnical requirements of ULDC 7.9 Interfaces and Transitions.

2.6.3 Interface of Sump Station No. 140 at Approximate RCSL Station 6032+00 Kleinfelder reviewed the levee construction as-built drawings (SAFCA, 2001) for Sump Station 140 at approximate RSCL Station 6032+00. The sump station improvements were constructed in 1997 when SAFCA raised RCSL. Sump Station 140 includes three 36-inch diameter, and one 20-inch diameter welded steel pipes that are buried sloping up the landside and waterside slopes and across the RCSL crest at an approximate invert elevation of 43 feet. A retaining wall with a maximum height of 8-feet is located at the landside toe and the pipes pass through the wall through the foundation. The sump station is located within a Kleinfelder analysis reach between RCSL Stations 6011+50 to 6053+00. Analysis cross sections were selected for the reach at RCSL Station 6016+00 and 6012+00 as having steep landside slopes and a detention basin at the landside toe. The seepage and slope stability analysis performed at Station 6012+00 and 6016+00 met criteria for seepage and slope stability for higher HTOLs with more critical levee geometry. No past performance issues were documented in this area. 24001006.001A/SAC24R169107_R2 Page 29 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
Based on review of the as-built records, the interface of Sump Station 140 does not present gaps or other three-dimensional effects. Therefore, it is Kleinfelder’s opinion that the interface of Sump Station 140 meets the geotechnical requirements of ULDC Interfaces and Transitions.

2.6.4 Interface of Rio Linda Boulevard Bridge and Floodwalls approximately between RCSL Stations 6078+00 to 6079+00
Kleinfelder performed a site visit in May 2024 and observed the Rio Linda Boulevard bridge approximately between RCSL Stations 6078+00 to 6079+00. The bridge spans the Robla Creek channel with the southern abutment on the RCSL crest. The bridge was constructed of reinforced concrete, included five spans, was 155 feet in length, and was 47.5 feet in width. An existing bridge was removed during construction of the new bridge. The bridge was constructed in 1988 under CVFPB Permit #14885. In the early 2000’s, two floodwalls on either side of the Rio Linda Bridge abutment were constructed as a part of the SAFCA project to raise RCSL. According to the as-built drawings, the floodwalls extend 5 feet into the levee embankment and were supported on continuous spread footings embedded approximately 2 feet below the ground surface. The top of the flood walls matched the top of levee at Elevation 47.4 feet. The walls were evaluated by Mead and Hunt for structural integrity.

Seepage and stability analyses were performed at RCSL Station 6057+00 and 6098+00 (Kleinfelder, 2016b) and met criteria at a higher WSE than the 2024 WSE. No past performance issues were documented in this area. Kleinfelder performed construction testing and observation on the RSCL levee raise (Kleinfelder, 2003).

Based on review of the existing site conditions, past performance history, seepage and stability analyses, and topography, the presence of the bridge foundation and floodwalls do not present a gap. Therefore, it is Kleinfelder’s opinion that the Rio Linda bridge foundation interface meets the geotechnical requirements of ULDC 7.9 Interfaces and Transitions.

2.6.5 Interface of a Sacramento Northern Bike Trail Near RCSL Station 6090+50 Kleinfelder performed a site visit in May 2024 and observed the Sacramento Northern Bike Trail that crosses RCSL at approximate Station 6090+50. The bike trail is an asphalt concrete paved trail that crosses RCSL at the crest and is the former Sacramento Northern railroad embankment. Seepage and stability analyses were performed at RCSL Station 6098+00 (Kleinfelder, 2016b) and met criteria at a higher WSE than the 2024 WSE. No past performance issues were documented in this area. 24001006.001A/SAC24R169107_R2 Page 30 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
Based on review of the existing site conditions, past performance history, seepage and stability analyses, and topography, the presence of the bike trail does not present a gap. Therefore, it is Kleinfelder’s opinion that the Sacramento Northern Bike Trail interface meets the geotechnical requirements of ULDC 7.9 Interfaces and Transitions.

2.6.6 Transition of a Dry Creek Road at RCSL Station 6118+20 to High Ground Kleinfelder performed a site visit in May 2024 and observed the end of RCSL at Station 6118+20 at Dry Creek Road. The ground surface elevation begins to rise upstream of RCSL Station 6055+00 until it matches the ground at Dry Creek Road. No past performance issues were documented in this area.

Based on review of the existing site conditions, past performance history, seepage and stability analyses, and topography, the presence of the transition to Dry Creek Road does not present a gap. Therefore, it is Kleinfelder’s opinion that the transition of Dry Creek Road meets the geotechnical requirements of ULDC

7.9 Interfaces and Transitions.

2.6.7 Interface of UPRR Embankment along the landside slope of NEMDCEL The UPRR embankment spans the entire length of NEMDCEL from Stations 3056+00 to 3192+25. The embankment was estimated to be constructed in the early 1900’s prior to the levee construction in the 1950’s. The embankment was believed to be constructed with local materials similar to the materials used to construct NEMDCEL. The UPRR embankment was approximately 9 feet below the NEMDCEL crest (between an elevation of 34 and 36) and had a landside slope between 2H:1V and 3H:1V. The UPRR embankment geometry was included in the seepage and stability analyses that met criteria. During the May 2024 site visit, no significant issues were observed (i.e., erosion or changes to the embankment configuration). No past performance issues have been noted along this interface, with the exception of seepage observed exiting from the toe of the UPRR embankment near the intersection of NEMDCEL with ACNL. The seepage was addressed by the drained stability berm constructed in 2025, which is discussed in Section 2.6.12.

Based on review of the existing site conditions, past performance history, and seepage and stability analyses, the interface of the UPRR embankment does not present gaps or other three-dimensional effects. Therefore, it is Kleinfelder’s opinion that the transition meets the geotechnical requirements of ULDC 7.9 Interfaces and Transitions.
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2.6.8 Interface of San Juan Road/Silver Eagle Road Bridge Foundation at NEMDCEL Stations 3090+00 to 3091+00
Kleinfelder performed a site visit in May 2024 and observed the San Juan Road/Silver Eagle Road Bridge approximately between Stations 3090+00 to 3091+00. The bridge spanned the NEMDC channel with the eastern abutment offset approximately 130 feet from the UPRR embankment toe. The bridge supports were spaced approximately 126 feet apart and consisted of two approximately 4-foot diameter concrete columns. According to 1984 construction records from Caltrans, the columns rested on a pile cap that is 9 by 12 feet supported by twelve cast-in-drilled-hole (CIDH) piles. The CIDH piles were installed approximately 30 to 20 feet below the footing depth. One set of columns was located on the UPRR embankment crest. Another set was located approximately 30 feet west of the waterside ACNL toe. No as-built drawings were found as a part of the document review. CVFPB Permit Number 13580 was reviewed. CVFPB performed inspections of the construction which took place between 1984 and 1985.

Based on the information from the permit, an existing timber bridge was removed except for the concrete footings, and the new bridge was constructed. Based on the CVFPB inspector field observations, NEMDCEL was degraded for installation of the bridge foundation, and the levee was restored by compacting layers of soil. Seepage and stability analyses were performed at NEMDCEL Station 3080+00 (Kleinfelder, 2016b) with similar stratigraphy to 3090+00 and met criteria at a higher WSE than the 2024 WSE. No past performance issues were documented in this area.

Based on review of the existing site conditions, past performance history, seepage and stability analyses, and topography, the presence of the bridge foundation does not present a gap. Therefore, it is Kleinfelder’s opinion that the San Juan Road/Silver Eagle Road Bridge foundation and pile interfaces meet the geotechnical requirements of ULDC 7.9 Interfaces and Transitions.

2.6.9 Interface of Interstate 80 Bridge Foundations at Approximately Between NEMDCEL Stations 3132+00 and 3134+00
The Interstate 80 bridge located approximately between NEMDCEL Stations 3132+00 and 3134+00 was built as two bridges in 1968 under CVFPB permit #5649. The CVFPB Permit #5649 includes construction inspection records that document the construction, compaction of the degraded levee, and removal of falsework used to support construction. As-built records of the 1968 construction along with foundation design reports were reviewed from Caltrans’ GeoDog website(https://geodog.dot.ca.gov/). The 1968 bridges piles were step-tapered-steel shells filled with concrete and driven to approximate elevations of - 3 to -20 feet according to the construction records. The Interstate 80 bridges were expanded in 2010 under CVFPB Permit #18614. The expansion included construction of a 42-foot-wide median bridge 24001006.001A/SAC24R169107_R2 Page 32 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
supported by seven pairs of 3-foot diameter columns joining the two existing bridges. The columns were supported by a 12- by 12- by 3-foot thick footings supported by H piles. The H piles had a design tip of approximately between elevation -27 and -52 feet according to the Caltrans foundation design report (Caltrans, 2008). CVFPB Permit #18614 does not include construction documentation; therefore, construction plan sheet excerpts for the 2010 bridge expansion from Caltrans’ GeoDog website were reviewed.

Kleinfelder performed a site visit in May 2024 and observed the Interstate 80 bridge. The bridge spans the NEMDC channel with the eastern abutment embankment toe approximately 150 feet from the UPRR embankment toe. The bridge supports were spaced approximately 100 feet apart and consisted of a row of four concrete columns that were on pile supported footings. Three rows of four bridge support columns were located at the waterside levee toe, landside slope, and landside toe.

Seepage and stability analyses were performed at NEMDCEL Station 3133+00 (URS, 2014) and met criteria at a higher WSE than the 2024 WSE. No past performance issues were documented in this area.

Based on review of the existing site conditions, past performance history, seepage and stability analyses, and topography, the presence of the bridge foundation does not present a gap. Therefore, it is Kleinfelder’s opinion that the Interstate 80 bridge foundation interface meets the geotechnical requirements of ULDC 7.9 Interfaces and Transitions.

2.6.10 Interface of Sump Station No 157 at NEMDCEL Station 3132+00 Kleinfelder performed a site visit in May 2024 and observed Sump Station No. 157 at the landside toe of NEMDCEL near Station 3132+00. The sump station has a northern outlet structure with three 54-inch diameter welded steel outlet pipes and a southern outlet structure comprised of four 54-inch by 54-inch reinforced concrete box culverts. The southern outlet structure was identified on the USACE 1954 as-built plans (USACE, 1954) as the Magpie Creek Drainage Structure and consisted of a landside wet well and pumps with four outlet box culverts that pass through the levee with sliding gate valves with actuators that extend to the levee crest. The northern outlet structure was constructed in 1974 by the City of Sacramento under CVFPB Permit #9596A and consisted of three 54-inch diameter pipes, of which only the southerly two have been installed through the levee, that passed up and over NEMDCEL with an approximate invert elevation of 38.8 feet (USED Datum) at the levee crest. A siphon breaker vault was situated on the waterside levee crest.
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The sump station included a sump that was a concrete lined ditch approximately 150 feet landward of the projected NEMDCEL toe. There were pressure relief valves in the bottom of the concrete lined ditch to relieve any pressure that may build up under the concrete lining during high water events in the NEMDC.

Seepage and stability analyses that included the ditch were performed at NEMDCEL Station 3133+00 (URS, 2014) and met criteria at a higher WSE than the 2024 WSE. No past performance issues were documented in this area.

Based on review of the existing site conditions, past performance history, seepage and stability analyses, and topography, the presence of Sump Station 157 does not present a gap. Therefore, it is Kleinfelder’s opinion that the Sump Station 157 interface meets the geotechnical requirements of ULDC 7.9 Interfaces and Transitions.

2.6.11 Interface of Del Paso Road /Main Avenue Bridge at NEMDCEL Stations 3184+00 to 3185+00 Kleinfelder performed a site visit in May 2024 and observed the Main Avenue bridge approximately between Stations 3184+00 and 3185+00. The bridge spanned the NEMDC channel with the eastern abutment embankment toe approximately 500 feet east of the UPRR embankment toe. The bridge supports were spaced approximately 100 feet apart and consisted of a row of three concrete columns.

The bridge replaced an existing timber pile bridge in 2004 to 2005 and the existing bridge was removed under CVFPB Permit #17818. Seepage and stability analyses were performed at NEMDCEL Station 3185+00 and met criteria at a higher WSE than the 2024 WSE. No past performance issues were documented in this area.

Based on review of the existing site conditions, past performance history, seepage and stability analyses, and topography, the presence of the bridge foundation does not present a gap. Therefore, it is Kleinfelder’s opinion that the Main Avenue bridge foundation interface meets the geotechnical requirements of ULDC 7.9 Interfaces and Transitions.

2.6.12 Interface of ACNL and NEMDCEL Drained Stability Berm In 2017 through 2023, seepage was noted exiting from the UPRR embankment toe where NEMDCEL intersected ACNL. Kleinfelder performed multiple investigations to identify the source of the seepage; however, the source was not definitively identified. Kleinfelder and MBK designed a drained stability berm to provide a filtered exit for the seepage and to reinforce ACNL and NEMDCEL. Kleinfelder prepared a geotechnical basis of design report with analysis at the DWSE (Kleinfelder, 2024a). The analysis was performed at the DWSE of 39.9 feet which is lower than the 2024 HTOL of 40.44 feet. The exit gradients 24001006.001A/SAC24R169107_R2 Page 34 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
in the seepage analysis are below 0.10 at the toe of the drained stability berm and factor of safety for stability are above 1.8 for the analyzed DWSE of 39.9 feet, which was inferred to meet seepage criteria for the 2024 HTOL.

The drained stability berm was constructed in 2025 by SAFCA; Kleinfelder provided Quality Assurance observation and testing during construction (Kleinfelder, 2025). The drainage portion of the berm consisted of sand and gravel layers and PVC drainpipes, which were covered by engineered fill that was used to construct the rest of the berm. As-built documentation and field and laboratory testing results are summarized in the MBK project completion report (MBK, 2025).

2.6.13 Transition of UPRR Stop log Structure at ACNL Station 5000+40 The stop log structure was originally constructed after it was reported a sandbag closure along ACNL was overtopped during a highwater event in 1986. The stop log structure was retrofitted to accommodate a levee raise in 1997 (Spink, 1997). Kleinfelder performed seepage and stability analyses of the embankment adjacent to the stop log structure (Kleinfelder, 2024a). The analyses were performed at the DWSE of 39.9 feet which is lower than the 2024 HTOL of 40.44 feet. The exit gradients in the seepage analysis are below 0.10 at the toe of the drained stability berm and factor of safety for stability are above

2.0 for the analyzed DWSE of 39.9 feet which can be inferred to meet seepage criteria for the 2024 HTOL.

The 1986 stop log structure construction was covered by CVFPB Permit #14479.

Based on review of the existing site conditions, past performance history, and seepage and stability analyses, the transition between ARNL and the UPRR stop log structure do not present gaps or other three-dimensional effects. Therefore, it is Kleinfelder’s opinion that the transitions between ARNL and the UPRR stop log structure walls meet the geotechnical requirements of ULDC 7.9 Interfaces and Transitions.

2.6.14 Transition of ACNL Landside Toe Relief Wells to ACNL Station 5023+00 Kleinfelder evaluated ACNL in the 2016 PIR by developing reaches based on stratigraphy and levee geometry. ACNL Stations 5000+00 to 5023+00 is characterized as consisting of a clayey sand levee embankment, clay blanket, and an approximately 6-foot-deep landside toe ditch. Upstream of Station 5023+00, the landside ditch gradually deepened to a depth of approximately 13 feet towards a sump station wet well, the blanket layer thinned, and the underlying aquifer contained more permeable sands.

The 2016 ULDC GRS and PIR seepage analysis at Station 5031+00 showed excessive seepage gradient build-up in the landside ditch. Based on this, Kleinfelder cited ACNL upstream of 5023+00 did not meet 24001006.001A/SAC24R169107_R2 Page 35 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
ULDC criteria. Therefore, SAFCA constructed relief wells in 2020 (SAFCA, 2020) along the landside toe of ACNL between Stations 5023+00 and 5031+25 that were designed by USR (AECOM) (URS, 2016). The relief well spacing was 85 feet, with the first relief well installed at Station 5023+00. The reach boundary at Station 5023+00 was centered on Boring KS-NAS12-012B which had generally consistent stratigraphy with the analytical cross section of Station 5003+00, which met ULDC seepage criteria at a higher WSE than the 2024 WSE.

Therefore, it is Kleinfelder’s opinion that the transition between ACNL Station 5023+00 and the 85-foot spaced relief wells continuing east up-station meets the geotechnical requirements of ULDC 7.9 Interfaces and Transitions.

2.6.15 Geotechnical Evaluation of Swimming Pools at or Near the Landside Toe No swimming pools were present within the landside levee easement. However, swimming pools near the landside levee toe can locally reduce the fine-grained blanket layer thickness and create a potential point of weakness for underseepage. Therefore, a review of swimming pools was performed. This evaluation was performed as outlined below.

1. A review of Google Earth aerial images was performed to locate swimming pools at or near the landside levee toe.

2. If identified, the distance of the swimming pool from the landside levee toe was measured.

3. The nearest seepage analysis was then reviewed. After adjusting the analyzed WSE for the 2024 200-yr WSE, the seepage analysis was used to calculate the exit gradients across the blanket layer at the bottom of the pool for full pool and empty pool scenarios as follows:
a. Empty Pool Average Exit Gradient: The average gradient is measured across the blanket layer at the bottom of the pool (assumed to be 7 feet deep) with the total head assumed to be equal the ground surface elevation at the bottom of the pool. b. Full Pool Average Exit Gradient: The average gradient is measured across the blanket layer at the bottom of the pool (assumed to be 7 feet deep) with the total head assumed to be equal the ground surface elevation adjacent to the pool.

4. The measured distance from the landside levee toe was compared to California Code of Regulations Title 23 and USACE Geotechnical Levee Practice Setback Guidance (May 2022). 24001006.001A/SAC24R169107_R2 Page 36 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
No swimming pools were identified along the ACNL or NEMDCEL. Six pools were identified outside of the landside levee easement on the RCSL and are summarized in Table 2.7 for the 2024 200-Year DWSE and Table 2.8 for the HTOL DWSE, below.
24001006.001A/SAC24R169107_R2 Page 37 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
Table 2.7
Swimming Pool Geotechnical Review Summary - 2024 200-Year DWSE USACE (2022)
Geotechnical Levee
Practice Setback
Requirements
Revised Average Exit Gradient
at bottom of Pool
Pool No./
Kleinfelder
Analysis
Reach
(2016a
and
2016b)
Station
at Pool
Location
Distance
from LS
Levee
Toe (ft)
Representative
Analysis Cross
Section
Ground
Surface
Elevation
Adjacent
to Pool,
Google
Earth (ft,
NAVD88)
Meets
Title 23
Minimum
10-ft
Setback?
Meets
Minimum
20-ft
Setback?
Meets
Minimum
10 x Pool
Depth
Setback?
2024
200-
Year
DWSE
(ft)
Blanket
Layer
Thickness
(ft)
Total
Head at
Bottom
of
Blanket
at Pool
Location
Gradient
at Pool
Location
[Full
Pool]
Gradient
at Pool
Location
(Empty
Pool)
Allowable
Gradient
RCSL-1/
DCSL-21
6027+00 32 6016+00 36 Yes Yes No 41.3 21.3 40.3 0.41 1.092 0.56 RCSL-2/
DCSL-2 6047+00 130 6057+00 40 Yes Yes Yes 41.3 32 36.7 <0.1 0.15 0.76 RCSL-3/
DCSL-2 6047+50 30 6057+00 40 Yes Yes No 41.3 32 36.7 <0.1 0.15 0.56 RCSL-4/
DCSL-2 6050+00 30 6057+00 40 Yes Yes No 41.3 32 36.7 <0.1 0.15 0.56 RCSL-5/
DCSL-2 6052+00 35 6057+00 40 Yes Yes No 41.3 32 36.7 <0.1 0.15 0.56 RCSL-6/
DCSL-3 6108+00 Above Ground Swimming Pool, No Impact
1- DCSL-Dry Creek South Levee, which was used for the RCSL in the GDR (Kleinfelder, 2013) and PIR (Kleinfelder, 2016a) 2- The exit gradient for the pool empty condition does not meet allowable gradient criteria. The gradient for the pool full condition meets. 24001006.001A/SAC24R169107_R2 Page 38 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
Table 2.8
Swimming Pool Geotechnical Review Summary - 2024 HTOL DWSE USACE (2022)
Geotechnical Levee
Practice Setback
Requirements
Revised Average Exit Gradient
at bottom of Pool
Pool No./
Kleinfelder
Analysis
Reach
(2016a
and
2016b)
Station
at Pool
Location
Distance
from LS
Levee
Toe (ft)
Representative
Analysis Cross
Section
Ground
Surface
Elevation
Adjacent
to Pool,
Google
Earth (ft,
NAVD88)
Meets
Title 23
Minimum
10-ft
Setback?
Meets
Minimum
20-ft
Setback?
Meets
Minimum
10 x Pool
Depth
Setback?
2024
HTOL
DWSE
(ft)
Blanket
Layer
Thickness
(ft)
Total
Head at
Bottom
of
Blanket
at Pool
Location
Gradient
at Pool
Location
[Full
Pool]
Gradient
at Pool
Location
(Empty
Pool)
Allowable
Gradient
RCSL-1/
DCSL-21
6027+00 32 6016+00 36 Yes Yes No 42.9 21.3 41.9 0.57 1.242 0.66 RCSL-2/
DCSL-2 6047+00 130 6057+00 40 Yes Yes Yes 42.9 32 38.3 <0.1 0.22 0.86 RCSL-3/
DCSL-2 6047+50 30 6057+00 40 Yes Yes No 42.9 32 38.3 <0.1 0.22 0.66 RCSL-4/
DCSL-2 6050+00 30 6057+00 40 Yes Yes No 42.9 32 38.3 <0.1 0.22 0.66 RCSL-5/
DCSL-2 6052+00 35 6057+00 40 Yes Yes No 42.9 32 38.3 <0.1 0.22 0.67 RCSL-6/
DCSL-3 6108+00 Above Ground Swimming Pool, No Impact
1- DCSL-Dry Creek South Levee, which was used for the RCSL in the GDR (Kleinfelder, 2013) and PIR (Kleinfelder, 2016a) 2- The exit gradient for the pool empty condition does not meet allowable gradient criteria. The gradient for the pool full condition meets. 24001006.001A/SAC24R169107_R2 Page 39 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
Based on review of the RCSL swimming pools, the swimming pools evaluated meet allowable gradient criteria if the swimming pools are full and four of the five swimming pools meet criteria if they are empty.

One swimming pool, RCSL-1 located 32 feet from the landside levee toe, does not meet criteria if it is empty. The Department of Water Resources pre and post flood season inspection checklist includes evaluation of residential pools. It is recommended that swimming pools be noted as features of interest during levee inspections and levee patrols.

2.6.16 Conclusion
Based upon the above information, it is Kleinfelder’s opinion that the interfaces and transitions described above meet the geotechnical requirements of ULDC (DWR, 2012) Section 7.9 Interfaces and Transitions.

2.7 ULDC SECTION 7.14 FLOODWALLS, RETAINING WALLS, AND CLOSURE STRUCTURES There were two floodwalls located along RCSL at either side of the Rio Linda Bridge abutment. Two closure structures (stop logs) were located along RCSL at Station 6000+00 and ACNL at Station 5000+40. Two sump stations were located along the subject levees. Sump plant No. 157 was located at NEMDCEL Station 3132+00 and Sump Plant No. 140 was located at RCSL Station 6032+00.

This evaluation included review of the construction details of specific structures in relation to the geotechnical aspects of slope stability and seepage as applicable to current ULDC criteria. The potential for future settlement was also considered in the evaluation of each structure. The structural integrity of the structures was evaluated by Mead and Hunt and not by Kleinfelder. This evaluation has not included performance of new analysis or field investigation. Where available, construction inspection records were reviewed.

2.7.1 Sump Station No 157 at NEMDCEL Station 3132+00
Kleinfelder performed a site visit in May 2024 and observed Sump Station No. 157 at the landside toe of NEMDCEL near Station 3132+00. The sump station had a northern outlet structure with three 54-inch diameter welded steel outlet pipes and a southern outlet structure comprised of four 54-inch by 54-inch concrete box culverts.

The southern outlet structure was identified on the USACE 1954 as-built plans (USACE, 1954) as the Magpie Creek Drainage Structure and consisted of a landside wet well and pumps with four 54-inch by 54-inch reinforced concrete box culvert outlets that passed through the levee with sliding gate valves with 24001006.001A/SAC24R169107_R2 Page 40 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
actuators that extended to the levee crest. The outfall structure included a retaining wall where the pipes exit out the levee waterside toe.

The northern outlet structure was constructed in 1974 by the City of Sacramento under CVFPB Permit #9596A and consisted of three 54-inch diameter pipes, of which only the southerly two have been installed through the levee, that passed up and over NEMDCEL with an approximate invert elevation of

38.8 feet (USED Datum) at the levee crest. A siphon breaker vault was situated on the waterside levee crest. The outfall structure included a retaining wall where the pipes exit out the levee waterside toe.

The NEMDCEL raise in 1995 included installation of a retaining wall along the waterside hinge. The retaining wall consisted of three separate sections including a southern section located south of the southern outlet slide gate structure, middle section located between the southern slide gate structure and northern outlet siphon breaker box, and northern section located north of the northern outlet siphon breaker box. The wall ranged between 3 ½-feet to 6 ½-feet and was anchored to the concrete vaults of the siphon breaker box and slide gate structure.

The sump station included a sump that was a concrete lined ditch approximately 150 feet landward of the projected NEMDCEL toe. There were pressure relief valves in the bottom of the concrete lined ditch to relieve any pressure that may build up under the concrete lining during high water events in the NEMDC.

The sump station pipes were equipped with mechanical closure devices. Evaluation of the mechanical and structural properties of the sump station was performed by Mead and Hunt in 2024. Based on review of as-built drawings and site visit, Kleinfelder concluded that the sump station embankment fill was placed and compacted against all sides of the sump station structure. Kleinfelder performed observation and testing during construction of the 1997 levee raise and this testing indicated fill construction met compaction criteria (Kleinfelder, 1997b). Backfill of the sump station structures did not utilize permeable soils (Kleinfelder, 1997b).

Seepage and stability analyses that included the ditch were performed at NEMDCEL Station 3133+00 (URS, 2014) and met criteria at a higher WSE than the 2024 WSE. No past performance issues were documented in this area. There was no reported distress from the 1997 high water event or more recent high-water events from 2002, 2004, 2005, 2006, 2017, or 2023.

Therefore, it is Kleinfelder’s opinion that backfill placed for the sump station meets the geotechnical requirements of ULDC for seepage and slope stability. Structures associated with the sump station that are in or on the levee have been in place since they were constructed in the late 1950s, 1974, and 1997; therefore, it is unlikely these structures will induce additional settlement of the levee embankment. 24001006.001A/SAC24R169107_R2 Page 41 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025

2.7.2 Sump Station No. 140 at RCSL Approximately Between Station 6032+00 Kleinfelder reviewed the levee construction as-built drawings (SAFCA, 2001) for the Sump Station 140 approximately between Station 6032+00. The sump station improvements were performed in 1997 when SAFCA raised RCSL. Sump Station 140 includes three 36-inch diameter and one 20-inch diameter welded steel pipes that were buried sloping up the landside and waterside slopes and across the RCSL crest at an approximate invert elevation of 43 feet. A retaining wall with a maximum height of 8-feet was located at the landside toe and the pipes pass through the wall through the foundation. The sump station was located within a Kleinfelder analysis reach between RCSL Stations 6011+50 to 6053+00. The seepage and slope stability analyses performed at Stations 6012+00 and 6016+00 met criteria for seepage and slope stability for higher HTOLs with more critical levee geometry. Based on review of as-built drawings and site visit, Kleinfelder concludes that the sump station embankment fill was placed and compacted against all sides of the sump station structure. Kleinfelder performed observation and testing during construction and this testing indicated fill construction met compaction criteria (Kleinfelder, 1997b). Backfill of the sump station structures did not utilize permeable soils (Kleinfelder, 1997b). There was no reported distress from the 1997 high water event or more recent high-water events from 2002, 2004, 2005, 2006, 2017, or 2023. Evaluation of the mechanical and structural properties of the sump station was performed by Mead and Hunt in 2024.

Therefore, it is Kleinfelder’s opinion that backfill placed for the sump station meets the geotechnical requirements of ULDC for seepage and slope stability. Structures associated with the sump station that are in or on the levee have been in place since the sump station was reconstructed in 1997; therefore, it is unlikely these structures will induce additional settlement of the levee embankment.

2.7.3 UPRR Closure Structures (RCSL at Station 6000+00 and ACNL Station 5000+40) The stop log structure across the UPRR tracks located at the intersection of NEMDCEL and RCSL was originally constructed under Central Valley Flood Protection Board (CVFPB) Permit #14477. The stop log structure was retrofitted and raised to accommodate a levee raise in 1995 (Spink, 1995b). The stop log structure was comprised of two retaining walls parallel to the UPRR tracks that were connected by a 6- foot-long by 4-foot-tall concrete filled box culvert beneath the tracks. The railroad tracks and ballast were constructed over the box culvert resulting in an approximately 16-foot-wide by 9-inch-thick layer of ballast between the top of a box culvert and the bottom of the railroad ties. The box culvert acts as a cutoff by extending between the retaining wall footings. According to as-built drawings (1995a, Spink) the box culvert was placed on a 4-inch-thick non-shrink grout base and compacted native UPRR embankment fill.

The elevation at the top of the UPRR tracks is approximately 36.4 feet. The 2024 200-year DWSE and HTOL 24001006.001A/SAC24R169107_R2 Page 42 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
at Station 6000+00 are 41.19 feet and 42.78 feet, respectively. The stop log structure would have approximately 5 to 6 1/2 feet of water against the structure. Based on the 2022 Union Pacific Railroad Stoplog Installation and Del Paso Floodgate Closure memorandum prepared by Mead and Hunt (2022, Mead and Hunt), sandbags are tucked between the rails and the concrete grade beam. A rubber bottom seal is secured between the bottom of stop log plank and the top of the concrete grade beam. Based on the 9-inch section of ballast between the bottom of the tracks and the top of the box culvert, some seepage along the ballast at this location is expected, which would be collected by drainage ditches and conveyed to the internal drainage system. The area should be monitored for excessive seepage and/or if the seepage becomes cloudy indicative of soil material erosion.

The UPRR stop log structure located along NEMDCEL at the intersection of ACNL was constructed with a 12-inch-wide cutoff wall crossing beneath the tracks extending a minimum of 3-feet below the ballast between the retaining walls.

The retaining walls at both stop log structures were backfilled with compacted embankment fill (Kleinfelder, 1997a, b). The construction of this closure structure was evaluated for geotechnical considerations related to slope stability and seepage at the transition from the levee to the UPRR closure structure and retaining walls (both sides) during a flood event. Kleinfelder visited the site and reviewed the UPRR stop log structure drawings (Spink, 1997 and 1995). Evaluation of the structural properties of the closure structure was performed by Mead and Hunt (Mead & Hunt, 2024). As-built drawings show that the requirement for pervious backfill behind the retaining walls was removed from the project plans during construction. We understand compacted embankment fill was placed against the retaining walls.

A ballast layer between the tracks and the underlying concrete slab is present to approximately a few inches thick below the railroad ties. During the 200-year DWSE event, the ACNL stop log structure will have approximately 1 ½ feet of water and the RCSL stop log structure will have approximately 5 feet of water retained by the stop log structure. We expect minor seepage to occur through the thin layer of ballast not cutoff by the concrete pad or cutoff wall. Therefore, it is Kleinfelder’s opinion that backfill placed for the retaining walls meets the geotechnical requirements of ULDC for seepage and slope stability. Further, minor through seepage around the ballast may occur, but is not considered a threat to the levee. These structures have been in place since 1986 and were enlarged in 1997; therefore, it is unlikely these structures will induce additional settlement of the underlying levee embankment.

2.7.4 Floodwalls at Rio Linda Boulevard Bridge Abutment In the early 2000’s, two floodwalls on either side of the Rio Linda Bridge abutment were constructed as a part of the SAFCA project to raise RCSL. According to the as-built drawings, the floodwalls extended 5 feet 24001006.001A/SAC24R169107_R2 Page 43 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
into the levee embankment and were supported on continuous spread footings embedded approximately 2 feet below the ground surface. The top of the floodwalls matched the top of levee at Elevation 47.4 feet.

The minimum top of levee at the base of the floodwalls was Elevation 45.7 feet according to the record drawings. The 2024 HTOL at Station 6081+00 is 43.54 feet, which is over 2 feet below the floodwall base.

The walls were evaluated by Mead and Hunt for structural integrity.

Seepage and stability analyses were performed at RCSL Station 6057+00 and 6098+00 (Kleinfelder, 2016b) and met criteria at a higher WSE than the 2024 WSE. No past performance issues were documented in this area. Kleinfelder performed construction testing and observation on the RSCL levee raise (Kleinfelder, 2003). These structures have been in place since the early 2000s; therefore, it is unlikely these structures will induce additional settlement of the underlying levee embankment.

2.7.5 Conclusion
Based upon the above data, Kleinfelder makes the following conclusions pertaining to ULDC 7.14 Floodwalls, Retaining Walls, and Closure Structures:
• Sump Station retaining walls meet the geotechnical requirements of ULDC for settlement, seepage and slope stability
• UPRR closure structure and retaining walls meet the geotechnical requirements of ULDC for settlement, seepage and slope stability
• Rio Linda Boulevard Bridge flood walls meet the geotechnical requirements of ULDC for settlement, seepage and slope stability
It should be noted that Kleinfelder did not evaluate the structures as far as conformance with structural integrity, operations, or maintenance per ULDC. It is our understanding this evaluation will be performed by Mead and Hunt.
24001006.001A/SAC24R169107_R2 Page 44 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
3 ROBLA-ARCADE LEVEE STUDY AREA SUMMARY OF RESULTS
____________________________________________________________________________________ Based on the review summarized in Section 2, above, Table 3.1 includes those reaches that it is Kleinfelder’s opinion meet or do not meet the geotechnical aspects of ULDC (DWR, 2012) for Sections 7.3 Soil Sampling, Testing, and Logging; 7.4 Slope Stability; 7.5 Underseepage; 7.7 Seismic Vulnerability; 7.8 Levee Geometry; 7.9 Interfaces and Transitions; and 7.14 Floodwalls, Retaining Walls, and Closure Structures.

Table 3.1
Geotechnical Aspects of ULDC Criteria Levee Reach Summary Project Levee Approximate Levee
Stationing
Meets
Criteria
Does Not
Meet
Criteria
ULDC Criteria Section
RCSL 6000+00 to 6118+20 X

7.3 Soil Sampling, Testing, and Logging1

7.4 Slope Stability

7.5 Underseepage,

7.7 Seismic Vulnerability

7.8 Levee Geometry

7.9 Interfaces and Transitions

7.14 Floodwalls, Retaining Walls, and
Closure Structures
NEMDCEL 3056+00 to 3192+25 X

7.3 Soil Sampling, Testing, and Logging1

7.4 Slope Stability

7.5 Underseepage,

7.7 Seismic Vulnerability

7.8 Levee Geometry

7.9 Interfaces and Transitions

7.14 Floodwalls, Retaining Walls, and
Closure Structures
ACNL 5000+00 to 5023+00 X

7.3 Soil Sampling, Testing, and Logging1

7.4 Slope Stability

7.5 Underseepage,

7.7 Seismic Vulnerability

7.8 Levee Geometry

7.9 Interfaces and Transitions

7.14 Floodwalls, Retaining Walls, and
Closure Structures

1. Meets criteria through Exception. See Section 2.1 for discussion of the exception.

It is Kleinfelder’s opinion that the subject levees outlined above meet the geotechnical aspects of ULDC (DWR, 2012) as outlined in Table 3.1, above.
24001006.001A/SAC24R169107_R2 Page 45 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
4 LIMITATIONS
____________________________________________________________________________________ This work was performed in a manner consistent with that level of care and skill ordinarily exercised by other members of Kleinfelder’s profession practicing in the same locality, under similar conditions and at the date the services are provided. The work performed was based on project information provided by client. Kleinfelder’s conclusions, opinions, and recommendations are based on a limited number of observations and data. It is possible that conditions could vary between or beyond the data evaluated.

Kleinfelder makes no other representation, guarantee, or warranty, express or implied, regarding the services, communication (oral or written), report, opinion, or instrument of service provided.

This report may be used only by the client and the registered design professional in responsible charge and only for the purposes stated for this specific engagement within a reasonable time from its issuance, but in no event later than two years from the date of the report.

Conclusions contained in this report are based on review of existing information referenced in this report and Kleinfelder’s present knowledge of the project. It is possible conditions could vary from that contained in those documents. If conditions are encountered that differ from those described herein, the client is responsible for ensuring that Kleinfelder is notified immediately so that we may reevaluate the conclusions of this report.

The scope of services was limited. It should be recognized that definition and evaluation of subsurface conditions are difficult. Judgments leading to conclusions and recommendations are generally made with incomplete knowledge of the subsurface conditions present due to the limitations of data from field studies. The conclusions of this assessment are based on the information presented herein. Although risk can never be eliminated, more detailed and extensive studies yield more information, which may help understand and manage the level of risk.

All rivers, streams and lakes will flood eventually. This fact means that all levees will be called upon to combat floodwaters at some point. Levees reduce the risk of flooding. But no levee system can eliminate all risk of flooding. The term “certification” is not intended to provide a guarantee or warranty of the conditions of the levee or its performance and assumes the following 1) a certification by a registered professional engineer or other party does not constitute a warranty or guarantee of performance, expressed or implied; 2) certification of data is a statement that the data is accurate to the best of the certifier’s knowledge; and 3) certification of analyses is a statement that the analyses have been 24001006.001A/SAC24R169107_R2 Page 46 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
performed correctly and in accordance with sound engineering practices. A levee certification does not address or mitigate the inherent flood risk proposed to a particular community. 24001006.001A/SAC24R169107_R2 Page 47 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
5 REFERENCES
____________________________________________________________________________________ Department of Water Resources, California, 2012, “Urban Levee Design Criteria”, State of California, Department of Water Resources, May 2012.

Department of Water Resources, California, 2015. “ Guidance Document for Geotechnical Analyses, Urban Levee Geotechnical Evaluations Program.” Dated April 27, 2015.

California Department of Transportation (Caltrans), 1967. “Natomas East Canal Bridge and Overhead, Log of Test Borings.” Drawing. Dated October 5, 1966. Approved August 21, 1967.

Caltrans, 1969. “Natomas East Canal O, Bridge and O.H., Br. No. 24-218 R/L. Pile Foundation, Field Report of Foundation Conditions.” Dated February 18, 1969.

Caltrans, 2008. “Foundation Report for Infill Walls.” File 03-SAC-80-PM M5.21, Natomas East Canal Bridge BOH, (Seismic Retrofit-Infill Walls), Br. No. 24-0218, EA#03-379701. Dated October 15, 2008.

Department of Water Resources, 2019. “Central Valley State-Federal Flood Protection System, 2019 Inspection and Local Maintaining Agency Report. Appendix G.” Dated 2019.

Kleinfelder, 1994, “Geotechnical Evaluation of Proposed Levee Improvements Dry Creek Levees.” Dated June, 1994.

Kleinfelder, 1997. “Final Report, Final Compaction Test Results, Pump Station, NEMDC – Units 2A/3C, and Robla Units 1B/1C, Sacramento, California.” Dated March 3, 1997.

Kleinfelder, 2003. “Compaction Test Results and Geotechnical Evaluation, Robla Creek and NEMDC West Levee Improvements, Rio Linda, California.” Dated March 14, 2003.

Kleinfelder, 2013. “Geotechnical Data Report, North Area Streams, SAFCA FEMA Levee Accreditation (North Area Streams, American River, Sacramento River Downstream of American River, and Beach Lake Levee).” Dated May 31, 2013
Kleinfelder, 2016a, “Problem Identification Report, North Area Streams, SAFCA FEMA Levee Accreditation (North Area Streams, American River, Sacramento River Downstream Of American 24001006.001A/SAC24R169107_R2 Page 48 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
River, and Beach Lake Levee). Sacramento County.” Dated September 18, 2013. Revised April 29, 2016.

Kleinfelder, 2016b, “ULDC Geotechnical Results Summary, North Area Streams, SAFCA FEMA Levee Accreditation (North Area Streams, American River, Sacramento River Downstream of American River, and Beach Lake Levee), Sacramento County.” Dated April 26, 2016.

Kleinfelder, 2020. “Geotechnical Data Summary, Arcade Creek North Levee Explorations, Station 5005+50, SAFCA FEMA, Sacramento County, California.” Dated August 12, 2020.

Kleinfelder, 2024a. “Geotechnical Basis of Design Report, Drained Stability Berm Seepage Repair, Arcade Creek North Levee and NEMDC East Levee, Sacramento County, California,” Kleinfelder Project 00129289.002A. Dated April 15, 2024.

Kleinfelder, 2024b. “Seismic Performance Summary Report North Area Streams Levee Areas, ULDC & FEMA Levee Certification Project, Sacramento Area Flood Control Agency Levee Systems, Sacramento County, California.” Dated September 10, 2024.

Kleinfelder, 2025. “Quality Assurance Construction Observation Report, Arcade Creek North Levee and NEMDC East Levee, Drained Stability Berm, Sacramento County, California. Dated August 2025.

MBK, Engineers (MBK), 2024a. “Technical Memorandum - Robla-Arcade Levee System - Determination of the Urban Levee Design Criteria Design Water Surface Elevation, Minimum Top of Levee, and Hydraulic Top of Levee.” Dated November 18, 2024.

MBK, Engineers (MBK), 2024b. “Robla-Arcade Levee System: Geometry Analysis (ULDC)." Sheets 1 through 13. Dated June 2024.

MBK, Engineers (MBK), 2025. “Project Completion Report, Arcade-NEMDC Drained Stability Berm Project, Sacramento Area Flood Control Agency, Contract #4600013250.” Dated August 2025.

Mead & Hunt, 2014. “Sacramento Area Levee Recertification Project, Third Draft Report, Levees Covered: Dry Creek North, Robla Creek South, NEMDC North of I-80, Portions of American River North and South Levees, Certification Elements Covered: Levee Encroachments, Penetrations, Floodwalls, Closure Structures, Wind-wave action, O&M Manuals.” Dated January 2, 2014.

Mead & Hunt, 2015. “UPRR Stop Log Foundations.” March 25, 2015. 24001006.001A/SAC24R169107_R2 Page 49 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
Mead & Hunt, 2024. “Robla-Arcade Levee System, Due Diligence Review for ULDC & FEMA Certification.” Dated August 2024.

SAFCA, 2001, “Robla Creek South Levee, and NEMDC West Levee Improvement Project, Natomas Area Flood Control Improvements, Sacramento, California.” Prepared by Ensign & Buckley and Mead & Hunt. As-built drawing. Dated June 21, 2001.

SAFCA, 2020. “Sacramento Area Flood Control Agency, Project Plans for Construction of North Area Streams Levee Improvement Project, NEMDC East Levee – Sta 3028+00 to Sta 3053+00, Arcade Creek South Levee – Sta 4000+00 to Sta 4084+00, Arcade Creek North Levee – Sta 5023+00 to Sta 5101+00, Volume 2 of 3.” Record Drawings. Prepared by URS. Dated October 2020.

Spink Corporation, 1995a. “Natomas East Main Drainage Canal, Unit 3A Levee Improvement Project, (El Camino Avenue to Main Avenue) Volume IV of V, Sacramento Area Flood Control Agency, Project Plans for Construction of Natomas Area Flood Control Improvement Project, Sacramento California.” Sacramento Area Flood Control Agency. Record Drawings. Dated March 20, 1995.

Spink Corporation, 1995b. “Natomas East Main Drainage Canal, Units 2A & 3C Levee Improvement Project, (1800’ South of Main Avenue to 3600’ North of Main Avenue – Unit 2A) (Main Avenue to Robla Creek – Unit 3C), Sacramento Area Flood Control Agency, Project Plans for Construction of Natomas Flood Control Improvement Project, Sacramento California.” Conformed drawings.

Dated July 20, 1995.

Spink Corporation, 1996. “Natomas East Main Drainage Canal, Units 2B & 3B, Levee Improvement Project, (American River to West El Camino Avenue – Unit 2B), (American River to 1800’ North of Arcade Creek – Unit 3B), Sacramento Area Flood Control Agency Project Plans for Construction of Natomas Area Flood Control Improvement Project, Sacramento, California.” Record Drawings. As-Built Date May 13, 1996.

Spink Corporation, 1997b. “NEMDC East Levee Improvements, Unit 3B.” Sacramento Area Flood Control Agency. As-Built Drawings Sheets L-18, S-7, S-8 for UPRR Stop log Structure. Dated May 5, 1997.

United States of America 2011. “Title 44 of the Code of Federal Regulations (44 CFR) Section 65.10.” Dated October 1, 2011.

URS, 2009. “Phase 1 Geotechnical Data Report (P1GDR), Natomas East Main Drainage Canal (NEMDC) East Study Area, Urban Levee Geotechnical Evaluations Program, Contract 4600007418.” Dated March 2009.
24001006.001A/SAC24R169107_R2 Page 50 of 50 June 18, 2024 © 2025 Kleinfelder Revised August 22, 2025
URS, 2011. “Supplemental Geotechnical Data Report (SGDR), Natomas East Main Drainage Canal (NEMDC) East Study Area, Urban Levee Geotechnical Evaluations Program, Contract 4600007418.” Dated November 2011
URS, 2014. “Technical Memorandum, Drain Trench System Design along Reach NAS-NE-3 (City of Sacramento Sump No. 157 at Magpie Creek).” Dated November 11, 2014.

URS, 2015, “Geotechnical Evaluations Report, Volume 1, Existing Conditions, NEMDC East Study Area, Urban Levee Evaluations Project.” Prepared by URS for DWR. Dated March 2015.

URS, 2016. “Geotechnical Engineering Report for Project Design, North Areas Streams Levee Improvement Project,” Prepared for SAFCA. Dated August 2016.

USACE 1954. “Levee Construction, American River- Natoma Canal, Arcade Creek and Linda Creek, Sacramento River, California, Flood Control Project.” Magpie Creek Drainage Structure as-built drawings. Sheets 392/21.1, 392/22.1, 392/23. Dated December 1954.

USACE 2000, “Design and Construction of Levees. US Army Corps of Engineers, Engineer Manual, EM 1110-2-1913.” Dated April 30, 2000.

USACE 2005, “Design Guidance for Levee Underseepage, US Army Corps of Engineers, Technical Letter ETL 1110-2-569.” Dated May 1, 2005.

USACE 2022, “CESPK-EDG, SOP 3 Geotechnical Levee Practice, May 2022, Standard Operating Procedure 3, Geotechnical Levee Practice, US Army Corps of Engineers, Sacramento District, Geotechnical Engineering Branch.” Dated May 2022.

FIGURES
____________________________________________________________________________________

LIST OF ATTACHMENTS
Figure 1 Robla Creek South Levee, Arcade Creek North Levee, NEMDC East Levee Site Vicinity Map Figure 2 Robla Creek South Levee, Arcade Creek North Levee, NEMDC East Levee Site Location Map PROJECT:

FILE NAME:

FIGURE
1 DRAWN:

CHECKED BY:

The information included on this graphic representation has been compiled from a variety of sources and is subject to change without notice. Kleinfelder makes no representations or warranties, express or implied, as to accuracy, completeness, timeliness, or rights to the use of such information. This document is not intended for use as a land survey product nor is it designed or intended as a construction design document. The use or misuse of the information contained on this graphic representation is at the sole risk of the party using or misusing the information.

DRAWN BY:
24001006.001A
JUNE 2024
M. BESWICK
A. LEONARD
F1_ROBLA_ARCADE_SITE
Explanation
Levee Alignment
SACRAMENTO, CA FILE: \\azrgisstorp03\GIS_Projects\Client\SAFCA\24001006.001A-SeismicPerformanceSumReport\PRO\SAFECA_working\SAFECA_working.aprx

ULDC FINDING AND FEMA LEVEE

CERTIFICATION PROGRAM

SACRAMENTO AREA FLOOD CONTROL

AGENCY LEVEE SYSTEMS

SACRAMENTO AND SUTTER COUNTIES, CALIFORNIA
Service Layer Credits: USA_Topo_Maps: Copyright: © 2011 National Geographic Society, i-cubed; ESRI World Imagery, Maxar Vivid Advanded image dates 4/12/2022, 4/26/2022, and 5/4/2022; SACOG Orthos image date 3/18/2022.

ALeonard 6/4/2024
0 1 2
Miles
Locations are Approximate
SITE

ROBLA CREEK SOUTH LEVEE

ARCADE CREEK NORTH LEVEE

NEMDC EAST LEVEE

SITE VICINITY MAP
3060+00
3070+00
3080+00
3090+00
3100+00
3110+00
3120+00
3130+00
3140+00
3150+00
3160+00
3170+00
3180+00
3190+00
3030+00
3040+00
3050+00
6010+00
6020+00
6030+00
6040+00
6050+00
6060+00
6070+00
6080+00
6090+00
6100+00
5010+00
5020+00
5030+00
5040+00
5050+00
5060+00
5070+00
5080+00
5090+00
5100+00
5110+00
5010+00
5020+00
5030+00
5040+00
5050+00
5060+00
5070+00
5080+00
5090+00
5100+00
5110+00
6110+00
DCSL-1
DCSL-3
DCSL-2
ACNL-1
NEMDCEL-4
NEMDCEL-5
NEMDCEL-3
5003+00
3080+00
6098+00
6057+00
3137+50
3126+00
3133+00
3167+00
3185+00
6003+00
6012+50
6016+00
PROJECT:

FILE NAME:

FIGURE
2 DRAWN:

CHECKED BY:

The information included on this graphic representation has been compiled from a variety of sources and is subject to change without notice. Kleinfelder makes no representations or warranties, express or implied, as to accuracy, completeness, timeliness, or rights to the use of such information. This document is not intended for use as a land survey product nor is it designed or intended as a construction design document. The use or misuse of the information contained on this graphic representation is at the sole risk of the party using or misusing the information.

DRAWN BY:
24001006.001A
JUNE 2024
M. BESWICK
A. LEONARD
F2_ROBLA_ARCADE_REACH
Explanation
Critical Cross Section

RCSL/ACNL/NEMDCEL
RCSL/ACNL/NEMDCEL to be
Certified by Others
Service Layer Credits: World Transportation: Esri, HERE World Imagery: Maxar; ESRI World Imagery, Maxar Vivid
Advanded image dates 4/12/2022, 4/26/2022, and 5/4/2022; SACOG Orthos image date 3/18/2022.
0 750 1,500
Feet
Locations are Approximate

ULDC FINDING AND FEMA LEVEE

CERTIFICATION PROGRAM

SACRAMENTO AREA FLOOD CONTROL

AGENCY LEVEE SYSTEMS

SACRAMENTO AND SUTTER COUNTIES, CALIFORNIA

ROBLA CREEK SOUTH LEVEE

ARCADE CREEK NORTH LEVEE

NEMDC EAST LEVEE

LOCATION MAP
SACRAMENTO, CA FILE: \\azrgisstorp03\GIS_Projects\Client\SAFCA\24001006.001A-SeismicPerformanceSumReport\PRO\SAFECA_working\SAFECA_working.aprx ALeonard 6/4/2024

APPENDIX A
____________________________________________________________________________________

LIST OF ATTACHMENTS
MBK Engineers, 2024. “Technical Memorandum - Robla-Arcade Levee System - Determination of the Urban Levee Design Criteria Design Water Surface Elevation, Minimum Top of Levee, and Hydraulic Top of Levee.” Dated November 18, 2024.

Water Resources Flood Control Water Rights

TECHNICAL MEMORANDUM
DATE: November 18, 2024
PREPARED FOR: SAFCA
PREPARED BY: Michael Archer, P.E.

REVIEWED BY: Don Trieu, P.E.

SUBJECT: Robla-Arcade Levee System - Determination of the Urban Levee Design Criteria Design Water Surface Elevation, Minimum Top of Levee, and Hydraulic Top of Levee
SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 2

Acronyms and Abbreviations
1-D one dimensional
2-D two dimensional
AEP annual exceedance probability
ARN American River north
cfs cubic feet per second
CVFED Central Valley Floodplain Evaluation and Delineation CVFPP Central Valley Flood Protection Plan
CVHS Central Valley Hydrology Study
DWR California Department of Water Resources
DWSE Design Water Surface Elevation
FEMA Federal Emergency Management Agency
HTOL Hydraulic Top of Levee
LAR Lower American River
MBK MBK Engineers
MTOL Minimum Top of Levee
NAS North Area Streams
NAVD88 North American Vertical Datum of 1988
NEMDC Natomas East Main Drainage Canal
RM River Mile
SAFCA Sacramento Area Flood Control Agency
SNRR Sacramento Northern Railroad
SVRP Seismic Vulnerability Restoration Profile
ULDC Urban Levee Design Criteria
ULOP Urban Level of Flood Protection
UPRR Union Pacific Railroad
USACE U.S. Army Corps of Engineers
WSE water surface elevation

1. Purpose
The Sacramento Area Flood Control Agency (SAFCA) is in the process of evaluating the levees within its jurisdictional boundaries for compliance with the State of California’s Urban Levee Design Criteria (ULDC) (DWR, 2012). This technical memorandum provides documentation of the determination of the hydraulic parameters listed in Table 1, which are necessary for the ULDC compliance evaluation of the Robla-Arcade levee system.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 3 Table 1. ULDC Hydraulic Parameters
Parameter ULDC Definition
Design Water Surface Elevation (DWSE) Median 200-year water surface elevation (WSE) Minimum Top of Levee (MTOL)
DWSE plus the higher of
• 3 feet, or
• wind setup and wave runup
Hydraulic Top of Levee (HTOL)
The lower of
• DWSE plus 3 feet, or
• Median 500-year WSE
Seismic Vulnerability Restoration Profile (SVRP)
10-year water surface elevation plus the higher of
• 3 feet, or
• wind setup and wave runup

2. Study Area
The Robla-Arcade levee system protects the floodplain bounded on the south by Arcade Creek, on the west by the Natomas East Main Drainage Canal (NEMDC), on the north by Robla Creek, and on the east by high ground (see Figure 1). The levee system is made up of the three levee segments summarized in Table 2.

Table 2. Robla-Arcade Levee System
Levee Segment Length (feet) Upstream Limit Downstream Limit Arcade Creek north levee 11,200 Marysville Blvd. NEMDC east levee NEMDC east levee 13,637 Robla Creek south levee Arcade Creek north levee Robla Creek south levee 11,820 Dry Creek Road NEMDC east levee SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 4 Figure 1. Robla-Arcade Levee System

3. Hydraulic Model
A HEC-RAS 6.4.1 hydraulic model was developed for this analysis. HEC-RAS is software developed by the USACE Hydrologic Engineering Center for the purpose of performing one-dimensional (1-D) and twodimensional (2-D) hydraulic calculations for a full network of natural and constructed channels (USACE, 2023).

The hydraulic model, referred to as the Sacramento north area streams, or NAS, model is made up of both 1-D elements and 2-D flow areas. The model was developed from an existing 1-D model. Reaches with small low flow channels and wide floodways, such as Dry Creek, Robla Creek and Magpie Creek, were replaced with 2-D flow areas. A schematic of the model is shown in Figure 2. The streams within the model study area are summarized in Table 3. The downstream boundary of the model is the NEMDC at the American River north levee.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 5 Table 3. Streams Within the Model Study Area
Stream Upstream Boundary Downstream Boundary Model
Element
Length
(miles)
Dry Creek Below Q Street NEMDC 2-D 3.5
Robla Creek Above 16th Street NEMDC 2-D 3.3
Magpie Creek Patrol Road Robla Creek 2-D 1.8
Don Julio Creek Patrol Road Magpie Creek 2-D 1.3
Arcade Creek Auburn Blvd. NEMDC 1-D 6.6
NEMDC D-15 Pump Station American R. north levee 1-D 4.3 Figure 2. North Area Stream HEC-RAS Model Schematic
HEC-RAS 2-D flow areas require a terrain model for the establishment of its geometric and hydraulic properties. The primary terrain used for the NAS model was developed by USACE for use in their hydraulic analysis of the Magpie Creek project (USACE, 2021). The USACE terrain did not provide coverage of the entire NAS model study area, as shown in Figure 3. Terrain developed for the California Department of Water Resources (DWR) Central Valley Floodplain Evaluation and Delineation (CVFED) program (Wood SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 6 Rodgers, 2014) was used to extend coverage to the entire NAS model study area, as shown in Figure 4.

The vertical and horizontal accuracy and resolution of the USACE terrain is not provided in the referenced documentation. The CVFED terrain has a vertical accuracy of 0.6 feet, a horizontal accuracy of 3.5 feet, and an average point spacing of 3.28 feet.

Figure 3. USACE Terrain Coverage (elevations are Figure 4. Final Terrain Coverage (elevations are in In feet NAVD88) feet NAVD88)
Manning’s n roughness coefficient values within the 2-D flow areas were defined using land classification mapping from the National Land Cover Database (USGS, n.d.), as shown in Figure 5. Manning’s n-values were initially assigned for the various land classifications based on suggestions in the HEC-RAS 2D User’s Manual (USACE, 2023b), and refined as necessary through the calibration process. The land classifications, suggested n-values, and final calibrated n-values are listed in Table 4.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 7 Figure 5. Land Classification Map
SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 8 Table 4. Land Classifications and Assigned Manning’s n-values Land Classification
Manning’s n-value
Suggested
Range
Model Calibrated
Value
Barren Land Rock-Sand-Clay 0.023 – 0.030 0.035
Cultivated Crops 0.02 – 0.05 0.038
Deciduous Forest 0.10 – 0.20 0.08
Developed, High Intensity 0.12 – 0.20 0.10
Developed, Low Intensity 0.06 – 0.12 0.05
Developed, Medium Intensity 0.08 – 0.16 0.07
Developed, Open Space 0.03 – 0.05 0.04
Emergent Herbaceous Wetlands 0.05 – 0.085 0.06
Evergreen Forest 0.08 – 0.16 0.08
Grassland-Herbaceous 0.025 – 0.05 0.035
Open Water 0.025 – 0.05 0.03
Pasture-Hay 0.025 – 0.05 0.042
Shrub-Scrub 0.07 – 0.16 0.08
Woody Wetlands 0.045 – 0.15 0.07
The model was calibrated to the high flow event that occurred during the end of December 2005 and the beginning of January 2006 (the “2006 flood”). Based on a flow-frequency analysis by USACE for the American River Common Features Project General Reevaluation Report (USACE, 2010), the 2006 flood is about the 6% annual-chance flood. Calibration results are provided and summarized in Appendix B.

4. Hydrology
Central Valley Hydrology Study (CVHS) procedures and hydrologic data were used in this analysis. The CVHS was commissioned by the California Department of Water Resources (DWR) and prepared by the USACE (USACE, 2015). For the Sacramento River and San Joaquin River basins, the CVHS defines a procedure in which a scaled flood event with a pattern based on a historical flood event is selected to represent the flood of a specific frequency at a specific location, or centering. The CVHS also developed hydrologic data for several smaller ungaged watersheds, including the Natomas-Area Stream Group, which includes Dry Creek, Robla Creek and Arcade Creek (USACE, 2013). The hydrologic data for the Natomas-Area Stream Group was developed for discrete N-year flood frequencies with centerings defined by contributing area (C) parameters. The Natomas-Area Stream Group hydrologic data was updated by USACE in 2019. There are four CVHS defined flood centerings that influence the NAS model study area:
• Natomas-Area Stream Group: Dry Creek
• Natomas-Area Stream Group: Robla and Magpie Creeks
• Natomas-Area Stream Group: Arcade Creek
• Sacramento River Basin: American River at Fair Oaks and Latitude of Sacramento The ULDC requires the computation of water surface elevations for the 10-year, 200-year, and 500-year flood events. The Sacramento River Basin scaled flood events and Natomas-Area Stream Group C parameters for these flood frequencies and flood centerings are summarized in Table 5. The final computed maximum WSE is the composite maximum of the maximum WSE’s computed for the four flood centerings.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 9 Table 5. CVHS Flood Events
Flood Centering
Flood
Frequency
(Recurrence
Interval)
Watershed
North Area Streams Sacramento River
Dry Creek 10-year 10yr_C=99.5 1
1995-60% 2, 3
200-year 200yr_C=99.5 1
1995-105% 2
500-year 500yr_C=99.5 1
1995-120% 2
Robla-Magpie Creeks 10-year 10yr_C=RIOLINDA_MAGPIE 1
1995-60% 2, 3
200-year 200yr_C=RIOLINDA_MAGPIE 1
1995-105% 2
500-year 500yr_C=RIOLINDA_MAGPIE 1
1995-120% 2
Arcade Creek 10-year 10yr_C=ARC 1
1995-60% 2, 3
200-year 200yr_C=ARC 1
1995-105% 2
500-year 500yr_C=ARC 1
1995-120% 2
Fair Oaks-latitude of
Sacramento
10-year 1986-55% 2 1986-55% with 40% on American
R. 1, 2
200-year 1986-110% 2 1986-110% with 125% on
American R. 2
500-year 1986-100% 4 1986-100% with 176% on
American R. 4
1 Data ID from USACE 2019 updated hydrologic data set, consisting of recurrence interval (Nyr) and contributing area (C=99.5) or centering (C=RIOLINDA_MAGPIE, C=ARC).
2 Event selection by USACE (USACE, 2019). “1995-60%” = 1995 flood pattern with a 60% scale factor. 3 CVHS hydrologic data does not include the 1995-60% flood event. The closest available flood event data, 1995-75%, was used in the analysis. The 1995-75% data approximately represents the 20-year flood event. 4 Event selection by USACE (USACE, 2020).

The County of Sacramento’s D-15 pump station, at the upstream end of the modeled NEMDC reach, is an inline pump station with gates (County of Sacramento, 2007). During large flood events the gates close automatically when the water surface elevation at the pump station reaches a pre-defined trigger elevation, preventing backwater due to high flows in Dry and Robla creeks from affecting flood stages north of the pump station. After the gates close, the pumps will automatically turn on to ensure positive flow from north to south. The station has three 333 cfs capacity pumps. The operation criteria specify a firm capacity based on use of two of the three pumps, keeping one for a backup. However, all three pumps may be operated concurrently if required. For the ULDC analysis, the conservative assumption of a three-pump operation, with a total flow of 999 cfs, was used.

5. Urban Levee Design Criteria (ULDC)
Section 7.1 of the ULDC allows for two options for the determination of the DWSE. The first option is the Federal Emergency Management Agency (FEMA) Approach, in which the DWSE is computed deterministically with a hydraulic model. The second option is the U.S. Army Corps of Engineers Approach, which incorporates uncertainty into the determination of the DWSE. The approach selected for this analysis was the FEMA Approach, due to its application and results being more straightforward and economical.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 10 The ULDC defines the DWSE as the “200-year stage or water level used to design a levee or floodwall”.

Section 7.1.1 of the ULDC specifies that the hydraulic modeling used to determine the DWSE must consider the following:
• Upstream, downstream, and nearby levees and floodwalls protecting urban areas are assumed to be raised to the median 200-year water surface elevation plus 3 feet and not allowed to breach, even if overtopped. Overtopping flows are assumed to leave the channel and remain in the 200- year floodplain.
• All project levees and floodwalls are to be modeled to incorporate a minimum crown elevation equal to the authorized (usually the 1955/1957) USACE design profiles – this affects nonurbanized areas for the most part – all such levees and floodwalls are to be allowed to overtop, act as weirs, and not breach for floods up to and including the median 500-year flood.

Overtopping flows are assumed to leave the channel and remain in the 200-year floodplain. • Non-project levees and floodwalls in non-urbanized areas in the region, to the extent they may affect the DWSE, are to be modeled at their existing or authorized height, whichever is higher, and to act as weirs without breaching if overtopped.
• Debris loading on bridges must be considered. Bridges with less than 3 feet of clearance above the DWSE may experience extraordinary debris loading that must be evaluated in addition to typical pier/bent debris loading. The evaluation should include historic and potential debris transport in the stream, an analysis of loading on the bridge, and analysis of backwater impacts on the DWSE in the vicinity of the bridge.

Section 7.1.3 of the ULDC requires adjustments to the DWSE for the effects of superelevation, when applicable. Superelevation is a tilting of the water surface, which may occur as water flows through a bend in the channel. Computational methods for determining superelevation adjustments are in the USACE Engineering Manual 1110-2-1601.

Section 7.1.3 of the ULDC also states that the “…the civil engineer should consider increasing the DWSE to account for the potential increases in water surface associated with climate change, updated hydrology, updated hydraulic models, and sea level rise”. This statement implies that adjustment for sea level rise is optional; however, Section 7.19 of the ULDC states, “the effects of sea level rise are to be estimated and addressed for the duration during which a Finding that the urban level of flood protection exists may be valid”. Based on the second statement, sea level rise adjustment appears to be mandatory.

Additionally, Section 7.1.3 of the ULDC states:
“[T]he civil engineer also needs to address two other situations: (1) whether upstream levee or floodwall breaches could produce overland flows that would reach the area protected by the levee system or increase the water surface elevation along the levee system, and (2) whether flooding in a nearby leveed area could fill that area and breach a nearby levee or floodwall, returning flow to the stream and increasing the DWSE for a portion of the levee system".

Neither of these conditions are applicable to the Study Area, and therefore were not evaluated.

The following sections address the requirements in the ULDC and discuss the application of each requirement for the American River North levee system.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 11

5.1 Levees
As per the ULDC, all urban levees were assumed to have a minimum top elevation of the median 200-year water surface elevation plus 3 feet. All non-urban State-Federal Project levees were assumed to have a minimum crown elevation equal to the authorized USACE design profiles.

5.2 Debris Loading
The ULDC specifies that debris loading on bridges must be considered, and that “bridges with less than 3 feet of clearance above the DWSE may experience extraordinary debris loading that must be evaluated in addition to typical pier/bent debris loading”.

Bridge pier debris are applied in accordance with guidelines provided in a July 2014 letter (USACE, 2014), sent by USACE to the California Central Valley Flood Protection Board in order to clarify the level of screening and analysis that should be included on encroachment permit applications that are sent to the USACE for review. A copy of the letter is provided in Appendix C. Included in the letter was guidance for modeling debris build-up. Based on this guidance, under the ULDC “typical” debris loading condition, the hydraulic analysis included floating debris with a width equal to double the pier width, and a depth of 2 feet below the water surface. Under the ULDC “extraordinary” debris loading condition, floating debris with a depth of 2 feet below the water surface were modeled for the full width with the “extraordinary” condition.

Debris were not applied to bridges in the model upstream of the levee reaches, as debris on these bridges would have no effect on the water surface elevation in the levee reaches.

A summary of the bridge pier debris conditions included in the hydraulic analysis is provided in Table 6.

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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 12 Table 6. Bridge Pier Debris Loading
River River
Station1
Bridge
Debris Loading Condition2
200-yr 500-yr
Dry Creek West Branch 1,340 ft Rio Linda Blvd. E E
Dry Creek East Branch 3,910 ft SNRR Bike Trail t t
640 ft Rio Linda Blvd. E E
Dry Creek (lower) 6,120 ft private bridge E E
110 ft UPRR (near mouth) E E
Robla Creek 9,680 ft SNRR Bike Trail E E
8,290 ft Rio Linda Blvd. E E
90 ft UPRR (near mouth) E E
Magpie Creek 6,120 ft Raley Blvd. E E
4,010 ft Vinci Ave. E E
1,130 ft Dry Creek Rd. E E
Arcade Creek 1.344 mi Rio Linda Blvd. E E

1.26 mi SNRR Bike Trail E E

0.722 mi Norwood Avenue E E

0.045 mi UPRR (near mouth) E E
NEMDC 6.139 mi Main Avenue t t

5.168 mi Interstate 80 t t

4.347 mi Silver Eagle Road t t

3.03 mi West El Camino Avenue mix E

2.653 mi Arden-Garden Connector t t
American River 13.46 mi Bike Trail bridge t E

9.31 mi Watt Ave t E

7.748 mi Howe Ave t E

7.065 mi Guy West t E

6.588 mi H St t E

3.989 mi Cap City Fwy t t

3.715 mi RR t E

2.333 mi RR t E

2.235 mi Bike Trail t E

2.068 mi CA-160 E t mix

2.046 mi CA-160 W t mix

0.355 mi I-5 t mix

0.242 mi Jibboom St mix E
1 River station in miles for 1-D reaches and in feet for 2-D flow areas. 2 t = typical; E = extraordinary; mix = combination of t and E.

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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 13

5.3 Superelevation
Superelevation is a tilting of the water surface that occurs on the outside of a river bend. The ULDC notes that, “on the outside of a bend, the superelevation needs to be added to the DWSE”. The superelevation adjustment, per USACE Engineer Manual 1110-2-1416, River Hydraulics, is specific to 1-D hydraulic modeling. There are no locations in the Robla-Arcade levee system subject to superelevation.

5.4 Climate Change
The effects of climate change on extreme precipitation events in the Central Valley are being studied, but there is no indication of what the outcome of that work will be. Therefore, the hydrology used in this analysis has not been adjusted for the effects of climate change.

5.5 Updated Hydrology
This analysis makes use of the most recent accepted hydrologic data for the Study Area, which was developed as part of the Central Valley Hydrology Study, as noted in Section 4 of this report.

5.6 Updated Hydraulic Model
The hydraulic model used for this analysis was developed from the most current available data. Due to the calibration process, an updated hydraulic model would not be expected to have a substantial effect on the computed results unless significant physical changes have occurred in the modeled system. Since no significant physical changes have occurred since the data used for the model development was collected, no adjustment for updated hydraulic model has been included.

5.7 Sea Level Rise
The ULDC notes that, “the effects of sea level rise are to be estimated and addressed for the duration during which a Finding that the urban level of flood protection exists may be valid”. The duration of finding proposed for the subject project is 20 years.

The analysis assumed a sea level rise of 3.68 feet at San Francisco. This is the 50-year sea level rise projection determined by the California Department of Water Resources (DWR) for the 2022 update of the Central Valley Flood Protection Plan (CVFPP) (DWR, 2022). Being that the duration of the Urban Level of Protection finding is 20 years, the use of a 50-year projection is a conservative assumption. The effects of this sea level rise were applied at the downstream boundaries of the Sacramento River systemwide hydraulic model simulations, which were used to determine the downstream boundary conditions for the LAR model.

6. Computed ULDC Hydraulic Parameters
The following sections present the computed ULDC hydraulic parameters that were described in Section 1 of this technical memorandum:
• Design Water Surface Elevation (DWSE)
• Minimum Top of Levee (MTOL)
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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 14 • Hydraulic Top of Levee (HTOL)
• Seismic Vulnerability Restoration Profile

6.1 Design Water Surface Elevation (DWSE)
The ULDC defines the DWSE as “[the] median 200-year water surface elevation”, with adjustments for the following factors:
• Bridge pier debris loading
• Superelevation
• Sea level rise
Debris loading and sea level rise are accounted for in the hydraulic model simulations, as described in Sections 5.2 and 5.7. As noted in Section 5.3, the superelevation adjustment is not applicable to the Robla-Arcade levee system.

Profile plots of the computed DWSE for each of the levee segments in the Robla-Arcade levee system are provided in Figures 6, 7 and 8. The levee crest profiles are included on the profile plots. The Robla Creek south levee (Figure 8) shows at the upstream end of the levee, at Dry Creek Road, that the DWSE appears to exceed the top of levee elevation. The implications of this are describe in detail in Section 6.2.

Tabulations of the DWSE profiles are provided in Appendix D.

Figure 6. ULDC DWSE Profile, Arcade Creek North Levee
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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 15 Figure 7. ULDC DWSE Profile, NEMDC East Levee
Figure 8. ULDC DWSE Profile, Robla Creek South Levee
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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 16

6.2 Minimum Top of Levee (MTOL)
The ULDC defines the MTOL as the higher of the DWSE plus 3 feet, or the DWSE plus the computed wind setup and wave runup. Wind setup and wave runup for the Robla-Arcade levee system has been computed by Mead & Hunt (Mead & Hunt, 2024). The maximum computed wind setup and wave runup for each of the Robla-Arcade levee segments is shown in Table 7. Since they are all less than 3.0 feet, the MTOL for each of the Robla-Arcade levee segments is the DWSE plus 3 feet. Profile plots of the MTOL for each of the levee segments in the Robla-Arcade levee system are provided in Figures 9, 10 and 11.

Tabulation of the MTOL profiles are provided in Appendix D.

Table 7. Wind Setup and Wave Runup
Levee Segment
Maximum Wind Setup
and Wave Runup (feet)
Arcade Creek north levee 1.4
NEMDC east levee 1.7
Robla Creek south levee 2.3
The Arcade Creek north levee and NEMDC east levee elevations exceed the MTOL. The Robla Creek south levee exceeds the MTOL except at its upstream end, immediately downstream of Dry Creek Road. A detailed look (Figure 12) shows that where the MTOL elevation is not met, between stations 6114+00 and 6118+00, the DWSE is below the landside toe of the levee. That is, where there is insufficient freeboard, the DWSE does not reach the levee.

Figure 9. ULDC MTOL Profile, Arcade Creek North Levee
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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 17 Figure 10. ULDC MTOL Profile, NEMDC East Levee
Figure 11. ULDC MTOL Profile, Robla Creek South Levee
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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 18 Figure 12. Detail of Profiles at Upstream End of Robla Creek South Levee

6.3. Hydraulic Top of Levee (HTOL)
The ULDC defines the HTOL as the lower of the DWSE plus 3 feet, or the median 500-year WSE. Profile plots of the HTOL for each of the levee segments in the Robla-Arcade levee system are provided in Figures 12, 13 and 14. For reference, the DWSE plus 3 feet and 500-year WSE profiles are also shown.

Refer to Section 6.2 for discussion regarding the upstream end of the Robla Creek south levee (Figure 14).

Tabulations of the HTOL profiles are provided in Appendix D.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 19 Figure 12. ULDC HTOL Profile, Arcade Creek North Levee
Figure 13. ULDC HTOL Profile, NEMDC East Levee
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Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 20 Figure 14. ULDC HTOL Profile, Robla Creek South Levee

6.4 Seismic Vulnerability Restoration Profile (SVRP)
The ULDC specifies that if there is the potential for levee damage due to a seismic event, a plan needs to be in place to “restore grade and dimensions for at least 10-year WSE plus 3 feet of freeboard or higher for wind setup and wave runup within 8 weeks”. An evaluation of seismic performance by Kleinfelder (Kleinfelder, 2024) determined that the levee segments in the Robla-Arcade levee system have low seismic vulnerability, as defined in the DWR Urban Levee Evaluation (ULE) program, making seismic vulnerability restoration profiles for the Robla-Arcade levee system unnecessary.

SAFCA November 18, 2024
Robla-Arcade Levee System - Determination of the UDLC DWSE, MTOL, and HTOL Page 21 References
County of Sacramento. (2007). D-15 NEMDC Drainage Pump Station Summary of Operations and Procedures Manual. May 2007.

DWR. (2012). Urban Levee Design Criteria. May 2012.

DWR. (2022). 2022 CVFPP Update - Technical Analyses Summary Report, Public Draft. May 2022.

Kleinfelder. (2024). Seismic Performance Summary Report, North Area Streams Levee Areas. February 12, 2024.

MBK Engineers. (2019). Technical Memorandum - Sacramento Weir Widening Project, Initial Hydraulic Impact Analysis. October 31, 2019.

Mead & Hunt. (2024). Wind-Wave Analysis for American River North and Robla-Arcade Levee Systems.

January 16, 2024.

USACE. (2013). Central Valley Hydrology Study: Natomas-area Stream Group - Pleasant Grove Creek, Dry Creek, and Arcade Creek Watersheds Hydrologic Analysis. March 26, 2013.

USACE. (2015). Central Valley Hydrology Study. November 29, 2015.

USACE. (2019). Memorandum for Record, Subject: CVHS Hydrograph Package for HEC-RAS Model Inputs.

February 20, 2019.

USACE. (2020). Hydrology Technical Memorandum for Developing WRDA 2016 Water Surface Profiles. April 10, 2020.

USACE. (2021). Hydraulic Model Summary Magpie Creek Canal For American River Common Features Project. USACE - Vicksburg District. April 2021.

USACE. (2023a). HEC-RAS User's Manual. Retrieved from
https://www.hec.usace.army.mil/confluence/rasdocs/rasum/6.4 USACE. (2023b). HEC-RAS 2D User's Manual. Retrieved from https://www.hec.usace.army.mil/confluence/rasdocs/r2dum/latest Wood Rodgers. (2014). Central Valley Floodplain Evaluation and Delineation, Lower Sacramento River Technical Memorandum. January 17, 2014.

APPENDIX A
Lower American River
Hydraulic Model Calibration
Lower American River November 18, 2024
Hydraulic Model Calibration Page A-1
Simulation Event Peak American River flow
Calibration January 1997 flow 117,000 cfs
Verification February 10, 2017 ~85,000 cfs
Figure A-1. Calibration, January 1997, Maximum Water Surface Elevation Profile with Surveyed High Water Marks, American River river miles 10 to 23 (Mayhew Drain to Nimbus Dam) Figure A-2. Calibration, January 1997, Maximum Water Surface Elevation Profile with Surveyed High Water Marks, American River river miles 0 to 11 (Sacramento River to Mayhew Drain) Figure A-3. Verification, February 10, 2017, Maximum Water Surface Elevation Profile with Surveyed Water Surface Elevation, American River river miles 10 to 23 (Mayhew Drain to Nimbus Dam)
Figure A-4. Verification, February 10, 2017, Maximum Water Surface Elevation Profile with Surveyed Water Surface Elevation, American River river miles 0 to 11 (Sacramento River to Mayhew Drain)

Lower American River November 18, 2024
Hydraulic Model Calibration Page A-2
Figure A-1. Calibration, January 1997, Maximum Water Surface Elevation Profile with Surveyed High Water Marks, American River, river miles 10 to 23 (Mayhew Drain to Nimbus Dam) Figure A-2. Calibration, January 1997, Maximum Water Surface Elevation Profile with Surveyed High Water Marks, American River, river miles 0 to 11 (Sacramento River to Mayhew Drain) Lower American River November 18, 2024
Hydraulic Model Calibration Page A-3
Figure A-3. Verification, February 10, 2017, Maximum Water Surface Elevation Profile with Surveyed Water Surface Elevations, American River, river miles 10 to 23 (Mayhew Drain to Nimbus Dam) Figure A-4. Verification, February 10, 2017, Maximum Water Surface Elevation Profile with Surveyed Water Surface Elevations, American River, river miles 0 to 11 (Sacramento River to Mayhew Drain)

APPENDIX B
North Area Streams
Hydraulic Model Calibration
North Area Streams November 18, 2024
Hydraulic Model Calibration Page B-1
Calibration flood event: December 2005-January 2006
The stream gages listed in Table B-1 provided the available observed data used for calibration of the Dry Creek and Robla Creek watershed area. All the gages are part of the Sacramento County ALERT system (https://www.sacflood.org/). The gage data was provided by Sacramento County. The gage locations are shown in Figure B-1.

Table B-1. Stream Gages with Observed Data Available for Calibration Gage Agency Sensor ID
Dry Creek West Branch at SNRR Bike Trail Sacramento County ALERT 2230 Dry Creek West Branch at Elkhorn Blvd. Sacramento County ALERT 1661 Dry Creek Bypass at Elkhorn Blvd. Sacramento County ALERT 1662 Dry Creek East Branch at Elkhorn Blvd. Sacramento County ALERT 2782 Robla Creek at SNRR Bike Trail Sacramento County ALERT 2753 D15/NEMDC Downstream Sacramento County ALERT 2772
Figure B-1. Stream Gage Location Map
A comparison of the observed and computed peak stages at the gage locations is provided in Table B-2.

Profile plots of the computed maximum water surface elevations with available observed gage peaks are North Area Streams November 18, 2024
Hydraulic Model Calibration Page B-2
provided in Figures B-2 through B-6.

Table B-2. Calibration Results, Comparison of Observed and Computed Peak Stages Gage Maximum Stage (feet NAVD88) Difference
Observed Computed (feet)
Dry Creek West Branch at SNRR Bike Trail 47.62 48.06 +0.44 Dry Creek West Branch at Elkhorn Blvd. 46.06 46.17 +0.11 Dry Creek Bypass at Elkhorn Blvd. 46.95 46.58 -0.37
Dry Creek East Branch at Elkhorn Blvd. 46.88 49.33 +2.45 a Robla Creek at SNRR Bike Trail 40.59 40.78 +0.19
D15/NEMDC Downstream 36.44 36.69 +0.25
a The Sacramento County ALERT website for this gage notes that “when the east branch reaches 49.9’ +/- the stage at the west branch is approximately 46.5’ +/-“. The computed peak stage difference for these locations of 3.2’ is similar to the reported difference of 3.6’. Therefore, it can be concluded that the reported peak stage of 46.88’ at the Dry Creek East Branch at Elkhorn Blvd gage is suspect.

Figure B-2. Calibration Analysis Maximum Water Surface Elevation Profile, Dry Creek West Branch North Area Streams November 18, 2024
Hydraulic Model Calibration Page B-3
Figure B-3. Calibration Analysis Maximum Water Surface Elevation Profile, Dry Creek East Branch Figure B-4. Calibration Analysis Maximum Water Surface Elevation Profile, Dry Creek (lower) North Area Streams November 18, 2024
Hydraulic Model Calibration Page B-4
Figure B-5. Calibration Analysis Maximum Water Surface Elevation Profile, Dry Creek Bypass Channel Figure B-6. Calibration Analysis Maximum Water Surface Elevation Profile, Robla Creek Appendix C
USACE Letter with Debris Loading Guidance
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-1
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-2
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-3
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-4
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-5
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-6
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-7
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-8
USACE November 18, 2024
Letter with Debris Loading Guidance Page C-9

APPENDIX D

Tabulation of ULDC Hydraulic Parameter Profiles
for the Robla-Arcade Levee System
Tabulation of ULDC Hydraulic Parameter Profiles November 18, 2024 for the Robla-Arcade Levee System Page D-1
Table D-1. ULDC Hydraulic Parameter Profiles, Arcade Creek North Levee Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
5000+00 37.10 40.10 40.10 5038+00 37.77 40.77 40.77 5076+00 38.50 41.50 41.50 5001+00 37.44 40.44 40.44 5039+00 37.78 40.78 40.78 5077+00 38.52 41.52 41.52 5002+00 37.54 40.54 40.54 5040+00 37.78 40.78 40.78 5078+00 38.54 41.54 41.54 5003+00 37.63 40.63 40.63 5041+00 37.78 40.78 40.78 5079+00 38.56 41.56 41.56 5004+00 37.64 40.64 40.64 5042+00 37.78 40.78 40.78 5080+00 38.58 41.58 41.58 5005+00 37.65 40.65 40.65 5043+00 37.78 40.78 40.78 5081+00 38.61 41.61 41.61 5006+00 37.65 40.65 40.65 5044+00 37.79 40.79 40.79 5082+00 38.64 41.64 41.64 5007+00 37.66 40.66 40.66 5045+00 37.79 40.79 40.79 5083+00 38.68 41.68 41.68 5008+00 37.66 40.66 40.66 5046+00 37.79 40.79 40.79 5084+00 38.71 41.71 41.71 5009+00 37.66 40.66 40.66 5047+00 37.79 40.79 40.79 5085+00 38.74 41.74 41.74 5010+00 37.67 40.67 40.67 5048+00 37.80 40.80 40.80 5086+00 38.80 41.80 41.80 5011+00 37.67 40.67 40.67 5049+00 37.80 40.80 40.80 5087+00 38.87 41.87 41.87 5012+00 37.67 40.67 40.67 5050+00 37.80 40.80 40.80 5088+00 38.94 41.94 41.94 5013+00 37.67 40.67 40.67 5051+00 37.81 40.81 40.81 5089+00 39.01 42.01 42.01 5014+00 37.67 40.67 40.67 5052+00 37.81 40.81 40.81 5090+00 39.08 42.08 42.08 5015+00 37.68 40.68 40.68 5053+00 37.82 40.82 40.82 5091+00 39.15 42.15 42.15 5016+00 37.68 40.68 40.68 5054+00 37.83 40.83 40.83 5092+00 39.20 42.20 42.20 5017+00 37.68 40.68 40.68 5055+00 37.83 40.83 40.83 5093+00 39.26 42.26 42.26 5018+00 37.68 40.68 40.68 5056+00 37.85 40.85 40.85 5094+00 39.31 42.31 42.31 5019+00 37.68 40.68 40.68 5057+00 37.86 40.86 40.86 5095+00 39.36 42.36 42.36 5020+00 37.69 40.69 40.69 5058+00 37.88 40.88 40.88 5096+00 39.41 42.41 42.38 5021+00 37.69 40.69 40.69 5059+00 37.89 40.89 40.89 5097+00 39.44 42.44 42.38 5022+00 37.69 40.69 40.69 5060+00 37.91 40.91 40.91 5098+00 39.47 42.47 42.38 5023+00 37.69 40.69 40.69 5061+00 37.91 40.91 40.91 5099+00 39.49 42.49 42.38 5024+00 37.70 40.70 40.70 5062+00 37.92 40.92 40.92 5100+00 39.52 42.52 42.39 5025+00 37.70 40.70 40.70 5063+00 37.93 40.93 40.93 5101+00 39.55 42.55 42.39 5026+00 37.71 40.71 40.71 5064+00 37.93 40.93 40.93 5102+00 39.76 42.76 42.41 5027+00 37.71 40.71 40.71 5065+00 37.92 40.92 40.92 5103+00 40.00 43.00 42.44 5028+00 37.71 40.71 40.71 5066+00 38.05 41.05 41.05 5104+00 40.25 43.25 42.48 5029+00 37.72 40.72 40.72 5067+00 38.11 41.11 41.11 5105+00 40.49 43.49 42.51 5030+00 37.73 40.73 40.73 5068+00 38.13 41.13 41.13 5106+00 40.73 43.73 42.54 5031+00 37.74 40.74 40.74 5069+00 38.14 41.14 41.14 5107+00 40.95 43.95 42.57 5032+00 37.74 40.74 40.74 5070+00 38.30 41.30 41.30 5108+00 41.12 44.12 42.60 5033+00 37.74 40.74 40.74 5071+00 38.36 41.36 41.36 5109+00 41.30 44.30 42.63 5034+00 37.74 40.74 40.74 5072+00 38.39 41.39 41.39 5110+00 41.47 44.47 42.66 5035+00 37.74 40.74 40.74 5073+00 38.42 41.42 41.42 5111+00 41.65 44.65 42.69 5036+00 37.73 40.73 40.73 5074+00 38.45 41.45 41.45 5112+00 41.82 44.82 42.73 5037+00 37.77 40.77 40.77 5075+00 38.48 41.48 41.48

Tabulation of ULDC Hydraulic Parameter Profiles November 18, 2024 for the Robla-Arcade Levee System Page D-2
Table D-2. ULDC Hydraulic Parameter Profiles, NEMDC East Levee Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
3055+86 37.10 40.10 40.10 3102+00 38.29 41.29 41.29 3149+00 39.33 42.33 42.33 3056+00 37.10 40.10 40.10 3103+00 38.31 41.31 41.31 3150+00 39.36 42.36 42.33 3057+00 37.13 40.13 40.13 3104+00 38.33 41.33 41.33 3151+00 39.38 42.38 42.34 3058+00 37.15 40.15 40.15 3105+00 38.35 41.35 41.35 3152+00 39.41 42.41 42.34 3059+00 37.17 40.17 40.17 3106+00 38.37 41.37 41.37 3153+00 39.43 42.43 42.34 3060+00 37.20 40.20 40.20 3107+00 38.39 41.39 41.39 3154+00 39.45 42.45 42.35 3061+00 37.22 40.22 40.22 3108+00 38.41 41.41 41.41 3155+00 39.48 42.48 42.35 3062+00 37.24 40.24 40.24 3109+00 38.43 41.43 41.43 3156+00 39.50 42.50 42.35 3063+00 37.27 40.27 40.27 3110+00 38.45 41.45 41.45 3157+00 39.53 42.53 42.36 3064+00 37.29 40.29 40.29 3111+00 38.47 41.47 41.47 3158+00 39.55 42.55 42.36 3065+00 37.31 40.31 40.31 3112+00 38.49 41.49 41.49 3159+00 39.57 42.57 42.36 3066+00 37.34 40.34 40.34 3113+00 38.52 41.52 41.52 3160+00 39.60 42.60 42.37 3067+00 37.36 40.36 40.36 3114+00 38.54 41.54 41.54 3161+00 39.62 42.62 42.37 3068+00 37.38 40.38 40.38 3115+00 38.56 41.56 41.56 3162+00 39.65 42.65 42.37 3069+00 37.40 40.40 40.40 3116+00 38.59 41.59 41.59 3163+00 39.68 42.68 42.38 3070+00 37.43 40.43 40.43 3117+00 38.61 41.61 41.61 3164+00 39.71 42.71 42.38 3071+00 37.45 40.45 40.45 3118+00 38.64 41.64 41.64 3165+00 39.75 42.75 42.39 3072+00 37.47 40.47 40.47 3119+00 38.66 41.66 41.66 3166+00 39.78 42.78 42.39 3073+00 37.49 40.49 40.49 3120+00 38.68 41.68 41.68 3167+00 39.81 42.81 42.40 3074+00 37.51 40.51 40.51 3121+00 38.70 41.70 41.70 3168+00 39.84 42.84 42.40 3075+00 37.53 40.53 40.53 3122+00 38.72 41.72 41.72 3169+00 39.87 42.87 42.41 3076+00 37.55 40.55 40.55 3123+00 38.74 41.74 41.74 3170+00 39.90 42.90 42.41 3077+00 37.57 40.57 40.57 3124+00 38.77 41.77 41.77 3171+00 39.93 42.93 42.42 3078+00 37.59 40.59 40.59 3125+00 38.79 41.79 41.79 3172+00 39.96 42.96 42.42 3079+00 37.61 40.61 40.61 3126+00 38.81 41.81 41.81 3173+00 39.99 42.99 42.43 3080+00 37.63 40.63 40.63 3127+00 38.83 41.83 41.83 3174+00 40.02 43.02 42.43 3081+00 37.65 40.65 40.65 3128+00 38.85 41.85 41.85 3175+00 40.05 43.05 42.43 3082+00 37.68 40.68 40.68 3129+00 38.87 41.87 41.87 3176+00 40.08 43.08 42.44 3083+00 37.70 40.70 40.70 3130+00 38.90 41.90 41.90 3177+00 40.10 43.10 42.44 3084+00 37.72 40.72 40.72 3131+00 38.91 41.91 41.91 3178+00 40.12 43.12 42.45 3085+00 37.73 40.73 40.73 3132+00 38.90 41.90 41.90 3179+00 40.15 43.15 42.45 3086+00 37.75 40.75 40.75 3133+00 38.93 41.93 41.93 3180+00 40.17 43.17 42.45 3087+00 37.77 40.77 40.77 3134+00 38.97 41.97 41.97 3181+00 40.19 43.19 42.46 3088+00 37.79 40.79 40.79 3135+00 39.02 42.02 42.02 3182+00 40.22 43.22 42.46 3089+00 37.79 40.79 40.79 3136+00 39.04 42.04 42.04 3183+00 40.24 43.24 42.46 3090+00 37.75 40.75 40.75 3137+00 39.06 42.06 42.06 3184+00 40.31 43.31 42.48 3091+00 37.77 40.77 40.77 3138+00 39.07 42.07 42.07 3185+00 40.44 43.44 42.50 3092+00 37.83 40.83 40.83 3139+00 39.09 42.09 42.09 3186+00 40.48 43.48 42.50 3093+00 37.89 40.89 40.89 3140+00 39.11 42.11 42.11 3187+00 40.53 43.53 42.51 3094+00 37.95 40.95 40.95 3141+00 39.13 42.13 42.13 3188+00 40.64 43.64 42.55 3095+00 38.00 41.00 41.00 3142+00 39.15 42.15 42.15 3189+00 40.75 43.75 42.59 3096+00 38.06 41.06 41.06 3143+00 39.18 42.18 42.18 3190+00 40.86 43.86 42.62 3097+00 38.11 41.11 41.11 3144+00 39.20 42.20 42.20 3191+00 40.97 43.97 42.66 3098+00 38.16 41.16 41.16 3145+00 39.23 42.23 42.23 3192+00 41.07 44.07 42.69 3099+00 38.22 41.22 41.22 3146+00 39.26 42.26 42.26 3192+23 41.10 44.10 42.70 3100+00 38.25 41.25 41.25 3147+00 39.28 42.28 42.28
3101+00 38.27 41.27 41.27 3148+00 39.31 42.31 42.31
Tabulation of ULDC Hydraulic Parameter Profiles November 18, 2024 for the Robla-Arcade Levee System Page D-3
Table D-3. ULDC Hydraulic Parameter Profiles, Robla Creek South Levee Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
Levee
Station
(feet)
DWSE
(feet)
MTOL
(feet)
HTOL
(feet)
6000+00 41.19 44.19 42.78 6040+00 41.31 44.31 42.89 6080+00 42.30 45.30 43.45 6001+00 41.25 44.25 42.83 6041+00 41.31 44.31 42.89 6081+00 42.46 45.46 43.54 6002+00 41.25 44.25 42.84 6042+00 41.32 44.32 42.89 6082+00 42.50 45.50 43.56 6003+00 41.26 44.26 42.84 6043+00 41.32 44.32 42.90 6083+00 42.54 45.54 43.59 6004+00 41.26 44.26 42.84 6044+00 41.32 44.32 42.90 6084+00 42.58 45.58 43.61 6005+00 41.26 44.26 42.85 6045+00 41.33 44.33 42.90 6085+00 42.62 45.62 43.63 6006+00 41.26 44.26 42.85 6046+00 41.33 44.33 42.90 6086+00 42.65 45.65 43.65 6007+00 41.27 44.27 42.85 6047+00 41.33 44.33 42.91 6087+00 42.67 45.67 43.67 6008+00 41.27 44.27 42.85 6048+00 41.34 44.34 42.91 6088+00 42.69 45.69 43.68 6009+00 41.27 44.27 42.85 6049+00 41.34 44.34 42.91 6089+00 42.70 45.70 43.69 6010+00 41.27 44.27 42.85 6050+00 41.35 44.35 42.92 6090+00 42.71 45.71 43.69 6011+00 41.27 44.27 42.85 6051+00 41.35 44.35 42.92 6091+00 42.72 45.72 43.70 6012+00 41.27 44.27 42.85 6052+00 41.36 44.36 42.93 6092+00 43.04 46.04 43.83 6013+00 41.27 44.27 42.85 6053+00 41.37 44.37 42.93 6093+00 43.17 46.17 43.89 6014+00 41.27 44.27 42.86 6054+00 41.38 44.38 42.94 6094+00 43.19 46.19 43.90 6015+00 41.27 44.27 42.86 6055+00 41.39 44.39 42.95 6095+00 43.22 46.22 43.91 6016+00 41.27 44.27 42.86 6056+00 41.40 44.40 42.96 6096+00 43.28 46.28 43.94 6017+00 41.27 44.27 42.86 6057+00 41.41 44.41 42.96 6097+00 43.33 46.33 43.97 6018+00 41.27 44.27 42.86 6058+00 41.42 44.42 42.97 6098+00 43.37 46.37 43.99 6019+00 41.27 44.27 42.86 6059+00 41.42 44.42 42.97 6099+00 43.41 46.41 44.03 6020+00 41.28 44.28 42.86 6060+00 41.43 44.43 42.98 6100+00 43.47 46.47 44.06 6021+00 41.28 44.28 42.86 6061+00 41.45 44.45 42.99 6101+00 43.52 46.52 44.09 6022+00 41.28 44.28 42.86 6062+00 41.45 44.45 42.99 6102+00 43.56 46.56 44.12 6023+00 41.28 44.28 42.86 6063+00 41.46 44.46 43.00 6103+00 43.60 46.60 44.15 6024+00 41.28 44.28 42.86 6064+00 41.48 44.48 43.01 6104+00 43.62 46.62 44.17 6025+00 41.28 44.28 42.87 6065+00 41.50 44.50 43.02 6105+00 43.65 46.65 44.18 6026+00 41.28 44.28 42.87 6066+00 41.52 44.52 43.03 6106+00 43.67 46.67 44.20 6027+00 41.28 44.28 42.87 6067+00 41.54 44.54 43.05 6107+00 43.71 46.71 44.23 6028+00 41.29 44.29 42.87 6068+00 41.56 44.56 43.06 6108+00 43.75 46.75 44.25 6029+00 41.29 44.29 42.87 6069+00 41.57 44.57 43.07 6109+00 43.78 46.78 44.28 6030+00 41.29 44.29 42.87 6070+00 41.59 44.59 43.08 6110+00 43.80 46.80 44.30 6031+00 41.29 44.29 42.87 6071+00 41.60 44.60 43.08 6111+00 43.82 46.82 44.31 6032+00 41.29 44.29 42.88 6072+00 41.61 44.61 43.09 6112+00 43.84 46.84 44.33 6033+00 41.30 44.30 42.88 6073+00 41.64 44.64 43.11 6113+00 43.86 46.86 44.35 6034+00 41.30 44.30 42.88 6074+00 41.67 44.67 43.13 6114+00 43.92 46.92 44.40 6035+00 41.30 44.30 42.88 6075+00 41.71 44.71 43.15 6115+00 44.00 47.00 44.47 6036+00 41.30 44.30 42.88 6076+00 41.75 44.75 43.17 6116+00 44.14 47.14 44.60 6037+00 41.30 44.30 42.88 6077+00 41.80 44.80 43.19 6117+00 44.41 47.41 44.97 6038+00 41.31 44.31 42.89 6078+00 41.85 44.85 43.22 6118+19 46.32 49.32 46.72 6039+00 41.31 44.31 42.89 6079+00 42.12 45.12 43.36

APPENDIX B
____________________________________________________________________________________

LIST OF ATTACHMENTS
2024 Robla-Arcade Levee System: Geometry Analysis (ULDC), Sheets 1 through 13, prepared by MBK Engineers
Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 1 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 2 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 3 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 4 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 5 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 6 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 7 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 8 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 9 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 10 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 11 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 12 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 13 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 14 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 15 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 16 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx Robla-Arcade Levee System: Levee Geometry Analysis (ULDC) Profile Sheet No. 17 of 17 R:\_Flood Control\SAFCA\FEMA_ULDC\ULOP\ULDC Cert - Robla-Arcade\7.8 Geometry\Robla Arcade Levee Geometry - ULDC June 2024.docx

APPENDIX C
____________________________________________________________________________________ Kleinfelder, 2024. “Seismic Performance Summary Report North Area Streams Levee Areas, ULDC & FEMA Levee Certification Project, Sacramento Area Flood Control Agency Levee Systems, Sacramento County, California.” Dated September 10, 2024. 24001006.001A/SAC24R172217 Page i of vi September 10, 2024 © 2024 Kleinfelder

SEISMIC PERFORMANCE SUMMARY REPORT

NORTH AREA STREAMS LEVEE AREAS

ULDC & FEMA LEVEE CERTIFICATION PROJECT

SACRAMENTO AREA FLOOD CONTROL AGENCY LEVEE SYSTEMS

SACRAMENTO COUNTY, CALIFORNIA
SEPTEMBER 10, 2024
Copyright 2024 Kleinfelder
All Rights Reserved
24001006.001A/SAC24R172217 Page ii of vi September 10, 2024 © 2024 Kleinfelder
September 10, 2024
File No.: 24001006.001A
Mr. Pete Ghelfi, PE
Director of Engineering
Sacramento Area Flood Control Agency
1325 J Street, Suite 1700
Sacramento, CA 95814
Subject: Seismic Performance Summary Report
North Area Streams Levee Areas
ULDC & FEMA Levee Certification Project
Sacramento Area Flood Control Agency Levee Systems
Sacramento County, California
Kleinfelder Project # 24001006.001A
Dear Mr. Ghelfi:

Kleinfelder has been tasked by the Sacramento Area Flood Control Agency (SAFCA) with evaluating the seismic vulnerability of the Sacramento area levees located in Sacramento and Sutter Counties, California in support of the Urban Levee Design Criteria (ULDC) (DWR, 2012) level certification. For the evaluation, the Sacramento area levees have been divided into three areas - Natomas Basin, American River/South Sacramento Basin, and North Area Streams (NAS). A separate Seismic Performance Summary Report (SPSR) will be prepared for each of the three areas.

The purpose of this SPSR is to document Kleinfelder’s findings, present evaluation results, and present anticipated seismic segment performance for the NAS area levees. This document provides the analysis to support the development of a forthcoming Post-Earthquake Response Plan (PERP).

NAS area includes Dry Creek North (DCNL) and South Levees (DCSL), Arcade Creek North (ACNL) and Arcade Creek South Levees (ACSL), Natomas East Main Drainage Canal East Levee (NEMDCEL), and American River North Levee (ARNL) located within Sacramento County California as shown on Figure 1-

1. 24001006.001A/SAC24R172217 Page iii of vi September 10, 2024 © 2024 Kleinfelder
This report has been prepared consistent with the requirements of the approved scope of work for the subject project outlined in Kleinfelder’s proposal dated May 5, 2023.

Sincerely,
KLEINFELDER, INC.

Meredith Beswick PE, PG Zia Zafir PE, GE
Senior Geologist Sr. Principal Geotechnical Engineer
Reviewed By:

Timothy A. Williams, PE, GE
Sr. Principal Geotechnical Engineer
CC: Mr. Pro Mitra, PE/MBK Engineers ([email protected]) Ms. Becky Money, PE/MBK Engineers ([email protected]) 24001006.001A/SAC24R172217 Page iv of vi September 10, 2024 © 2024 Kleinfelder

TABLE OF CONTENTS

SECTION PAGE
1 INTRODUCTION .........................................................................................................................1

1.1 PURPOSE AND SCOPE ......................................................................................................... 1

1.2 BACKGROUND..................................................................................................................... 1

1.3 REFERENCED REPORTS........................................................................................................ 2

1.4 SEISMIC VULNERABILITY EVALUATION METHODOLOGY.................................................... 2

1.4.1 Preliminary Work ................................................................................................... 3

1.4.2 Phase 1: Screening Review of Existing Analysis..................................................... 3

1.4.3 Phase 2: Targeted Evaluation ................................................................................ 4

1.4.4 Seismic Vulnerability.............................................................................................. 4 2 GEOLOGY AND GEOMORPHOLOGY.............................................................................................8

2.1 REGIONAL GEOLOGIC SETTING........................................................................................... 8

2.2 LOCAL GEOLOGY ................................................................................................................. 9

2.2.1 Surficial Geology .................................................................................................... 9

2.2.2 Generalized Near Surface Stratigraphy ............................................................... 11

2.3 SEISMOTECTONIC SETTING............................................................................................... 12 3 GROUND MOTION HAZARD ANALYSIS ......................................................................................14

3.1 SEISMIC HAZARD ANALYSIS .............................................................................................. 14

3.1.1 Seismic Analysis Results....................................................................................... 15 4 PREVIOUS EVALUATION...........................................................................................................16

4.1 SUMMARY......................................................................................................................... 16

4.1.1 General................................................................................................................. 16

4.2 SEISMIC ANALYSIS WATER SURFACE ELEVATIONS ........................................................... 17 5 CURRENT EVALUATION ............................................................................................................18

5.1 SEISMIC EVALUATION SEGMENT SELECTION ................................................................... 18

5.1.1 Liquefaction Analysis of ULDC Segments............................................................. 18

5.2 VULNERABILITY CLASSIFICATIONS FOR TARGETED SEGMENTS........................................ 20

5.2.1 Segment AR-12 .................................................................................................... 20

5.2.2 Segment AR-14 .................................................................................................... 21

5.2.3 Segment NMDE-3 ................................................................................................ 23 6 SEISMIC PERFORMANCE...........................................................................................................24

6.1 SUMMARY......................................................................................................................... 24 7 LIMITATIONS ...........................................................................................................................25 8 REFERENCES ............................................................................................................................26 24001006.001A/SAC24R172217 Page v of vi September 10, 2024 © 2024 Kleinfelder
TABLES

3.1 Seismic Hazard Analysis Site Parameters

3.2 Probabilistic Peak Horizontal Acceleration and Controlling Earthquake Magnitude

4.1 Phase 1 - Seismic Vulnerability Results Screening

5.1.1 Liquefaction Layer Changes for Targeted Segments

5.1.2 Liquefaction Factor of Safety Changes for Targeted Segments

5.2.1 2015 URS Post-Seismic Stability Analysis Factors of Safety for Targeted Segments

5.2.2 Material Properties for Segment AR-14 Post-Seismic Stability Analysis

5.2.3 Segment AR-14 Post-Seismic Slope Stability Factors of Safety

5.2.4 2015 URS Post-Seismic Stability Analysis Factors of Safety for Segment NMDE-2

6.1 Seismic Vulnerability Classifications for North Area Streams Levees

FIGURES
1-1 Site Map
1-2 Table 6-1 from DWR Guidance Document, Section 6.4
1-3 Flow Chart
2-1 Regional Geology
2-2 North Area Streams Levees Geologic Map
2-3 American River North Levee Geologic Map

APPENDIX
A Seismic Technical Approach Memo
B Ground Motion Parameter Selection Memo
C Section 6, Seismic Analysis, Guidance Document for Geotechnical Analyses, Urban Levee Evaluations Project
D Updated SPT-Based Liquefaction Calculations for Targeted Segments E Post-Seismic Slope Stability Analysis for Segment AR-14 F Original URS Liquefaction Spreadsheet Analyses
24001006.001A/SAC24R172217 Page vi of vi September 10, 2024 © 2024 Kleinfelder

REPORT ACRONYMS
______________________________________________________________________________________________ 200-year 200-year median (i.e., flood recurrence period) ACNL Arcade Creek North Levee
ACSL Arcade Creek South Levee
ARCF American River Common Features
ARNL American River North Levee
DCNL Dry Creek North Levee
DCSL Dry Creek South Levee
DRMS Delta Risk Management Strategy
DWR California Department of Water Resources
FEMA Federal Emergency Management Agency
FOS Factor of Safety
FWLA Fugro William Lettis & Associates, Inc.

GER Geotechnical Evaluation Report
GMHA Ground Motion Hazard Analysis
KLF Kleinfelder
km Kilometer
Mw Earthquake Magnitude
NASL North Area Streams Levees
NEMDC Natomas East Main Drainage Canal
NEMDCEL Natomas East Main Drainage Canal – East Levee
PHA Peak Horizontal Acceleration
SAFCA Sacramento Area Flood Control Agency
SETAM Seismic Evaluation Technical Analysis Memorandum
SNGV Sierra Nevada-Great Valley block
SPSR Seismic Performance Summary Report
SPT Standard Penetration Test
ULDC Urban Levee Design Criteria
ULE Urban Levee Evaluation
URS URS Corporation
USACE United States Army Corps of Engineers
WUS Western United States
24001006.001A/SAC24R172217 Page 1 of 29 September 10, 2024 © 2024 Kleinfelder
1 INTRODUCTION
___________________________________________________________________________________

1.1 PURPOSE AND SCOPE
Kleinfelder has been tasked by the Sacramento Area Flood Control Agency (SAFCA) with evaluating the seismic vulnerability of the Sacramento area levees located in Sacramento and Sutter Counties, California in support of the Urban Levee Design Criteria (ULDC) (DWR, 2012) level certification. For the evaluation, the Sacramento area levees have been divided into three areas - Natomas Basin, American River/South Sacramento Basin, and North Area Streams (NAS). A separate Seismic Performance Summary Report (SPSR) will be prepared for each of the three areas.

The purpose of this SPSR is to document Kleinfelder’s findings, present evaluation results, and present anticipated seismic segment performance for the NAS area levees. This document provides the analysis to support the development of a forthcoming Post-Earthquake Response Plan (PERP).

NAS area includes Dry Creek North (DCNL) and South Levees (DCSL), Arcade Creek North (ACNL) and Arcade Creek South Levees (ACSL), Natomas East Main Drainage Canal East Levee (NEMDCEL), and American River North Levee (ARNL) located within Sacramento County California as shown on Figure 1-

1. This report has been prepared consistent with the requirements of the approved scope of work for the subject project outlined in Kleinfelder’s proposal dated May 5, 2023.

1.2 BACKGROUND
NAS levees in the greater Sacramento area were constructed over a period of years, with original construction of many reaches started around the turn of the last century. Since that time many changes have been made to the system to improve the system to meet modern flood control standards, to accommodate changes in land use, and to make the system more resilient to impacts from climate change and other factors.

Recently as part of modernization efforts, The American River Common Features (ARCF) Project improvements were authorized by the Federal Government for construction by Section 1401(2)(7) of the Water Infrastructure Improvements for the Nation Act of 2016 (Pub. L. No. 114-322, § 1401(2)(7), 130 24001006.001A/SAC24R172217 Page 2 of 29 September 10, 2024 © 2024 Kleinfelder
Stat. 1708, 1710 (2016)). The ARCF authorized work is nearing completion under the oversight of the U.S. Army Corps of Engineers (USACE) in cooperation with SAFCA and the California Department of Water Resources. Other locally sponsored modernization efforts and repair work are also or will soon be completed. As such, it is expected that by or about 2026, SAFCA will be working to apply for FEMA certification and will as part of that effort show compliance with ULDC requirements.

To better understand the potential flood risk to urban areas of California posed by levees, the California Department of Water Resources (DWR) conducted the Urban Levee Evaluations (ULE) project. As part of this effort, URS classified the seismic vulnerability of the NAS levees in the Geotechnical Evaluation Reports for the American River Study Area (URS, 2015a) and the NEMDC East Study Area (URS, 2015c).

1.3 REFERENCED REPORTS
The following reports were reviewed in support of this NAS SPSR:
• “ULE Geotechnical Evaluation Report (GER) Volume 1 and 2, American River Study Area, Urban Levee Evaluations Project, Contract 4600008101,” dated January 2015 (Issue date: 01-2015), URS (2015a).
• “ULE Geotechnical Evaluation Report Volume 2, Remedial Alternatives, NEMDC East Study Area, Urban Levee Evaluations Project, Contract 4600008101,” dated April 2015 (Issue date: 04-2015), URS (2015c).

1.4 SEISMIC VULNERABILITY EVALUATION METHODOLOGY
The seismic vulnerability evaluation was performed in accordance with Kleinfelder’s Seismic Evaluation Technical Approach Memorandum (Kleinfelder, 2023a) (SETAM) contained in Appendix A, which is generally consistent with the Urban Levee Evaluations Project Guidance Document for Geotechnical Analysis (URS, 2015b) (Guidance Document) Section 6, Seismic Analysis for intermittently loaded levees1. High, Moderate, and Low Vulnerability classifications from the Guidance Document (URS, 1 The ULDC requires classifying the levee as frequently loaded or intermittently loaded. A frequently loaded levee is defined in the ULDC as a levee with water at least one foot above the landside levee toe for more than 36 days in a year. As stated in the ULDC Geotechnical Results Summary North Area Streams (Kleinfelder, 2016) and in the ULE Geotechnical Evaluation Report Volume 1 and 2 American River Study Area (URS, 2015b), the study area levees generally do not contain water above the landside toe for this time interval. Therefore, the levees within the study area are considered intermittently loaded for this study.
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2015b) will be based on the seismic deformation estimates, see Figure 1-2 in Section 1.4.4, below. The steps for evaluating and classifying the levee are outlined in the SETAM and are described briefly below.

Figure 1-3 presents a flow chart describing the evaluation criteria.

1.4.1 Preliminary Work
Kleinfelder performed a review of the existing geotechnical analysis and subsurface data. During this process, seismic segment data gaps were identified and the updated peak horizontal acceleration (PHA) and magnitude values were developed.

Previous development of ground motion parameters in the area was performed by URS in 2007 as part of the Delta Risk Management Strategy (DRMS), which was updated and expanded on in 2012 by URS as part of the DWR ULE project. Updated ground motion parameters were developed following assumptions of this previous work, and detailed methodology is presented in our Seismic Evaluation Ground Motion Parameter Selection Memorandum (GMPSM) (Kleinfelder, 2023b), which is included in Appendix B. A probabilistic seismic hazard analysis was performed to determine PHA and earthquake magnitude as discussed in the GMPSM and Section 3, Ground Motion Hazard Analysis (GMHA), of this report.

1.4.2 Phase 1: Screening Review of Existing Analysis
The levees are organized by selection of “segments” instead of reaches due to the variable nature of subsurface conditions under levees. Segments may overlap multiple reaches or reaches may be subdivided into multiple segments. Levee segments, which were based on portions of the levees with similar soil types and liquefaction results, and analysis sections for each segment for seismic evaluation were developed for the 2015 ULE evaluations and were adopted for this study. Levee segments are shown on Figure 1-1.

The screening process was performed to identify which analysis sections were classified as Low, Medium, and High Vulnerability in 2015. All sections identified as High Vulnerability were not considered for reanalysis because they would remain High Vulnerability since the updated ground motions were slightly higher than those used for the ULE evaluations. Low and Medium Vulnerability segments were reanalyzed based on the updated ground motions described in the GMPSM in Appendix B. Analysis sections determined to be non-critical for seismic performance were not used in the current analyses and are not presented in report.
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Kleinfelder performed probabilistic seismic hazard analyses at select control points in the North Area Streams area, as discussed in the GMPSM (Kleinfelder, 2023b). Newly developed PHAs and earthquake magnitudes from these analyses for critical sections were compared to ground motion parameters from previous reports. No further analysis was required for analysis sections where any of the below conditions are true:

1. The new PHA and/or earthquake magnitude are lower than the original PHA and/or earthquake magnitude and the original analysis is determined to be adequate.

2. The original analysis determined the section is not susceptible to deformation and the new PHA and/or earthquake magnitude are not higher than the original analysis PHA and/or earthquake magnitude.

3. The analysis section is found to have High Vulnerability or Flow Failure based on the original PHA and earthquake magnitude.

1.4.3 Phase 2: Targeted Evaluation
A targeted evaluation was required for critical sections under two conditions, as follows:

1. The original analysis classified the section as Low or Medium Vulnerability.

2. The new earthquake magnitude and/or PHA exceeds the original magnitude/PHA used in the 2015 analysis (except for High Vulnerability).

High, Medium, and Low Vulnerability classifications were based on the seismic deformation estimates from the Guidance Document (URS, 2015a). As explained in Section 1.4.2, all segments classified as High Vulnerability in the Phase 1 screening process were not analyzed, and the High Vulnerability classification remained unchanged for this study.

1.4.4 Seismic Vulnerability
The following steps were involved in assessing seismic vulnerability, Step numbers are associated with Key Steps described in Figure 6-1 of the Guidance Document (URS, 2015b); see Appendix C. These steps were performed for the ULE American River Study Area GER (URS, 2015a) and the NEMDC East Study 24001006.001A/SAC24R172217 Page 5 of 29 September 10, 2024 © 2024 Kleinfelder
Area (URS, 2015c) and were reviewed by Kleinfelder for this study. Liquefaction analysis spreadsheets prepared for the ULE GER were provided to Kleinfelder by DWR for review.

Step 1. Kleinfelder performed a liquefaction analysis using revised PHA and earthquake magnitude values. The URS SPT-based liquefaction spreadsheets were used to delineate zones of liquefaction.

Based on the results of liquefaction, any additional cross sections were identified for analysis.

The analysis cross sections developed for the 2015 ULE project were used for this study where relevant.

Step 2. For selected cross sections, FOS against flow failure were estimated using residual strength for liquefiable materials and static slope stability analysis. If FOS was less than 1, the section was classified as “High Vulnerability” and no further analysis was needed.

If FOS against flow failure was greater than 1.3, the analysis section was classified as “Low Vulnerability”, unless analysis for volumetric strain resulted in a higher vulnerability class.

Kleinfelder and others have previously performed extensive slope failure modeling along the levee alignments using SLOPE/W, a two-dimensional finite element computer modeling, a package included in the GEOSTUDIO software package, which was developed by Bentley Systems, Inc. Where necessary, these models were updated to the current version of GEOSTUDIO (2023.1.2) and utilized for Targeted Flow Failure analyses. Idealized soil properties were based on previous investigations and generalized parameters from the Guidance Document (URS, 2015a). Water surface elevations for seismic flow failure analyses were the higher of either average summer or average winter water surfaces, in accordance with the Guidance Document (URS, 2015a).

Slope failure analyses considered all potential failure modes, including:
• Waterside and landside
• Deep and shallow
• Circular and wedge-shaped
Step 3. If FOS against flow failure was between 1.0 and 1.3, a simplified seismic deformation analysis was performed on the section. This involved computing a maximum horizontal seismic coefficient (Kmax) and performing a pseudo-static stability analysis using a horizontal seismic 24001006.001A/SAC24R172217 Page 6 of 29 September 10, 2024 © 2024 Kleinfelder
coefficient of 50% of the maximum value. This analysis was performed using the same updated SLOPE/W models used in Step 2. If the resulting FOS greater than 1.0, the section was classified as “Low Vulnerability”.

Yield acceleration (Ky) values were then estimated using pseudo-static analyses using the same SLOPE/W models used in Step 2. Yield acceleration was defined as the minimum horizontal acceleration resulting in a just-stable slope condition, i.e. FOS = 1.0. Yield acceleration was developed for each potential failure mode.

A vertical Newmark-type deformation analysis was performed based on the Kmax and Ky values determined above. The calculated Newmark displacement was reduced by 30% for estimation of freeboard loss.

Volumetric settlement was considered for sections with potentially liquefiable soils thicker than 20 feet. Previous work performed by URS on ULE considered (N1)60-cs blow counts less than 15 as liquefiable and subject to volumetric settlement. This blow count criteria was evaluated against new research and revised, if warranted.

Seismic vulnerability classification was determined by calculating freeboard loss as the sum of Newmark-type vertical deformation and volumetric settlement (if applicable). Freeboard loss was evaluated as a percentage of levee height (as measured from hinge point on the landside toe). Engineering judgment was used to determine damage to internal levee structures, and the seismic vulnerability class was evaluated based on Table 6-1 from the Guidance Document (URS, 2015b) shown below in Figure 1-2.

Figure 1-2: Table 6-1 from DWR Guidance Document, Section 6.41 24001006.001A/SAC24R172217 Page 7 of 29 September 10, 2024 © 2024 Kleinfelder
Step 4. Advanced seismic deformation analyses as described in Appendix C only apply to frequently loaded levees and were not applicable to this study.

The stages of our evaluation were described in detail in our SETAM (KLF, 2023a) as well as Section 6 of the Guidance Document (DWR, 2015b).
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2 GEOLOGY AND GEOMORPHOLOGY
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2.1 REGIONAL GEOLOGIC SETTING
The study area is located within the southern portion of the Sacramento Valley, within the Great Valley geomorphic province. The Great Valley province is a north-south trending 400-mile by 50-mile long alluvial plain in central California comprised of the Sacramento Valley in the north and the San Joaquin Valley in the south. The Sacramento Valley contains thousands of feet of accumulated fluvial, overbank, and alluvial fan deposits derived from erosion of the adjacent Sierra Nevada mountains to the east, northern Coast Range mountains to the west, and Klamath and Cascade mountains to the north. These deposits are primarily comprised of Quaternary and Tertiary age (present day to 56 million years ago) alluvial deposits and include clays, silts, sands, and gravels. The alluvial deposits thin out at the margins of the Great Valley province, exposing the underlying bedrock units. The Foothills Metamorphic Belt and the basement complex of the Sierra Nevada Batholith to the east are exposed along the eastern boundary of the valley. Sedimentary and mélange bedrock of the northern Coast Range mountains are exposed to the west. Meta-sedimentary, mélange, igneous, and volcanic bedrock of the Klamath and Cascade mountains are exposed to the north.

Geologic maps covering the study area on a regional scale were reviewed as a part of this study.