San Luis Obispo City Council
August 4, 2026

F?
Figure 22. 50-year Velocity Comparison (Proposed - Existing) within Project Vicinity 39 Appendices
Appendix A. FIS Excerpts
Appendix B. HEC-RAS Model Results: Grid Extents View
Appendix C. HEC-RAS Model Results: Project Vicinity View Appendix D. Scour Calculations
June 25, 2026 | v
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project

Abbreviations
vi | June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
one-dimensional
two-dimensional
American Association of State Highway and Transportation Officials Arizona
Bridge Design Specifications
base flood elevation
California
California Department of Transportation
Code of Federal Regulations
cubic feet per second
City of San Luis Obispo
centimeter
County of San Luis Obispo
cone penetration test
Drainage Design Manual
Digital Elevation Model
Federal Emergency Management Agency
Federal Highway Administration
Flood Insurance Rate Map
Flood Insurance Study
feet, foot
feet per second
Highway Design Manual
Hydraulic Engineering Circular No. 18
Hydrologic Engineering Center's River Analysis System
Load and Resistance Factor Design
meter
mile
mechanically stabilized earth
North American Vertical Datum of 1988
northbound
National Cooperative Highway Research Program
National Flood Insurance Program
Original Product Resolution
Pacific Gas and Electric
Post Mile
U.S. Route 101 (US 101) at Prado Road Interchange Project Quality Level 2
Region 9
river station
Storage Area
U.S. Route 101
United States Army Corps of Engineers
United States Geological Survey
water surface elevation
1D
2D
AASHTO
AZ
BDS
BFE
CA
Caltrans
CFR
cfs
City
cm
County
CPT
DDM
DEM
FEMA
FHWA
FIRM
FIS
ft
ft/s
HDM
HEC-18

HEC-RAS
LRFD
m
mi
MSE
NAVD 88
NB
NCHRP
NFIP
OPR
PG&E
PM
Project
QL2
R9
RS
SA
US 101
USACE
USGS
WSE

F?
This page is intentionally left blank.

June 25, 2026 | vii
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project

F2
1 General Description

1.1 Project Description

1.2 Study Purpose

1.3 Key Tasks
June 25, 2026 | 1
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Key tasks performed in this study included: 1) a review of available hydrologic data, 2) a hydrologic analysis, 3) a hydraulic analysis to determine design water surface elevations (WSE) and flow velocities for the existing and proposed conditions, 4) and a scour analysis to estimate potential scour depths for the proposed condition.

This Bridge Design Hydraulic Study focuses on the new bridges at the Prado Road overcrossing (west and east overcrossing bridges), US 101 NB off-ramp to Prado Road, and the US 101 NB on-ramp from Prado Road, which are located within the floodplain of San Luis Obispo Creek. The general plans for the proposed bridges are shown in Figure 3, Figure 4, and Figure 5. The purpose of this Bridge Design Hydraulic Study is to present the design flow characteristics for San Luis Obispo at the Project, the hydraulic characteristics associated with the pre-Project (existing condition) and post-Project (proposed condition), and the scour potential for the proposed condition. As part of a separate project, the Prado Road bridge over San Luis Obispo Creek (Existing Bridge Number 49C0107), which is located east of the proposed Project bridges, is proposed to be replaced. This Bridge Design Hydraulic Study incorporates data from the Prado Road bridge over San Luis Obispo Creek (Existing Bridge Number 49C0107) replacement, but the bridge is not part of this study.

The proposed U.S. Route 101 (US 101) at Prado Road Interchange Project (Project) includes improvements to extend Prado Road over US 101 to connect with Dalidio Drive, reconstruct the existing US 101 northbound (NB) off-ramp and on-ramp connections with Prado Road, and construct an auxiliary lane on NB US 101 between the Prado Road and Madonna Road interchanges in order to provide congestion relief, operational efficiency, and multimodal connectivity. The interchange is located in the city of San Luis Obispo in the county of San Luis Obispo at Post Mile (PM) 26.8 and improvements on NB US 101 extend from PM 26.5 to PM 27.3. The preferred alternative includes a partial interchange with the proposed Prado Road overcrossing constructed over US 101, a new US 101 NB off-ramp to Prado Road, and a new NB on-ramp from Prado Road. The Project location map is shown in Figure 1. These bridges are shown in the Project vicinity map in Figure

2.

Figure 1. Project Location Map
PA AA ri " C
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2 | June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
San Luis
Obispo
El Chorro
Regional Park
San Luis Obispo
County
Regional
Airport
ESRI, NASA. NGA, USGS, FEMA, SOURCES:

ESRI. TOMTOM, GARMIN. FAO, NOAA. USGS,
(C) OPENSTREETMAP CONTRIBUTORS, AND

THE GIS USER COMMUNITY
4 120

1.3 mi
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Obispo
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Sources: Esri and Consor Engineers 2026a
June 25, 2026 | 3
Chum
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
US101 NB
On-Ramp
Bridge
US101 NB
Off-Ramp
Bridge
3 H
9s
4111.1 ow-sae
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-------- Proposed Bridges
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Figure 3. Proposed Prado Road Interchange Bridges General Plan Dist COUNTY SCUTE
5 SLO SR xx X 46+37.70 EVC
Elev 150.20
PRELIMINARY DESIGNDN —===
. 7/BHUG- B- Ca
-2 Bridge PC a§i W[. ee

REGISTERED CIVL ENGINEER
L
250’ VC
L 0.87%

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R/C = -2.1046% / Sia R/C - -1.56185? / Sto Notes R/C = 1.6787% / Sto R/C = 1.8191% / Sto

2. T ACCLe4C) Cr cowteeneSs a- SCAED
cOnS C IS AAV SEET.

PROFILE GRADE CCNSOR NORTH AMERICA. INC.

Aconsors
2858 PROSPECT PARK OR. SiE 250 No Scale RANCHO CORDOVA, CA 95670 916.368.9181
875‘-0" Measured along "P" Line
450'-0" 300'—0”
SB- West Overcrossing BB
East Overcrossing EB EB- 65'-a"
28-6" 36'-6'
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| Borrier (Type SR —I L
Abut 1 Bent 2 Abut 4 Abut 1
Datum Elev = 80.0
46+00 ♦7+00 ♦8+00 ♦9+00 50+00 51+00 52+00 53+00 54+ 00 55+03 56+00 LT

ELEVATION TYPICAL SECTION - WEST OC
50‘ 10‘
"P" Line
r 87-0" Max& Vor
t 1
32+03.10 BC
39—6" Max & Var 47‘—6" Max & Var
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6255’107 E "p- Line S 62*45’46" E = 10'
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BRIDGE NO. PRADO ROAD INTERCHANGE

DESN OVERSIGNIT
QlATntS SPECIFICATIONS POST MILE GENERAL PLAN NO. 1
03BFR-S2ST“oe"C vrT X
Source: Consor Engineers 2026b
4 | June 25, 2026
Preliminary Bridge Design Hydraulic Study US 101 at Prado Road Interchange Project CIP/PT Canc
Box Girder
53+36 37 EVC
Elev 153.39 '
50+86.37 BVCElev 160.75
150‘-0"
Span 6
PLAN
1" = 50'
LoAD a RESISTANCE

FACTOR RESIGN
150'-flSpan 5
732SW or
511HSW). Typ
150-0* 150-0"
Spon 3
BB 51-98.75
Elev 158.65
EB 55+00.00
Elev 145.37
15O‘-O“
Spon 2
EB 50+75.00Elev 160.87
Legend
(1) Paint "xxx Bridge"(2) Paint "No. XXX-XXXX"(3) MSE Wall P/S CA
Wide Flange
Conc Girder -
Concrete
Barrier (Type
732SW or
511HSW), Typ
Note:The Contractor must verify all
controlling field dimensions before ordering or fabricating any moteriol. 50+32.48 EVC
Elev 161.29
BB 46+27.50
Elev 149.71
“OFF-RAMP"
Line
60" Dio
Column. Typ
55+53.17 BVC
/ Elev 142.77
—60" Dia
Column, Typ
11—0"
"&Vor
I
UNIT: UNIT
PROJECT NUMBER & PHASE: PROJECT EONBERT NO.: CONTRACT
58+23.17 EVC
Elev 136.17
PLANS APPROVAL DATE______________
weSIA7Ec calCP84 oP ns o=CERS
O? ACDVTS SHALL NO EE RESPOVSELE FOP
Abut 3
BridgePROJECT ENGINEER

PREPARED FOR THE

CITY OF SAN LUIS OBISPO

PUBLIC WORKS DEPARTMENT
47+52.48 BVC
Elev 155.82
280’ VC
—wr WILIS—r
IOTAL PROECT i
M

TOTAL PROJECT
&
8 56
To S. Higuera
, Street,
HLs3 w"Low-por" ArPERMIT DESIGN VEHICLE

CURVE DATA
R=675. OO'
A =35' 0 7 53“
T=21 3.68'
L=413.88'
san cer DATE
DESCN DETAIL SHEET (CLSH) (REV. 7/15/10]
43+97.70 BVC
/ Elev 143.27
/ 240" VC
—F
Bent 3
-Approx OG
For General Notes, see "Deck Contours" sheet.For Hydrologic Summary, see "Foundation Plan” sheet.For Utilities, see "Typical Section" sheet. —Bent 2
—

F?
Figure 4. Proposed US 101 NB Off-Ramp Bridge General Plan Dist COUNTY ROUTE
5 SLO SRxx 2 X TOTAL PROJECT

PRELIMINARY DESIGN JI
7( AGRIDCEPA)
W
\u=/

REGISTERED CIVL ENGNEERDATE
250' VC 2.00%
500’ VC

0.51% R/C = -1.3828% /Sta
R/C= 0.9888% / Sto
M Accue4cy &r coweress & SCAEDconS 4 Js RA SEE7
PROFILE GRADE CONSCR NORTH AMERICA, INC.

A consor s
2868 PROSPECT PARK DR. STE 250
No Scale RANCHO CORDOVA, CA 95670
916.368.9161
250‘-0" Mecsured along "NB-OFF" Line
EB
’NB-OFF" Line
BB39—6"
L T-9" +'-0” 12-0" 12'—0" 8-0" r-9"
- — P( 1
a
MSE WallSR
T
Approx OGV'
Abut 1 Abut 3
Datum Elev = 100.0 I
76+00 77+00 78+00
I

ELEVATION
20’

TYPICAL SECTION
1/4" = I'-
"NB-OFF" Line \
Z
N 36T03h*e t N 27′04′50" E
76 f 77 8
I
"P" LineA

2.3. S
X&RoA BESI&NANCE T

L VE LOADING

BRIDGE NO PRADO ROAD INTERCHANGE
"I A. Hanson

DESICN GVRSGHIT
QuAnTTES SPECIFICATIONS E6548 POST MILE GENERAL PLAN NO. 2 T 3”=—-= 12 I
DESSN DETAL SHEET (CUSH) REV.7/16/10)
P&PR&bJERE-EUMSOS X
Source: Consor Engineers 2026c
June 25, 2026 | 5
" A. Honson
A. Hansan
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
-in-9
MSE Woll
LOL. TypProdo Rd
not shown
125-0"
Span 2
Conc Barrier
Type 836, Typ
To Prodo
Rood
48” Dia Conc
Calumn, TypCIP/PT Core
Box Girder —
TOIAL
SHEETS
EB 77+98.50Elev 159.19
125‘-0"
Span 1
Legend.
(1) Paint "XXx Bridge"
(2) Paint "No. xxx-xxxx”
(3) MSE Woll

PLANS APPROVAL PATE
weSPIEO- caroaea or Is ancersiCAGEVS St NO & fSOSa£ AW
Q
BB 75+48 50Elev 149.42
75+19.30 EVC
Elev 147.82
75+61.81 BVC
Elev 150.14
Note:

The Contractor must verify all
controlling field dimensions before ordering or fabricating any material. 70+19.30 BVC
Flev 132.90
Conc Barrier
Tonsition
UNIT:UNIT
PROJECT NUMBER & PHASE: PROJECT COMBERT NO.: CONTRACT
Bridge

PROJECT ENGINEER
PLAN
1" = 20‘
—POSTMLES SHEET

TOTAL PROJECT

POST MILE

PREPARED FOR THE

CITY OF SAN LUIS OBISPO

PUBLIC WORKS DEPARTMENT
78+11.81 EVCEiev 15S.47
J
Notes

1. For General Noles, see "Deck Contours" sheet.
wL93 w/“Low-noy‘ Ar PERMIT DESICN VEHICLE
Bent 2 U
For Hycrologic Summary, see "Foundation
Pl on sheet
For Utilities, see "Typical Section” sheet.

CURVE DATA
R=750.00‘
A =9* 05‘ 42"
T=59.65‘
L=119.05‘

Figure 5. Proposed US 101 NB On-Ramp Bridge General Plan Dist COUNTY ROUTE SHeeT
33+75.00 EVC 5 SLO SRxx 3
I Elev 150.53
L-s /

PRELIMINARY DESIGN
1 storESsio, REGISTERED CIVIL ENGINEER
-2.00% 300’ VC
400' VC 0.84%
R/C 0.4849% / Sto
R/C - 1.0743% / Sto i__ CW/.

CIVIL

PROFILE GRADE
Aconsor
No Scale
B3 250‘-0" Measured along "NB-ON" Line
EB
"NB-ON" Line
42‘-8" & Var
1-9“ 4-0" 12'-0“ 12-0” 11'—2“
-
I F MSE Woll 7
SR
# ---
Approx OG Abut 1 Bent 2 Abut 3
Box Girder
O
Datum Elev = 100.0
31+00 32+00 33+00

ELEVATION
20'

TYPI CAL SECTION
1/4" T-O"
in L ■"NB-ON" Line
?=1200.00‘
33 31 32 N 27-04′50" E
"P" Line I Notes
To US101

2. ■
PLAN
Note:

I
Live LOADING .

BRIDGE NO PRADO ROAD INTERCHANGE
" A. Hanson

CESION GVERSICHT
Sc । F । CAT । ONS POST MILE GENERAL PLAN NO. 3
UTT i st
DESCN DEtALL SHEET (ENCLSHO (REv.7/15/10)
X
Source: Consor Engineers 2026d6 | June 25, 2026
Preliminary Bridge Design Hydraulic Study US 101 at Prado Road Interchange Project Conc Barrier
Type 836, TypA. Hanson
" A. Hanson
125‘-0"
Span 2
48" Dia Conc
Column, Typ—
Prodo Rd not shown
125-0”
A
Q| C
o
sot.

EB 33+10.76
Elev 152.64
Conc Barrier
Tonsition------
BB 30+67.55
Elev 158 86
38+43.73 EVC
"Elev 142.93
-MSE Wall LOL.

Typ
The Contractor mst verify all
controlling field dimensions before
ordering or fabricating any material.

BridgePROJECT ENGINEER
Legend
(1) Paint "Xxx Bridge"
(2) Paint "No. xxx-xxxx"
(3) MSE Wall
UNIT: UNITPROJECT NUMBER & FHASE: PROJECT EOMRERT NO.: CONTRACT PLANS APPROVAL DATE Is(aridde
w sza Ie or cuiCa4 az /s omcsts ’
Gr AGCVIS Snl NOF dE FCSGKSEE riTE ACCURACY C? CCWIETEAES5 CF SC-MD CORES C ITS ALA. SEE7.
30+75.00 BVC
Elev 158.71 34+43.73 BVC
Elev 148.15
42+39.82 BVC
Elev 146.26

PREPARED FOR THE

CITY OF SAN LUIS OBISPO

PUBLIC WORKS DEPARTMENT
Ne
A6
CONSOR NCRTH AVERICA, INC.
2868 PROSPECT PARK DR. SiE 250
RANCHO CORDOVA, CA 95670
P: 916.358.9181
------Post MiLeS--

TOTAL PRCECT

POST MILE------

TOTAL PROJECT
HLs3 w/“LoN-BOY" AND HX&Tot SESI&NANCE PEFMIT DESIGN VEHIC-E

CURVE DATA
R=1200.00
A =13 43‘ 09"
T=144.36‘
L= 287.33
For Generd Notes, see "Deck Contours" sheet. For Hydrologic Summery, see "Foundation Plan sheet.

For Utilities, see "Typical Section” sheet.
ocraL scAE IN INCHES

FO RDUCEO PLAIS
peincooap pojns pcagnd.

EMRUERAEMSCN DATES
/
CIP/PT Conc . 5W

F2

1.4 Design Criteria
The following criteria were used in the design of the proposed bridges.

1.4.1 Hydraulic Design Criteria

1.4.1.1 Federal Highway Administration (FHWA) Standards

1.4.1.2 Caltrans Standards

1.4.1.3 County of San Luis Obispo Standards

1.4.1.4 June 25, 2026 | 7
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
From Memo to Designers 16-1 Hydraulic Design for Structures over Waterways, the proposed bridge soffit should provide adequate freeboard to pass anticipated drift for the 50-year design flood, or to pass the 100-year base flood without freeboard, whichever is greater (Caltrans 2017).

From Chapter 820 of the Caltrans’ Highway Design Manual (HDM), the criterion for the hydraulic design of bridges is that they be designed to pass the 2% probability of annual exceedance flow (50-year design discharge) with adequate freeboard to pass anticipated bedload and debris. Two (2) feet (ft) of freeboard is commonly used in bridge designs.

Alternatively, the bridge can also be designed to pass the 1% probability of annual exceedance flow (100-year design discharge, or base flood). No freeboard is added to the base flood (Caltrans 2025a).

Per Title 23 Chapter I Subchapter G Part 650 Subpart A Section 650.115 (23 Code of Federal Regulations [CFR] 650.115), “freeboard shall be provided, where practicable, to protect bridge structures from debris- and scour-related failure.” (FHWA 2026).

City of San Luis Obispo Standards
The City of San Luis Obispo (City) developed a Waterway Management Plan comprised of three volumes, which discuss watershed management, management and maintenance for waterways in the San Luis Obispo Creek watershed, and policies for floodplain management with the City. The Waterway Management Plan also includes guidelines for designs of channels, storm drain systems, stormwater facilities, and erosion control, but does not specify bridge freeboard requirements. While bridge freeboard is not specified, the San Luis Obispo Creek Waterway Management Plan Volume III Drainage Design Manual (DDM) indicates that the San Luis Obispo Creek channel design requirement is for the 50-year flow in the reach from Madonna Road to The Public Improvement Standards (San Luis Obispo County [County] Department of Public Works 2022) did not specify bridge freeboard criteria. However, the Public Improvement Standards does include a list of federal and state supplemental design standards, and includes a hierarchy to indicate which standards should take precedence.

According to the Public Improvement Standards, “[i]f the County standard does not address the issue, then the appropriate State standard (Caltrans) governs. In cases where the County and State standards do not discuss the design issue, then the appropriate Federal standard governs.” (San Luis Obispo County Department of Public Works 2022)

1.4.1.5 Project Freeboard Criteria

1.4.2 Foundation Criteria
8 | June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Per the California Amendments to the AASHTO LRFD BDS (2017 Eighth Edition) (Caltrans 2019), foundations should be designed to withstand the conditions of scour.

Caltrans’ Memo to Designers 16-1 (Caltrans 2017) provides additional guidance on foundation placement:

Bridge Design Memo 10.7 (Caltrans 2025b) includes information pertaining to the design of driven piles used as deep foundations. According to AASHTO LRFD BDS, deep foundations "shall meet requirements for Service, Strength, Extreme Event." The pile foundations are required to be designed to withstand the effects of scour with pile resistance accounting for potential material loss due to scour.

If the abutments are designed as piers, the foundations should be designed such that they are stable during the scour conditions, including loss of approach fill. This assumes an unsupported pile length above the total scour elevation.

Structure Technical Policy 2.6 (STP 2.6) addresses design criteria for the hydraulic design and scour criteria for new bridges and bridge widenings over waterways (Caltrans 2025c). Similarly to Memo to Designers 16-1, STP 2.6 refers to BDS, but also requires that the foundations consider the check flood conditions based on frequencies up to the 200-year flood. Per STP 2.6, “[t]he design of piers shall ignore the presence and function of scour countermeasures, and the streambed material above the scour elevation is The top of a spread footing must be placed at or below the anticipated total scour (Degradation + Contraction + Local) elevation (LRFD 2.6.4.4.2 and LRFD-BDS-CA Figure C2.6.4.4.2-1) unless founded on competent, scour-resistant bedrock.

Bridges must be designed per the California Amendments to the American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specifications (BDS) (2017 Eighth Edition) (California Department of Transportation [Caltrans] 2019). The California Amendments to the AASHTO LRFD BDS (2017 Eighth Edition) Section 2.6.3 defers to state requirements for hydraulic studies.

The City and County do not specify freeboard criteria for the hydraulic design of bridges.

FHWA and Caltrans freeboard criteria are applicable to the Project: both of which require that bridges pass the 100-year design flow without additional freeboard, or the 50-year design flow with adequate freeboard to pass drift and debris (with 2 ft commonly used).

The Project has been designed to meet FHWA and Caltrans freeboard criteria.

Prado Road and 100-year flow in the reach from Prado Road to the confluence with Prefumo Creek (City of San Luis Obispo Department of Public Works and County of San Luis Obispo Flood Control District - Zone 9 2003).

The top of a pile cap footing must be placed at or below the estimated degradation plus contraction scour depth (LRFD 2.6.4.4.2 and LRFD-BDS-CA Figure C2.6.4.4.2- 2). The bottom of a pile cap footing should be placed at or below the anticipated Total Scour elevation. (Caltrans 2017)

F?

1.4.3 Scour Design Criteria

1.5 Vertical Datum
The Project references the North American Vertical Datum of 1988 (NAVD 88).

June 25, 2026 | 9
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
For abutments supported on deep foundations, the presence and function of scour countermeasures shall not be considered, and the streambed material above the scour elevation is assumed to have been removed (except as noted below). The foundations shall be located so that the bottom of the pile cap is below the scour elevation determined for the Scour Design Flood and shall satisfy the Extreme Event II limit state for scour conditions determined for the Scour (Design) Check Flood. However, the abutment foundation may be designed assuming the soil protected by the scour countermeasure remains in place under all limit states, except the Extreme Event II limit state for the Scour (Design) Check Flood, if the following criteria are satisfied:

The scour countermeasure is properly designed as described in HEC-23 and TechBrief FHWA-HIF-23-048 (Caltrans 2025c)
assumed to have been removed.” The following requirements apply to the deep foundations at the piers and abutments:

Piers supported on pile groups shall be located so that the bottom of the pile cap is below the scour elevation determined for the Scour Design Flood and shall satisfy the Extreme Event II limit state for scour conditions determined for the Scour (Design) Check Flood.

The current or projected annualized average daily traffic (AADT) multiplied by the detour length is less than or equal to 10,000 vehicle-miles, and the AADT is less than or equal to 2000 vehicles. The detour route shall not include scourcritical bridges.

The evaluation of potential scour at the proposed bridge followed the criteria described in the FHWA’s Hydraulic Engineering Circular No. 18 (HEC-18), “Evaluating Scour at Bridges” (FHWA 2012). The evaluation of potential scour was based on the hydraulic characteristics of the scour design flood, which is the 100-year design discharge. Per STP 2.6, scour was also evaluated for the check flood, which is the 200-year design discharge. The total scour was estimated based upon the cumulative effects of the longterm bed elevation change, general (contraction) scour, and local scour.

The exception for abutment foundation design does not apply to the Project site because the AADT exceeds the value noted and scour countermeasures are not proposed for the Project.

2 Geographic Setting

2.1 Geographic Location

2.2 Watershed Description
10 I June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
The Project site is within the San Luis Obispo Creek watershed. The San Luis Obispo Creek watershed is approximately 84-square miles (mi) and located within the Estero Bay Hydrologic Unit, Point Buchon Hydrologic Area, and San Luis Obispo Creek subarea. The upstream limits are in the Santa Lucia Range northeast of San Luis Obispo.

The San Luis Obispo Creek generally flows southwest and discharges into the Pacific Ocean at Avila Beach. Prefumo Creek and Froom Creek are tributaries to San Luis Obispo Creek downstream of the Project location. The Project site is located approximately 50 ft from San Luis Obispo Creek in the floodplain where surface water flows from San Luis Obispo Creek toward Prefumo Creek located approximately 0.25 mi west of the Project site. See Figure 6 for a map of the San Luis Obispo Creek watershed.

The watershed drainage areas for San Luis Obispo Creek, Prefumo Creek, and Froom Creek are shown in Table 1 and the associated watershed delineations are shown in Figure 7. These Project watersheds are associated with the flows at the upstream boundary conditions used in the hydraulic model; the flows are discussed later in Section 3 and the hydraulic model is discussed later in Section 4. The San Luis Obispo Creek watershed area associated with Prado Road is also shown in Figure 7.

The intersection of Dalidio Drive with Froom Ranch Way at the western limits of the Project is at 35°15'30.44" North latitude and 120°40'36.14" West longitude (Google Earth 2025). The intersection of Prado Road with South Higuera Street at the eastern limits of the Project is at 35°15'16.62" North latitude and 120°40'8.42" West longitude (Google Earth 2025). The Project bridges are located within the San Luis Obispo Creek floodplain within the city of San Luis Obispo. The Project bridges are at the intersection of Prado Road with US 101. The Prado Road bridge over the San Luis Obispo Creek (Existing Bridge Number 49C0107) bridge crossing is located east of the proposed Project bridges.

F?
Figure 6. San Luis Obispo Creek Watershed Map
wood Park
Osos
Avil: each
0 1.25 2.5 5 Miles PisT.o Beach NPS, USDA
I । । J__ I__I__ I__I__ .

Data Source: Watersheds - County Department of Public Works (2014); Creeks - HDR (2019a) Table 1. Watershed Drainage Areas
San Luis Obispo Creek At intersection of Marsh Street and Archer Street 24.7 I
At Prado Road 26.6
Prefumo Creek Upstream of confluence of San Luis Obispo Creek 14.2 Froom Creek Upstream of confluence of San Luis Obispo Creek 1.7 Source: United States Geological Survey (USGS) 2026a
June 25, 2026 | 11
Flooding Source Location along Flooding Source
California State Parks, Esri, HERE, Garmin, SafeGraph,
METI/NASA, USGS, Bureau of Land Management, EPA,
Project
Location
Drainage Area
(square mi)
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
San Luis
Obispo
Creek
Pismo Creek
Watershed
is Obispo
Vatershed
Arroyo Grande
Creek Watershed
San Li
Creel/
Coastal
Irish Hills
Watershed
Morro Bay
Watershed
Mid Salinas River
- Atascadero
Area Watershed
San Lui
Obispb
Prefumo
Creek ,
Froom Creek
N
A

Figure 7. Project Watershed Map
XI
Prefumo Creek Watershed
7 Creek
o 0 8 mi
y
-0
Os 0/ OSoS
/.
sr
f roject Location
ine Hill
QBENSTREETMAP CONTRIBUTORS. USGS. NGA.
1 . NPS. NRCAN. ORDNANCE SUR’ ICE SURVEgtQDEl
INTERMAPAANbTE GIS USER COMMUNITY, SOURCES ESRI.

TOMTOM, GARMIN. FAO. NOAA. USGS,J9 OPENSTREETMAP CONTRIBUTORS. AND THE ©
Sources: Esri, USGS 2026a, USGS 2026b
12 | June 25, 2026Preliminary Bridge Design Hydraulic Study US 101 at Prado Road Interchange Project El Chorro
Regional Park
Lopez
Mountain
O
(D
COUNTY OF SAN LUIS OBISPO, VANTOR. SOURCES: ESRI. HERE. DELORME INCREMENT P COJNASA. CGIAR, N ROBINSON. NCEAS. NLS. OS. NMA. GEODATASTYRELSEN. RIJKSWATERSTAA San Luis Obispo Creek
Watershed at the Intersection of
Marsh Street and Archer Street
(T, GSA. GEOLAND FEMA, II

IS USER COMMUNITY
San Luis Obispo
County
Choro
San Luis Obispo Creek
Watershed at Prado Road
| | Froom Creek Watershed
Major Rivers and Creeks
Legend
( Project Location
Zobiso” 2/
©
out
3 (
AI
Ke

F?
3 Hydrologic Assessment
Table 2. Hydrologic Data Summary for Project
FIS 10,300 13,500 17,040
FIS 2,400 3,100 3,930
Froom Creek USGS 278 358 445
June 25, 2026 | 13
Location
50-year 100-year 200-year
At intersection of Marsh
Street and Archer Street
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Upstream of confluence
of San Luis Obispo Creek
Upstream of confluence
of San Luis Obispo Creek
Flooding
Source
Method/Data
Source
The streams that were assessed for the Project include San Luis Obispo Creek, Prefumo Creek, and Froom Creek. Peak flows for San Luis Obispo Creek and Prefumo Creek were obtained from the Federal Emergency Management Agency (FEMA) Flood Insurance Study (FIS); however, the FIS did not include peak flows at Froom Creek.

San Luis
Obispo Creek
Prefumo
Creek
The peak flows at Froom Creek were calculated using the USGS regional regression (flood-frequency) equations. The flood-frequency equations were developed by the USGS and based on analysis of data from gage stations. California is divided into six regions. These flood-frequency equations are generally used to estimate stream flow for ungaged sites that are not affected by substantial urban development and that are natural (unregulated) streams. On July 18, 2012, USGS issued Methods for Determining Magnitude and Frequency of Floods in California, Based on Data through Water Year 2006 (Gotvald et al. 2012), which contains updated regional flood-frequency equations, and revised the boundaries of the six unique regions within California. These equations are based on annual peak-flow data through water year 2006 for 771 streamflow-gaging stations in California with 10 or more years of data. The updated equations were used in support of the hydrologic analysis of Froom Creek. Basin characteristics for the Froom Creek watershed at US 101 (just upstream of its confluence with San Luis Obispo Creek) were obtained from StreamStats (USGS 2026a). The drainage area of Froom Creek at US 101 is 1.7 square mi (see Section 2.1) and the mean annual precipitation is 21.2 inches (USGS 2026a). See Table 2, which presents the calculated 50-year, 100-year, and 200-year flows for Froom Creek.

Note: the 100-year and 50-year flows were taken directly from the FIS for San Luis Obispo Creek and Prefumo Creek. The 200-year flows were extrapolated based on the ratios of the FEMA to regional regression estimates and using the extrapolated ratio to estimate a FEMA 200-year flow.

FEMA is the nationwide administrator of the National Flood Insurance Program (NFIP).

As part of the NFIP, typically, each participating county (or community) has a FIS, which is used to locally develop Flood Insurance Rate Maps (FIRM) and base flood elevations (BFE). The FIS for San Luis Obispo County, California and Incorporated Areas included peak flows along San Luis Obispo Creek and Prefumo Creek for the 100-year, 50-year, and 10-year return periods. The FIS included multiple flow change locations along the creeks (excerpts from the FIS are included in Appendix A); the intersection of Marsh Street and Archer Street is located upstream/north of the Project site approximately at Peak Flow
(cubic ft per second [cfs])

14 | June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
the upstream boundary of the two-dimensional (2D) model domain (see Section 4 for additional details related to the hydraulic model).

The 10-year, 50-year, 100-year, and 200-year flows for San Luis Obispo Creek and Prefumo Creek were also calculated using the USGS regional regression equations. The ratios of the flows listed in the FEMA FIS and the USGS regional regression estimates for the 10-year, 50-year, and 100-year flows were used to extrapolate a ratio for the 200- year flow, and the ratio was multiplied by the USGS regional regression estimate for the 200-year flow to estimate an extrapolated 200-year FEMA flow for the two streams.

Table 2 presents the 100-year and 50-year peak flows from the FIS for San Luis Obispo and Prefumo creeks (FEMA 2024) and the extrapolated 200-year flows for the two streams.

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4 Hydraulic Analysis

4.1 Design Tools

4.2 Hydraulic Model Development

4.2.1 Computational Grid/2D Flow Areas

4.2.2 Model Boundary Conditions
June 25, 2026 | 15
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
The hydraulic analyses were performed for the existing and proposed conditions using the United States Army Corps of Engineers’ (USACE) Hydrologic Engineering Center’s River Analysis System (HEC-RAS) modeling software, Version 6.6 (USACE 2024).

Refinements to the computational grid were made by placing breaklines and refinement regions as needed to provide added definition in controlling flow direction through the creeks, around roads, piers, approach ramps, and abutments for the Project, which are modeled in the terrain. The computational points and breaklines were copied from the proposed condition geometry to the existing condition geometry so that both geometries have the same computational grid to minimize the impacts of model differences on the results.

The following sections discuss the development of the hydraulic models and summarize the results for the existing and proposed conditions. The model results are included in Appendix B and Appendix C.

Boundary conditions of the 2D mesh areas were placed at the upstream and downstream ends of the channels where flows could enter and exit the model during the simulated flows. Figure 8 shows the 2D flow area cells included in the mesh of the model domain as well as the upstream and downstream boundary condition locations. The model has three upstream boundary conditions and one downstream boundary condition.

A 2D model was developed for the Project to assess the existing and proposed conditions. The following sections describe the parameters used in the hydraulic model development. The hydraulic modeling utilized the 2D hydraulic model that was developed as part of the Floodplain Evaluation Report from the previous phase of the Project (HDR 2023) as the base model. The model was refined to include updated information as available and to incorporate additional detailed Project improvement details.

The Project was modeled using a single 2D flow area in the vicinity of the Project (see Figure 8). The 2D mesh was used in the hydraulic model to encompass San Luis Obispo Creek as well as the Prefumo Creek tributary and Froom Creek tributary, both of which contribute flows to San Luis Obispo Creek. The mesh in the 2D hydraulic model has an average cell size of 50 ft and included a total of 54,568 cells that are the same in both the existing and proposed conditions model geometries.

Figure 8. 2D Flow Areas and Boundary Conditions
LEGEND
[ 2D Flow Area Cells
I Boundary Conditions
Proposed Project
. f
S
—
S ■'
t
)-es. 7
w?
___
San Luis Obispo Downstream
Boundary Condition
2000 ft L J
Sources: USACE 2024 and Consor Engineers 2026a (with 2D flow area cells, boundary conditions, and notes from HDR) 16 | June 25, 2026
e
-----
-
Preliminary Bridge Design Hydraulic Study US 101 at Prado Road Interchange Project Froom Creek Upstream
Boundary Condition
Prefumo Creek Upstream Boundary Condition
San Luis Obispo Upstream
Boundary Condition
i
II
Vo
7 -0
AP. i
s
________

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4.2.3 Existing Condition Geometry
Table 3. Data Sources Used to Develop the Hydraulic Model Geometry 1 USGS
2 Wallace Group
3 Wallace Group
4 Wallace Group
5 Prefumo Creek HDR
I I I Froom Ranch development6 HDR
7 Project grading for approaches and Elks Lane Consor Engineers I I I 8 Project linework for abutments, MSE walls, and piers Consor Engineers

4.2.3.1 Terrain
June 25, 2026 | 17
No. Short Description Source of Data
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
San Luis Obispo Creek has an upstream boundary approximately 220 ft upstream of the Pacific Gas and Electric (PG&E) access bridge near Lower Marsh Street.

Project topography based on aerial mapping with survey
conforms
The geometries for the hydraulic model were developed using a combination of the following data sources listed in Table 3.

The data sources listed in Table 3 from USGS, Wallace Group, and HDR (numbers 1 through 6) were used to develop the existing condition hydraulic model and as a basis for the proposed condition hydraulic model. The proposed condition incorporated the proposed Project improvements based on the data sources listed in Table 3 that were provided by Consor Engineers (numbers 7 and 8). These data sources are described in greater detail in Section 4.2.3.

Prado Road bridge over San Luis Obispo Creek (Existing
Bridge Number 49C0107)
The terrain for the existing condition hydraulic model utilized the data sources from USGS, Wallace Group, and HDR (see Table 3).

Topography with newly added digital terrain model in the farm/agricultural portion of the San Luis Ranch southwest of the intersection of US 101 with Prado Road
The upstream boundary for Prefumo Creek is at the downstream face of the Madonna Road bridge. Froom Creek has an upstream boundary in the foothills southwest of Los Osos Valley Road at approximately 275 ft NAVD 88. Both Prefumo Creek and Froom Creek are tributaries to San Luis Obispo Creek. The upstream boundary conditions were set to constant inflow values equal to the peak flows (see Table 2 in Section 3 for a summary of the peak flows) at the respective creek locations. The downstream boundary of the model is on San Luis Obispo Creek approximately 1,800 ft downstream of the Los Osos Valley Road over San Luis Obispo Creek bridge. The downstream boundary condition was set to a slope of 0.006 ft/ft, which was measured from the Original Product Resolution (OPR) Digital Elevation Model (DEM) (USGS 2018) along the boundary edge of the model domain.

OPR California (CA) Arizona (AZ) FEMA Region 9 (R9)
lidar 2017

The existing merged terrain within the model domain is shown in Figure 9.

4.2.3.2 Bridges
18 | June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
The following Project-specific terrain sources from Wallace Group, and HDR were used to supplement the OPR DEM (USGS 2018).

Cross sections from Prefumo Creek were converted to a 2D surface using survey data that was used to develop the Floodplain Evaluation Report for the previous phase of the Project (HDR 2023), to encompass the area of Prefumo Creek at its confluence with San Luis Obispo Creek, which is located south of the Project improvements.

The Prado Road bridge over San Luis Obispo Creek (Existing Bridge Number 49C0107), which is located east of the proposed Project bridges is proposed to be replaced as a part of a separate project. The terrain for San Luis Obispo Creek in the vicinity of Prado Road at Existing Bridge Number 49C0107 included the existing terrain incorporated with the proposed improvements for the Prado Road bridge over San Luis Obispo Creek bridge replacement project, and was provided to the Project team (Wallace Group 2025a). This bridge is assumed to be replaced prior to the Project, and was modeled as a storage area (SA)/2D connection using data from the Floodplain Evaluation Report for the previous phase of the Project (HDR 2023).

Existing bridges were modeled as SA/2D connections as described in the Floodplain Evaluation Report for the previous phase of the Project (HDR 2023). The structures are shown in Figure 9.

Topography was developed for the Project based on aerial mapping with areas of survey conforms and augmentation from ground surveys (Wallace Group 2025b), which encompasses the areas of improvement within the Project limits. Additional topography with newly added digital terrain model was used to supplement the area in the farm/agricultural portion of the San Luis Ranch southwest of the intersection of US 101 with Prado Road (Wallace Group 2025c), which is in an area west of US 101 and west of the Project improvements.

According to the “CA AZ FEMA R9 2017 D18 Airborne Lidar Report” (USGS 2019), the OPR DEM encompasses areas within California and Arizona; the target resolution of the OPR DEM for the portion of the data within California was Quality Level 2 (QL2) with 2 points per square meter and 0.7-meter (m) nominal point spacing. QL2 lidar has a vertical accuracy of 10 centimeters (cm) and a DEM cell size of 1 m. The OPR DEM (USGS 2018) terrain was imported into HEC-RAS using the function in the RAS Mapper tool built-in to HEC-RAS (USACE 2024).

The Froom Ranch development is located west of the agricultural portion of the San Luis Ranch, and the terrain that encompasses that area was clipped from a terrain that was used in the development of the 2-Dimensional Hydraulic Model Update Draft Report (HDR 2019b).

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Figure 9. Bridges as SA/2D Connections in Hydraulic Model A LEGEND N.
2000 ft L J
Sources: USACE 2024 and Consor Engineers 2026a (with SA/2D connections, boundary conditions, 2D model boundary, and notes from HDR) June 25, 2026 | 19
Proposed Project
2D Model Domain
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Froom Creek Upstream Boundary Condition
Prefumo Creek Upstream
Boundary Condition
San Luis Obispo Downstream
Boundary Condition
San Luis Obispo Upstream
Boundary Condition
| SA/2D Connection
____ Boundary Conditions

4.2.3.3 Manning’s Roughness Coefficients
Table 4. Manning's n Values
Asphalt 0.016

0.04 Open Water 0.03

0.04 Urban Area 0.04
Pasture - No Brush 0.025
Urban-Parking Lot Area 0.04
Pasture - Short Grass 0.03
Urban-Cemetery 0.04
Pasture - High Grass 0.04
Urban Planned Development 0.08 I I Cultivated Area - No Crop 0.03 Urban-Open Grass Areas 0.05
Cultivated Area - Mature Row Crop 0.035
Urban-Cemetery - Short Grass 0.035
Cultivated Area - Mature Field Crop 0.045
Chain link Fence 9

0.05 0.065

0.07 Prefumo Creek -1D model 0.07
Heavy Stands of Timber and Brush 0.1
Froom Creek - 1D model 0.04
Asphalt - Smooth 0.013
Ag Hoop Houses 0.28
20 | June 25, 2026
Description Manning's n Description Manning's n
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Brush - Scattered Brush, Heavy
Weeds
Minor Stream - Clean, Winding,
Some Rock
Minor Stream - Some Weeds and
Stones
SLO Creek - one-dimensional (1D)
model Brush - Light Brush and Trees, in
Summer
Manning’s roughness coefficients (n values) were used in the hydraulic model to estimate energy losses in the flow due to friction. Table 4 lists the Manning’s n values that were used to represent land cover conditions within the hydraulic model domain.

Manning’s n values were selected based upon standard documented values of similar stream conditions from aerial imagery; common channel types are extensively researched in Open-Channel Hydraulics (Chow, V.T. 1959) and have been compiled in the HEC-RAS River Analysis System, Hydraulic Reference Manual (USACE 2016). The Manning’s n value used to represent the areas surrounding the fences were based on engineering judgement, with the assumption that debris would accumulate along the fence line and significantly impact the conveyance across the fence line. Manning’s n values for the areas of San Luis Obispo Creek, Prefumo Creek, and Froom Creek are based on values established in the Floodplain Evaluation Report for the previous phase of the Project (HDR 2023). The Manning’s n value used for the area in the agricultural portion of the San Luis Ranch (described as “Ag Hoop Houses”) was based on a floodplain value that considered obstructions and vegetation estimated following Cowan’s procedure (USACE 2016).

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4.2.4 Proposed Condition Geometry Adjustments

4.2.4.1 Terrain

4.2.4.2 Bridges

4.2.4.3 Manning’s Roughness Coefficients
June 25, 2026 | 21
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
The existing condition hydraulic model geometry was used as a basis for the proposed condition hydraulic model. The following adjustments were incorporated in the proposed condition geometry to represent the Project improvements.

The bridges included in the existing condition geometry remained the same in the proposed condition geometry (Figure 9). Elements of the Project bridges that would be within contact with the evaluated flows were modeled using terrain modifications to represent the piers, abutments, and MSE walls. The bridge superstructures would be elevated above the 100-year WSE and were not included in the model.

The existing condition merged terrain described in Section 4.2.3 was used as the base terrain for the proposed condition terrain. Additional modifications were made to the base terrain using the data sources listed in Table 3 that were provided by Consor Engineers (numbers 7 and 8) to account for the proposed Project improvements. The grading for roadway approaches for the Project bridges and Elks Lane realignment were updated based on information provided by Consor Engineers (Consor Engineers 2025). The piers, abutments, and mechanically stabilized earth (MSE) walls that support the Project bridges (Figure 3, Figure 4, and Figure 5) were imported into the HEC-RAS hydraulic model based on information provided by Consor Engineers (Consor Engineers 2026e) and the elevations were modeled using terrain modifications to be above the 100-year WSE. See the top image in Figure 10 for an enlarged version of the existing condition merged terrain, which is zoomed in (as compared to the terrain in Figure 9 that shows the terrain within the model domain) to better discern the changes to the terrain in the proposed condition. The terrain in the areas beyond the visible areas in Figure 10 are the same in both the existing and proposed condition geometries. See the bottom image in Figure 10 for the proposed condition merged terrain.

The same values were used in both the existing and proposed conditions models except in the areas in the vicinity of the proposed Project bridges where the existing at-grade US 101 ramps and Prado Road subgrade would be removed. The Project is proposing landscaping in the areas where the subgrade will be removed, and the Manning’s n values were set to 0.04 in the proposed condition.

Figure lO.Terrain Comparison in Vicinity of Project
Existing Terrain (top image)
Selected: ‘OG_2025_101 7_Terrain Mods_1f NoDat pws
J
d _ ■
4 24
/
0 6 ■ —
s 9 w
=
J
J
—
■ 5001 L
Proposed Terrain (bottom image)
■ Selected ‘FG_2025_ 1023_ Terrain Mods_vOs
- 7
LJ
/3 3. J
JP
6 ■
A
s 9 j
s , 117-
22 | June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
188-
148-
141-
14-
126-
117-
109
s.
7 r
285—
1 : 1484
1414 134-
$52
US
101
US
101
/
P
/
s
<
0)

F2

4.3 Hydraulic Model Results
16,900 Intersection of Marsh Street and Archer Street
13,600 Madonna Road
8,360 Prado Road
2,150 Confluence with Prefumo Creek
1,765 Los Osos Valley Road
1,050 Confluence with Froom Creek
June 25, 2026 | 23
RS Location/Description
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
The cross section lines were chosen to be parallel to the bridges and to represent the locations upstream of the bridges. References to the profile line and cross section lines are made in the following hydraulic model results summary in Section 4.3. Additional detailed hydraulic model results are available in Appendix B (showing the results within the extents of the model) and Appendix C (showing the results within the Project vicinity).

The profile line follows the channel alignment along San Luis Obispo Creek through the model domain. The downstream limit of the model domain is at approximately 0 ft and the upstream limit of the model domain is at approximately 17,500 ft measured along the profile line of San Luis Obispo Creek. These main channel distance measurements will be referred to as river stations (RS) in this study, and the RS decreases numerically in the downstream direction. For reference, a few geographical features in the Project vicinity and within the model domain are identified in Table 5.

As previously stated in Section 4.2.2, the hydraulic models were computed using constant flow values at the upstream boundaries and a normal depth at the downstream boundary. San Luis Obispo Creek flows in a southerly direction within the model domain.

The model simulations were run for a period long enough for the model results to stabilize to a steady state, which was confirmed by result hydrographs from various locations throughout the model. The hydraulic model results are reported at the final timestep of the model simulations. The hydraulic model results are presented in this section as detailed maps of the 2D HEC-RAS results and as tables and graphs extracted from the 2D results using a profile along San Luis Obispo Creek (see Figure 11, which shows the profile line) and cross section lines (see locations of cut lines in Figure 12, which were cut along the upstream faces of the bridges).

Table 5. River Stations along San Luis Obispo Creek at Geographical Locations

Figure 11. Location of Profile Used to Summarize Model Results LEGEND
17530
San Luis Obispo Creek Profile
15000
12500
10000
m
7500
5000
2500
5)
J
24 | June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Proposed Project
2D Model Domain
fl
2000 ft I___________
Sources: USACE 2024 and Consor Engineers 2026a (with 2D model boundary, San Luis Obispo Creek profile, and notes from HDR)

F?
Figure 12. Locations of Cross Sections Used to Summarize Model Results LEGEND X Selected: ‘San Luis Obispo Creek Profile’
11256.
11000
10750
10500
/
-0250
/ f 10000/
% 9750
7 9500
9250
//
9000
//
/ 7
8750
/
8500
% Y
8250
8000
7000
7250The
7500
6750
scon L
Sources: USACE 2024 and Consor Engineers 2026a (with San Luis Obispo Creek profile, cross section lines, and notes from HDR) June 25, 2026 | 25
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
I
II

7.i'.v
4/s
---------- Proposed Project ---------- San Luis Obispo
Creek ProfileCross Section Lines
9a
7 7750
/

4.3.1 Water Surface Elevations
Figure 13. Existing Condition 100-year Flow Depths
LEGEND
- 17530
San Luis Obispo Creek Profile
15000
See Figure 14
12500
10000
7500
%
‘ 5000
a
2500
2000ft L J
26 | June 25, 2026
Proposed Project
2D Model Domain
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
The results of the hydraulic models indicate that flows spill out of the banks of San Luis Obispo Creek upstream of the Project area until approximately RS 10,500 where the modeled flows are contained within the San Luis Obispo Creek channel. Prado Road is located approximately at RS 8,360. The spill flows occur in the 100-year and 50-year events and is an existing condition that is perpetuated in the proposed condition (see Figure 13, which shows the 100-year flow depths in the existing condition; Appendix B and Appendix C include additional results for the 50-year flow and for the proposed condition). Figure 14 shows the 100-year flow depths in the existing condition, which is a larger scale version of Figure 13 to show greater detail in the Project vicinity. As shown in Figure 14, the 100-year and 50-year flows are contained within San Luis Obispo Creek in the reach starting from RS 10,500 and downstream past Prado Road within the limits of the model domain.

Sources: USACE 2024 and Consor Engineers 2026a (with 2D model boundary, San Luis Obispo Creek profile, depth raster, and notes from HDR)
Max
15-

14. 13-
12-
11-
1 9-
8 7-
6-
5-
4 3
2 1-
0-
01JAN2000 02:00 00
___ , 11

F?
June 25, 2026 | 27
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
The water surface profiles along the San Luis Obispo Creek profile line are shown in Figure 15, which compares the 100-year water surface profiles in the existing and proposed condition, and Figure 16, which compares the 50-year water surface profiles in the existing and proposed condition. Figure 15 and Figure 16 show insignificant changes in WSEs along the San Luis Obispo Creek profile. Comparison rasters were also generated in HEC-RAS to calculate the difference in WSEs between the proposed and existing conditions. A comparison of the WSEs within the model domain are shown in Figure 17 for the 100-year and 50-year storm events.

Figure 18 and Figure 19 show larger scale versions of Figure 17 to show greater detail in the Project vicinity. In general, the comparisons in WSEs show insignificant changes along San Luis Obispo Creek; the model shows increases in WSE that are 0.2 ft or less (or decreases in WSE) within the model domain. There are localized increases and decreases in WSE within the vicinity of the Project improvements. During the 100-year storm event, the maximum increase in the WSE is 2.4 ft, and it occurs at the upstream corner of the western abutment (Abut 1) at the Prado Road west overcrossing bridge.

During the 50-year storm event, the maximum increase in WSE is 1.9 ft, and it also occurs at the upstream corner of the western abutment (Abut 1) at the Prado Road west overcrossing bridge.

WSEs were also extracted along the cross section lines shown in Figure 12 along the upstream faces of the bridges. The maximum WSEs along those lines are shown in Table 6 for the 100-year storm and Table 7 for the 50-year storm. Based on a comparison of the WSEs extracted along the respective cross section lines, the maximum WSE in the proposed condition compared with the maximum WSE in the existing condition increases by 0.1 ft or less. The average WSEs along those lines are also shown in Table 6 for the 100-year storm and Table 7 for the 50-year storm. Based on a comparison of the WSEs extracted along the respective cross section lines, the average WSE in the proposed condition compared with the average WSE in the existing condition increases by 0.3 ft or less.

Figure 14. Existing Condition 100-year Flow Depths at Project Vicinity 01JAN200002: 00 00
LEGEND
A
N
San Luis Obispo Creek Profile 10750
10500
10250
,10000
9750
9500
9250
9000
3750
■ 8500
/
8250 .
-
-8000
F
7750
700D
72!
7500
'6750
500ft L J
Sources: USACE 2024 and Consor Engineers 2026a (with San Luis Obispo Creek profile, depth raster, and notes from HDR)28 | June 25, 2026 Proposed Project
2D Model Domain
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
/
/ /
6’5-
4-
3-
2-1- C —
Max -
15-
14-
13-12-11-10-
9-
8-
Selected 'Existing 100-year ELM v02 - Depth
5'
/

F?
Figure 15. San Luis Obispo Creek 100-Year Water Surface Profile within Model Domain 180170160150140
d 130
120110100
9080
0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000
Main Channel Distance (ft)
Terrain Existing 100-yearWSE Proposed 100-yearWSE
June 25, 2026 | 29
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
co
co
Q<Z
CO o
o
LU

Figure 16. San Luis Obispo Creek 50-Year Water Surface Profile within Model Domain 180170160150140
d 130
120110100
9080
0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000
Main Channel Distance (ft)
Terrain Existing 50-year WSE Proposed 50-year WSE
30 | June 25, 2026
Preliminary Bridge Design Hydraulic Study US 101 at Prado Road Interchange Project co
co
Q<Z
CO o
o
LU

F?
Figure 17. Changes in WSE within the 2D Model Domain
100-year WSE Comparison 50-year WSE Comparison
01JAN2000 02:00:00 O1JAN2000 00 00:00
/
7530 . -17530
15000 15000
/
12500 r 12500
10000
r
10000
7500 CL 7500
5000 5000
/
2500 2500
I
1 |
2000f L J 2000 It L J
Sources: USACE 2024 and Consor Engineers 2026a (with 2D model boundary, San Luis Obispo Creek profile, and WSE raster from HDR) June 25, 2026 | 31
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
I
fl
/
/
/
/
1 Max— 100-

0.21- 0.00-
-0.50-
-1 00-*
/
/
/
I
Max

1.00-
021-

0.00-
-0.50--100
/
/
4 N
/
/
/
/

Figure 18. 100-yearWSE Comparison (Proposed - Existing) within Project Vicinity ▼ 01JAN2000 02:00 00
11256
N
11000
107
10500
10250
10000
9750
9500
I
a '9250
4 .9000
87 a 8500
8000
7000
■ 7500
>6750
500ft L J
Sources: USACE 2024 and Consor Engineers 2026a (with San Luis Obispo Creek profile, and WSE raster from HDR) 32 | June 25, 2026
Preliminary Bridge Design Hydraulic Study US 101 at Prado Road Interchange Project Mae100- 021-
000-
050
-100
■T775° .

Selected ’ Com pore WSE v03 .
500
«
i
/

F?
Figure 19. 50-year WSE Comparison (Proposed - Existing) within Project Vicinity X254
Com pa r e_50y ear WSE 01JAN2000 00 00 00
J
II
11000
.10500
10250
,10000
dy
9750
9500
9250
9000
sr
f
s -8500
) Alt
8250 —e
3- 8000 "A
7-50
7000
725 7500
6750 7 5004 L j
Sources: USACE 2024 and Consor Engineers 2026a (with San Luis Obispo Creek profile, and WSE raster from HDR) June 25, 2026 | 33
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
3 J
/
‘/s Max

1.00. 0.21- 0.00-
-0.50
-1.00-
/
-

Table 6. 100-year Water Surface Elevations Upstream of Bridges WSE (ft NAVD 88) WSE (ft NAVD 88)
Existing Proposed Existing Proposed
136.9 136.9 0 133.7 133.9 0.2
137.3 137.4 0.1 137.3 137.4 0.1
US 101 NB Off-Ramp 136.8 136.5 -0.3 136.3 136.2 -0.1
US 101 NB On-Ramp 137.5 137.6 0.1 137.4 137.5 0.1
Table 7. 50-year Water Surface Elevations Upstream of Bridges WSE (ft NAVD 88) WSE (ft NAVD 88)
Existing Proposed Existing Proposed
136.6 136.7 0.1 133.2 133.5 0.3
136.9 136.9 0 136.9 136.9 0
US 101 NB Off-Ramp 136.5 136.2 -0.3 136.1 135.9 -0.2
US 101 NB On-Ramp 137.0 137.1 0.1 137.0 137.0 0
34 | June 25, 2026
Structure Name Maximum WSEs Average WSEs
Structure Name Maximum WSEs Average WSEs
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
(Proposed
-Existing)
(Proposed
-Existing)
(Proposed
-Existing)
(Proposed
-Existing)
Prado Road East
Overcrossing
Prado Road East
Overcrossing
Change in
WSE (ft)
Change in
WSE (ft)
Change in
WSE (ft)
Change in
WSE (ft)
Prado Road West
Overcrossing
Prado Road West
Overcrossing
According to Memo to Designers 16-1 (Caltrans 2017), a hydrologic summary table shall be placed on the Project Foundation Plan. The hydrologic summary is shown in Table 8 for the proposed Prado Road west overcrossing, Table 9 for the proposed Prado Road east overcrossing, Table 10 for the proposed US 101 NB off-ramp to Prado Road, and Table 11 for the proposed US 101 NB on-ramp from Prado Road. The reported WSEs are based on the upstream cross section at the proposed respective bridges. The WSE varies along the cross sections, and the reported value is the maximum at each of the bridge locations.

F?
Table 8. Hydrologic Summary Table for Prado Road West Overcrossing Discharge 2,330 3,470 4,510
136.7 136.9 137.2
Table 9. Hydrologic Summary Table for Prado Road East Overcrossing Discharge 1,600 2,610 3,630
136.9 137.4 137.8
Table 10. Hydrologic Summary Table for US 101 NB Off-Ramp Discharge 1,600 2,610 3,630
136.2 136.5 136.7
June 25, 2026 | 35
Frequency
Frequency
Frequency
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Check Flood
200-year
Check Flood
200-year
Check Flood
200-year
Base Flood
100-year
Base Flood
100-year
Base Flood
100-year
Water Surface Elevation at
Bridge
Floodplain data are based upon information available when the plans were prepared and are shown to meet federal requirements. The accuracy of said information is not warranted by the state and interested or affected parties should make their own investigation.

Floodplain data are based upon information available when the plans were prepared and are shown to meet federal requirements. The accuracy of said information is not warranted by the state and interested or affected parties should make their own investigation.

Floodplain data are based upon information available when the plans were prepared and are shown to meet federal requirements. The accuracy of said information is not warranted by the state and interested or affected parties should make their own investigation.

Water Surface Elevation at
Bridge
Water Surface Elevation at
Bridge
Design Flood
50-year
Design Flood
50-year
Design Flood
50-year
Hydrologic Summary for
Bridge No. 49C####
Drainage Area: 26.6 mi2
Hydrologic Summary for
Bridge No. 49C####
Drainage Area: 26.6 mi2
Hydrologic Summary for
Bridge No. 49 #####
Drainage Area: 26.6 mi2

Table 11. Hydrologic Summary Table for US 101 NB On-Ramp Discharge 1,600 2,610 3,630
137.1 137.6 138.1

4.3.2 Freeboard
Table 12.100-Year Water Surface Elevations and Freeboard Prado Road West Overcrossing 142.7 136.9 5.8
Prado Road East Overcrossing 139.4 137.4 2.0
US 101 NB Off-Ramp 144.4 136.5 7.9
US 101 NB On-Ramp 144.4 137.6 6.8
Table 13. 50-Year Water Surface Elevations and Freeboard Prado Road West Overcrossing 142.71 136.7 6.0
Prado Road East Overcrossing 139.37 136.9 2.5
US 101 NB Off-Ramp 144.42 136.2 8.2
US 101 NB On-Ramp 144.42 137.1 7.3
36 | June 25, 2026
Frequency
Structure Name
Structure Name WSE (ft NAVD 88)
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Check Flood
200-year
Minimum Soffit
Elevation
(ft NAVD 88)
Minimum Soffit
Elevation
(ft NAVD 88)
Base Flood
100-year
Water Surface Elevation at
Bridge
Floodplain data are based upon information available when the plans were prepared and are shown to meet federal requirements. The accuracy of said information is not warranted by the state and interested or affected parties should make their own investigation.

As described in Section 1.4, the hydraulic design criteria applicable to the Project require that bridges pass the 100-year design flow without freeboard and the 50-year flow with 2 ft of freeboard from the lowest portion of the bridge span. The WSEs and available freeboard are presented in Table 12 for the 100-year storm and Table 13 for the 50-year storm. The minimum soffit elevations are based on the bridge general plans (Consor Engineers 2026b, 2026c, and 2026d). The soffit elevations account for the depth of the proposed girders but do not incorporate the roadway cross slope. Based on the results of the hydraulic modeling, the bridges would provide applicable freeboard during the 100- year and 50-year flows.

Design Flood
50-year
WSE
(ft NAVD 88)
Freeboard
(ft)
Freeboard
(ft)
Hydrologic Summary for
Bridge No. 49 #####
Drainage Area: 26.6 mi2

F?

4.3.3 Flow Velocities
June 25, 2026 | 37
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Comparison rasters were generated in HEC-RAS to calculate the difference in velocities between the proposed and existing conditions. A comparison of the velocities within the model domain are shown in Figure 20 for the 100-year and 50-year storm events. Figure 21 and Figure 22 show larger scale versions of Figure 20 to show greater detail in the Project vicinity. In general, the comparisons in velocities show insignificant changes along San Luis Obispo Creek; the model shows the increases in velocities are 0.2 ft per second (ft/s) or less (or that there are decreases in velocities) within the model domain.

There are localized increases in velocities within the vicinity of the Project improvements.

During the 100-year storm event, the maximum increase in velocity is 4.9 ft/s, and it occurs at the western abutment (Abut 1) at the Prado Road west overcrossing bridge.

During the 50-year storm event, the maximum increase in velocity is 4.7 ft/s, and it also occurs at the western abutment (Abut 1) at the Prado Road west overcrossing bridge.

Figure 20. Changes in Velocities within the 2D Model Domain 100-year Velocity Comparison 50-year Velocity Comparison 01JAN2000 00 00 00
i
N
17530
— 15000 15000
[12500 12500
10000 4 10000
' $.
.4. s
7500
PNy
7500
5000 5000
2500 2500
/
2000ft L J 2000ft L J
Sources: USACE 2024 and Consor Engineers 2026a (with 2D model boundary, San Luis Obispo Creek profile, and velocity raster from HDR)38 | June 25, 2026 Preliminary Bridge Design Hydraulic Study US 101 at Prado Road Interchange Project J J.
5$
Max100-
021 - 000-

0.50-
-100-
/
/
/
/
/
/
/
/
/
/
(1
01JAN2000 00:00:00
i
II
Max100-0.21- 0 00-
-050- -100-
/
/

F?
Figure 21.100-year Velocity Comparison (Proposed - Existing) within Project Vicinity ’ Selected • Comporev el_o 100 C 01JAN200000 00 00
11000
)
&,
10500
7 10250
k
10C00
897s
K
$500
K
9250
9000
y
—W
B750
re”
4 aw , E,
2 *
4 “7 /
Mar. 7I 7750 7
7500
5001 L
Figure 22. 50-year Velocity Comparison (Proposed - Existing) within Project Vicinity 2ediod CoP"yd "% 01JAN200000 00 00
11000
3 *
10500
10250
10000
6 *
— 600
,‘s
/
d
$000 • J
9 4i i
8750 YA
8500 *
v % f
A ■«DO
er 1
0 -7so 3
4w 7000
" 7500 67so 7 5001 L
June 25, 2026 | 39
Sources: USACE 2024 and Consor Engineers 2026a (with San Luis Obispo Creek profile, and velocity raster from HDR)
Sources: USACE 2024 and Consor Engineers 2026a (with San Luis Obispo Creek profile, and velocity raster from HDR)
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
V0
*C
. o
2 dinice A
Fl.
9750).
5yLr
-
A
t
I4
2 RM
%,
— dhet»
2--== Mex100-
021

0.00-
050
-100-

5 Scour Analysis
Abut 1 (at BB end) NCHRP abutment
I
Bent 2 Pier
Bent 3 Pier
NCHRP abutment
NCHRP abutment
I
Bent 2 Pier
Abut 3 (at EB end) NCHRP abutment
I
Abut 1 (at BB end) NCHRP abutment
Bent 2 Pier
NCHRP abutment
NCHRP abutment
I
Bent 2 Pier
Abut 3 (at EB end) NCHRP abutment
The following sub-sections summarize the results of the scour analysis.

5.1 Caltrans Bridge Inspection Reports
Bridge Inspection Reports do not exist because the Project is proposing new structures. 40 | June 25, 2026
Structure Name Support
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Prado Road West
Overcrossing
Type of Local Scour
Assessed for Support
Prado Road East
Overcrossing
Table 14. Summary of Structures within Floodplain and Type of Scour Assessed
HDR evaluated bridge scour per the criteria described in “Evaluating Scour at Bridges” (FHWA 2012). HDR evaluated the scour potential using the results of the proposed condition 2D hydraulic model analysis from HEC-RAS for the 100-year design storm as the scour design flood and the 200-year design storm as the scour (design) check flood (see Section 4.3 for the hydraulic model results) and the soil properties at the Project site from the geotechnical studies (see Section 5.2 for a summary of the existing channel bed characteristics). The calculations were performed for the Project bridges (US 101 NB offramp to Prado Road, US 101 NB on-ramp from Prado Road, and the Prado Road overcrossing) that will be located within the San Luis Obispo Creek floodplain. The Prado Road west and east overcrossing structures comprise the Prado Road overcrossing. The US 101 NB off-ramp and US 101 NB on-ramp intersect Prado Road in the area between the west and east overcrossing structures. The abutments in the area of the intersection of Prado Road with the US 101 off- and on-ramps are enclosed by MSE walls. The abutment scour equations were used to estimate the scour at the MSE walls (Table 14).

Abut 1 (at BB end)
(enclosed by MSE Wall)
Abut 3 (at EB end)
(enclosed by MSE Wall)
Abut 1 (at BB end)
(enclosed by MSE Wall)
Abut 4 (at EB end)
(enclosed by MSE Wall)
US 101 NB On-Ramp from
Prado Road
US 101 NB Off-Ramp to
Prado Road

F?

5.2 Existing Channel Bed

5.3 Long-Term Bed Elevation Change
Contraction Scour5.4
June 25, 2026 | 41
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Long-term bed elevation changes (degradation) are typically based on historical data at the bridge site. As previously stated in Section 5.1, Bridge Inspection Reports do not exist at the Project, and long-term bed elevation change was not assessed at the Project.

Under the existing conditions, the locations of the proposed structures are currently impervious. As part of the Project, the pavement subgrade will be removed, and will be pervious, which would be susceptible to scour. According to the Draft Structure Preliminary Geotechnical Report Bridges for the Project (Yeh and Associates, Inc. 2025), the regional geology at the proposed Project bridges is young alluvial floodplain deposits.

The Draft Structure Preliminary Geotechnical Report Bridges also describes the subsurface conditions at the Project, which were based on cone penetration tests (CPT) soundings, which showed surficial units of existing artificial fill and alluvium (Qya); in the area of the proposed Project bridges, the ground surface underlying the existing fill was predominantly younger alluvium (Qya) with the Qyai subunit generally in the upper zone compared to the Qya2 subunit (Yeh and Associates, Inc. 2025). The Qyai subunit consisted of “predominantly soft to hard clay and sandy clay...” and the Qya2 subunit consisted of “predominantly soft to medium stiff clay...” (Yeh and Associates, Inc. 2025).

Based on borings in the vicinity of the Project bridges, the soil classifications at the proposed supports are flat clay (CH) and lean clay (CL). Based on these soil classifications, the channel bed in the floodplain areas underlying the proposed foundations was considered to be cohesive for the purpose of analyzing scour.

Contraction scour occurs when the flow area of a stream is reduced by: 1) the natural contraction of the stream channel; 2) a bridge structure; 3) the overbank flow forced back to the channel, 4) natural stream constrictions, or 5) long highway approaches to the bridge over the floodplain. From the continuity equation, a decrease in flow area results in an increase in average velocity and bed shear stress through the contraction. Hence, there is an increase in erosive forces in the contraction section, and more bed material is removed from the contracted reach than is transported into the reach. This increase in transport of bed material from the reach lowers the natural bed elevation. As the bed elevation is lowered, the flow area increases. Thus, the velocity and shear stress decrease until relative equilibrium is reached (i.e., the quantity of bed material that is transported into the reach is equal to that removed from the reach, or the bed shear stress is decreased to a value such that no sediment is transported out of the reach).

Contraction scour, in a natural channel or at a bridge crossing, involves removal of material from the bed across all or most of the channel width (FHWA 2012).

There are two conditions for contraction scour: clear-water or live-bed. Clear-water contraction scour occurs when the bed material is not in motion in the flow upstream of the bridge crossing. Clear-water conditions are typical in floodplain overbank areas such as at the Project site.

Table 15. Calculated Contraction Scour Depths
Abut 1 (at BB end) 1.7 2.1
Bent 2 1.4 1.7
Bent 3 0.9 1.4

1.2 1.2

1.2 1.2
Bent 2 0.8 1.1
Abut 3 (at EB end) 0.7 1.0
Abut 1 (at BB end) 1.1 1.3
Bent 2 1.1 1.3

1.2 1.2

1.2 1.2
Bent 2 0 0.0
Abut 3 (at EB end) 0.9 1.3

5.5 Pier Scour
42 | June 25, 2026
Structure Name Support Contraction Scour Depth (ft)
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
US 101 NB On-Ramp
from Prado Road
Prado Road West
Overcrossing
Prado Road East
Overcrossing
As previously stated in Section 5.2, the channel bed in the floodplain was considered to be cohesive for the purpose of analyzing scour. Equation 6.6 from HEC-18 was used to calculate contraction scour for cohesive materials for the bridge supports (FHWA 2012).

A summary of the calculated contraction scour depths is included in Table 15 and the detailed calculations are included in Appendix D.

Pier scour is caused by vortices (known as a horseshoe vortex) forming at the base of the pier. The horseshoe vortex results from the pileup of water on the upstream surface of the pier and subsequent acceleration of the flow around the base of the pier. The scour depth at a pier is influenced by pier design (shape and dimension), flow characteristics (flow rate, local velocity, and depth at the pier), and sediment particle size distribution. As previously stated in Section 5.2, the channel bed in the floodplain was considered to be cohesive for the purpose of analyzing scour. Equation 7.35 from HECAbut 1 (at BB end) (enclosed by MSE Wall)
Abut 1 (at BB end)
(enclosed by MSE Wall)
Abut 3 (at EB end)
(enclosed by MSE Wall)
Abut 4 (at EB end)
(enclosed by MSE Wall)
US 101 NB Off-Ramp
to Prado Road
200-year
(Scour Check
Flood)
100-year
(Scour Design
Flood)

F?
Table 16. Calculated Local Pier Scour Depths
Bent 2 4.7 5.9
Bent 2 5.6 6.4
Bent 2 2.0 2.7
Abutment Scour5.6
June 25, 2026 | 43
Local Scour Depth (ft)
Structure Name Support
Bent 2
Bent 3

6.7 13.0

5.9 11.0
Prado Road West
Overcrossing
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
A summary of the calculated local scour depths for the abutments and MSE walls is included in Table 17 and the detailed calculations are included in Appendix D. 18 was used to calculate pier scour for cohesive materials (FHWA 2012). The pier scour calculation assumes the footings will not be exposed to flow.

Some of the abutments are proposed to be enclosed by MSE walls, and the NCHRP equation was also used to estimate the local scour at the MSE walls.

A summary of the calculated local pier scour depths is included in Table 16 and the detailed calculations are included in Appendix D.

Abutment scour occurs when the bridge abutments and roadway embankments block approaching flow. A vortex is formed at the upstream end of the abutment and along the toe of the abutment due to the flow obstruction caused by the abutments. The highly turbulent flow caused by the abutments generates the erosive shear action and subsequently causes scouring. According to HEC-18 (FHWA, 2012), local scour at bridge abutments is commonly evaluated using either the Froehlich or HIRE live-bed scour equations. The National Cooperative Highway Research Program (NCHRP) developed alternative abutment scour equations based on a range of abutment types, locations, flow conditions, and sediment transport conditions.

Because of these reasons, the NCHRP method was used to estimate scour at the abutments. The NCHRP method calculates a scour depth that includes both local and contraction scour components at the abutment. The NCHRP scour was calculated using the equations presented in Section 8.6.3 of HEC-18 (FHWA 2012). The contraction scour depth calculated in Section 5.4 of this report was subtracted from the calculated scour depth to determine the local abutment scour.
200-year
(Scour Check
Flood)
While the Froehlich, HIRE, and NCHRP equations are acceptable methods that can be used to estimate scour at abutments, the NCHRP equations have several advantages.

Unlike the Froehlich and HIRE equations, the NCHRP equations do not use an effective embankment length, which can be difficult to determine. The NCHRP equations are also considered to be more representative of the physical scouring processes at the abutments.

Prado Road East
Overcrossing
US 101 NB Off-Ramp
to Prado Road
US 101 NB On-Ramp
from Prado Road
100-year
(Scour Design
Flood)

Table 17. Calculated Local Abutment (and MSE Wall) Scour Depths I
Abut 1 (at BB end) 6.2 7.8

1.7 2.8

1.4 2.1
Abut 3 (at EB end) 1.6 2.9
I
Abut 1 (at BB end) 4.8 5.8

1.4 2.1

1.7 2.8
Abut 3 (at EB end) 5.6 7.7

5.7 Total Scour
Table 18. Scour Summary Table: Prado Road West Overcrossing Abut 1 N/A 1.7 6.2
I I I N/ABent 2 1.4 5.9
Bent 3 N/A 0.9 11.0
I I I Abut 4 N/A 1.2 1.7
Table 19. Scour Summary Table: Prado Road East Overcrossing Abut 1 N/A 1.2 1.4
I I I N/ABent 2 0.8 4.7
Abut 3 N/A 0.7 1.6
44 | June 25, 2026
Structure Name Support Local Scour Depth (ft)
Long Term & Short Term Scour Depths
Prado Road West Overcrossing, Bridge No. 49C####
Support No.

Long Term & Short Term Scour Depths
Prado Road East Overcrossing, Bridge No. 49C####
Support No.

US 101 NB On-Ramp
from Prado Road
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Prado Road West
Overcrossing
Prado Road East
Overcrossing
Degradation
Scour Depth (ft)
Degradation
Scour Depth (ft)
Contraction
Scour Depth (ft)
Contraction
Scour Depth (ft)
Total scour is the sum of the long-term bed elevation change (degradation scour), contraction scour, and local scour (see Table 18 through Table 21 for the scour depths for the proposed bridges based on the scour design flood estimates).

Abut 1 (at BB end)
(enclosed by MSE Wall)
Abut 3 (at EB end)
(enclosed by MSE Wall)
Abut 1 (at BB end)
(enclosed by MSE Wall)
Abut 4 (at EB end)
(enclosed by MSE Wall)
200-year
(Scour Check
Flood)
US 101 NB Off-Ramp
to Prado Road
100-year
(Scour Design
Flood)

F?
Table 20. Scour Summary Table: US 101 NB Off-Ramp
Abut 1 N/A 1.1 4.8
I I I N/ABent 2 1.1 5.6
Abut 3 N/A 1.2 1.4
Table 21. Scour Summary Table: US 101 NB On-Ramp
N/AAbut 1 1.2 1.7
I I I Bent 2 N/A 0.0 2.0
N/AAbut 3 0.9 5.6
Table 22. Scour Data Table: Prado Road West Overcrossing Abut 1 127.8 6.2
I
Bent 2 127.2 5.9
Bent 3 130.9 11.0
Abut 4 131.8 1.7
Table 23. Scour Data Table: Prado Road East Overcrossing Abut 1 131.8 1.4
I
Bent 2 132.2 4.7
Abut 3 132.3 1.6
June 25, 2026 | 45
Long Term & Short Term Scour Depths
US 101 NB Off-Ramp, Bridge No. 49 ####
Support No.

Long Term & Short Term Scour Depths
US 101 NB On-Ramp, Bridge No. 49 ####
Support No.

Support No.

Support No.

Long Term (Degradation and
Contraction) Scour Elevation (ft)
Long Term (Degradation and
Contraction) Scour Elevation (ft)
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Degradation
Scour Depth (ft)
Contraction
Scour Depth (ft)
Degradation
Scour Depth (ft)
Contraction
Scour Depth (ft)
According to Memo to Designers 16-1 (Caltrans 2017), a scour data table shall be placed on the Project Foundation Plan. The scour data tables (see Table 22 through Table 25) for the Project present the long-term scour elevations (based upon the long-term bed degradation and contraction scour depths) and the short-term scour depths (based upon the local scour depth). The long-term scour elevations reference the finish grade elevations at the supports.

Table 24. Scour Data Table: US 101 NB Off-Ramp
Abut 1 131.9 4.8
I
Bent 2 131.9 5.6
Abut 3 131.8 1.4
Table 25. Scour Data Table: US 101 NB On-Ramp
Abut 1 131.8 1.7
I
Bent 2 133.0 2.0
Abut 3 132.1 5.6
46 | June 25, 2026
Support No.

Support No. Long Term (Degradation and
Contraction) Scour Elevation (ft)
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Long Term (Degradation and
Contraction) Scour Elevation (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)

F?
6 References
California Department of Transportation (Caltrans)
2014
2017
2019
2025a
2025b
2025c
Open-Channel Hydraulics. New York: McGraw-Hill Book Co.

City of San Luis Obispo Department of Public Works and County of San Luis Obispo Flood Control 2003
Censor Engineers
2025
Federal Emergency Management Agency (FEMA)
2024
Federal Highway Administration (FHWA)
2012
June 25, 2026 | 47
2026a
2026b
2026c
2026d
2026e
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
“Evaluating Scour at Bridges.” Hydraulic Engineering Circular No. 18. Fifth Edition.

Publication No. FHWA-HIF-12-03.

District - Zone 9
Drainage Design Manual. Volume III. Accessed February 4, 2026. https://www.slocitv.orq/home/showpublisheddocument/4400/638121531708370000.

Chow, V.T.
1959
Prado IC_Surfaces for HDR_20251023.dwg. [Project grading for approaches and Elks Lane]
Prado Plan.dwg [Proposed roadway linework]
D218721a-a-gp01 -General Plan.pdf. [Prado Overcrossing Bridge General Plan] D218721b-a-gp01 -OFF-Ramp GP.pdf. [US 101 NB Off-Ramp Bridge General Plan] D218721c-a-gp01 -ON-Ramp GP.pdf. [US 101 NB On-Ramp Bridge General Plan] D218721_BRIDGE-PLAN.dwg. [Project linework for abutments, MSE walls, and piers] Design Information Bulletin No 87-01. (DIB 87-01). “Hybrid Streambank Revetments:

Vegetated Rock Slope Protection.” Accessed February 4, 2026. https://dot.ca.gov/- /media/dot-media/programs/design/documents/dib87-01.pdf.

Memo to Designers 16-1 Hydraulic Design for Structures over Waterways. Accessed February 4, 2026. https://dot.ca.qov/-Zmedia/dotmedia/proqrams/enqineerinq/documents/memotodesiqner/f0006651-mtd-16-1-final.pdf.

California Amendments to the AASHTO LRFD Bridge Design Specifications (2017 Eighth Edition). Accessed February 4, 2026. https://dot.ca.qov/proqrams/enqineerinqservices/manuals/aashto-lrfd-ca-amendments. “Chapter 820: Cross Drainage” in Highway Design Manual. Accessed February 16, 2026. https://dot.ca.gOv/-/media/dot-media/proqrams/desiqn/documents/chp0820--a11y.pdf Bridge Design Memo 10.7. “10.7 Piles and Shafts.” Accessed October 30, 2025. https://dot.ca.qov/-/media/dotmedia/proqrams/enqineerinq/documents/bridqedesiqnmemos/10/202506bdm1007pilesa ndshafts-a11y.pdf.

Structure Technical Policy 2.6. “2.6 Hydraulic Design for Structures over Waterways.” Accessed June 8, 2026. https://dot.ca.qov/-/media/dotmedia/proqrams/enqineerinq/documents/structure-technical-policy/section-2/stp-26- hydraulic-design-for-structures-over-waterways-121025-a11y.pdf.

Flood Insurance Study. San Luis Obispo County, California and Incorporated Areas.

Flood Insurance Study Number 06079CV001D. Version Number 2.6.3.6. Effective Date:

June 6, 2024. Accessed February 4, 2026.
https://msc.fema.qov/portal/downloadProduct?productTypelD=FINAL PRODUCT&produ ctSubTypelD=FISREPORT&productID=06079CV001D.

2026
Google Earth
Google Earth Pro 7.3.6.10441.2025
Gotvald, A.J., N.A. Barth, A.G. Veilleux, and C. Parrett 2012
2023
San Luis Obispo County Department of Public Works
2014
2022
United States Army Corps of Engineers (USACE)
United States Geological Survey (USGS)
2019
2018
48 | June 25, 2026
2016
2024
2026a
2026b
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
HDR
2019a
2019b
Methods for determining magnitude and frequency of floods in California, based on data through water year 2006. United States Geological Survey Scientific Investigations Report 2012-5113. Accessed January 8, 2026. http://pubs.usgs.gov/sir/2012/5113.

HEC-RAS River Analysis System, Hydraulic Reference Manual, Version 5.0. CPD-69.

Hydrologic Engineering Center’s River Analysis System (HEC-RAS) [Modeling software] Version 6.6. Accessed February 4, 2026.
https://qithub.com/HydroloqicEnqineerinqCenter/hecdownloads/releases/download/1.0.33/HEC-RAS 66 Setup.exe.

Title 23 Chapter I Subchapter G Part 650. “Bridges, Structures, and Hydraulics” Subpart A Section 650.115. Accessed February 16, 2026. https://www.ecfr.gov/current/title23/chapter-l/subchapter-G/part-650.

SLO County Watersheds. (Computer file). Accessed July 20, 2023. https://www.slocounty.ca.qov/Departments/Public-Works/FormsDocuments/Projects/SLO-Watershed-Project/Resources/SLO-County-Watersheds- (1).aspx.

Public Improvement Standards. Accessed February 4, 2026. https://www.slocounty.ca.qov/departments/public-works/forms-documents/developmentservices/public-improvements/public-improvement-standards/county-publicimprovement-standards-2022. “CA AZ FEMA R9 2017 D18 Airborne Lidar Report.” Contract # G16PC00022. Task Order# 140G0218F0027. Contractor Woolpert. Project # 78262. Accessed February 6, 2026. https://prdtnm.s3.amazonaws.com/StaqedProducts/Elevation/metadata/CA AZ FEMA R9 Lidar 2017 D18/CA FEMA Z4 B2 2018/reports/CA AZ FEMA R9 Lidar 2017 D18 Lidar Project Report.pdf.
“USGS Original Project Resolution CA_AZ_FEMA _R9_Lidar_2017_D18 60521606." Accessed February 6, 2026.
https://www.sciencebase.qov/cataloq/item/60491c1fd34eb120311ac439.

StreamStats. Accessed February 4, 2026. https://streamstats.usqs.gov/ss/.

National Hydrography Dataset. Accessed February 11,2026. https://www.usgs.gov/national-hvdrographv/national-hydrographv-dataset. 2-Dimensional Hydraulic Model Update Draft Report.

EC_wPB_08.02.2019.tif. [Existing condition terrain used in development of 2- Dimensional Hydraulic Model Update Draft Report]
Floodplain Evaluation Report. Prado Road Overcrossing Project On U.S. 101 05-SLO101-PM 26.5-27.3.

F?
Wallace Group
2025a
2025b
2025c
Yeh and Associates, Inc.
2025
June 25, 2026 | 49
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
0061-0077 DSGN-Creek Grading.dwg. [San Luis Obispo Creek surface associated with the separate proposed bridge replacement at Existing Bridge Number 49C0107]. 5-1H640 US 101 and Prado Road - TOPO.dwg. [Project topography based on aerial mapping with survey conforms].
5-1H640 US 101 and Prado Road - TOPO_091525.dwg. [Topography with newly added digital terrain model in the farm/agricultural portion of the San Luis Ranch southwest of the intersection of US 101 with Prado Road].

Draft Structure Preliminary Geotechnical Report Bridges. US 101 and Prado Road Interchange Project. San Luis Obispo, California. 05-SLO-101-PM 26.5-27.3. Caltrans Project No. 113-0000-0405; EA 05-1H640. City Specification No. 2091613-02. Yeh Project No.: 223-400.

F?
Appendix A. FIS Excerpts
June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project

FLOOD INSURANC
VOLUME 1 OF 4

SAN LUIS OBISPO

COMMUNITY NAME
060309
060310
060304

2.“eAPTNc,
“oakel 0 FEMA

COMMUNITY
NUMBER
060305
060700
060308
060306
060307

FLOOD INSURANCE STUDY NUMBER
06079CV001D
Version Number 2.6.3.6
REVISED:

JUNE 6, 2024

ARROYO GRANDE, CITY OF

ATASCADERO, CITY OF

EL PASO DE ROBLES, CITY OF

GROVER BEACH, CITY OF

MORRO BAY, CITY OF

PISMO BEACH, CITY OF

SAN LUIS OBISPO, CITY OF

SAN LUIS OBISPO COUNTY,

UNINCORPORATED AREAS

COUNTY, CALIFORNIA

AND INCORPORATED AREAS

Table 9: Summary of Discharges (Continued)
Peak Discharge (cfs)

1.08 260 620 800 1,500
At Verde Drive 0.92 220 530 700 1,300At Cuesta Drive 0.76 180 430 600 1,100At Tassajara Drive 0.57 140 340 400 830At Rockview Place 0.33 100 190 250 470 Paloma Creek 5.8 600 1,730 2,290 2,880
Paloma Creek 3.4 440 1,180 1,550 1,940Paloma Creek 1.1 108 450 570 720

0.9 652 1452 3802 560

0.9 100 340 420 560

37.9 3,200 10,200 14,700 32,000

3.4 600 1,400 1,900 3,500
Prefumo Creek 14.3 1,000 2,400 3,100 5,800
Salinas River 387 16,000 33,000 43,000 66,000Salinas River 331 15,500 32,000 42,000 62,500Salinas River 200 7,800 14,500 21,000 31,000 54 2% Annual
Chance
4% Annual
Chance
1% Annual
Chance
Existing
1% Annual
Chance
Future
Drainage
Area
(Square
Miles)
10% Annual
Chance

0.2%
Annual
Chance
Peachy Canyon
Creek
Peachy Canyon
Creek
Pismo CreekPrefumo Canyon
Creek
Flooding Source
Old Garden Creek Old Garden Creek Old Garden Creek Old Garden Creek Old Garden Creek At Union Pacific
Railroad
At U.S. Highway 101 Approximately 6,400
feet upstream of U.S.

Highway 101
Downstream of Vine
Street
Upstream of Vine
Street
At U.S. Highway 101 At Prefumo Canyon
Road
Upstream of
confluence of San Luis Obispo Creek
At USGS gage at Paso
Robles
Downstream of Paso
Robles Creek
Downstream of Santa Margarita Creek
Location
At Northwest of Murray
Street

Table 9: Summary of Discharges (Continued)
Peak Discharge (cfs)
2,538 33,800 59,900 85,000 112,000 186,000
1,832 32,700 58,100 82,400 108,000
*
181,000
1,721 27,400 49,900 71,800 95,500
*k
162,000
1,561 25,000 45,600 65,700 87,500
*k
149,000
611 19,200 31,700 43,100 54,600
*k
85,300
389 14,500 23,600 31,700 39,800
*
48,600
At Mouth 83.1 4,900 15,300 22,000 50,700

81.4 8,991 14,079 18,290 22,251
*k
30,665

64.8 8,759 13,548 17,381 20,318
*
26,988

56.1 7,876 12,032 15,340 17,746
*
23,921

42.60 4,300 10,200 13,400 25,10026.40 4,1002 9,8002 12,9002 24,200223.40 4,300 10,300 13,500 25,400 55 2% Annual
Chance
4% Annual
Chance
1% Annual
Chance
Existing
1% Annual
Chance
Future
Drainage
Area
(Square
Miles)
10% Annual
Chance

0.2%
Annual
Chance
San Luis Obispo CreekSan Luis Obispo CreekSan Luis Obispo CreekSalinas River Reach 1
Salinas River
Reach 1
Salinas River
Reach 1
San Luis Obispo CreekSan Luis Obispo Creek South San Luis Obispo Creek South San Luis Obispo Creek South Approximately 4,000
feet upstream of mouth Just Upstream of
Davenport Creek
Just Upstream of
Froom Creek Downstream of
confluence of Prefumo Creek
Upstream of
confluence of Prefumo Creek
At intersection of
Marsh Street and
Archer Street
Flooding Source
Salinas River
Reach 1
Salinas River
Reach 1
Salinas River
Reach 1
Location
At USGS Gage near
Bradley
Just Downstream of
San Antonio River
Just Downstream of
Nacimiento River
Just Downstream of
Estella River
Confluence
Just Upstream of
Estella River
Confluence
At USGS Gage at
Paso Robles

Table 9: Summary of Discharges (Continued)
Peak Discharge (cfs)
Flooding Source

12.60 2,500 6,000 7,800 14,60011.50 2,400 5,800 7,600 14,300 3,152 5,8343,152 5,384
607 1,880

23.2 4,800 11,300 13,800
*
18,100
At El Camino Real 22.4 3,450 7,850 9,435 12,300

11.2 2,130 4,580 5,400 7,04011.2 2,130 4,580 5,400 7,040 At Mouth 46.4 3,900 12,500 18,000
*
39,200
At State Highway 41 20.9 2,900 9,200 13,300
* 28,800
At Cambria Road 3 3 1,800 2,700 7,600

3.93 2,538 3 3 3
56 San Luis Obispo Creek SplitflowSan Luis Obispo Creek Splitflow 2% Annual
Chance
4% Annual
Chance
1% Annual
Chance
Existing
1% Annual
Chance
Future
Drainage
Area
(Square
Miles)
10% Annual
Chance

0.2%
Annual
Chance
Santa MargaritaCreekSan Luis Obispo CreekSan Luis Obispo CreekSee Canyon Creek Approximately 600 feet
upstream of confluence
with Davis Canyon
Creek
At confluence of Yerba
Buena CreekNear El Camino Real
approximately 400 feet southwest of
Wilhelmina Avenue
San Luis Obispo Creek Overflow Santa Margarita Creek Santa Margarita Creek Santa Margarita CreekSanta RosaCreekSanta RosaCreekSanta RosaCreek Split Flow Location
At intersection of
Carmel Street and
Higuera Street
South of U.S. Highway
101
At the upstream
confluence with San
Luis Obispo Creek
At the downstream
confluence with San
Luis Obispo Creek
At confluence with
Prefumo Creek
At confluence with
Trout Creek

June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Figure B 1. Depth (ft) at 100-year Flow
Figure B 2. Depth (ft) at 50-year Flow
Figure B 3. Velocity (ft/s) at 100-year Flow
Figure B 4. Velocity (ft/s) at 50-year Flow
Figure B 5. Water Surface Elevation (ft NAVD 88) at 100-year Flow Figure B 6. Water Surface Elevation (ft NAVD 88) at 50-year Flow Figure B 7. Comparison of Velocity and Water Surface Elevation at 100-year Flow Figure B 8. Comparison of Velocity and Water Surface Elevation at 50-year Flow Appendix B. HEC-RAS Model Results: Grid
Extents View

F?
01JAN2000 02:00:00 01JAN2000 02:00:00
k k
7 17530.1 17530.1
N N
17000 17000
16000 16000
15000 15000
14000 14000
13000 ,13000 71
■12000 12000
11000 11000
10000 10000
U
L ,9000 .9000
at
8000 8000
A
5000 5900
4000 4000
13000 13000
1000 1000
0-
2000 ft L J 2000ft L J
June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
6-
5-
Mar15-
14-
13-
12-11-10-
9-
8-
Proposed Conditionroposed 100-yearELM v03 - Depth'
Figure B-1. Depth (ft) at 100-year Flow
Existing Condition
Existing 100-year ELM v02 - Depth'
/
/
/
/
3 2-
Max15-
14-
13-
12-11-10-
9-0-7-6-5-
4-
3-
2-
1-
u-
“17000
6000
*17000
6000
/
/
/

01JAN2000 02:00:00 01JAN2000 02:00:00
/530.1 7
/
N
17000 17003
16LDU - 16000
/
15000 15000
14000 14000
13WUU T30WD
I
12000 i 12000
11000 11000
10000 10003
J 0000 9000 /
8)00 8000
V 5000 5000
4000 —er4000
13001
1000 10m
0- 0-
2000 ft L 2000 ft L J
June 25, 2026
Preliminary Bridge Design Hydraulic Study US 101 at Prado Road Interchange Project Proposed Condition
raposed 50-year ELM v03 - Dopth’
ri
Figure B-2. Depth (ft) at 50-year Flow
Existing Condition
Existing 50-year ELM v02 - Dopth’
1 A.X
Max15-
14-
13-12-11-
10-
9-
8-6-
53-
2-
/
/
Max15-
14-13-
12-11-
I0-
9-
8-
7-6-5-4- 3-2-
“77000
6000
*17000
60JO
3000
1/530.1

F?
01JAN2000 02:00:00 01JAN2O0DO2 00:00
7 N
/
15000 15000
14000 14000
I
1300) 13000
1 A 2
I
11000
— 10000 10000» MOO
/
8OCO ■ 8000
7000
600)
5003 5000
4000 4C0O / 7
/
Max Max
1000 1000
15- 2m
0- 10-
0-
2000ft L J 2000ft L J
June 25, 2026
V
/
/
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
/
/
/
/
/
/
i
N
20-
/
/
1 /
/
/
/
/
Proposed Condition
oposed 100-year ELM v03-Velocity
Figure B-3. Velocity (ft/s) at 100-year Flow
Existing Conditionxisting 100-year ELM v02 - Velocity’
/
/
/
16000
s
0-
6-
(17530. r
%
/
/
0 *=3000
2000
16000
4J
17530.

T17000
7000
6000

01JAN2000 02:00:00 01JAN2000 02:00:00
7 1/520.1
17000 q 7
1/53U.1
/ 1
N
1700)
T6LUU T6U00
15000 115000
14000 14000
13WUU 130U
12000) 12000)
11000 11000
10000 10003
,9000 9000
8)00 —8000
7000 7000
6UUU 60JU
5000 5000
•1000 4000
7 7
11000 10m
8-6-
2000 ft L J 2000 ft L J
June 25, 2026
Preliminary Bridge Design Hydraulic Study US 101 at Prado Road Interchange Project 20-
Proposed Condition
oposed 50-year ELM v03 - Velocity’
Max15-
10-
ri
/
/
w 300U
2000
Figure B-4. Velocity (ft/s) at 50-year Flow
Existing Condition
ixisting 50-year ELMv02 - Velocity’
Max15-
10-
8-
0-
w30DU
2000
/
/
/
/
/
/

F?
01JAN2000 02:00:00 01JAN2000 02:00:00
i
/530.1 7
/
N N
17000 1700)
16WUU 16UUD
/
15000 15000
14000 14000
13UUU 13000
1 12000 12000
1100) ... 11000
10000 1000)
r
5000 .9000
f •800 8000
4 / 5000 5000
4000 4000
300U
4 ift)
1000 10m
2000 ft L J 2000 ft L J
June 25, 2026
*
98 ;
3,
A
I |
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
268-239-209-180-150-121-
01-
268239209
180150121
31 Proposed Condition
‘roposed 100-year ELM v03 -WSE’
Figure B-5. Water Surface Elevation (ft NAVD 88) at 100-year Flow Existing Condition
Existing 100-year ELM v02 -WSE’
/
“77000
6000
s
——,
-
J------------1
*17000
60JO
1/530.1

01JAN2000 02:00:00 01JAN2000 02:00:00
i
1/530.1 7 —1/530.1
/
N N
17(00 17003
16WUU 16000
/
15000 15000
14000 14000
13000 13000
12000 12000
1100) 11000
10000 10003
)
,9000 .9000
/
8)00 •8000
7000
60JU
5000 5000
4000 4000
300U 130UU
ift)
1000 10m
2000 ft L J 2000 ft L J
June 25, 2026
*
si
/
I |
Preliminary Bridge Design Hydraulic Study US 101 at Prado Road Interchange Project 268239209
180150121
91 268-239-209-180-150-121-
91-
Proposed Condition
Proposed 50-year ELM v03 - WSE’
Figure B-6. Water Surface Elevation (ft NAVD 88) at 50-year Flow Existing Condition
‘Existing 50-year ELM v02 -WSE’
B
*17000
6000
——
—U

F?
Figure B-7. Comparison of Velocity and Water Surface Elevation at 100-year Flow 01JAN2000 00:00:00 01 JAN2000 02:00:00
i
1/530.1 ~l
1/530.1
/
t
N N
F 17000 17003
—16WU 16000
-ued
aut -
E .
15000 15000
fr
I r
14000 14000
3 - 13UUO 13000
sie
|
12000 12000
J
I
110 113
j
10000 — 10003
0000
/
•8)00 - 8000
f y
7000 MM e 6030
fertwsia
STU,
h
5000 .5000
4000 4CO0
1 - a-
-
..
_/3LW izuoU
SP
1000 1000
/
a -
-----
s
2000 ft L J vs 2000ft L J
June 25, 2026
Velocity (ft/s) Comparison acted: ‘CompareVel_Q100
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Water Surface Elevation (ft NAVD 88) Comparisonacted: 'CompareWSEvOS' /
/
4 —9000
Max—

1.00-

0.21- 0.00-
-0.5C- .-1.00—
Far 7
“h
100—
021- 000-
-050—
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a
/
/
/
“17000
6000
Du
7"‘dta
-aus —
-
er
sal b
L.
tlu ■ 12000 — S’

Figure B-8. Comparison of Velocity and Water Surface Elevation at 50-year Flow 01JAN2000 00:00:00 OUAN2000 00:00:00
i
1/530.1 7
!
N N
F 17000 17003
16WU —— 16000
/
15000 15000
14000 14000
- 13UUO 13000
12000 - 12000
11000 11300
P
10000 10003
9000 t 9000 /
■ 8300 8000
/
5000 5000
4000 4000
I
(
20OU
1000
2000 ft L J 2000 ft L J
June 25, 2026
Preliminary Bridge Design Hydraulic Study US 101 at Prado Road Interchange Project —3UDU -2000
Velocity (ft/s) Comparison
ected: ‘CompareVel_Q5D
Water Surface Elevation (ft NAVD 88) Comparison
ed: ‘Compare_50_year_WSE‘
/
/
Max— 100 J
021-0.00-
-0.50-|-1.00 J
Max—

1.00-

0.21- 0.00-
-0.5C- .-1.00—
/
/
“17000
6000
*17000
6030
1/530.1

F?
June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Figure C 1. Depth (ft) at 100-year Flow
Figure C 2. Depth (ft) at 50-year Flow
Figure C 3. Velocity (ft/s) at 100-year Flow
Figure C 4. Velocity (ft/s) at 50-year Flow
Figure C 5. Water Surface Elevation (ft NAVD 88) at 100-year Flow Figure C 6. Water Surface Elevation (ft NAVD 88) at 50-year Flow Figure C 7. Comparison of Velocity and Water Surface Elevation at 100-year Flow Figure C 8. Comparison of Velocity and Water Surface Elevation at 50-year Flow Figure C 9. Proposed Condition Depth (ft) at 200-year Flow Figure C 10. Proposed Condition Velocity (ft/s) at 200-year Flow Appendix C. HEC-RAS Model Results: Project
Vicinity View

F?
Figure C-1. Depth (ft) at 100-year Flow
Existing Condition
Selected: ‘Existing 100-year ELMv02- Depth’ 01JAN2000 02:00:00 I
11000
|
10750
os
1 0000
/
I'
z
9000
39 8750 ,
8-
7750 .
7000
7500 6750 500 * L
Proposed Condition
Selected: ‘Proposed 100-year ELM v03 - Depth’ 01JAN2000 02:00:00 e A
10750
1 s
9500
9000
8750
r Hie
£
7750 .■ ss
", r
7500 6750 500* L
June 25, 2026
/ 1
MS te
3 • •
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
S
y
1 207 Max15-
14-
13-
12-
• 11-
10-
Max15-
14-
13-
12-
• 11-
10-
ved
...

Figure C-2. Depth (ft) at 50-year Flow
Existing Condition
Selected: ‘Existing 50-year ELM v02 - Depth’ 01JAN2000 02:00 00 11000
15750
s
I
9500
10-
8-
5-
7750 .
7500 6750 500 * L
Proposed Condition
01JAN2000 02:00 00
11000,
10750
-
10250
/
9500 a 7 4
rf
i
18 /
if 10-
7// 6-
7/ 7750
/
• 7500 6750 500 * L
June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Max15-
14-
13-
12-
Selected: ‘Proposed 50-year ELM v03 - Depth’
sm n
Max15-
14-
13- o I.l 12-
/IIV
//
7;
Hr
5 VP

F?
Figure C-3. Velocity (ft/s) at 100-year Flow
Existing Condition
Selected: ‘Existing 100-year ELM v02 Velocity’ 01JAN2000 02:00:00 4 Ps
/
A
110000
19250
r 4(
\
Max- P2
,7000
0-
T 7500
500 * L
Proposed Condition
Selected: ‘Proposed 100-year ELM v03 Velocity’ 01JAN2000 02:00 00 4 Ps
10750
9 10000
7 19250
{(
1 A
Max-
"I ,7000
0-
7500
500 * L
June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
10250 \
A9750
A9750
/J
10250 \

Figure C-4. Velocity (ft/s) at 50-year Flow
Existing Condition
. Selected:‘Existing 50-year ELM v02 Velocity 01JAN2000 02:00 00 $
4 10750
J
/ W 10000
\
$
L
/
Max750
,7000
0-
‘ 7500
500* L
Proposed Condition
01JAN2000 02:00 00
4 10750
1 / w 10000
\
4 77
7 Max-
,7000 .
' 7500
500* L a
June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
*
10250 \
10250 \
,11000 %
A9750
A9750
(
9000
(
9000
. Selected:‘Proposed 50-year ELM v03 Velocity’
\ J IIm

F?
Figure C-5. Water Surface Elevation (ft NAVD 88) at 100-year Flow Existing Condition
Selected: ‘Existing 100-year ELM v02 WSE‘ 01JAN2000 02:00:00 11000
10750
10500
' 10250
10000
9750
9500
" 9250
9000
$ '
s is T te
8500
8250 s 5s
268-(ft) 28 T 239-
209-—=- 10
150-
121———— 91 -
7 '8000 2 4A7,
s — 7750 , l... $
91- 7500 6750 500* L
Proposed Condition
Selected: ‘Proposed 100-year ELM v03 WSE’ 01JAN2000 02 00 00 11256.
11000
10750
10500
' 10250
10000
9750
19500
( *
" 9250
2 9000
$ 4
i L; • re.,
s
Y”)
x hi 268- 8000 -1 7750 . l..
7000
7500 6750 500* L
June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
239-
209-
180-
150-
121-
91-
9 P
S

Figure C-6. Water Surface Elevation (ft NAVD 88) at 50-year Flow Existing Condition
Selected: ‘Existing 50-year ELM v02 - WSE‘ 01JAN2000 02:00:00 11000
10250
1 10000
9750
9500
9250
t
- #
8500
8250 s
268—-
239-
209-=--
—91 ‘
'8000 to -A0(.
7750 ,
17000'
91- ' 7500
500ft L
Proposed Condition
Selected: ‘Proposed 50
‘ XPod‘Proposed 50-year ELMv03- WSE’ 01JAN2000 02:00:00 1125
11000
10500
10250
10000
9750'
9500
ll 2 ** 12250 9250 ‘ -
(
gt 9000
3 timmm' 8750 5
8500 Lue
8250.
=
'8000
■
7750 . 5 . alrig
A 1, 7500
d 500* L
June 25, 2026
11 s
as
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
s
268-
239-
209-
180-
150-
121-
91-
smmeyt
10500
e
2 y -
Y

F?
Figure C-7. Comparison of Velocity and Water Surface Elevation at 100-year Flow Velocity (ft/s) Comparison
Soleclod "CompareVel_ow. 01JAN2000 00:00 00
■
1 . 10750
4 7/ s
10250
1 4,” K 9500
K 9000
8750
8500
’A [8250 .
8000
“I ? 7750 .
7000
-1.00-
7500 ‘6750 500* L
Water Surface Elevation (ft NAVD 88) Comparison
Selected: ‘CompareWSE_v03 01JAN2000 02:00:00 506, “G"
M 10500
10250
10000
'i *■
M 9500
W 9250
4"
AB
te= t 5
8250.
8000
tsh — 6is wr af-MPiie
AlAB -
1 hi 7750 l.
5 17000'
'• 7500 6750 500* L
June 25, 2026
!-
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
d

3.4 " 9750
at ’
Max1.00-

0.21-

0.00-
-0.50-
-1.00-
3 —ss’aas ‘-ir
• 8500
2,
1o—— -050-=== 860—— 00-===

Figure C-8. Comparison of Velocity and Water Surface Elevation at 50-year Flow Velocity (ft/s) Comparison
Selected: 'CompareVelQW*. 01JAN2000 00:00 00 500,
K * 2 ’
* 10750
10250
!
10000
9500
I 9250 '
23 9000
pj 8750 5
A
A $
18250.

Ty
-8000 af Pima’s
f.
7000
• 7500 0
7 . 6750 500 * L
Water Surface Elevation (ft NAVD 88) Comparison
Selected: ‘Compare_50_year_WSE‘ 01JAN2000 00:00 00
f
11000
t
10250
10000
9500
9250 ‘
9000
*
$
te t —imeyt
tind f
8500
4 -8250.
fy a w05. ■8000 Ali ae *
17750 ,
i 7500 7 5001 L
June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
Max1.00-

0.21-

0.00-
-0.50-
-1.00-
X
9750.
10500
7750 d it
- / f
9750
Max1.00-

0.21-

0.00-
-0.50-
-1.00-
(
-8500
titheeyerd
X 17000 (
- 6750
i...
■ 5 Le —ng

F?
Figure C-9. Proposed Condition Depth (ft) at 200-year Flow Selected ‘Proposed 200 -year ELM v03 - Depth’ 01JAN2000 02 00 00 10250
10000
975.
5500
8500
I
Sa
7750
/
6750 5006 L
Figure C-10. Proposed Condition Velocity (ft/s) at 200-year Flow Selected: "Proposed 200 yearELM v03 Velocity’ 01JAN2000 02.00 00 4 11000
r 10250
10000
19500
9250 \
(
‘A 9000
I - * "T -85 1
18250.
#-la het +
5 7750 -
,7000
7500 AA 5004t L J
June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project
mcaalims, —
—= H 5 -she
i
700 , ’
"“4
‘ "ft
BL
d4
K1: 1—
e —“lP?
9750 7

Appendix D. Scour Calculations
June 25, 2026
Preliminary Bridge Design Hydraulic Study
US 101 at Prado Road Interchange Project

US 101 at Prado Road Interchange Project (Project No. 2091613-02 | Caltrans EA 05-1H640) Contraction Scour Depth (ft)
Structure Name 200-year 100-year

1.2 1.2

1.2 1.2
Local Scour Depth (ft)
Structure Name 200-year 100-year

2.8 1.7

2.1 1.4
Prado Road East
Overcrossing
Prado Road East
Overcrossing
Prado Road West
Overcrossing
Prado Road West
Overcrossing
US 101 NB On-Ramp
from Prado Road
US 101 NB On-Ramp
from Prado Road

1.2 0.0

0.9 1.2

0.0 1.3

2.1 5.9

2.9 5.8

6.4 1.4

4.7 1.6

4.8 5.6

1.2 0.8

0.7 1.1

1.1 1.2

1.1 1.0

1.3 1.3

6.2 5.9

11.0 1.7

1.4 0.9

2.8 2.7

7.7 2.1

1.7 1.4

7.8 6.7

13.0 1.7

2.0 5.6
US 101 NB Off-Ramp to
Prado Road
US 101 NB Off-Ramp to
Prado Road
Support___________
Abut 1 (at BB end)
Bent 2_____________
Bent 3_____________
Abut 4 (at EB end)
(enclosed by MSE Wall)
Abut 1 (at BB end)
(enclosed by MSE Wall)
Bent 2_____________
Abut 3 (at EBend)
Abut 1 (at BB end)
Bent 2_____________
Abut 3 (at EB end)
(enclosed by MSE Wall)
Abut 1 (at BB end)
(enclosed by MSE Wall)
Bent 2_____________
Abut 3 (at EBend)
Support___________
Abut 1 (at BB end)
Bent 2_____________
Bent 3_____________
Abut 4 (at EB end)
(enclosed by MSE Wall)
Abut 1 (at BB end)
(enclosed by MSE Wall)
Bent 2_____________
Abut 3 (at EBend)
Abut 1 (at BB end)
Bent 2_____________
Abut 3 (at EB end)
(enclosed by MSE Wall)
Abut 1 (at BB end)
(enclosed by MSE Wall)
Bent 2_____________
Abut 3 (at EBend)

US 101 at Prado Road Interchange Project (Project No. 2091613-02 | Caltrans EA 05-1H640) Scour Data Tables
Prado West Overcrossing, Bridge No. 49C#### Prado West Overcrossing, Bridge No. 49C#### I
N/AAbut 1 1.7 6.2 Abut 1 127.8 6.2
I I I I N/ABent 2 1.4 5.9 Bent 2 127.2 5.9
I
N/ABent 3 0.9 11.0 Bent 3 130.9 11.0
I I I I N/AAbut 4 1.2 1.7 Abut 4 131.8 1.7
Prado East Overcrossing, Bridge No. 49C#### Prado East Overcrossing, Bridge No. 49C#### Abut 1 N/A 1.2 1.4 Abut 1 131.8 1.4
Bent 2 N/A 0.8 4.7 Bent 2 132.2 4.7
Abut 3 N/A 0.7 1.6 Abut 3 132.3 1.6
US 101 NB Off-Ramp, Bridge No. 49 #### US 101 NB Off-Ramp, Bridge No. 49 #### I
N/AAbut 1 1.1 4.8 Abut 1 131.9 4.8
I I I I N/ABent 2 1.1 5.6 Bent 2 131.9 5.6
I
N/AAbut 3 1.2 1.4 Abut 3 131.8 1.4
US 101 NB On-Ramp, Bridge No. 49 #### US 101 NB On-Ramp, Bridge No. 49 #### Abut 1 N/A 1.2 1.7 Abut 1 131.8 1.7
Bent 2 N/A 0.0 2.0 Bent 2 133.0 2.0
Abut 3 N/A 0.9 5.6 Abut 3 132.1 5.6
ContractionDegradation
Scour Depth (ft) 1 Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Degradation
Scour Depth (ft)
Degradation
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Contraction
Scour Depth (ft)
Degradation
Scour Depth (ft)
Contraction
Scour Depth (ft)
Contraction
Scour Depth (ft)
100-year
Scour Summary Tables
Support
No.

Support
No.

Support
No.

Support
No.

Support
No.

Support
No.

Support
No.

Support
No.

Long Term (Degradation and
Contraction) Scour Elevation
(ft)
Long Term (Degradation and
Contraction) Scour Elevation
(ft)
Long Term (Degradation and
Contraction) Scour Elevation
(ft)
Long Term (Degradation and
Contraction) Scour Elevation
(ft)

F?
Bridge Prado Road West Overcrossing
Abut 1Support Bent 2 Bent 3
Equation 6.7:
2 T=Y
u
Equation 6.6:
(183V, Kz)
V V9y gny^3
ys-utt = 0.94y,
u
hdrinc.com
pg-1

62.4 3.6

0.04 1.486

2.2 1.3
V;
K,
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Ultimate (Contraction) Scour
100-year
Calculation guideline from HEC-18 5th Edition
Project Bridges

62.4 2.9

0.04 1.486

1.5 1.3
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
Unit
lb/ftA3
ft/s
Value

62.4 4.3

0.04 1.486

2.2 1.3

0.7 1.1
1 1000

9.81 0.4

1.4 0.5

0.9 1
1000

9.81 0.3

0.9 Unit
m
m/s
Value

0.7 1.3
1 1000

9.81 0.5

1.7 kg/mA3
m/sA2
m
ft
Description
unit weight of water (62.4 1 b/ftA3 and 9800 N/mA3)
average velocity in contracted section
Manning's roughness coefficient

1.486 for U.S. Customary, and 1.0 for S.I.

Upstream flow depth
Critical shear stress of channel bed material (From Figure 6.11) n
K
Description
Upstream average flow depth
Average velocity in contracted section

1.486 for U.S. Customary, and 1.0 for S.I.

Density of water
acceleration due to gravity
Ultimate contraction scour
Ultimate contraction scour
Variable
Yi
ft
N/mA2=Pa
P
g
Ys ult
Ysult
V2n
Ku
Vo
Te
Variable
g
V2
yo"1/3

F?
Bridge Prado Road East Overcrossing
Abut 3Support Bent 2
Equation 6.7:
2 T=Y
u
Equation 6.6:
(183V, Kz)
V V9y gny^3
ys-utt = 0.94y1
u
hdrinc.com
pg- 2
v:

K,
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Ultimate (Contraction) Scour
100-year
Calculation guideline from HEC-18 5th Edition
Project Bridges
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700

62.4 1.8

0.04 1.486

3.5 1.3
Unit
lb/ftA3
ft/s
Value

62.4 2.0

0.04 1.486

3.1 1.3

1.1 0.5
1 1000

9.81 0.2

0.7 Unit
m
m/s
Value

1.0 0.6
1 1000

9.81 0.2

0.8 kg/mA3
m/sA2
m
ft
Description_______________________________________________ unit weight of water (62.4 1 b/ftA3 and 9800 N/mA3)_______________ average velocity in contracted section
Manning's roughness coefficient

1.486 for U.S. Customary, and 1.0 for S.I.

Upstream flow depth
Critical shear stress of channel bed material (From Figure 6.11) n
K
Description
Upstream average flow depth
Average velocity in contracted section

1.486 for U.S. Customary, and 1.0 for S.I.

Density of water
acceleration due to gravity
Ultimate contraction scour
Ultimate contraction scour
Variable
Yi
P
g
Ys ult
Ysult
ft
N/mA2=Pa
V2n
Ku
Vo
Te
Variable
g
V2
yo"1/3

F?
Bridge US 101 NB Off Ramp
Abut 1Support Bent 2
Equation 6.7:
2 T=Y
u
Equation 6.6:
(183V, Kz)
V V9y gny^3
ys-utt = 0.94yj
u
hdrinc.com
pg- 3
v:

K,

62.4 2.6

0.04 1.486

2.8 1.3
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Ultimate (Contraction) Scour
100-year
Calculation guideline from HEC-18 5th Edition
Project Bridges
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
Unit
lb/ftA3
ft/s
Value

62.4 3.0

0.04 1.486

2.0 1.3
Unit
m
m/s

0.9 0.8
1 1000

9.81 0.3

1.1 Value

0.6 0.9
1 1000

9.81 0.3

1.1 kg/mA3
m/sA2
m
ft
Description_______________________________________________ unit weight of water (62.4 1 b/ftA3 and 9800 N/mA3)_______________ average velocity in contracted section
Manning's roughness coefficient

1.486 for U.S. Customary, and 1.0 for S.I.

Upstream flow depth
Critical shear stress of channel bed material (From Figure 6.11) n
K
Description
Upstream average flow depth
Average velocity in contracted section

1.486 for U.S. Customary, and 1.0 for S.I.

Density of water
acceleration due to gravity
Ultimate contraction scour
Ultimate contraction scour
Variable
Yi
P
g
Ys ult
Ysult
ft
N/mA2=Pa
V2n
Ku
Vo
Te
Variable
g
V2
yo"1/3

F?
Bridge US 101 NBOn Ramp
Abut 3Support Bent 2
Equation 6.7:
2 T=Y
u
Equation 6.6:
(183V, Kz)
V V9y gny^3
ys-utt = 0.94y1
Variable Unit
Y
u
hdrinc.com
pg-4
V;
K,
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Ultimate (Contraction) Scour
100-year
Calculation guideline from HEC-18 5th Edition
Project Bridges

62.4 2.0

0.04 1.486

4.2 1.3
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
m
m/s
Value

62.4 0.4

0.04 1.486

2.2 1.3
Unit
lb/ftA3
ft/s

1.3 0.6
1 1000

9.81 0.3

0.9 Value

0.7 0.1
1 1000

9.81 0.0

0.0 kg/mA3
m/sA2
m
ft
Description_______________________________________________ unit weight of water (62.4 1 b/ftA3 and 9800 N/mA3)_______________ average velocity in contracted section
Manning's roughness coefficient

1.486 for U.S. Customary, and 1.0 for S.I.

Upstream flow depth
Critical shear stress of channel bed material (From Figure 6.11) n
K
Description
Upstream average flow depth
Average velocity in contracted section

1.486 for U.S. Customary, and 1.0 for S.I.

Density of water
acceleration due to gravity
Ultimate contraction scour
Ultimate contraction scour
P
g
Ys ult
Ysult
ft
N/mA2=Pa
V2n
Ku
Vo
Te
Variable
g
V2
yo"1/3

F?
Bridge MSE Walls
Support
Equation 6.7:
2 T=Y
u
Equation 6.6:
(183V, Kz)
V V9y gny^3
ys-utt = 0.94y1
Variable Unit
Y
u
hdrinc.com
pg- 5
Intersection of Prado
Rd with US 101 Ramps
V;
K,
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Ultimate (Contraction) Scour
100-year
Calculation guideline from HEC-18 5th Edition
Project Bridges
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
Unit
lb/ftA3
ft/s
m
m/s
Value

62.4 2.4

0.04 1.486

4.8 1.3
Value

1.5 0.7
1 1000

9.81 0.4

1.2 kg/mA3
m/sA2
m
ft
Description_______________________________________________ unit weight of water (62.4 1 b/ftA3 and 9800 N/mA3)_______________ average velocity in contracted section
Manning's roughness coefficient

1.486 for U.S. Customary, and 1.0 for S.I.

Upstream flow depth
Critical shear stress of channel bed material (From Figure 6.11) n
K
Description
Upstream average flow depth
Average velocity in contracted section

1.486 for U.S. Customary, and 1.0 for S.I.

Density of water
acceleration due to gravity
Ultimate contraction scour
Ultimate contraction scour
ft
N/mA2=Pa
P
g
Ys ult
Ysult
V2n
Ku
Vo
Te
Variable
g
V2
yo"1/3

F?
Equation 7.35:

0.7 0.65 ys = 2.2K1Kza
g
Unit Description
Support Bent 2 Bent 3
degrees
Pier Scour
hdrinc.com
pg-6
Variable
Bridge
ft
ft
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Piers - Cohesive
100-year
Calculation guideline from HEC-18 5th Edition
Project Bridges
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
K1
K2
VI
Vc
Vc
g
ys
Value
Prado Road West Overcrossing
ft/s
m/s
ft/s
ft/sA2
ft
Pier width
Pier length
If L/a is larger than 12, then use 12 as a maximum
Angle of attack of flow
Pier shape
Correction factor for pier shape
Correction factor for angle of attack
Approach velocity
critical velocity (from Figure 4.7 in HEC-18)
critical velocity (from Figure 4.7 in HEC-18)
3 5
15 3
30 Group of
cylinders
1 1.8

2.8 0.5

1.7 32.2

11.0 # of Columns
a
L
_________L/a
e
3 5
15 3
0 Group of
cylinders
1 1.0

2.6 0.5

1.7 32.2

5.9 2.6V1 - Ve

F?
Equation 7.35:

0.7 0.65 2.6V1 - Vc ys = 2.2K1Kza
g
Unit Description
Support Bent 2 Bent 2
degrees
Pier Scour
hdrinc.com
pg-7
Variable
Bridge
ft
ft
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Piers - Cohesive
100-year
Calculation guideline from HEC-18 5th Edition
Project Bridges
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
K1
K2
VI
Vc
Vc
g
ys
ft/s
m/s
ft/s
ft/sA2
ft
Pier width
Pier length
If L/a is larger than 12, then use 12 as a maximum
Angle of attack of flow
Prado Road
East
Overcrossing
Bent 2
Pier shape
Correction factor for pier shape
Correction factor for angle of attack
Approach velocity
critical velocity (from Figure 4.7 in HEC-18)
critical velocity (from Figure 4.7 in HEC-18)
US 101 NB Off
Ramp
Value
US 101 NBOn
Ramp
4 5
20 4
0 Group of
cylinders
1 1.0

2.1 0.5

1.7 32.2

4.7 2
4 8
2 0
Group of
cylinders
1 1.0

1.2 0.5

1.7 32.2

2.0 2
4 8
2 0
Group of
cylinders
1 1.0

2.9 0.5

1.7 32.2

5.6 # of Columns
a
L
L/a
e

F?
Units = (Metric or English) English
Abutment scour equation = Alternative Clear-Water
Alternative Clear-Water Condition Abutment Scour
(
3/7
Equation 8.7 yc =
lb/ftA t 2 c = Critical shear stress for the floodplain material 0.112 Ib/ft/3
ft
Equation 8.3
Vs = Vmax Vo Equation 8.4
ft
hdrinc.com
pg-8
ft
ft
ft
ft
ft
ft
ft/s
cfs
ft
ft2/s
ft
ft/s
cfs
ft
ft2/s

2.2 2.5
2802.0
552.4

5.5 yc = Flow depth including live-bed or clear-water
contraction scour
q2/ql
Type of abutment (Wingwall vs Spill-through)
aB = Amplification factor for clear-water conditions
y max = Maximum flow depth resulting from abutment
scour
yO = Flow depth prior to scour
ys = Abutment scour depth
Contraction scour component
Local scour component
Note: ys is a combination of local and contraction scour.

0.040

62.4 1.486

5.5 Flow depth through bridge
Velocity through bridge
Flowthrough bridge
Bridge opening width less pier widths
q2 = Unit discharge in the constricted opening
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Abutments - NCHRP
100-year
Calculation guideline from HEC-18 5th Edition
Prado Road West Overcrossing

2.6 4.3
2968.7
409.5

11.4 3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
n = Manning n of the floodplain material under the bridge Y = Unit weight of water
Ku = 1.486 English units, 1.0 SI units
yc = Flow depth including contraction scour
ymax = ^AVC or ymax = aByc
Right Overbank = Abutment 1 (West)
yl = Upstream flow depth
Upstream velocity
Upstream flow
Upstream channel width
ql = Upstream unit discharge

5.5 2.1
Wingwall

1.93 Y

10.5 2.6

7.9 1.7

6.2 n(2f
| K, ,

F?
Units = (Metric or English) English
Abutment scour equation = | Alternative Clear-Water |
Alternative Clear-Water Condition Abutment Scour
(
3/7
Equation 8.7 yc
=
lb/ftA TC = Critical shear stress for the floodplain material 0.027 2 lb/ftA3
ft
Equation 8.3
Vs Vmax Vo Equation 8.4
ft
hdrinc.com
pg-9
ft
ft
ft
ft
ft
ft
ft/s
cfs
ft
ft2/s
ft
ft/s
cfs
ft
ft2/s

0.040

62.4 1.486

5.6 Flow depth through bridge
Velocity through bridge
Flowthrough bridge
Bridge opening width less pier widths
q2 = Unit discharge in the constricted opening
yc = Flow depth including live-bed or clear-water
contraction scour
q2/ql
Type of abutment (Wingwall vs Spill-through)
aB = Amplification factor for clear-water conditions
y max = Maximum flow depth resulting from abutment
scour
yO = Flow depth prior to scour
ys = Abutment scour depth
Contraction scour component
Local scour component
Note: ys is a combination of local and contraction scour.

3.5 2.2
2416.9
210.1

7.6 US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Abutments - NCHRP
100-year
Calculation guideline from HEC-18 5th Edition
Prado Road East Overcrossing

3.3 1.8
1530.2
261.1

5.8 3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
n = Manning n of the floodplain material under the bridge Y = Unit weight of water
Ku = 1.486 English units, 1.0 SI units
yc = Flow depth including contraction scour
Vmax = ^-AVC or Vmax = ^BVC

5.6 0.8
Wingwall

1.00 Left Overbank = Abutment 3 (East)
yl = Upstream flow depth
Upstream velocity
Upstream flow
Upstream channel width
ql = Upstream unit discharge
Y
te
nQ2f
. K,

5.6 3.3

2.3 0.7

1.6

F?
Units = (Metric or English) English
Abutment scour equation = | Alternative Clear-Water |
Alternative Clear-Water Condition Abutment Scour
(
3/7
Equation 8.7 yc
=
lb/ftA TC = Critical shear stress for the floodplain material 0.112 2 lb/ftA3
ft
Equation 8.3
Vs Vmax Vo Equation 8.4
ft
hdrinc.com
pg. 10
ft
ft
ft
ft
ft
ft
ft/s
cfs
ft
ft2/s
ft
ft/s
cfs
ft
ft2/s

2.0 3.0
1319.9
232.4

6.2 0.040

62.4 1.486

3.2 Flow depth through bridge
Velocity through bridge
Flowthrough bridge
Bridge opening width less pier widths
q2 = Unit discharge in the constricted opening
yc = Flow depth including live-bed or clear-water
contraction scour
q2/ql
Type of abutment (Wingwall vs Spill-through)
aB = Amplification factor for clear-water conditions
y max = Maximum flow depth resulting from abutment
scour
yO = Flow depth prior to scour
ys = Abutment scour depth
Contraction scour component
Local scour component
Note: ys is a combination of local and contraction scour.

2.0 2.3
1514.1
337.3

4.5 3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Abutments - NCHRP
100-year
Calculation guideline from HEC-18 5th Edition
US 101 NB Off Ramp
n = Manning n of the floodplain material under the bridge Y = Unit weight of water
Ku = 1.486 English units, 1.0 SI units
yc = Flow depth including contraction scour
Vmax = ^-AVC or Vmax = ^BVC
Left Overbank = Abutment 1 (South)
yl = Upstream flow depth
Upstream velocity
Upstream flow
Upstream channel width
ql = Upstream unit discharge

3.2 1.4
Wingwall

2.47 Y
te
nQ2f
. K,

8.0 2.0

5.9 1.1

4.8

F?
Units = (Metric or English) English
Abutment scour equation = | Alternative Clear-Water |
Alternative Clear-Water Condition Abutment Scour
(
3/7
Equation 8.7 yc
=
lb/ftA TC = Critical shear stress for the floodplain material 0.112 2 lb/ftA3
ft
Equation 8.3
Vs Vmax Vo Equation 8.4
ft
hdrinc.com
pg. 11
ft
ft
ft
ft
ft
ft
ft/s
cfs
ft
ft2/s
ft
ft/s
cfs
ft
ft2/s

4.0 2.0
2119.5

93.3 8.1
Flow depth through bridge
Velocity through bridge
Flowthrough bridge
Bridge opening width less pier widths
q2 = Unit discharge in the constricted opening
yc = Flow depth including live-bed or clear-water
contraction scour
q2/ql
Type of abutment (Wingwall vs Spill-through)
aB = Amplification factor for clear-water conditions
y max = Maximum flow depth resulting from abutment
scour
yO = Flow depth prior to scour
ys = Abutment scour depth
Contraction scour component
Local scour component
Note: ys is a combination of local and contraction scour.

4.2 1.6
2602.6
154.3

6.5 0.040

62.4 1.486

4.1 3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Abutments - NCHRP
100-year
Calculation guideline from HEC-18 5th Edition
US 101 NBOn Ramp
n = Manning n of the floodplain material under the bridge Y = Unit weight of water
Ku = 1.486 English units, 1.0 SI units
yc = Flow depth including contraction scour
Vmax = ^-AVC or Vmax = ^BVC
Right Overbank = Abutment 3 (North)
yl = Upstream flow depth
Upstream velocity
Upstream flow
Upstream channel width
ql = Upstream unit discharge

4.1 1.3
Wingwall

2.57 Y
te

10.5 4.0

6.5 0.9

5.6 nQ2f
. K,

F?
Units = (Metric or English) English
Abutment scour equation = Alternative Clear-Water
Alternative Clear-Water Condition Abutment Scour
(
3/7
Equation 8.7 yc =
lb/ftA t 2 c = Critical shear stress for the floodplain material 0.027 Ib/ft/3
ft
Equation 8.3
Vs = Vmax Vo Equation 8.4
ft
hdrinc.com
pg- 12
ft
ft
ft
ft
ft
ft
ft/s
cfs
ft
ft2/s
ft
ft/s
cfs
ft
ft2/s
yc = Flow depth including live-bed or clear-water
contraction scour
q2/ql
Type of abutment (Wingwall vs Spill-through)
aB = Amplification factor for clear-water conditions
y max = Maximum flow depth resulting from abutment
scour
yO = Flow depth prior to scour
ys = Abutment scour depth
Contraction scour component
Local scour component
Note: ys is a combination of local and contraction scour.

0.040

62.4 1.486

6.8 Flow depth through bridge
Velocity through bridge
Flowthrough bridge
Bridge opening width less pier widths
q2 = Unit discharge in the constricted opening

4.1 2.3
1128.2
146.5

9.5 3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700

4.2 1.7
1361.0
172.1

7.2 US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Abutments - NCHRP
100-year
Calculation guideline from HEC-18 5th Edition
MSE Walls
n = Manning n of the floodplain material under the bridge Y = Unit weight of water
Ku = 1.486 English units, 1.0 SI units
yc = Flow depth including contraction scour
ymax = ^AVC or ymax = aByc
Left Overbank = MSE Walls at the South
yl = Upstream flow depth
Upstream velocity
Upstream flow
Upstream channel width
ql = Upstream unit discharge

6.8 0.8
Wingwall

1.00 Y

6.8 4.2

2.6 1.2

1.4 n(2f
| K, ,

F?
Units = (Metric or English) English
Abutment scour equation = Alternative Clear-Water
Alternative Clear-Water Condition Abutment Scour
(
3/7
Equation 8.7 yc =
lb/ftA t 2 c = Critical shear stress for the floodplain material 0.027 Ib/ft/3
ft
Equation 8.3
Vs = Vmax Vo Equation 8.4
ft
hdrinc.com
pg. 13
ft
ft
ft
ft
ft
ft
ft/s
cfs
ft
ft2/s
ft
ft/s
cfs
ft
ft2/s

3.0 2.1
955.2
290.5

6.2 yc = Flow depth including live-bed or clear-water
contraction scour
q2/ql
Type of abutment (Wingwall vs Spill-through)
aB = Amplification factor for clear-water conditions
y max = Maximum flow depth resulting from abutment
scour
yO = Flow depth prior to scour
ys = Abutment scour depth
Contraction scour component
Local scour component
Note: ys is a combination of local and contraction scour.

0.040

62.4 1.486

5.9 Flow depth through bridge
Velocity through bridge
Flowthrough bridge
Bridge opening width less pier widths
q2 = Unit discharge in the constricted opening

4.7 2.1
1127.4
262.5

9.9 3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Abutments - NCHRP
100-year
Calculation guideline from HEC-18 5th Edition
MSE Walls
n = Manning n of the floodplain material under the bridge Y = Unit weight of water
Ku = 1.486 English units, 1.0 SI units
yc = Flow depth including contraction scour
ymax = ^AVC or ymax = aByc

5.9 0.6
Wingwall

1.00 Right Overbank = MSE Walls at the North
yl = Upstream flow depth
Upstream velocity
Upstream flow
Upstream channel width
ql = Upstream unit discharge
Y

5.9 3.0

3.0 1.2

1.7 n(2f
| K, ,

US 101 at Prado Road Interchange Project (Project No. 2091613-02 | Caltrans EA 05-1H640) Scour Data Tables
Prado West Overcrossing, Bridge No. 49C#### Prado West Overcrossing, Bridge No. 49C#### I
N/AAbut 1 2.1 7.8 Abut 1 127.4 7.8
I I I I N/ABent 2 1.7 6.7 Bent 2 126.9 6.7
I
N/ABent 3 1.4 13.0 Bent 3 130.4 13.0
I I I I N/AAbut 4 1.2 2.8 Abut 4 131.8 2.8
Prado East Overcrossing, Bridge No. 49C#### Prado East Overcrossing, Bridge No. 49C#### Abut 1 N/A 1.2 2.1 Abut 1 131.8 2.1
Bent 2 N/A 1.1 5.9 Bent 2 131.9 5.9
Abut 3 N/A 1.0 2.9 Abut 3 132.0 2.9
US 101 NB Off-Ramp, Bridge No. 49 #### US 101 NB Off-Ramp, Bridge No. 49 #### I
N/AAbut 1 1.3 5.8 Abut 1 131.7 5.8
I I I I N/ABent 2 1.3 6.4 Bent 2 131.7 6.4
I
N/AAbut 3 1.2 2.1 Abut 3 131.8 2.1
US 101 NB On-Ramp, Bridge No. 49 #### US 101 NB On-Ramp, Bridge No. 49 #### Abut 1 N/A 1.2 2.8 Abut 1 131.8 2.8
Bent 2 N/A 0.0 2.7 Bent 2 133.0 2.7
Abut 3 N/A 1.3 7.7 Abut 3 131.7 7.7
ContractionDegradation
Scour Depth (ft) 1 Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Degradation
Scour Depth (ft)
Degradation
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Short Term (Local)
Scour Depth (ft)
Contraction
Scour Depth (ft)
Degradation
Scour Depth (ft)
Contraction
Scour Depth (ft)
Contraction
Scour Depth (ft)
200-year
Scour Summary Tables
Support
No.

Support
No.

Support
No.

Support
No.

Support
No.

Support
No.

Support
No.

Support
No.

Long Term (Degradation and
Contraction) Scour Elevation
(ft)
Long Term (Degradation and
Contraction) Scour Elevation
(ft)
Long Term (Degradation and
Contraction) Scour Elevation
(ft)
Long Term (Degradation and
Contraction) Scour Elevation
(ft)

F?
Bridge Prado Road West Overcrossing
Abut 1Support Bent 2 Bent 3
Equation 6.7:
2 T = Y
Variable

2.5 2.5 1.7

1.3 1.3 1.3
Equation 6.6:
y % s-uit = 0.94y1
Variable Unit

0.8 0.5

1.5 1.3 1.2
K.

2.1 1.7 1.4
hdrinc.com
pg- 1
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Ultimate (Contraction) Scour
200-year
Calculation guideline from HEC-18 5th Edition
Project Bridges

62.4 4.0

0.04 1.486

62.4 4.1

0.04 1.486
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
Value

62.4 4.9

0.04 1.486
1 1000

9.81 0.6
1 1000

9.81 0.5
1 1000

9.81 0.4
Unit
lb/ftA3
ft/s
Value

0.7 m
m/s
Description
Upstream average flow depth
Average velocity in contracted section

1.486 for U.S. Customary, and 1.0 for S.I.

Density of water
acceleration due to gravity
Ultimate contraction scour
Ultimate contraction scour
Description
unit weight of water (62.4 1 b/ftA3 and 9800 N/mA3)
average velocity in contracted section
Manning's roughness coefficient

1.486 for U.S. Customary, and 1.0 for S.I.

Upstream flow depth
Critical shear stress of channel bed material (From Figure 6.11) ft
N/mA2=Pa
kg/mA3
m/sA2
m
ft
n
K

1.83V2
gy.
8 V2
Yi
V,
P
g
Ys ult
Y,ult
Yo
Ku
1/3 gny1
'
Yo”1/3

F?
Bridge Prado Road East Overcrossing
Abut 3Support Bent 2
Equation 6.7:
2 T = Y
Variable

3.5 3.8

1.3 1.3
Equation 6.6:
y % s-uit = 0.94y1
Variable Unit

1.2 0.8 0.7
K.

1.1 1.0
hdrinc.com
pg- 2

62.4 2.2

0.04 1.486
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Ultimate (Contraction) Scour
200-year
Calculation guideline from HEC-18 5th Edition
Project Bridges
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
Value

62.4 2.5

0.04 1.486
1 1000

9.81 0.3
1 1000

9.81 0.3
Unit
lb/ftA3
ft/s
Value

1.1 m
m/s
Description
Upstream average flow depth
Average velocity in contracted section

1.486 for U.S. Customary, and 1.0 for S.I.

Density of water
acceleration due to gravity
Ultimate contraction scour
Ultimate contraction scour
Description
unit weight of water (62.4 1 b/ftA3 and 9800 N/mA3)
average velocity in contracted section
Manning's roughness coefficient

1.486 for U.S. Customary, and 1.0 for S.I.

Upstream flow depth
Critical shear stress of channel bed material (From Figure 6.11) ft
N/mA2=Pa
kg/mA3
m/sA2
m
ft
n
K

1.83V2
gy.
8 V2
Yi
V,
P
g
Ys ult
Y,ult
Yo
Ku
1/3 gny1
'
Yo”1/3

F?
Bridge US 101 NB Off Ramp
Abut 1Support Bent 2
Equation 6.7:
2 T = Y
Variable

2.2 3.3

1.3 1.3
Equation 6.6:
y % s-uit = 0.94y1
Variable Unit

1.0 1.0 0.9
K.

1.3 1.3
hdrinc.com
pg- 3

62.4 2.9

0.04 1.486
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Ultimate (Contraction) Scour
200-year
Calculation guideline from HEC-18 5th Edition
Project Bridges
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
Value

62.4 3.4

0.04 1.486
1 1000

9.81 0.4
1 1000

9.81 0.4
Unit
lb/ftA3
ft/s
Value

0.7 m
m/s
Description
Upstream average flow depth
Average velocity in contracted section

1.486 for U.S. Customary, and 1.0 for S.I.

Density of water
acceleration due to gravity
Ultimate contraction scour
Ultimate contraction scour
Description
unit weight of water (62.4 1 b/ftA3 and 9800 N/mA3)
average velocity in contracted section
Manning's roughness coefficient

1.486 for U.S. Customary, and 1.0 for S.I.

Upstream flow depth
Critical shear stress of channel bed material (From Figure 6.11) ft
N/mA2=Pa
kg/mA3
m/sA2
m
ft
n
K

1.83V2
gy.
8 V2
Yi
V,
P
g
Ys ult
Y,ult
Yo
Ku
1/3 gny1
'
Yo”1/3

F?
Bridge US 101 NB On Ramp
Abut 3Support Bent 2
Equation 6.7:
2 T = Y
Variable

2.7 4.7

1.3 1.3
Equation 6.6:
y % s-uit = 0.94y1
Variable Unit

1.4 0.1 0.8
K.

0.0 1.3
hdrinc.com
pg- 4

62.4 2.5

0.04 1.486
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Ultimate (Contraction) Scour
200-year
Calculation guideline from HEC-18 5th Edition
Project Bridges
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
Value

62.4 0.5

0.04 1.486
1 1000

9.81 0.0
1 1000

9.81 0.4
Value

0.8 Unit
lb/ftA3
ft/s
m
m/s
Description
Upstream average flow depth
Average velocity in contracted section

1.486 for U.S. Customary, and 1.0 for S.I.

Density of water
acceleration due to gravity
Ultimate contraction scour
Ultimate contraction scour
Description
unit weight of water (62.4 1 b/ftA3 and 9800 N/mA3)
average velocity in contracted section
Manning's roughness coefficient

1.486 for U.S. Customary, and 1.0 for S.I.

Upstream flow depth
Critical shear stress of channel bed material (From Figure 6.11) ft
N/mA2=Pa
kg/mA3
m/sA2
m
ft
n
K

1.83V2
gy.
8 V2
Yi
V,
P
g
Ys ult
Y,ult
Yo
Ku
1/3 gny1
'
Yo”1/3

F?
Bridge MSE Walls
Support
Equation 6.7:
2 T = Y
Variable

4.8 1.3
Equation 6.6:
y % s-uit = 0.94y1
Variable Unit

0.7 K.

1.2 hdrinc.com
pg- 5
Intersection of Prado
Rd with US 101 Ramps
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Ultimate (Contraction) Scour
200-year
Calculation guideline from HEC-18 5th Edition
Project Bridges
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
Value

62.4 2.4

0.04 1.486
1 1000

9.81 0.4
Value

1.5 Unit
lb/ftA3
ft/s
m
m/s
Description
Upstream average flow depth
Average velocity in contracted section

1.486 for U.S. Customary, and 1.0 for S.I.

Density of water
acceleration due to gravity
Ultimate contraction scour
Ultimate contraction scour
Description
unit weight of water (62.4 1 b/ftA3 and 9800 N/mA3)
average velocity in contracted section
Manning's roughness coefficient

1.486 for U.S. Customary, and 1.0 for S.I.

Upstream flow depth
Critical shear stress of channel bed material (From Figure 6.11) ft
N/mA2=Pa
kg/mA3
m/sA2
m
ft
n
K

1.83V2
gy.
8 V2
Yi
V,
P
g
Ys ult
Y,ult
Yo
Ku
1/3 gny1
'
Yo”1/3

FD?
Equation 7.35:

0.7 0.65 ys = 2.2K1K2 a1
Unit Description
Support Bent 2 Bent 3
degrees
Pier Scour
hdrinc.com
pg- 6
ft
ft
Variable
Bridge
K1
K2
VI
Vc
Vc
g
ys
ft/s
m/s
ft/s
ft/sA2
ft
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Piers - Cohesive
200-year
Calculation guideline from HEC-18 5th Edition
Project Bridges
Pier width
Pier length
If L/a is larger than 12, then use 12 as a maximum
Angle of attack of flow
Pier shape
Correction factor for pier shape
Correction factor for angle of attack
Approach velocity
critical velocity (from Figure 4.7 in HEC-18)
critical velocity (from Figure 4.7 in HEC-18)
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
3 5
15 3
0 Group of
cylinders
1 1.0

3.0 0.5

1.7 32.2

6.7 3
5 15
3 30
Group of
cylinders
1 1.8

3.4 0.5

1.7 32.2

13.0 Value______________________
Prado Road West Overcrossing

2.6V1 - VC
. vg
#of Columns
a
L
L/a
e

FD?
Equation 7.35:

0.7 0.65 ys = 2.2K1K2 a1
Unit Description
Support Bent 2 Bent 2 Bent 2
degrees
Pier Scour
hdrinc.com
pg- 7
Prado Road East
Overcrossing
ft
ft
Variable
Bridge
K1
K2
VI
Vc
Vc
g
ys
ft/s
m/s
ft/s
ft/sA2
ft
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Piers - Cohesive
200-year
Calculation guideline from HEC-18 5th Edition
Project Bridges
Pier width
Pier length
If L/a is larger than 12, then use 12 as a maximum
Angle of attack of flow
Pier shape
Correction factor for pier shape
Correction factor for angle of attack
Approach velocity
critical velocity (from Figure 4.7 in HEC-18)
critical velocity (from Figure 4.7 in HEC-18)
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
4 5
20 4
0 Group of
cylinders
1 1.0

2.6 0.5

1.7 32.2

5.9 2
4 8
2 0
Group of
cylinders
1 1.0

3.4 0.5

1.7 32.2

6.4 2
4 8
2 0
Group of
cylinders
1 1.0

1.5 0.5

1.7 32.2

2.7 2.6V1 - VC
g
US 101 NB Off
Ramp
Value
US 101NB On
Ramp
#of Columns
a
L
L/a
e

F?
Units = (Metric or English) English
| Alternative Clear-Water |
6 3/7
Equation 8.7 yc =
lb/ftA Te = Critical shear stress for the floodplain material 0.112 2 lb/ftA3
ft
ymax Vo
ft
hdrinc.com
pg. 8
ft
ft
ft
ft
ft
Y
T.
ft
ft/s
cfs
ft
ft2/s
ft
ft/s
cfs
ft
ft2/s
Abutment scour equation =
Alternative Clear-Water Condition Abutment Scour
Flow depth through bridge
Velocity through bridge
Flowthrough bridge
Bridge opening width less pier widths
q2 = Unit discharge in the constricted opening

2.5 2.8
3628.7
559.6

6.9 y max = Maximum flow depth resulting from abutment scour yO = Flow depth prior to scour
ys = Abutment scour depth
Contraction scour component
Local scour component
Note: ys is a combination of local and contraction scour. yc = Flow depth including live-bed or clear-water contraction scour
q2/ql
Type of abutment (Wingwall vs Spill-through)
aB = Amplification factor for clear-water conditions
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Abutments - NCHRP
200-year
Calculation guideline from HEC-18 5th Edition
Prado Road West Overcrossing

12.9 3.0

9.9 2.1

7.8 3.0

4.9 3890.8
420.4

14.7 3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
n = Manning n of the floodplain material under the bridge Y = Unit weight of water
Ku = 1.486 English units, 1.0 SI units
yc = Flow depth including contraction scour
ymax ^AVC or ymax ^Byc

6.8 2.1
Wingwall

1.89 Right Overbank = Abutment 1 (West)
yl = Upstream flow depth
Upstream velocity
Upstream flow
Upstream channel width
ql = Upstream unit discharge

0.040

62.4 1.486

6.8 Equation 8.3
Equation 8.4
nQ2f
. K,

F?
Units = (Metric or English) English
Abutment scour equation = | Alternative Clear-Water |
Alternative Clear-Water Condition Abutment Scour
6 3/7
Equation 8.7 yc =
lb/ftA Te = Critical shear stress for the floodplain material 0.027 2 lb/ftA3
ft
Vs ymax Vo
ft
hdrinc.com
pg. 9
ft
ft
ft
ft
ft
Y
T.
ft
ft/s
cfs
ft
ft2/s
ft
ft/s
cfs
ft
ft2/s

3.8 2.2
2300.0
284.6

8.3 Flow depth through bridge
Velocity through bridge
Flowthrough bridge
Bridge opening width less pier widths
q2 = Unit discharge in the constricted opening
y max = Maximum flow depth resulting from abutment scour yO = Flow depth prior to scour
ys = Abutment scour depth
Contraction scour component
Local scour component
Note: ys is a combination of local and contraction scour. yc = Flow depth including live-bed or clear-water contraction scour
q2/ql
Type of abutment (Wingwall vs Spill-through)
aB = Amplification factor for clear-water conditions

3.8 2.7
3353.3
220.4

10.3 US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Abutments - NCHRP
200-year
Calculation guideline from HEC-18 5th Edition
Prado Road East Overcrossing

7.6 3.8

3.8 1.0

2.9 3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700
n = Manning n of the floodplain material under the bridge Y = Unit weight of water
Ku = 1.486 English units, 1.0 SI units
yc = Flow depth including contraction scour
ymax ^AVC or ymax ^Byc

7.6 0.8
Wingwall

1.00 Left Overbank = Abutment 3 (East)
yl = Upstream flow depth
Upstream velocity
Upstream flow
Upstream channel width
ql = Upstream unit discharge

0.040

62.4 1.486

7.6 Equation 8.3
Equation 8.4
nQ2f
. K,

F?
Units = (Metric or English) English
Abutment scour equation = | Alternative Clear-Water |
Alternative Clear-Water Condition Abutment Scour
6 3/7
Equation 8.7 yc =
lb/ftA Te = Critical shear stress for the floodplain material 0.112 2 lb/ftA3
ft
Vs ymax Vo
ft
hdrinc.com
pg. io
ft
ft
ft
ft
ft
Y
T.
ft
ft/s
cfs
ft
ft2/s
ft
ft/s
cfs
ft
ft2/s
Flow depth through bridge
Velocity through bridge
Flowthrough bridge
Bridge opening width less pier widths
q2 = Unit discharge in the constricted opening
y max = Maximum flow depth resulting from abutment scour yO = Flow depth prior to scour
ys = Abutment scour depth
Contraction scour component
Local scour component
Note: ys is a combination of local and contraction scour. yc = Flow depth including live-bed or clear-water contraction scour
q2/ql
Type of abutment (Wingwall vs Spill-through)
aB = Amplification factor for clear-water conditions

2.2 2.5
1845.0
337.3

5.4 3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700

2.2 3.4
1587.8
237.3

7.3 US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Abutments - NCHRP
200-year
Calculation guideline from HEC-18 5th Edition
US 101 NB Off Ramp

9.3 2.2

7.1 1.3

5.8 n = Manning n of the floodplain material under the bridge Y = Unit weight of water
Ku = 1.486 English units, 1.0 SI units
yc = Flow depth including contraction scour
ymax ^AVC or ymax ^Byc
Left Overbank = Abutment 1 (South)
yl = Upstream flow depth
Upstream velocity
Upstream flow
Upstream channel width
ql = Upstream unit discharge

3.7 1.4
Wingwall

2.49 0.040

62.4 1.486

3.7 Equation 8.3
Equation 8.4
nQ2f
. K,

F?
Units = (Metric or English) English
Abutment scour equation = | Alternative Clear-Water |
Alternative Clear-Water Condition Abutment Scour
6 3/7
Equation 8.7 yc =
lb/ftA Te = Critical shear stress for the floodplain material 0.112 2 lb/ftA3
ft
Vs ymax Vo
ft
hdrinc.com
pg-11
ft
ft
ft
ft
ft
Y
T.
ft
ft/s
cfs
ft
ft2/s
ft
ft/s
cfs
ft
ft2/s
Flow depth through bridge
Velocity through bridge
Flowthrough bridge
Bridge opening width less pier widths
q2 = Unit discharge in the constricted opening
y max = Maximum flow depth resulting from abutment scour yO = Flow depth prior to scour
ys = Abutment scour depth
Contraction scour component
Local scour component
Note: ys is a combination of local and contraction scour. yc = Flow depth including live-bed or clear-water contraction scour
q2/ql
Type of abutment (Wingwall vs Spill-through)
aB = Amplification factor for clear-water conditions
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700

4.7 1.8
3621.2
144.7

8.3 US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Abutments - NCHRP
200-year
Calculation guideline from HEC-18 5th Edition
US 101 NB On Ramp

4.7 2.5
2886.0
103.3

11.9 13.7

4.7 9.0

1.3 7.7
n = Manning n of the floodplain material under the bridge Y = Unit weight of water
Ku = 1.486 English units, 1.0 SI units
yc = Flow depth including contraction scour
ymax ^AVC or ymax ^Byc
Right Overbank = Abutment 3 (North)
yl = Upstream flow depth
Upstream velocity
Upstream flow
Upstream channel width
ql = Upstream unit discharge

5.7 1.4
Wingwall

2.42 0.040

62.4 1.486

5.7 Equation 8.3
Equation 8.4
nQ2f
. K,

F?
Units = (Metric or English) English
Abutment scour equation = Alternative Clear-Water
Alternative Clear-Water Condition Abutment Scour
6 3/7
Equation 8.7 yc =
lb/ftA Te = Critical shear stress for the floodplain material 0.027 2 lb/ftA3
ft
Vs ymax Vo
ft
hdrinc.com
pg. 12
Equation 8.3
Equation 8.4
ft
ft
ft
ft
ft
Y
T.
ft
ft/s
cfs
ft
ft2/s
ft
ft/s
cfs
ft
ft2/s
Flow depth through bridge
Velocity through bridge
Flowthrough bridge
Bridge opening width less pier widths
q2 = Unit discharge in the constricted opening
y max = Maximum flow depth resulting from abutment scour yO = Flow depth prior to scour
ys = Abutment scour depth
Contraction scour component
Local scour component
Note: ys is a combination of local and contraction scour. yc = Flow depth including live-bed or clear-water contraction scour
q2/ql
Type of abutment (Wingwall vs Spill-through)
aB = Amplification factor for clear-water conditions

4.5 2.9
1615.4
146.5

12.9 4.4

1.9 1875.2
192.4

8.4 US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Abutments - NCHRP
200-year
Calculation guideline from HEC-18 5th Edition
MSE Walls
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700

7.7 4.4

3.3 1.2

2.1 0.040

62.4 1.486

7.7 n = Manning n of the floodplain material under the bridge Y = Unit weight of water
Ku = 1.486 English units, 1.0 SI units
yc = Flow depth including contraction scour
ymax ^AVC or ymax ^Byc
Left Overbank = MSE Walls at the South
yl = Upstream flow depth
Upstream velocity
Upstream flow
Upstream channel width
ql = Upstream unit discharge

7.7 0.7
Wingwall

1.00 nQ2f
. K,

F?
Units = (Metric or English) English
Abutment scour equation = Alternative Clear-Water
Alternative Clear-Water Condition Abutment Scour
6 3/7
Equation 8.7 yc =
lb/ftA Te = Critical shear stress for the floodplain material 0.027 2 lb/ftA3
ft
Vs ymax Vo
ft
hdrinc.com
pg. 13
Equation 8.3
Equation 8.4
ft
ft
ft
ft
ft
Y
T.
ft
ft/s
cfs
ft
ft2/s
ft
ft/s
cfs
ft
ft2/s

5.0 2.6
1519.9
266.2

13.0 Flow depth through bridge
Velocity through bridge
Flowthrough bridge
Bridge opening width less pier widths
q2 = Unit discharge in the constricted opening
y max = Maximum flow depth resulting from abutment scour yO = Flow depth prior to scour
ys = Abutment scour depth
Contraction scour component
Local scour component
Note: ys is a combination of local and contraction scour. yc = Flow depth including live-bed or clear-water contraction scour
q2/ql
Type of abutment (Wingwall vs Spill-through)
aB = Amplification factor for clear-water conditions

0.040

62.4 1.486

7.2 7.2

3.2 4.0

1.2 2.8
US 101 at Prado Road Interchange Project
City of San Luis Obispo
Local Scour at Abutments - NCHRP
200-year
Calculation guideline from HEC-18 5th Edition
MSE Walls
3003 Oak Road, Suite 500, Walnut Creek, CA 94597
925.465.2700

3.2 2.4
1308.2
297.3

7.7 n = Manning n of the floodplain material under the bridge Y = Unit weight of water
Ku = 1.486 English units, 1.0 SI units
yc = Flow depth including contraction scour
ymax ^AVC or ymax ^Byc

7.2 0.6
Wingwall

1.00 Right Overbank = MSE Walls at the North
yl = Upstream flow depth
Upstream velocity
Upstream flow
Upstream channel width
ql = Upstream unit discharge
nQ2f
. K,

DRAFT
7consor
APPENDIX F: Draft Structure Preliminary Geotechnical
Report (SPGR) Bridges

US 101 and Prado Road Interchange Project
San Luis Obispo, California
05-SLO-101- PM 26.5-27.3
Caltrans Project No. 113-0000-0405; EA 05-1H640
City Specification No. 2091613-02
Yeh Project No.: 223-400
December 23, 2025

INITIALS DATE

DESIGNER/ORIGINATOR

PE-RC CONFIRMS READY FOR QC

INDEPENDENTQC REVIEW DONE

PE- RC CONCURS WITH QC REVIEW
" s ; ]r 11 . • h

QC COM MENTS INCORPORATED
QC COMMENTS BACKCHECKED/VERIFIED M 12/23/25
-
—r
y
11 Credit: Consor North America, Inc.
12/23/25
12/23/25
12/18/25
12/18/25
12/22/25

STRUCTURE PRELIMINARY GEOTECHNICAL REPORT

BRIDGES
Prepared by:

Yeh and Associates, Inc.
391 Front Street, Suite D
Grover Beach, California 93433
Phone:805-481-9590
Yeh and Associates, Inc.

Geotechnical • Geological • Construction Services
Prepared for:

Consor North America, Inc.
2868 Prospect Park Drive, Suite 250
Rancho Cordova, CA 95670
Attn: Dace Morgan, P.E.

INDEPENDENT QUALITY CONTROL REVIEW
US 101 and Prado Road Interchange Project

11 December 23, 2025 Project No. 223-400
Attn: Dace Morgan, P.E.

Subject:

Dear Ms. Morgan:

DRAFT DRAFT
We appreciate the opportunity to be of service. Please contact Judd King at 805-481-9590 x285 or [email protected] if you have questions or require additional information.

Jamie L. Ross, PE, GE
Senior Project Engineer
Yeh and Associates, Inc. is pleased to submit this Structure Preliminary Geotechnical Report for the design of the US 101 overcrossing and viaducts for improvements associated with the U.S. Route 101 (US 101) and Prado Road Interchange Project in San Luis Obispo, California. This report was prepared in accordance with the terms of agreement between Yeh and Associates and Consor North America, Inc. (Consor) dated April 11, 2025. This Structure Preliminary Geotechnical Report (SPGR)for Bridges provides preliminary geotechnical recommendations for the foundations for the overcrossing. This report was prepared in general accordance with Caltrans guidelines for Structure Preliminary Geotechnical Reports (Caltrans 2024c) and provides a discussion of the project alternatives, site conditions, geologic conditions, seismicity and faulting, geotechnical considerations regarding overcrossing structure and ramp foundation alternatives, as well as additional field and laboratory data needed for design.

Consor North America, Inc.
2868 Prospect Park Drive, Suite 250
Rancho Cordova, CA 95670
DRAFT Structure Preliminary Geotechnical Report - Bridges, US 101 and Prado Road Interchange Project, San Luis Obispo, California, 05-SLO-101-PM26.5-27.3, Caltrans Project No. 113-0000-0405; EA 05-1H640, City Specification No. 2091613-02 Judd J. King, PE, GE
Senior Geotechnical Engineer
Sincerely,
YEH AND ASSOCIATES, INC.

Yeh and Associates, Inc.

Geotechnical • Geological • Construction Services
391 Front Street, Suite D
Grover Beach, CA 93433
(805) 481-9590
www.yeh-eng.com
Colorado
Denver | Colorado Springs | Durango | Glenwood Springs | Grand Junction | Greeley California
Grover Beach | Ventura

Reviewed by:

DRAFT DRAFT
Katrina Ocampo, EIT
Engineering Intern
Project No. 223-400
December 23, 2025
Gregg L. Fiegel, PhD, PE, GE
Senior Project Specialist
DRAFT Structure Preliminary Geotechnical Report - Overcrossing US-101 at Prado Road Interchange Project
______California_____
Grover Beach | Ventura
_______________________________Colorado______________________________ Denver | Colorado Springs | Durango | Glenwood Springs | Grand Junction | Greeley

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 Table of Contents

1. INTRODUCTION 3

2. PROJECT DESCRIPTION 3

3. GEOTECHNICAL EXPLORATION 5

3.1 CONE PENETRATION TEST (CPT) SOUNDINGS 6

3.2 PREVIOUS STUDIES 6

4. GEOTECHNICAL CONDITIONS 7

4.1 GEOLOGY 7

4.2 SURFACE CONDITIONS 9

4.2.1 TERRAIN AND TOPOGRAPHY. 9

4.2.2 SURFACE WATER AND DRAINAGE. 9

4.2.3 EXISTING FACILITY 9

4.2.4 EXISTING UTILITIES 10

4.3 SUBSURFACE CONDITIONS 10

5. GROUNDWATER 11

6. SCOUR DATA 13

7. CORROSION EVALUATION 13

8. SEISMIC INFORMATION 14

8.1 GROUND MOTION HAZARD 14

8.2 OTHER SEISMIC HAZARDS 16

8.2.1 SURFACE FAULT RUPTURE 16

8.2.2 LIQUEFACTION POTENTIAL 17

8.2.3 SEISMICALLY INDUCED GROUND SETTLEMENTS 17

8.2.4 LIQUEFACTION-INDUCED LATERAL SPREADING 17

8.2.5 SEISMIC SLOPE STABILITY 17
GEOTECHNICAL RECOMMENDATIONS9. 18

9.1 PRELIMINARY FOUNDATION RECOMMENDATIONS 18

9.1.1 CAST-IN-DRILLED-HOLE (CIDH) PILES 20

9.1.2 DRIVEN PILES 21

9.1.3 CAST-IN-STEEL-SHELL (CISS) PILES 23

9.1.4 SPREAD FOOTINGS. 24
11 1

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025

9.1.5 PREFERRED PILE FOR DESIGN 25

10. ADDITIONAL FIELD WORK AND LABORATORY TESTING 27

11. LIMITATIONS 27

12. REFERENCES 27
List of Figures
FIGURE 1: PROJECT LOCATION MAP 3
FIGURE 2: PROPOSED LAYOUT (CONSOR 2025B) 4
FIGURE 3: GEOLOGIC MAP (WIEGERS 2010) 8
FIGURE 4: PRELIMINARY ARS CURVE 15
FIGURE 5: PRELIMINARY FACTORED NOMINAL AXIAL PILE RESISTANCE VERSUS EMBEDMENT DEPTH INTO ROCK 26 List of Tables
TABLE 1: SUMMARY OF GROUNDWATER DATA (ERS) 11
TABLE 2: RECOMMENDED GROUND MOTION PARAMETERS FOR PRELIMINARY GEOTECHNICAL DESIGN 14 TABLE 3: RECOMMENDED HORIZONTAL PSEUDOSTATIC COEFFICIENT FOR SLOPE STABILITY 18 List of Plates
List of Appendices
Page
A-1to 28
11 2
1 2
3 Previous and Current Field Exploration Map
Subsurface Profile A-A'.................................

Subsurface Profile B-B'.................................

Appendix A - CPT Plots and Liquefaction Analyses
25CPT-01 to 04...............................................................................................

Appendix B - Relevant Historical Data - Borings, CPTs, Geophysical Surveys and Laboratory Madonna Road OC (Caltrans 1961)...............................................................

Laguna Lift Station (Fugro 1999).................................................................................

San Luis Obispo Water Reuse (Fugro 2002)......................................................

Prado Road OC at US 101 (Parikh 2002)...................................................................

SLO PCE Plume Characterization (WSC 2022)..........................................................

Prado Road Bridge (Yeh 2024).................................................................................... .............B-1
... B-2 to 17
. B-18to 34
...........B-35
. B-36to 49
B-50 to 100

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 5O
/
(o X
9 I PROJECT LOCATION
PM Y
26 5 Prado Road
C-eev—.. /
O 927
6 North
|
0 3,000
I
Figure 1: Project Location Map
11 3
PM
? ' !

1. INTRODUCTION
Censor North America, Inc. (Consor)
retained Yeh and Associates (Yeh) to
provide preliminary geotechnical
recommendations for the design of
the US 101 and Prado Road
Interchange Project in San Luis
Obispo, California. The project
includes reconstruction of the
northbound ramps, a new auxiliary
lane connecting to the Madonna
Road interchange to the north,
realignment of Elks Lane, and the
new Prado Road overcrossing at US
101. Project limits extend about a %-
mile south from the existing
Madonna Road Interchange and
through the existing at-grade
intersection with the northbound
ramps at the existing Prado
Interchange.

The project location is shown in Figure 1. This Structure Preliminary Geotechnical Report (SPGR)for Bridges provides preliminary geotechnical recommendations for foundations as input for type selection for Phase 1 of the PS&E process for the project. Preliminary geotechnical considerations and recommendations are provided for the proposed overcrossing structure and associated ramp structures relative to foundation support, scour, corrosion, seismic hazards, structure type, construction, and additional field work and laboratory testing for design. The preliminary characterization of the subsurface conditions is based on boring information from previous explorations performed in the vicinity of the project site as well as cone penetration test (CPT) soundings performed for Phase 1 of the project (see Section 4.3). A Structure Preliminary Geotechnical Report (SPGR) for Earth Retaining Structures (ERS) and a Preliminary Geotechnical Design Report (PGDR) will be submitted separately.

2. PROJECT DESCRIPTION
Preliminary alignment and design information for the project was provided by Consor (2025a, 2025b).

The project generally consists of the extension of Prado Road over US 101 to connect to Dalidio Drive )
/

CITY OF

SAN LUIS OBISPO
A
9, 5°
feet
Base Map: ArcGIS Earth (2017)
sl
2 2.9" o
/ 5,
2 S
.Qo
(
/ Q 9
3o
/

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 \ 1 • ts 4ew 5
l 4 V J
A
*
I i) t.
? I- U.

North Tis •• sa &- 9 e- &-
t
7 4 J2
J
0 400
7 consor
feet
Figure 2: Proposed Layout (Consor 2025b)
The proposed bridge structures generally include the following:
11 4
The new interchange will essentially be a half-diamond, consisting of northbound ramps and at-grade controlled intersections. The project components include the west side and east side approaches to the overcrossing, the elevated northbound US 101 on- and off-ramps, and the northbound US 101 auxiliary lane between Prado Road and Madonna Road. Both the west side and east side approaches for the overcrossing need to be elevated to connect to the proposed bridge over US 101. Earth retaining structures (ERS) are proposed to support the approaches to the overcrossing and the elevated northbound ramps. The project is also within the mapped 100-year flood zone. As a result, the structures will be elevated above grade to limit impacts to the mapped flood zone (GHD 2018). • A new overcrossing will be provided to extend Prado Road over US 101. Preliminary plans (Consor 2025a) show the overcrossing with seven spans and a total length of approximately 1,050 feet. The overcrossing will be approximately 65 feet wide to accommodate two travel lanes, a left turn lane, 5-foot shoulders, a shared-use path on the south side, and a sidewalk on the north side of the structure. The east end of the overcrossing would be wider to accommodate two travel lanes in each direction at the new Prado Road and Elks Lane within the City of San Luis Obispo and reconstruction of the interchange. The project limits will extend along US 101 from approximately Post Mile 26.5 at the southern limits of the project site to Post Mile 27.3 at the Madonna Road northbound offramp. The approach from Prado Road will extend for about 1,000 feet from the existing Prado Road Bridge at San Luis Obispo Creek Bridge to an existing roundabout at the eastern terminus of Dalidio Drive about 500 feet west of US 101. The approved project is described as Alternative 3 in the Project Report (GHD 2018) and environmental documents for the project (Caltrans 2023). The City and Consor have been conducting a Value Analysis to determine if improvements to the approved project could be made to reduce the overall construction cost of the improvements. On November 4, 2025, the City Council approved modifying the approved project from the Project Report to the one shown in Figure 2. —5
Iwei
t
st
T"9%
4

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 o
o
o
11 5
The project will also include retaining walls to support the bridge approaches as well as a new auxiliary lane, stormwater improvements, realigning Elks Lane, and the approach and roadway improvements. Associated utility, roadway striping, signage, pedestrian, and landscaping improvements will also be provided.

The viaduct for the northbound off-ramp will be approximately 285 feet long with 2 spans before connecting to the overcrossing. The viaduct is shown as a 40-foot-wide cast-in-place box girder that will accommodate left and right turn lanes. The southern end of the ramp would be supported by a seat-type abutment. Each bent is shown as being supported on two 48-inch-diameter columns with each column supported on a single cast-in-drilled hole pile foundation.

The viaduct for the northbound on-ramp will be approximately 295 feet long with 2 spans connected to the overcrossing. The viaduct is shown as a 28-foot-wide cast-inplace box girder that will accommodate a single lane with shoulder onto northbound US 101. The northern end of the ramp would be supported by a seat-type abutment.

The first bent is shown as being supported on three 48-inch-diameter columns; the second bent will be supported by two 48-inch diameter columns. Each column will be supported on a single cast-in-drilled hole pile foundation.

The intersection of the northbound off-ramp viaducts and overcrossing will occur at approximately 28 feet above existing site grades. The bridge ends of the viaducts will be approximately 20 feet above existing site grades.

3. GEOTECHNICAL EXPLORATION
This geotechnical evaluation was based on review of geotechnical data collected from various previous studies and the results of four Cone Penetration Test (CPT) soundings performed for this phase of the project. The locations of the CPTs performed for this study are shown on Plate 1 along with explorations completed for previous studies. The logs for the CPT soundings are presented in Appendix A and previous study data is presented in Appendix B. intersection. There will be a 11-foot-wide median separating the eastbound and westbound lanes. The current plans show the overcrossing with a clear span of about 150 feet across US 101. The bridge will be constructed on a vertical curve over US 101. While the bridge alignment is relatively straight across US 101 it also includes a horizontal curve toward Dalidio Drive leading into the west approach. The overcrossing will provide at least 16.5 feet of vertical clearance above US 101.
• The northbound ramps will include viaducts intersecting with Prado Road at the new overcrossing:

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 11 6
The soundings were performed in general accordance with ASTM D-5778 using an electric piezocone penetrometer. The piezocone penetrometer had a diameter of approximately 1.7 inches with a tip area of 15 square centimeters (cm2) and a sleeve area of 225 cm2. The cone tip resistance (qc), sleeve friction (fs), and penetration pore water pressures measured behind the tip (in the u2 location) were recorded at approximately 3-centimeter intervals during penetration using an on-board computer.

The friction ratio (FR, the ratio of sleeve friction to tip resistance in percent) was computed for each value of qc and fs recorded. The data and soil behavior type classifications were used in subsequent geotechnical analyses and to evaluate soil types and boundaries for analyses. Upon removal of the CPT rod, the soil generally collapsed to near the groundwater level (if encountered).

3.2 PREVIOUS STUDIES
Previous geotechnical studies that were performed at or near the project location were reviewed for this project. Logs and laboratory data pertinent to this project included in Appendix B. The locations of the previous borings and CPT soundings are shown on Plate 1. Pertinent studies and data that were reviewed include:

Seismic shear wave velocity testing was performed in CPT soundings 25CPT-01 through 04. To conduct the seismic shear wave test, the penetration of the cone was stopped, and the rods were decoupled from the rig. An automatic hammer was then triggered to send a shear wave into the ground. The distance from the source to the cone was calculated knowing the total depth of the cone and the horizontal offset distance between the hammer and the cone. A minimum of two tests must be performed at two different depths to calculate an interval shear wave velocity. The data collected were used to estimate an average shear wave velocity extrapolated to a depth of 100 feet below the existing ground surface at the project site (VS3o).

3.1 CONE PENETRATION TEST (CPT) SOUNDINGS
The CPT subcontractor for this project was Gregg Drilling (Gregg) of Signal Hill, California. Gregg advanced four soundings using a hydraulic ram mounted inside a 30-ton truck on July 10,11, and 29, 2025. CPT soundings were advanced to depths ranging from approximately 57 to 62 feet below the ground surface. Each sounding was terminated once refusal was encountered. Refusal was characterized by lifting or tilting of the CPT rig due to high push load. Once a sounding was completed, the void above the refusal depth was backfilled with bentonite chips. Plate 1 shows the approximate locations of the four CPT soundings (25CPT-01 through 25CPT-04) relative to the proposed interchange improvements.. Logs of the CPT soundings are presented in Appendix A. • Nine borings (B-1 through B-9) drilled by Caltrans (Caltrans 1961b) for the design of the overcrossing structure at US 101 and Los Osos Valley Road;

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025

4. GEOTECHNICAL CONDITIONS
11 7

4.1 GEOLOGY
The project site lies east of the Santa Lucia Range and within the Coast Ranges Geomorphic Province, which extends from the Transverse Ranges in southern California to the Klamath Mountains in northern California and into Oregon. The province is characterized by north to northwest trending mountain ranges bounded by the Pacific Ocean to the west and the Central Valley of California to the east. The ranges are predominantly composed of Jurassic- and Cretaceous-age rocks with Tertiary-age rock and Holocene sediments commonly overlying the older formations along the flanks and foothills • Four borings (B-1 through B-4) drilled by Caltrans (Caltrans 1963) for the design of the overcrossing structure at US 101 and Madonna Road;
• Pile driving records from 1961,1986, and 2015 (Caltrans 1961a, Caltrans 1986, MNS 2015) for the overcrossing structure at US 101 and Los Osos Valley Road as well as pile driving records from 1962 (Caltrans 1962) for the overcrossing structure at US 101 and Madonna Road; • A study performed by Unocal in 1990 (GeoResearch-Unocal 1990) for the evaluation of contaminated soil on Elks Lane at San Luis Obispo Creek. The evaluation included three borings (B-1 through B-3) and a monitoring well installed at the site. A well destruction report for the well was also prepared by Arcadis (Arcadis 2019); • Three borings (DH 1 through 3) drilled by Fugro (1999) for a proposed lift station at the SLO Water Reclamation Facility (WRF);
• Five borings (B-305, 306, 401 through 403) drilled by Fugro (2002) for a proposed pipeline and reservoir for a recycled water project at the WRF;
• Two borings (B-1 and B-2) drilled by Parikh (2002) for a proposed overcrossing structure at US 101 and Prado Road;
• A study performed by Caltrans (Caltrans 2005) for the evaluation of an auxiliary lane on northbound US 101 between Prado Road and Madonna Road;
• A study performed by Dokken (Dokken 2009) for the widening of the overcrossing structure at US 101 and Los Osos Valley Road. The evaluation included twenty-seven borings (B-1 through B-27) drilled at the overcrossing;
• A study performed by Water Systems Consulting (WSC 2022) for characterization and remediation of a PCE plume. The study included exploratory borings and cone penetration test (CPT) soundings, including two borings (B-21 and B-24) as well as four CPT soundings (B18R and B-22 through B-24) within the project limits; and • A geotechnical study performed by Yeh and Associates (2025) for the Prado Road Bridge Replacement Project immediately east of the project limits. The study includes data from exploratory borings and a geophysical survey.

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 1 I X ) X
■
Landslide Deposits (Holocene and Pliestocene)
ly
Qya1
Serpentinized Ultramafic Rocks (Jurassic)
Franciscan Melange (Cretaceous to Jurassic)
1 )(
Oe
Jos
)
North J
Qya2
SW
Ch0 2,000
/
feet
11 8
LEGEND:
on
Qya
of those ranges. Quaternary sediments are found within intervening drainages, valleys, and coastal areas.

The regional geology as mapped by Wiegers (2010) is shown in Figure 3. Wiegers maps the surface geology in the site vicinity as units of Holocene to late Pleistocene age young alluvial floodplain deposits (Qya2). The young alluvial floodplain deposits are described by Wiegers as "unconsolidated sand, silt, and clay-bearing alluvium deposited on floodplains and along valley floors." The upper unit of the young alluvial floodplain deposits (Qya2) are bound by older young alluvial flood plain deposits (Qyal). Franciscan Melange (KJfm) is expected to underlie the alluvium at the project site. The Franciscan melange and serpentine (Jos) are mapped by Wiegers on hillsides northeast and northwest of the project site. Wiegers describes the Franciscan Melange as a "chaotic mixture of fragmented rock masses embedded in a penetratively sheared matrix of argillite and crushed metasandstone" with "individual rock masses contained in the matrix range from less than a meter to kilometers in scale." Mapped outcrops of greywacke sandstone, serpentine, and melange are common within the Franciscan melange.

APPROXIMATE PRELIMINARY

PROJECT ALIGNMENT
Qyc
Jos
KJfm
Base Map: Wiegers, Mark O. 2010. Geologic Map of the San Luis Obispo 7.5 Quadrangle, San Luis Obispo, California Figure 3: Geologic Map (Wiegers 2010)
Young Alluvial Flood-Plain Deposits, undivided (Holocene to late Pleistocene) ' Qya. Young Alluvial Flood-Plain Deposits, Unit 1
Qya, Young Alluvial Flood-Plain Deposits, Unit 2
Young Colluvial Deposits (Holocene to late Pliestocene) . Oya2
1 ch
\
)) / W
V
La\ w.

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025

4.2 SURFACE CONDITIONS
11 9

4.2.3 EXISTING FACILITY
The existing US 101 and roadway improvements were generally made near or just above previous site grades. Existing embankment fills along US101 generally appear to be less than about 5 feet high.

Prado Road is generally an at-grade street with intermittent curb, gutter and sidewalks. The streets and US 101 are paved with asphalt pavement. The existing pavements along Prado Road are generally in poor condition with areas of severe fatigue cracking. The pavements along the northbound ramps and US 101 are generally in fair to good condition with areas of light raveling of the pavement surface and along cold joints, and areas with low severity longitudinal cracks in the wheel paths.

4.2.1 TERRAIN AND TOPOGRAPHY
The project site is located along the San Luis Obispo Creek Valley in the City of San Luis Obispo. The layout of the existing site and project limits is shown on Plate 1. Prado Road currently has an at grade interchange with US 101 consisting of only northbound on- and off-ramps. Existing terrain along the project alignment is generally flat ground sloping easterly toward San Luis Obispo Creek at average grades of approximately 0.5 to 1 percent. Existing land use generally consists of commercial development within Madonna Plaza to the northwest of the proposed interchange. Land use along the west approach to the proposed interchange is currently being converted from agricultural row crops to mixed residential and commercial development. Land use northeast of the proposed interchange is mixed business, commercial, residential, and agricultural development. Existing developments along the north side of Prado Road include social services, charging stations, and a transit facility. The City of San Luis Obispo's Water Reclamation Facility is located on the south side of Prado Road and southeast of the proposed interchange.

4.2.2 SURFACE WATER AND DRAINAGE
San Luis Obispo Creek flows southerly along the easterly side of US 101. The creek channel is generally incised with a thalweg elevation about 20 feet below the adjacent grades. The creek crosses beneath the Prado Road Bridge approximately 1,000 feet east of US 101. The creek meanders and runs alongside of the existing Caltrans right-of-way fence for about 200 to 300 feet ahead of the northbound off-ramp to Madonna Road, and adjacent to the proposed auxiliary lane alignment.

Geologic structure in the region is generally characterized by a series of northwest trending faults and folds; such as predominant Quaternary faulting along the Los Osos Fault Zone, Edna Fault, Cambria Fault, and the Oceanic (West Huasna) Fault systems mapped approximately 1 miles southwest, 2 miles southwest, 3 miles northeast, and 5 miles northeast, respectively of the project site (USGS 2025).

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 11 10
Qya2. This subunit consisted of predominantly soft to medium stiff clay with varying amounts of sand and gravel with thin interbedded layers of loose to medium dense clayey sand with Alluvium (Qya). Young alluvium was encountered in most of the explorations at the ground surface or underlying existing fill and pavement materials. The young alluvium encountered is interpreted to extend to depths of approximately 30 to 40 feet below the existing ground surface. This unit consisted of two predominant subunits (Qyai and Qya?) that were mainly differentiated based on their consistency. The young alluvium was underlain by older alluvium (Qoa) in most of the explorations.

Qyai. This subunit consisted of predominantly soft to hard clay and sandy clay. The unit was locally interbedded with layers and lenses of loose to medium dense clayey sand and clayey gravel. The unit appears to be desiccated and moderately over-consolidated clayey soil near or above the groundwater table. This subunit is generally considered to be the upper zone of the young alluvial deposits described by Wiegers (2010).

Artificial Fill (Af). Artificial fill is generally present along the existing roadways as well as in developed areas in association with existing pavements and utilities. The existing fill within the proposed improvement areas is generally expected to be less than about 5 feet thick. The fill is likely to be derived from clayey soil associated with local borrow sources, with the exception of select material that could have been used as fill for the existing pavement and utility trench backfills.

4.2.4 EXISTING UTILITIES
Existing utilities generally consist of buried pipelines and services, as well as overhead power and utility services along Prado Road, along Elks Lane, and that cross US 101 near the proposed interchange. High voltage overhead power transmission lines cross US 101 above the existing northbound on-ramp. Other utilities include buried pipelines that cross underneath US 101 and likely along the Madonna Road Interchange. Location and mapping of existing utilities is not within scope of the geotechnical services for this report.

4.3 SUBSURFACE CONDITIONS
The predominant geologic units encountered in previous studies (see Section 3.2 of this report) and interpreted from the cone penetration test (CPT) soundings performed by Yeh are surficial units of existing artificial fill (Af), alluvium (Qya), and older alluvium (Qoa) that overlie Franciscan melange (KJfm) bedrock. The approximate locations of current study and previous explorations are shown on Plate 1. Generalized north-south and east-west subsurface profiles based on those previous data are shown on Plates 2 and 3. Descriptions of the units, as encountered in the explorations are summarized below.

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 Table 1: Summary of Groundwater Data (ERS)

22.0-28.0 5/25-6/5/1961 Elevations are likely 1929 datum. 11 11
Date Measured Notes
Groundwater
Ground Measurements
Surface El.
(feet)
Depth
(feet)
Elevation
(feet)
B-l to B-4
Caltrans (1961)
Madonna Rd OC
varying amounts of gravel. This unit appears to be associated with lightly to moderately over consolidated clayey soil that is most often below the groundwater table. Historically this unit is prone to consolidation settlement. This subunit is generally considered to be the lower zone of young alluvial deposits described by Wiegers (2010).

Older Alluvium (Qoa). Older alluvium was encountered below the upper units in most of the explorations that were deep enough to penetrate the young alluvium. The older alluvium was typically encountered at depths ranging between about 40 and 60 feet below the ground surface but may be encountered at shallower depths below Prado Road closer to San Luis Obispo Creek. The unit was a mixture of sediments that were composed of medium to very dense silty sand, clayey sand and gravel and stiff to very hard clay and sandy clay. The extents and composition of fine-grained, sand and gravel sediments varied between explorations. The older alluvium was underlain by Franciscan melange bedrock where penetrated.

Franciscan Melange (KJfm/KJfmv). Franciscan melange was encountered below the alluvium and older alluvium and is the predominant geologic unit that underlies all other sediments in the project vicinity. Borings and CPT soundings from the explorations commonly met refusal near the bedrock surface or shallow depths into it. The depth to bedrock is estimated to be about 60 feet below the ground surface near the center of the proposed interchange. The melange primarily consisted of blocks of moderately hard to hard graywacke in a matrix of soft intensely fractured and sheared claystone (KJfm). Borings performed by Yeh (2025) for the Prado Road Bridge project were cored to a depth of about 100 feet, or approximately 60 feet into the Franciscan melange bedrock.

5. GROUNDWATER
Groundwater conditions in the vicinity of the project site are generally influenced by stream flow levels in San Luis Obispo Creek, and the depth to bedrock below the site. Groundwater was encountered at various depths and locations in previous studies. A summary of groundwater measurements reported from the previous studies is presented in Table 1. Table 1 includes borings presented in referenced studies (see Section 3.2) that encountered groundwater. Data reported in metric units were converted to imperial units before listing them in Table 1. 148.0-
153.2
125.2-
128.0
Boring No.

Study
Location/Project

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 10/25/1999122.0 107.514.5
132.7 11.3 121.4 6/26/2000 West abutment vicinity
135.5 17.5 118.0 6/27/200 East abutment vicinity
2/5-8/2002136.1 24.5-25.0
3/24/2022152 22 130

35.267142°, - 120.672137'
25 113 6/29/2022138

35.263172°, -120.674106'
6/27/2022120 9 111

35.256650°, -120.678056' O
129 18 111 3/22/2022

35.260627°, - 120.675801
3/23/2022130 13 117

35.259395°, -120.674163 o
30 95 3/24/2022125

35.256498°, - 120.673503 o
128 20 118 3/25/2022

35.255653°, - 120.671779' 1°
130 16 114 3/31/2022

35.255172°, -120.670586'
11 12
Date Measured Notes
Groundwater
Ground Measurements
Surface El.
(feet)
Lift station is located south of the
City water reclamation plant and
east side of US 101 near PM26.0
Elevation
(feet)
Depth
(feet)
B-402, 403
Fugro (2002)
SLO Water Reuse
Drilled in Prado Road between US
101 and Prado Road Bridge
Ground elevations are not
reported and are estimated from
Google Earth at
Ground elevations are not
reported and are estimated from
Google Earth at
Ground elevations are not
reported and are estimated from
Google Earth at
Ground elevations are not
reported and are estimated from
Google Earth at
Ground elevations are not
reported and are estimated from
Google Earth at
Ground elevations are not
reported and are estimated from
Google Earth at
About 600 feet south of western
terminus of project
Ground elevations are not
reported and are estimated from
Google Earth at
Ground elevations are not
reported and are estimated from
Google Earth at
B-18R
WSC (2022)
Froom Ranch Way
B-20
WSC (2022)
El Mercado
B-23
WSC (2022)
Prado Rd
B-24
WSC (2022)
Prado Rd
111.1-
111.6
B-22
WSC (2022)
Prado Rd
B-21
WSC (2022)
El Mercado
DH-1
Fugro (1999)
Laguna Lift Station
B-13
WSC (2022)
Madonna Rd
east of OC
B-17
WSC (2022)
US101 SB Onramp at
Madonna Rd
Boring No.

Study
Location/Project
B-2
Parikh (2002)
Prado Rd-USlOl OC
B-1
Parikh (2002)
Prado Rd-USlOl OC

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 139.0 20.4-20.9
139.0 20.5 118.5 1/18/2022
138.0+ 21-25

6. SCOUR DATA

7. CORROSION EVALUATION
11 13
Date Measured Notes
Groundwater
Measurements
Elevation
(feet)
2/10 to
3/3/2015
Depth
(feet)
1/18 to
4/28/2022
Ground
Surface El.
(feet)
ESP B-1 to B-4
Yeh (2025)
Prado Rd. Bridge
San Luis Obispo Creek flows southerly along the eastern side of US 101. The channel of San Luis Obispo Creek is incised with a thalweg elevation that is about 20 feet below adjacent grades.

Groundwater conditions and gradients generally appear to follow San Luis Obispo Creek with the shallowest depths to groundwater of about 10 feet in explorations performed on the west approach to the proposed Prado Road Overcrossing, and to depths of about 15 to 20 feet in explorations performed on the east approach to the proposed overcrossing. Groundwater levels and soil moisture conditions will vary seasonally and in association with changes in precipitation, runoff, irrigation, pumping, and other factors. Additionally, groundwater and the control of groundwater have been an issue on projects in the vicinity such as the Laguna Lift Station (Fugro 1999) and the SLO WRF Water Reuse project (Fugro 2002). There are reported difficulties associated with dewatering of excavations as well as impacts to adjacent structures as a result of dewatering.

Soil within the project area is not considered corrosive based on laboratory data from previous studies in the site vicinity (Yeh 2025). Corrosion testing should be performed on soil and water samples obtained from the site-specific field exploration program for the final design of the project.

The project site is approximately 6 miles from the Pacific Ocean; therefore, it is not considered to be within a marine environment based on the Caltrans (2021b) Corrosion Guidelines.

The site is within the 100-year flood plain and will be subject to episodic flooding. Newly graded slopes and fills will be vulnerable to erosion. Scour analyses will be performed by others for the next phase of the project. Design of foundations for the overcrossing and ramp structures should consider potential impacts from scour, if needed.
118.1-
118.9
113.0-
116.0
Monitoring well installed near
eastern limit of project on Prado
Road alignment.

West abutment. Monitoring
shows groundwater between el.
118.0 and 119.0 for period
through April 27, 2022.

High to low groundwater
elevation are from west to east
across the bridge.
22RC-01-MW
Yeh (2025)
Prado Rd. Bridge
22RC-01
Yeh (2025)
Prado Rd. Bridge
Boring No.

Study
Location/Project

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025

8. SEISMIC INFORMATION

8.1 GROUND MOTION HAZARD
Table 2: Recommended Ground Motion Parameters for Preliminary Geotechnical Design

35.2569 -120.6748 320 0.39 257.1
11 14
Site Parameters
Location
Latitude,
degrees
Longitude,
degrees

1. 2.

Based on ARS Online 4.0 accessed July 17, 2025.

Based on value from seismic CPT for this study and Yeh (2025) report for Prado Rd. Bridge based on boring and geophysical data.

Seismic data were generated using the selected site parameters and ARS Online (Caltrans 2025b) to estimate ground motion parameters in accordance with Appendix B of the Caltrans (2025a) Seismic Design Criteria (SDC) and the Caltrans (2021a) Geotechnical Manual - Design Acceleration Response Spectrum. The SDC defines the Safety Evaluation Earthquake (SEE) as an earthquake having a 975- year-return period and is used for geotechnical design for slopes, retaining walls, bridges, and other structures. Seismic data were generated for site conditions using the location of the proposed overcrossing.

The shear wave velocity for the project site was estimated from the seismic CPT data obtained for this project and the Yeh (2025) report prepared for the Prado Bridge Replacement Project. The Yeh (2025) data were used because the geologic conditions appear to be similar to those at the project site based on previous data (Parikh 2002). Table 2 presents the preliminary seismic data used in Yeh's preliminary analyses. These data provide the basis for estimating seismic parameters for seismic slope stability analyses and input for analyzing liquefaction hazards. Seismic data will be generated for specific structure and point of analyses as the project design progresses and geotechnical data are collected for those improvements. The preliminary design response spectrum estimated for the SEE is presented in Figure 4.

Horizontal Peak
Ground
Acceleration
(HPGA)
(g)
Deaggregated
Mean
Earthquake
M, Moment
Magnitude
Deaggregated
Mean Site-toFault Source
Distance for 1.0
Period Spectral
Acceleration, R
(km)
Shear-Wave
Velocity
Vs30
(m/sec)2
Design Ground Motion Parameters1
(Return Period = 975 years)

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025

1.4 1.2
1 : \

0.8 0.6

0.4 0.2
0 0.0 10.0
-- - Design Response Spectrum
O Peak Ground Accleration = 0.39g
Figure 4: Preliminary ARS Curve
11 15
1 i
V
\
The Caltrans (2025a) Seismic Design Criteria notes that a site-specific ground response analysis is required for sites that include any of the following criteria:

V4.0

7.05 at 25.37 km
5 percent

35.2569 degrees
-120.6748 degrees
320 meters/second
ARS Online:

Mean Magnitude:

Spectral Damping:

Latitude:

Longitude:

V,30:
2 t
0 S
• The estimated shear wave velocity in the upper 100 feet (or 30 meters) of the site, Vs30, is less than 180 meters per second;
• The soil profile contains one or more layers that are at least 5 feet thick which have a shear wave velocity less than 120 meters per second;
• The site contains soil that has a potential for strength loss or volume change during seismic loading including liquefiable, sensitive clay, or collapsible soil; • The site contains one or more layers of peat and/or highly organic clay which has a thickness of at least 10 feet;
• The site contains a layer of highly plastic clay (with a plastic index, PI, greater than 75) which has a thickness of at least 25 feet; and/or
■ । .

1.0 ■ ।

2.0 S
e
9 2
IA
»

7.0 ■

4.0 -

3.0 --------

5.0 Period, T (sec)
■

8.0 ■

9.0 —_

6.0

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025

8.2 OTHER SEISMIC HAZARDS
11 16
A site-specific dynamic ground response analysis may be required for design, in accordance with Caltrans Seismic Design Criteria. The Caltrans Seismic Design Criteria notes that for sites requiring a site-specific ground response analysis, that "the design spectral acceleration at any period shall not be taken less than 80% of the design spectrum obtained from the 2023 USGS Hazard Model with a vs30 = 180 m/sec."The design ARS will be provided after a foundation alternatives are selected, additional boring data are available for the site following drilling for the project, and a site-specific ground response analysis is performed (if required).

8.2.1 SURFACE FAULT RUPTURE
The project site is not within the Alquist-Priolo Earthquake Fault Zone and is not within 1,000 feet of an un-zoned Holocene mapped fault. Fault rupture does not need to be considered in the design of the interchange improvements per Caltrans Geotechnical Manual - Fault Rupture (Caltrans 2022b).

Multi-span structures will be used for the overcrossing and ramp structures. However, the fundamental period of vibration for the proposed structures is not yet available. The potentially liquefiable soil is within a unit preliminarily mapped as older alluvium based on the previous studies and CRTs performed by Yeh. While older alluvial deposits (Pleistocene age) are typically not considered susceptible to liquefaction due to their age (Caltrans 2020a), additional exploration and evaluation should be performed in future phases of design to whether liquefaction will be a design constraint.

Layers of sand encountered within the older alluvium are considered potentially liquefiable, as discussed in Section 8.2.2. The Caltrans (2022a) Geotechnical Manual for Site-Specific Dynamic Ground Response Analysis also notes that for sites considered potentially susceptible to liquefaction, a site-specific analysis is not required if any of these conditions are applicable:
• The site contains a layer of soft to medium stiff clay (with an undrained shear strength, Su, less than 1,000 pounds per square foot).
• The bridge structure is single-span;
• The fundamental period of vibration of the bridge structure is less than or equal to 0.5 seconds;
• Only the surficial soil layer is considered potentially liquefiable; • The total thickness of all liquefiable soil layers (excluding the surficial layer) is less than or equal to 5 feet.

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 11 17

8.2.5 SEISMIC SLOPE STABILITY
The preliminary horizontal coefficients of ground acceleration (kh) for the proposed structures were estimated using procedures described in the FHWA (2011) LRFD Seismic Analysis and Design of Transportation Features and Structural Foundations Reference Manual and referenced in Section All.5.2 of the AASHTO (2020) LRFD Bridge Design Specifications. The procedures consider the design earthquake, duration, and a tolerable seismic displacement of up to 2 inches. The preliminary design peak ground acceleration for the SEE earthquake used to estimate the horizontal coefficient of ground acceleration (kh) is presented in Section 8.1. Estimated preliminary horizontal coefficient of

8.2.2 LIQUEFACTION POTENTIAL
Liquefiable soil conditions are generally associated with loose to medium dense sand that is below the groundwater table at the time of an earthquake. Older alluvium consisting of loose to medium sand deposits were encountered below the groundwater table in selected previous explorations and recent CPT soundings. The younger alluvium previously encountered in the vicinity of the proposed overcrossing (Parikh 2002) generally consisted of stiff or dense clay and silt sediments that would not be considered vulnerable to liquefaction.

Medium dense layers of sand which are potentially liquefiable were encountered in the older alluvium in CPT soundings advanced by WSC (2022) and soundings performed for this project at depths of 44 to 55 feet below the ground surface. A summary of the liquefaction analysis using Cliq (Geologismiki 2025) is included in Appendix A. Liquefiable materials are not likely to impact roadways or surface improvements (other than those adjacent to San Luis Obispo Creek near Madonna Road) but could have an impact on deep foundations for the project. While older alluvial deposits (Pleistocene age) are not considered susceptible to liquefaction due to their age (Caltrans 2020a), additional exploration and evaluation should be performed in future phases of design to ascertain whether liquefaction will be a design constraint.

8.2.4 LIQUEFACTION-INDUCED LATERAL SPREADING
Liquefaction- induced lateral spreading is not a consideration for design of the overcrossing and ramp structures based on review of previous data collected at the overcrossing site and the CPT soundings performed for the project.

8.2.3 SEISMICALLY INDUCED GROUND SETTLEMENTS
Seismically induced settlements of up to % inch were estimated based analyses using Cliq version

3.5.3.15 (Geologismiki 2025). As a result of the depth of the potentially liquefiable materials, the potential for seismically induced total and differential ground settlement to impact surface improvements at the proposed overcrossing location is considered low. However, deep foundation elements could be impacted by liquefaction induced settlement (see Section 8.2.2).

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 Table 3: Recommended Horizontal Pseudostatic Coefficient for Slope Stability General - Prado Road-USlOl Interchange 0.19

9. GEOTECHNICAL RECOMMENDATIONS
11 18
Project Component ID kh
ground acceleration (kh) shown in Table 3 should be used for preliminary design of abutments and retaining walls under seismic loading.

9.1 PRELIMINARY FOUNDATION RECOMMENDATIONS
Foundation alternatives that were evaluated for the proposed overcrossing and ramp structures include spread footings, driven piles, cast-in-steel-shell (CISS) piles, and cast-in-drilled-hole (CIDH) piles. The following are key geotechnical considerations that will influence the foundation design and selection of the foundation type for support of the new overcrossing and ramp structures:
• The subsurface conditions at the site generally consist of units of younger and older alluvium overlying Franciscan melange bedrock, as described in Section 4.3. The top of the Franciscan melange bedrock was encountered at approximately 60 feet below the ground surface at the proposed overcrossing location. Franciscan melange typically consists of blocks of harder, more resistant rock within a matrix of softer, intensely sheared and fractured rock. We consider the melange bedrock the likely bearing layer for deep foundations for the overcrossing and ramp structures.
• Groundwater at its shallowest depth was encountered at about 10 feet below the existing ground surface near the west side approach to the proposed overcrossing. Groundwater depth appears to vary by location and proximity to San Luis Obispo Creek. Foundation design and construction will need to consider the potential to encounter shallow groundwater. • Layers of lightly to moderately over-consolidated alluvium were encountered near and below the water table, generally from the ground surface to depths of 30 to 40 feet below the ground surface. This unit consists predominantly of soft to medium stiff clay that is considered potentially compressible relative to the expected foundation or embankment loads and could be subject to long-term post-construction settlement. Foundation design will need to consider the bearing resistance of the clay foundation soil and the potential for long-term, postconstruction settlement to result in the need for settlement periods or surcharges, downdrag forces on piles, and phasing of a longer bridge construction schedule associated with the approach work.

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 11 19
• Potentially liquefiable layers of loose to medium dense sandy alluvium were generally encountered at depths of approximately 44 to 55 feet below existing site grades during previous explorations and in the CPT soundings performed for this project. Special recommendations that could be needed for design to address liquefaction include site-specific design response spectra, seismic settlement, negative skin friction on piles, loss of lateral foundation support, and loads on abutments and foundation due to slope instability or lateral spreading. Due to the depth of the potentially liquefiable materials, the amount of estimated seismic settlement and impact to surface improvements such as shallow foundations is considered low (see Section 8.2.2). However, deep foundation elements could be impacted by liquefaction.
• Potentially contaminated soil and groundwater has been reported at the site. A plume of Tetrachloroethylene (PCE) was documented by WSC (2022) in the site vicinity. The PCE was present within the alluvium and older alluvium from approximately 20 feet below the ground surface to approximately the contact with the Franciscan melange bedrock. The presence of contaminated soil and ground could require special handling and disposal during construction of CIDH piles or other types of excavation.
• This site could be submerged or partially submerged due to the potential for flooding at the proposed overcrossing and ramp locations. Foundation design may need to consider the potential for uplift pressure on foundations, reduced support in the foundation soil, and potential for scour to impact the foundations. The potential for scour to occur in association with flooding has not been assessed at this time.
• The site soils are likely not considered corrosive based on laboratory data from previous studies in the site vicinity. The project site is not considered a marine environment based on Caltrans (2021b) guidelines. Steel piles would be designed for appropriate section losses in accordance with Caltrans and AASHTO BDS procedures. Additional corrosion testing will be performed for the Foundation Report during design.
• The center bents of the proposed overcrossing structure will be located directly outside the limits of the US 101 mainline. Bents for the ramp structures will also be located directly adjacent to the existing City of San Luis Obispo maintenance yard and Elks Lane. The construction footprint and final layout of the proposed overcrossing foundations may be constrained spatially by the existing facilities for bent construction. Considerations for spatial constraints will likely be needed for both construction and final layout of the proposed structures and foundations.
• Existing overhead and underground utilities are present at the proposed overcrossing location that would likely conflict with construction of the proposed overcrossing and would require

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 Benefits of the use of CIDH piles as a foundation alternative would include:

Constraints of the use of CIDH piles as a foundation alternative would include:
11 20
• Wet methods (slurry displacement) would likely be needed to construct CIDH piles because of the groundwater elevation encountered in the previous borings at the project site. Drill rigs used to construct CIDH piles can be equipped with temporary casings and other tooling to help support the shaft during drilling and advance the hole through soft ground, caving soil layers, and groundwater. Post-construction inspection and non-destructive testing of CIDH piles constructed in the wet is required by the Standard Specifications. Anomalies are often identified that require delays, review of the design loads, and possible mitigation or pile replacements to address anomalies;
temporary or permanent relocation. The exact services and extent of lines that will be in conflict are not known.

9.1.1 CAST-IN-DRILLED-HOLE (CIDH) PILES
A cast-in-drilled-hole (CIDH) piles consists reinforced concrete pile cast-in-place within in a drilled hole. Soft ground, groundwater, and other conditions may necessitate the use of drilling fluids and casings during construction and concrete placement for CIDH piles. Design of CIDH piles should consider axial and lateral resistance, initial and post construction settlement of soft clay soil, and the potential for liquefaction of layers within the alluvium. • CIDH piles can be designed with larger diameters (compared to standard driven piles) to provide additional axial or lateral resistance, or to reduce the total number of piles needed; • A single CIDH pile can be designed with a structural connection to a bridge column without the need for a pile cap (and associated excavation);
• CIDH pile installation is generally considered to have less vibrations and noise associated with the drilling as compared to the pile driving.
• CIDH piles can be designed to develop higher capacities in hard or dense bearing material where a smaller-, standard-size driven pile may have a limited capacity and meet refusal near the surface of the bearing material. The anticipated bearing material is the Franciscan melange bedrock encountered at approximately 60 feet below the site. CIDH piles need to be embedded a sufficient depth into the rock to provide the needed axial and lateral resistance for the design loads; and
• CIDH piles can be designed to provide resistance to scour as well as downdrag forces from both consolidation and liquefaction, if needed.

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 Benefits of driven piles as a foundation alternative may include:

Constraints of the use of driven piles as a foundation alternative would include:
11 21
• Hard driving conditions could be associated with denser layers within the older alluvium or within the Franciscan melange encountered in previous studies within the site vicinity (i.e., the refusal depth encountered within the CPT soundings). Franciscan melange bedrock may CIDH piles are considered a feasible foundation support for the proposed overcrossing and ramp structures. CIDH piles would likely be designed to develop resistance to axial loads from the portion of the shaft embedded in the Franciscan melange. Drilling within the Franciscan melange will likely be variable due to the presence of harder, more resistant blocks within the melange.

9.1.2 DRIVEN PILES
Driven piles typically consist of Caltrans standard plan steel pipe or square precast concrete piles or nonstandard H-piles. Design of driven piles should consider axial and lateral resistance, initial and post construction settlement of soft clay soil, and the potential for downdrag forces to develop within compressible layers of the alluvium or potentially liquefiable layers. Driven piles were used for a portion of the widening project at US 101 and Los Osos Valley Road (MNS 2015). • Tanks for slurry and spoils associated with wet-method CIDH pile construction can require a larger construction footprint compared to driven piles; and • CIDH pile construction would involve cutting and slurry disposal that would likely encounter groundwater conditions and potentially contaminated soil that would require special handling and disposal.
• Driven piles extending below the groundwater level may have less construction challenges than drilled methods below the groundwater table;
• Driven piles could reduce the amount of excavation within contaminated soil and groundwater (if pre-drilling is not needed) as compared to cast-in-drilled-hole (CIDH) piles; • Driven piles can be coated with friction reducing coatings which would lower downdrag loads from liquefaction and consolidation settlement resulting in higher net individual pile capacities;
• Driven piles would not require slurry or cutting disposal (if pre-drilling is not needed); • Steel pipe piles or H-piles can be cut off or spliced to accommodate variations in pile length in relation to variable depth to bedrock, if encountered during pile driving; and • Driven piles can be designed to provide resistance to scour as well as downdrag loads, if needed.

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 11 22
have variable driving conditions based on the presence of harder, more resistant blocks within the formation. These conditions may result in the need for pre-drilling for pile installation, if needed to penetrate within the Franciscan melange to achieve the needed axial and lateral resistance. If driven piles are used to avoid excavation of contaminated soil and groundwater, pre-drilling would likely not be allowed or special considerations for spoil disposal might be needed. Pre-drilling will likely encounter groundwater and generate wet, clayey cuttings (and potentially encountered contaminated soil) that will need to be handled and disposed of. • Closed-end or displacement type piles (such as concrete piles) would likely result in harder driving conditions and more likely pile refusal compared to open-ended or non-displacement type piles (such as H-piles). Open end pipe or H-piles may run during driving, resulting in an uncertain pile tip elevation and driving conditions during construction. Close-end pipe piles would help to control the pile tip elevation for design and construction. However, H-piles may be more cost effective and could be used provided there are provisions in the project specifications to account for the conditions noted above; • If the lateral pile resistance is limited within the alluvium, battered piles could be used to provide additional lateral resistance. However, other stiffer pile types (such as cast-in-steelshell or cast-in-drilled-hole piles) may be needed to provide additional lateral resistance. • Driven piles would need to be driven into the underlying bedrock that was encountered about 60 feet below the existing ground surface elevation and could require pile splicing. Pile driving could be delayed if splicing of steel piles is needed because of requirements for inspection and testing of field welds;
• Pile driving will generate noise. The duration and impacts of pile driving should be considered relative to the proximity of the site to downtown, local businesses and residents, and San Luis Obispo Creek;
• Pile driving vibrations attenuate away from the foundation location relatively quickly.

However, pre-construction condition surveys of nearby buildings, video and photo documentation, distress surveys, and noise and vibration monitoring during pile driving should be performed prior to pile driving to help document baseline conditions for historic structures, nearby buildings or residences that may be impacted by pile driving and whether they were impacted by the construction;
• The clay alluvium could be prone to setup when driving is stopped and could require higher driving energies to restart the pile after driving resumes; • A group of driven piles would likely be needed to support structure loads above the standard pile capacity for single piles. A group of piles would need a pile cap for structural connection between the foundation and superstructure. Pile cap excavation and construction for the

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 Benefits of the use of CISS piles as a foundation alternative would include:

Constraints of the use of CISS piles as a foundation alternative would include:
11 23
• Hard driving conditions could be associated with denser layers within the older alluvium or within the Franciscan melange encountered in previous studies within the site vicinity (the refusal depth encountered within the CPT soundings). Franciscan melange bedrock may have Driven piles are considered a feasible foundation support for the proposed overcrossing and ramp structures, and could be preferred for the project depending on final layout and loading conditions as well as the need to avoid excavation within contaminated soil or groundwater. The piles should be driven at least to Franciscan melange bedrock and consider potential lateral forces and additional downdrag associated with settlement and liquefaction, if needed.

9.1.3 CAST-IN-STEEL-SHELL (CISS) PILES
CISS piles typically consist of driving a steel pipe pile into the ground and casting reinforced concrete into the head of the pile to form a structural connection to the superstructure. The concrete can be placed in a closed-end pile, or by removing a portion of the soil plug within an open-end pipe pile to allow for concrete placement. Design of CISS piles should consider axial and lateral resistance, initial and post construction settlement of soft clay soil, and the potential for liquefaction of layers within the alluvium.
• Larger diameter CISS piles are commonly used to resist lateral loads for relatively large structures and may be preferred over standard steel pipe piles if a larger lateral resistance is needed to satisfy special structural considerations or loading conditions; • CISS piles can be coated with friction reducing coatings which would lower downdrag loads from liquefaction and consolidation settlement resulting in higher net individual pile capacities;
• CISS piles can be designed to resist scour as well as downdrag forces from both consolidation and liquefaction and could provide greater resistance to liquefaction-related effects than standard piles, if needed; and
• Steel pipe piles for CISS piles can be cut off or spliced to accommodate variations in pile length in relation to variable depth to bedrock, if encountered during pile driving. driven piles could include shoring, subgrade stabilization, and/or dewatering depending on the final depth of the excavations within the alluvium; and • Pile caps for driven piles could require a larger final design footprint compared to largediameter CIDH piles connected directly to the structural column.

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 11 24
CISS piles are considered a feasible foundation support for the proposed overcrossing and ramp structures. CISS could be preferred over CIDH piles if higher lateral load demands are needed. The piles should be driven at least to Franciscan melange bedrock and consider potential lateral forces and additional downdrag associated with settlement and liquefaction, if needed.

9.1.4 SPREAD FOOTINGS
Design of spread footings should consider bearing resistance as well as initial and post construction settlement of soft clay soil. Benefits of the use of spread footings as a foundation alternative would include:
• Potential reduced cost of construction compared to other foundation methods, if footings can be constructed in the dry without excessive shoring, ground modification, and dewatering, and
• Spread footings are a conventional foundation type. Specialty contractors are not typically required for construction.
variable driving conditions based on the presence of harder, more resistant blocks within the formation. These conditions may result in the need for pre-drilling for pile installation, if needed to penetrate within the Franciscan melange to achieve the needed axial and lateral resistance. A closed end pile could likely not be driven to the design tip elevations without pre-drilling;
• CISS installation using an open-end pipe pile would involve disposal for the soil plug.

Groundwater was encountered at about 10 feet below the ground surface at its shallowest point. If the plug needs to penetrate contaminated soil or groundwater, special handling and disposal may be required;
• CISS piles are typically more costly than CIDH piles or standard driven pile foundation systems, depending on the load demands and structural considerations; • Pile driving will generate noise and vibration. Pre-construction surveys of nearby residences, distress surveys, and noise and vibration monitoring may be needed for pile driving; • CISS piles would need to be driven into the underlying bedrock that was encountered about 60 feet below the existing ground surface elevation and could require pile splicing. Pile driving could be delayed if splicing of steel piles is needed because of requirements for inspection and testing of field welds;
• The clay alluvium could be prone to setup when driving is stopped and will likely require higher driving energies to restart the pile after driving resumes; and • A group of CISS piles will likely be needed to support structure loads above the standard pile capacity or to provide a structural connection between the foundation and superstructure.

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 11 25
Spread footings are not recommended for preliminary design of the proposed overcrossing and ramp structure foundations based on the preliminary analyses and review of previous and current study geotechnical data. Spread footings would likely not allow for tolerable settlement under the design service loads without some type of ground improvement to reduce the potential for short and longterm settlement of the alluvium. The alluvium may also require ground modification below the footing area to be able to support the anticipated design loads for the structures. The design and construction of spread footing foundations may be relatively complex and could include risks for unanticipated costs associated with disposal of excavated clay soil, contaminated soil, shallow groundwater, and spatial constraints.

Constraints and considerations that could adversely impact the cost and feasibility of supporting the proposed overcrossing and ramp structures on spread footings foundations include:

9.1.5 PREFERRED PILE FOR DESIGN
CIDH piles embedded below the compressible and liquefiable layers (if present) and bearing within the Franciscan melange bedrock at the site are considered the most suitable foundation support for the proposed overcrossing and ramp structures. Preliminary factored nominal axial pile resistance versus CIDH pile embedment depth into the underlying Franciscan melange bedrock for the Strength Limit state is presented in Figure 5 for various pile diameters. The axial pile resistances provided in Figure 5 include contribution from side resistance but neglect contribution of end bearing resistance.

The pile resistances provided in Figure 5 should not be extrapolated outside of the limits provided.

CIDH pile embedment depths into the Franciscan melange bedrock will depend on the loads from the structures as well as any loading due to downdrag (from consolidation settlement or from • Long-term settlement and consolidation within clay layers could require pre-loading, settlement waiting periods, or ground modification to support anticipated foundation loads; • Ground modification may be needed to mitigate settlement or strengthen the alluvium to provide adequate support for spread footings;
• Spread footings would provide less lateral resistance to seismic loading than deep foundations;
• Dewatering, shoring, and subgrade stabilization would likely be needed if footings are to be constructed below groundwater;
• Special handling and disposal would be needed if excavations encounter contaminated soil; and
• Shoring with adequate lateral support systems may be needed to limit the footprint of footing excavations to avoid potential impacts to US 101 as well as other existing facilities and utilities that may be present in the vicinity of the work.

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 Preliminary Factored Nominal Axial Resistance (kips)
0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 0 10
Min. 10'Embedment into the Franciscan Melange (KJfm)
20 E 30
40 50
60 70
80 90
100
110
120
Figure 5: Preliminary Factored Nominal Axial Pile Resistance versus Embedment Depth into Rock 11 26
— 60in. Dia. CIDH - Extreme Limit State
— 72-in. Dia. CIDH - Extreme Limit State
84-in. Dia. CIDH - Extreme Limit State
-- 96-in. Dia. CIDH - Extreme Limit State
— 108-in. Dia. CIDH - Extreme Limit State

3. Pile embedment depths limited to a
depth of approximately 30 times the
diameter of the pile for constructability.

Limiting pile depth includes approximate
depth to bedrock plus embedment.

Driven piles or CISS piles are also considered feasible alternatives, but may have limitations as noted above. Driven piles should preliminarily be embedded to at least the top of the Franciscan melange bedrock. Embedment within the Franciscan melange will likely be variable due to the presence of harder, more resistant blocks within the melange. Piles may need to be ordered longer than the preliminary recommended embedment elevation to account for variability of the melange.

Preliminary axial pile resistance and embedment will likely be controlled by the structural capacity of the pile. Pile loads will need to consider the loads from the structures as well as any loading due to downdrag (from consolidation settlement or from liquefaction settlement, if it occurs, as noted in Section 8.2.2). Driven pile embedment recommendations should be updated based on the data liquefaction settlement if occurs, as noted in Section 8.2.2). These values will need to be updated based on data obtained from additional field work and laboratory testing anticipated for the project (see Section 10).
a.

Q
Q
NOTES:

1. Franciscan melange (KJfm) bedrock encountered at
approximately 60 feet below the ground surface in the site vicinity based on previous studies.

2. Preliminary factored nominal axial resistance versus embedment depths shown were estimated according to the
latest Caltrans (2019) Amendments to the AASHTO (2017)
LRFD Bridge Design Specifications for the Strength Limit state (resistance factor of 0.7) and Extreme Limit State (resistance factor of 1.0). These values do not include the effects of static or seismic downdrag, lateral pile capacity, or group efficiency. ------ 60-in. Dia. CIDH - Strength Limit State
------ 72-in. Dia. CIDH - Strength Limit State
84-in. Dia. CIDH - Strength Limit State
------ 96-in. Dia. CIDH - Strength Limit State
------ 108-in. Dia. CIDH - Strength Limit State
0)
E
O
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DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025

11. LIMITATIONS

12. REFERENCES
11 27
Yeh prepared this report for Consor and their authorized agents only. It is not intended to address issues or conditions pertinent to other parties, projects or for other uses. This report is for preliminary planning purposes only and is not intended for use in final design or construction. The results of this study are preliminary and subject to change pending the results of our design-level field exploration and geotechnical evaluation. No services have been performed to evaluate environmental impacts, or the presence of hazardous or toxic materials.

Site conditions will vary between points of observation or sampling, seasonally, and with time. The nature and extent of subsurface variations across the site may not become evident until excavation is performed. If during construction, fill, soil, or water conditions appear to be different from those described herein, Yeh should be advised and provided the opportunity to evaluate those conditions and provide additional recommendations, if necessary.

10. ADDITIONAL FIELD WORK AND LABORATORY TESTING
Subsurface exploration, laboratory testing, and analyses should be performed in preparation of the Geotechnical Design Report (GDR) and Foundation Reports for Earth Retaining Structures (FRfor ERS) and structures (FR) for the project. The design-level field explorations will be checked and modified for the selected design alternatives. The future field exploration program will supplement the CPT soundings performed in July 2025 and include drilling vertical borings at the proposed overcrossing and ramp structure supports, retaining wall locations (where applicable), pavement areas, infiltration basin areas, and proposed overhead sign structures. The types and numbers of tests may vary based on the results of the field exploration program.
obtained from additional field work and laboratory testing anticipated for the project (see Section 10).

Arcadis (Arcadis 2019), Well Destruction Report; Chevron Site No. 306466, 300 Block of Elks Lane, San Luis Obispo, California, CCRWOCB Case No. SLT3S569, dated June 6, 2019.

American Association of State Highway and Transportation Officials (AASHTO 2022), Guide Specifications for Bridges Subjected to Tsunami Effects, issued 2022.

California Department of Transportation (Caltrans 2025b), ARS Online v4.0, website, accessed June 24, 2025, https://arsonline.dot.ca.gov.

American Association of State Highway and Transportation Officials (AASHTO 2017), AASHTO LRFD Bridge Design Specifications, 8th Edition, issued 2017.

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 Consor (2025b), Strip Map, provided via email December 5, 2025. 11 28
California Department of Transportation (Caltrans 2023). U.S. 101/Prado Road Interchange Project, on U.S. 101 in San Luis Obispo County, 05-SLO-101-PM 26.5-27.3, Project ID Number 0516000105, Initial Study with Proposed Mitigated Negative Declaration, dated January 2023.

California Department of Transportation (Caltrans 2024b), Geotechnical Manual, Foundation Reports for Bridges, issued July 2024.

California - Department of Public Works - Division of Highways (1962), Pile driving records, Bridge No. 49-190, dated October 1, 1962.

California Department of Transportation (Caltrans 2025a), Seismic Design Criteria Version 2.1, issued January 2025.

California - Department of Public Works - Division of Highways (Caltrans 1961b), Log of Test Borings, Los Osos Road Overcrossing, Bridge No. 49-185, as-built sheet, dated December 12,1961.

California Department of Transportation (Caltrans 2021a), Geotechnical Manual, Design Acceleration Response Spectrum, dated January 2021.

California Department of Transportation (Caltrans 2019). California Amendments to the AASHTO LRFD Bridge Design Specifications, Eighth Edition, Sacramento, California, issued April 2019.

California Department of Transportation (Caltrans 2024a), Standard Specifications, Sacramento, California, issued 2024.

California Department of Transportation (Caltrans 2022a), Geotechnical Manual, Site-Specific Dynamic Ground Response Analysis, dated March 2022.

California Department of Transportation (Caltrans 2021b), Corrosion Guidelines, Version 3.2, Division of Engineering Services, Structure Design, issued May 2021.

California Department of Transportation (Caltrans 2001), Field Review Memorandum, 05-0g780K, 101-SLO-PM27.0/27.5, Auxiliary Lane, dated July 23, 2001.

California Department of Transportation (Caltrans 1986), Pile Quantities and Driving Records, Bridge No. 49-185, dated October 2 to 10, 1986.

California - Department of Public Works - Division of Highways (Caltrans 1963), Log of Test Borings, Madonna Road Overcrossing, Bridge No. 49-190, as-built sheet, dated January 8,1963.

California - Department of Public Works - Division of Highways (Caltrans 1961a), Pile driving records, Bridge No. 49-185, dated October 2 to December 4,1961.

California Department of Transportation (Caltrans 2022b), Geotechnical Manual, Fault Rupture, Sacramento, California, issued October 2022.

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 Consor (2025a), Strip Map Profile, provided via email December 3, 2025. 11 29
United States Department of Agriculture, Natural Resources Conservation Service (NRCS 2025), Web Soil Survey, "San Luis Obispo County, California, Coastal Part (CA664)", accessed June 23, 2025, available online at http://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx Unites States Department of the Interior - United States Geological Survey (USGS 2025). Earthquake Hazards Program, Interactive Fault Map and Quaternary Fault and Fold Database of the United States, accessed June 28, 2025, https://www.usgs.gov/programs/earthquake-hazards/faults7qtscience_support_page_related_con=4#qt-science_support_page_related_con Dokken Engineering (Dokken 2009), Technical Memorandum, Seismic Evaluation, U.S. 101/Los Osos Valley Road Interchange Improvements Project, San Luis Obispo, California, dated January 22, 2009.

United States Department of Transportation - Federal Highway Administration (FHWA 2011), LRFD Seismic Analysis and Design of Transportation Geotechnical Features and Structural Foundations Reference Manual, Geotechnical Engineering Circular No. 2, NHI Course No. 130094, Publication No. FHWA-NHI-11-032.

GHD (GHD 2018), Project Study Report - Project Development Support (PSR-PDS) to Request Approval to Proceed to the Project Approval and Environmental Document Phase for a Locally Funded Project on Route 101 between 0.3-mile south of Prado Road and 0.2-mile south of Madonna Road Overcrossing, EA 05-1H640K, dated March 2018.

Fugro West, Inc. (Fugro 2002), Geotechnical Report, City of San Luis Obispo Water Reuse Project, San Luis Obispo, California, Project No. 01-52-0721, consultant report prepared for Brown and Caldwell, dated April 2, 2002.

MNS Engineers, Inc. (MNS 2015), Pile driving records and quantities, Bridge No. 49-185L, dated February 3 to 16, 2015.

Parikh Consultants, Inc. (Parikh 2002), Log of Test Borings, Route 101/Prado Road Overcrossing, last revision dated November 15, 2002.

Fugro West, Inc. (Fugro 1999), Geotechnical Engineering Report, Laguna Lift Station Force Main Upgrade and Replacement Project, San Luis Obispo, California, Project No. 99-42-0411, consultant report prepared for Brown and Caldwell, dated November 23,1999.

GeoResearch-Unocal (GeoResearch-Unocal 1990), Site Investigative Report, Elks Lane and San Luis Obispo Creek, San Luis Obispo, California, dated April 16,1990.

Geologismiki (Geologismiki 2025), Cliq Liquefaction Analyses Software v3.5.3.15, release date June 3, 2025.

DRAFT Structure Preliminary Geotechnical Report-Overcrossing Project No. 223-400 US 101 at Prado Road Interchange Project December 23, 2025December 23, 2025 M
11 30
Yeh and Associates, Inc. (Yeh 2025), Foundation Report, Caltrans Bridge No. 49C0107, Prado Road Bridge Replacement at San Luis Obispo Creek, San Luis Obispo, California; Project No. 216-323, consultant report prepared for the Wallace Group/City of San Luis Obispo, draft report dated November 25, 2025.

Yeh and Associates, Inc. (Yeh 2025), Draft Preliminary Geotechnical Design Report, US-101 and Prado Road Interchange Project, San Luis Obispo, California, 05-SLO-101-PM 26.5-27.3, Caltrans Project No. 113-0000-0405; EA 05-1H640, City Specification No. 2091613-02, Project No. 223-400, draft report dated December 23, 2025.

Water Systems Consulting, Inc. (WSC 2022), Remedial Investigation Report, City of San Luis Obispo Tetrachloroethylene (PCE) Plume Characterization Project Summary, dated December 2022.

Wiegers, Mark O. (Wiegers 2010) Geologic Map of the San Luis Obispo 7.5’ Quadrangle, San Luis Obispo, California, scale 1:24,000.

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£ Prado Road Proposed
A
West B-B‘
NB Ramps
160 -- —160
San Luis Obispo Creek
Elks Lane
25CPT-03
Yeh (2025) B-2
B-401
B-1 Parikh (2002)
US101 Existing Grade
140 1 --140
Af
\
Af Af
Qyal Qyal
Qyal Qyal Qyal V
V 120 - - - 120
-5 -
Qya2 V Qya2
Qya2 Qya2
Qya2 V
p 100 - - Qya2 --100
Qoa Qoa
Qoa
Qoa
Qoa
80 -- --80
,TD=60‘
TD=61.5’ KJfm
6/26/00 KJfm
7/10/25 TD=62.7'
7/10/25 KJfm
60 — --60
KJfm
40 -- --40
KJfm
20 -- --20
+ + + + +
45+00 50+00 60+00 65+00

PROFILE

SUBSURFACE PROFILE A-A'
KJfm (Franciscan Melange Bedrock): Pervasively sheared soft clay CLAYSTONE matrix with blocks of moderately hard to hard GRAYWACKE PLATE
Geologic contact, dashed or queried where uncertain
■-----Inferred groundwater surface from previous borings. Conditions vary over time of record. 2 San Luis Obispo, CA
V Groundwater level encountered during drilling
A
East
25CPT-02
Yeh(2025)
22RC-02
Yeh (2022)
16‘ South
Fugro (2002)
20‘ South
TD=100.0'
9/12/22
TD=73'
6/27/22
22RC-01
Yeh (2022)
11' South
TD=66.3'
3/31/22
(anomalous)
1 in. = 20 ft. vertical
1 in. = 200 ft. horizontal
B-22A
WSC (2022)
TD=63.0'
3/25/22
/
/
B-18R
WSC (2022)
550' SW
TD=91.0'
1/20/22
B-23
WSC (2022)
LEGEND:

Qya (Younger Alluvium):

Qya1: Very stiff to hard CLAY with varying amounts and interbedded layers of medium dense clayey SAND and GRAVEL Qya2: Medium stiff to stiff CLAY to sandy CLAY with trace amounts and lenses of clayey SAND and GRAVEL Qoa (Older Alluvium): Interbedded units of very stiff sandy CLAY and medium dense clayey SAND TD=60‘ (refusal)
6/27/00
B-24
WSC (2022)
TD=64.5'
3/24/22
PROJECT NUMBER:
223-400
Z
O
55+00

STATION (FEET)
See text and logs of exploration for description
of subsurface conditions.

All boundaries and locations are approximate.

REVISION DATE:
12/23/2025
}
o
Z
PROJECT NAME:

PRADO ROAD-US101 INTERCHANGE PROJECT
05-SLO-101-PM26.5/27.3
/
TD=13.5'
-------2/5/02
\
Oyal
Parikh (2002)
Yeh and Associates, Inc.

Geotechnical • Geological • Construction Services

A-A‘
B-17
Af
DH-1
140 - -fugro (1999) -- 140
700’ South
Af
Af
Qyal
Qyal
Qyal Qyal
120 -- -- 120
V
V
Qya2 Qya2
— 100 - - Qya2 -- 100
?
?
Qoa Qoa Qoa
80 — Qoa - - 80
TD=40.5‘
10/25/99
?
60 -- -- 6040 -- --40 KJfm
20 — -- 20
+ + + + + 70+00 75+00 35+00 45+0040+00

STATION (FEET)

PROFILE

SUBSURFACE PROFILE B-B'
KJfm (Franciscan Melange Bedrock): Pervasively sheared soft clay CLAYSTONE matrix with blocks of moderately hard to hard GRAYWACKE PLATE Geologic contact, dashed or queried where uncertain
3 ?------Inferred groundwater surface from previous borings. Conditions vary over time of record.

V Groundwater level encountered during drilling
25CPT-02
Yeh (2025)
Existing
Grade
25CPT-04
25CPT-01 Yeh (2025)
Yeh (2025)
US 101 Auxiliary Lane
TD=58.3'
7/11/25
1 in. = 20 ft. vertical
1 in. = 200 ft. horizontal
B
South
160 --
TD=66.3'
3/31/22
TD=62.7'
7/10/25
TD=56.6'
7/29/25
TD=11‘
10/25/99
LEGEND:

Qya (Younger Alluvium):

TD=57.2'
3/23/22
B'
North
— 160
-
30+00
DH-3
Fugro (1999)
250' East
Qyal: Very stiff to hard CLAY with varying amounts and interbedded layers of medium dense clayey SAND and GRAVELQya2: Medium stiff to stiff CLAY to sandy CLAY with trace amounts and lenses of clayey SAND and GRAVEL Qoa (Older Alluvium): Interbedded units of very stiff sandy CLAY and medium dense clayey SAND B-21
WSC (2022)
275' West
Z
O
PROJECT NUMBER:
223-400
WSC (2022)
600’ North-Northwest
}
O
Z
See text and logs of exploration for description
of subsurface conditions.

All boundaries and locations are approximate.

End NB On-Ramp
Viaduct
Begin NB Off-Ramp
Viaduct
— TD=60‘ (refusal)
6/27/00
REVISION DATE:
12/23/2025
PROJECT NAME:

PRADO ROAD-US101 INTERCHANGE PROJECT
05-SLO-101-PM26.5/27.3
San Luis Obispo, CA
L Prado Road
A-A'
Yeh and Associates, Inc.

Geotechnical • Geological • Construction Services
B-2
Parikh (2002)
50‘ west

APPENDIX A - CPT PLOTS AND LIQUEFACTION ANALYSES

EGG CPT: 25CPT-01
[
CLIENT: YEH & ASSOCIATES
SITE: PRADO RD, SAN LUIS OBISPO, CA Total depth: 56.63 ft, Date: 7/29/2025 Cone resistance qt Sleeve friction Friction ratio Shear Wave velocity Soil Behaviour Type o —
— ]
Measured Vs

HAND AUGER HANDAUGER HANDAUGER HAND AUGER HAND AUGER
Clay
V V
20-22-
Clay
32-
38-
E
san
70 70 70 70 70 T T T 1Innnnn/nmnn/Bn/B/noT
0 400 0 10 0 10 0
Tip resistance (tsf) Friction (tsf) Rf (%)
CPeT-IT v.20.0.2.33 - CPTU data presentation & interpretation software - Report created on: 7/30/2025, 6:02:12 PM A-1 of 32
□ 5. Silty sand to sandy silt
| | 6. Clean sand to silty sand
16-18-
46-484
50;52;
54456-
38-
40542-44546-48;
50-52;54;56458;60-62;64;66;68-
38;
40;42-44;46-48;
50;52;54;56;58;60-62;64;66;68-
58;
60-62;64;66;68-
0 2 4 6 8 10 12 14 16 18
SBT (Robertson, 2010)
40-
425
44-|
38;
40;42- 44;46-48;
50;
52;
54456;58;
60- 62; 64;66;68-
2 -
4 -
38;
40;| 42- 44 ;| 46- 48;'
50;52554; 56;.
58;
60-62;64;66;68-
O
Ci
Clay & silty clay Clay & silty clay ClayClay & silty clay Clay & silty clay Sand & silty sandClayClay & silty clay Clay & silty clay Clay & silty clay Sand & silty sand Sand & silty sand Silty sand & sandy s Very stiff sand/claye'
Sand & silty sand
■ Very stiff sand/claye
O
Q
O
Q
CD
Q
O
Q
Clay & silty clayClay & silty clayClayClay & silty claySand & silty sand | | 7. Gravelly sand to sand□ 8. Very stiff sand to clayey sand| | 9. Very stiff fine grained It
san

GREGG DRILLING, LLC
https://www.greggdrilling.com/
24;
26-
28; 30;
£
32^
e
34 “
8 36-
■ 2. Organic material
1 | 3. Clay to silty clay
6 "8 "
10-12514-
0 1
2 ;
4 -
6 “8-
10-12
;
144 i6;i8;
20;22;24426-28;30;
£32-e 34;
8 36-
01 2 -
4 -
6 ;|8 -
10-125
144
2 is° ; |22-'24;26-28
;
30-
0 12
;
4 -
6;8-
10-12
;
14; i6;18
;
2°;
22-
244
26-
28 ;|
30;
1 £
32^l
e
34 .
8 364
FIELD REP: JAMIE R.

Cone ID: 231135
SBTn legend
• 1. Sensitive fine grained • 4. Clayey silt to silty clay 500 1,000 1,500 2,000
Vs (ft/s)
c 34 -
8 36-
—L
100
T
6 T
4 T
4 ° 12
;
4 -
6 “8-
10-12-
14;
164 18
;
2°;22-24426428
; 3
°;
£
32 “
34“
836-
T
8 T
8 T
6 —L
300
—L
200
T
2 T
2

EGG CPT: 25CPT-02
[
CLIENT: YEH & ASSOCIATES
SITE: PRADO RD, SAN LUIS OBISPO, CA Total depth: 62.73 ft, Date: 7/10/2025 Cone resistance qt Sleeve friction Friction ratio Shear Wave velocity o 0 0 0
It
]
Measured Vs
10 1 £
18- &silty clay
ty clay‘la si
f 28
& si ty clay
ItIt
o 36
It
Sand & silty sand
Silty sand & sandy sIt
& silty clay
70 T T T T T T T T T T T T 70 Tunnmmuo
0 400 0 10 0 6 4 10 0
Tip resistance (tsf) Friction (tsf) Rf (%)
CPeT-IT v.20.0.2.33 - CPTU data presentation & interpretation software - Report created on: 7/14/2025, 3:10:07 PM A-2 of 32
• 5. Silty sand to sandy silt
| | 6. Clean sand to silty sand
18-
20-22 -24426-
1416
0 2 4 6 81012141618
SBT (Robertson, 2010)
202224
38-
40-42544-465484
50“52454456458560-62-64-66-68-
1416
38-
40442-44-464484
50“52454456458“
60-62-64-
12“145164185
20-22-24426-28530-
666870
2 -
4 -
6 "8 -
38-
40-42 -44 J46448;
50 452454456458“60-62;64-66-68;701
38-
40;42-44;46;48;
50-52 ;54456;58
;
60-62;64;66;68;70-
(1)
0 | | 7. Gravelly sand to sand
• 8. Very stiff sand to clayey sand
| | 9. Very stiff fine grained
O
Q
O
Q
O
Q
O
O

GREGG DRILLING, LLC
https://www.greggdrilling.com/
i ty sand & sandy s
ClaySilty sand & sandy s
Clay
Clay & silty clay
Clay
Clay
Clay & silty clayClay & silty clay ClaySand & silty sand Silty sand & sandy s
2 ;
4 ;6 “8-
10-12-
■ 2. Organic material
• 3. Clay to silty clay
2 -
4 -
6 -8 -
10 '
12-
500 1,000 1,500 2,000
Vs (ft/s)
FIELD REP: JAMIE R.

Cone ID: 231228
SBTn legend
| | 1. Sensitive fine grained • 4. Clayey silt to silty clay 30-
£32--34- c 34-
8364
26-28-
30-
£32-
-34-
8364
2 -
4 -
6 -
8 "
10 '
12514- 16-18 "I
20 "22 "24-26-28 "
_
30 -
£ 32-
e 344
8364
0 72 -
4 -
6 -
8 -
10-12-14416‘18^
20-22-24-26-28“
30-
£
32"
-345
8364
Soil Behaviour Type
Silty sand & sandy s
Clay & silty clayClay & silty clayClay | |
T
4 —L
300
T
6 —1—
100
T
8 T
2 T
2 —I
-
200
1 ClayClay & silty clay
38-
40;42-44;46;48;
50;52 ;54;____ .56;58
;
60-62;64;66;68-
T
8

EGG CPT: 25CPT-03
[
CLIENT: YEH & ASSOCIATES
SITE: PRADO RD, SAN LUIS OBISPO, CA Total depth: 61.48 ft, Date: 7/10/2025 Cone resistance qt Sleeve friction Friction ratio Shear Wave velocity Soil Behaviour Type oT 0 0
]
2 - Measured Vs Clay
Clay & silty clayClayClay & silty clay
10 V
silty clay
ty clay
Clay & silty clay
38 -
ItIt
I It
Sand & silty sand
B
SiltIy sand sandy s It
70 T T T T T T T T T T 70 70 T T 1——
0 400 0 10 0 6 8 4 10 0
Tip resistance (tsf) Friction (tsf) Rf (%)
CPeT-IT v.20.0.2.33 - CPTU data presentation & interpretation software - Report created on: 7/14/2025, 3:10:07 PM A-3 of 32
| | 5. Silty sand to sandy silt
| | 6. Clean sand to silty sand
6 -
8 -
Silty sand & sandy s Silty sand & sandy s
Silty sand & sandy s
Silty sand & sandy s
Sand & silty sand
202224
1012
64 -66-68-
0 2 4 6 81012141618
SBT (Robertson, 2010)
38-'
40^| 42 "
44 -465
484
50“52
-
54456458-60-62- 64-66-68-
202224
14-16418-
ItItItIt
38-
40442-44 J464484
50“52454456458“
60-62“64466-68-
12- 144
16“
18-
2 -
44 38-
40-42 -44446448;
50 452454456458“60-62 -64-66-68;701
40 -42-—44;46;____48;
50;52454;56;58 460-62 -
38-
40; 42-44;46;48;
50-52
;
54456;5S;
60-62;64;66;68;70-
(1)
0 | | 7. Gravelly sand to sand
• 8. Very stiff sand to clayey sand
| | 9. Very stiff fine grained
O
Q
O
Q
O
Q
O
O

GREGG DRILLING, LLC
https://www.greggdrilling.com/
2 ;
4 ;6 “8-
■ 2. Organic material
• 3. Clay to silty clay
500 1,000 1,500 2,000
Vs (ft/s)
FIELD REP: JAMIE R.

Cone ID: 231228
26-28;l
_
30^|
C
32 .
e 344
8 36-1
0 2
;
4 ;
6 “8-
10 ;
12 ;
144i6;
218-
°;
22424 26- 28“ 30“
C
32 e 34;
8 36-
SBTn legend
• 1. Sensitive fine grained • 4. Clayey silt to silty clay — 30“
S' 3
2 -
5345 o 36-1
26-284
30- C
32 ;
34“
8 364
0 —2
;
4 -
6 “8-
10 ;
12 ;
14-16418
;
2°;22424426428“
304
£32-
e
34“
8 36-
8 “I
10-125144164
2185
°;
22“24426428-
Clay .Clay & silty clay Silty sand & sandy sClay
Silty sand & sandy s
Sand & silty sand Silty sand & sandy s
T
4 —L
300
T
6 Li
100
T
8 T
2 T
2 —L
200

EGG CPT: 25CPT-04
[
CLIENT: YEH & ASSOCIATES
SITE: PRADO RD, SAN LUIS OBISPO, CA Total depth: 58.33 ft, Date: 7/10/2025 Cone resistance qt Sleeve friction Friction ratio Shear Wave velocity Soil Behaviour Type o 0 0 0
— ]
Measured Vs
HAND AUGER HANDAUGER HAND AUGER HAND AUGER HAND AUG ER 4- silty clay
—silty clay
ty claysi
16 16 16
Clay
—
ty clay& si
—
Clay
ItIt
••
%
70 T T T T T T T T T T 70 70 T T 11——
0 400 0 10 0 4 6 8 10 0
Tip resistance (tsf) Friction (tsf) Rf (%)
CPeT-IT v.20.0.2.33 - CPTU data presentation & interpretation software - Report created on: 7/14/2025, 3:10:08 PM A-4 of 32
18-
20-22 -24426--
8 38-
40-42-44 J464484
50“52
-
54“56458-60-62-64-66-68-
38-
40442- 44 J464484
50“52454456458“
60-62- 644 66-68-
0 2 4 6 81012141618
SBT (Robertson, 2010)
• 5. Silty sand to sandy silt • 8. Very stiff sand to clayey sand | | 6. Clean sand to silty sand • 9. Very stiff fine grained o
0 O
Q
O
Q
O
Q 38-
40-42-44 J46448;
50 452454456458“60-62;64-66-68;701
O
O

GREGG DRILLING, LLC
https://www.greggdrilling.com/
38-
40-4244;46;48;
50-52
;
54456-58
;
60-62;64;66;68;70-
2 ;
4 ;6 “8-
10-12-14-
38-
40;42-44;.46;!48;'
5°;52454;56;58 460-62-
64;
66;68-
6 ;8 “
10;12514-165
2185
°;
22“
24426-l
2 ;
4 -
6 -
8 "
10-12514-|
T
2 ;
4 -
6 “
8 -
10-12 -14-
□ 2. Organic material
1 | 3. Clay to silty clay
H
FIELD REP: JAMIE R.

Cone ID: 231228
SBTn legend
• 1. Sensitive fine grained • 4. Clayey silt to silty clay • 7. Gravelly sand to sand — 30“
C
32^
e 344
8 364
500 1,000 1,500 2,000
Vs (ft/s)
28 _
3 °;
£32-
34 ;
8 36-
18 ;
20;22;24426-128;|
_
30^
C
32 “
e 344
8 367
0 12 ;
4 -
6 “8-
10 ;
12 ;
14-16418
;
20;22424426428“
305
£32-
e 34;
8 36-
18 ;
2°;224244264284 _
3 °;
C 32;
e 34;
8 36-
2-
.1
— Sand & silty sand
Sand & silty sand
—I
T
4 ClayClay & (
T
6 —L
300
—r100
T
8 T
2 T
2 —L
200
Clay & silty clay
Clay & silty clay Clay & silty claySilty sand & sandy s I Sand & silty sand Sand & silty sand Sand & silty sand — Silty sand & sandy s

Cyclic Stress Ratio* (CSR*) Depth (ft) ( O O 5 5 • O

2.4579 5
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This software is licensed to: Yeh and Associates CPT name: 25CPT-01 CPT basic interpretation plots
Friction Ratio Soil Behaviour Type
______ HAND AUGER
0 6- 6- 6-
2-
8- 8- 8- 8-
4- HAND AUGER
10- 10- 10- 10-
6-
12- 12- 12- 12- 8-14- 14- 14- 14- 10- Clay16- 16- 16- 16- Insitu 12-
14- 18- 18- 18- 18-16- 20 - 20 - 20 - 20-18-
22- 22- 22- 22-
20- Clay
24- 24- 24- 24- Clay & silty clay
Silty sand & sandy
22-
26 - 26 - 26- 26- silt
24-
28 - 28- 28- 28-
26-
e 30- 30 - 30- 30- Clay £ 28-
32- 32 - 32 - 32-
34 - 34 - 34 - 34- 32-
36 - 36- 36 - 36- 34-38 - 38 - 38- 38- 36-
38- 40 - 40 - 40 - 40-
B
40- 42- 42 - 42 - 42-
>
44- 42-
44-
44- 44-
44 -
46 - 46- 46 - 46-
46-
48 - 48- 48- 48-
48-
50 - 50 - 50 - 50- 50-52 - 52 - 52 - 52- 52-
Silty sand & sandy
11 r i • i • 111' i' 1
ly silt
54 - 54 - 54 - 54- 54-
56- 56- 56- 56- 56-
T
1 I
1 I
1 I
1 I
1 I
1 I
1 I
1 I
1 I
1 I
400 0 10 1 4
Rf (%) u (psi) Ic(SBT)
Input parameters and analysis data
Depth to water table (erthq.): 15.00 ft
| | 7. Gravely sand to sand
23 A-6 of 32
CLiq v.3.5.3.15 - CPT Liquefaction Assessment Software - Report created on: 7/30/2025, 3:02:30 PM Project file: C:\Users\jking\Yeh and Associates, Inc\223-400 Prado Road IC - General\3.2 CPT\223-400 Prado Road IC Liquefaction CPT-01 to 04.clq | | 5. Silty sand to sandy silt • 8. Very stiff sand to| | 6. Clean sand to silty sand • 9. Very stiff fine grained Q
C
or
C
Q
C
Q
a
Analysis method:

Fines correction method:Points to test:Earthquake magnitude M: Peak ground acceleration: Depth to water table (insitu):

SBT Plot
___ HAND AUGER
N/A
YesYes
Sands onlyNoN/A
Average results interval:

Ic cut-off value: Unit weight calculation: Use fill: Fill height:

Fill weight:

Transition detect, applied:

Kg applied:

Clay like behavior applied:

Limit depth applied:Limit depth:

52.40Based on SBTNoN/A
• 2. Organic material • 3. Clay to silty clay
clay & silty clay
Clay
NCEER (1998)NCEER (1998)Based on Ic value

7.100.39

15.00 ft
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
SBT (Robertson et al. 1986)
TI
3 Silt
TIT
Cone resistance
_______ HAND AUGER
SBT legend
| | 1. Sensitive fine grained • 4. Clayey silt to silty Pore pressure
______ HAND AUGER
Clay & silty clay
Silty sand & sandy silt Clay _ Clay & silty clay clay & silty clay SlysHXGaKy siSand & silty sand Silty sand & sandy silt lay & silty clay
lay
T
4 TIr
2 T0
T
0 T
6 2 30-
T
2 L
10 Li
100
T
8 ------1-----
200
qt (tsf)
——
300
647

This software is licensed to: Yeh and Associates CPT name: 25CPT-01 interpretation plots (normalized)CPT basic
Norm. Soil Behaviour Type
0 6- 6- 6- 6-
2-
8- 8- 8- 8-
4-
i
10- 10- 10- 10- 6-12- 12- 12- 12- 8-
14- 14- 14- 14- 10- Clay16- 16- 16- 16- 12-
14- 18- 18- 18- 18-16- 20 - 20 - 20 - 20-18-
22- 22- 22- 22-
20-
24- 24- 24- 24-
22-
26 - 26 - 26- 26-
24-
28 - 28- 28- 28-
26-
e 30- 30 - 30- 30- Clay
£ 28-
r
32-1 32 - 32 - 32-
34 - 34 - 34 - 34- 32- Clay & silty clay36 - 36- 36 - 36- 34- Clay
38 - 38 - 38- 38- 36-
38- 40 - 40 - 40 - 40-
k
40-
42- 42 - 42 - 42- L 42- 44- 44- 44- 44-
44-
46 - 46- 46 - 46 -
46-
48 - 48- 48 - 48-
48 50 - 50 - 50 - 50 - Silty sand„& sand'
Sana & silty sandSilty sand & sand'
50 52 - 52 - 52 - 52 - 52
54 - 54- 54 - 54 - 54 Silty sand & sandy silt
Sand & silty sand 56- 56- 56- 56- 56
T T
0 200 0 10 -0.2 1 1 4
Fr (%) Ic (Robertson 1990)
Input parameters and analysis data
Depth to water table (erthq.): 15.00 ft
| | 7. Gravely sand to sand
24 A-7 of 32
CLiq v.3.5.3.15 - CPT Liquefaction Assessment Software - Report created on: 7/30/2025, 3:02:30 PM Project file: C:\Users\jking\Yeh and Associates, Inc\223-400 Prado Road IC - General\3.2 CPT\223-400 Prado Road IC Liquefaction CPT-01 to 04.clq ly silt ly silt
| | 5. Silty sand to sandy silt • 8. Very stiff sand to| | 6. Clean sand to silty sand • 9. Very stiff fine grained Q
C
or
C
Q
C
Q
a
Analysis method:

Fines correction method:Points to test:Earthquake magnitude Mw: Peak ground acceleration: Depth to water table (insitu):

Fill weight:

Transition detect, applied:

Kg applied:

Clay like behavior applied:

Limit depth applied:Limit depth:

N/A
YesYes
Sands onlyNoN/A
SBTn Plot
___ HAND AUGER
Average results interval:

Ic cut-off value: Unit weight calculation: Use fill: Fill height:

0.4 0.6Bq

52.40Based on SBTNoN/A
• 2. Organic material • 3. Clay to silty clay
NCEER (1998)NCEER (1998)Based on Ic value

7.100.39

15.00 ft
TT
3 Tr
2 SBTn legend
| | 1. Sensitive fine grained • 4. Clayey silt to silty Norm, friction ratio
________ HAND AUGER_______
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
SBTn (Robertson 1990)
Norm, cone resistance
__________HAND AUGER_
Clay & silty clay Clay & silty clay
ClayClay & silty clayClay
Clay & silty clay
Nom. pore pressure ratio

HANDAUGER
T
4 2 30-
T
0 T
6 L

0.2 Li

0.8 T
2 L
50 L
150
, HAND AUGER
Clay
—I
-
100
Qtn
T
8 Clay & silty clay
Clay
Clay & silty clay
Silty sand & sandy silt

This software is licensed to: Yeh and Associates CPT name: 25CPT-01 Liquefaction analysis overall plots (intermediate results) Total cone resistance
__________ HAND AUGER_____
Norm, cone resistance
___________ HAND AUGER____
Grain char. factor Corrected norm, cone resistance

HAND AUGER
6- 6- 6- 6- 6-8- 8- 8- 8- 8-
10- 10 - 10- 10- 10 -
12- 12- 12- 12- 12-14- 14- 14- 14- 14-16- 16- 16- 16- 16-18- 18- 18- 18- 18- 20 - 20 - 20- 20- 20-
22- 22- 22- 22- 22-24- 24- 24- 24- 24-
26 - 26- 26- 26- 26-28 - 28- 28- 28- 28 -
d d
e 30- e 30- e 30- 30 - 30-
r
32 32 - 32- 32- 32-34- 34- 34- 34- 34-
36 - 36 - 36- 36- 36-38 - 38 - 38- 38- 38 -
40 - 40 - 40- 40- 40 -
42- 42 - 42- 42- 42-44- 44- 44- 44- 44-
46 - 46 - 46- 46 - 46 -
48 - 48- 48- 48- 48-
50 - 50 - 50- 50 - 50 -52 - 52 - 52- 52 - 52 -54 - 54 - 54- 54- 54 - 56- 56- 56- 56- 56-
T 1
I
1 I
1 I
1 I
1 I
1 I
1 I
1 1
1 1
1 400 1 4 0 200 0 1 2 3 7 8 9 10 0 200
Ic (Robertson 1990)
Input parameters and analysis data
Depth to water table (erthq.): 15.00 ft
25 A-8 of 32
CLiq v.3.5.3.15 - CPT Liquefaction Assessment Software - Report created on: 7/30/2025, 3:02:30 PM Project file: C:\Users\jking\Yeh and Associates, Inc\223-400 Prado Road IC - General\3.2 CPT\223-400 Prado Road IC Liquefaction CPT-01 to 04.clq O
Q
Q
a
Q
C
Q
C
Q
C
Analysis method:

Fines correction method:Points to test:Earthquake magnitude Mw: Peak ground acceleration: Depth to water table (insitu):

Fill weight:

Transition detect, applied:

Kg applied:

Clay like behavior applied:

Limit depth applied:Limit depth:

N/A
YesYes
Sands onlyNoN/A
Average results interval:

Ic cut-off value: Unit weight calculation: Use fill: Fill height:
4 5 6
KC

52.40Based on SBTNoN/A
NCEER (1998)NCEER (1998)Based on Ic value

7.100.39

15.00 ft
SBTnIndex
_____ HAND AUGER
T0
T
3 —L
100
Qtn
—i—
100
Qtn,cs
L
50 T
2 L
50 L
100
Li
150
-----1----
200
qt(tsf)
Li
150
——300

This software is licensed to: Yeh and Associates CPT name: 25CPT-01 Liquefaction analysis overall plots
CRR plot FS Plot Liquefaction potential Vertical settlements Lateral displacements o 0 0 0 0
2- 2- 2- 2- 2-
4- HAND AUGER HAND AUGER HAND AUGER 4- 4- 4- 4 HAND AUGERHAND AUGER 6- 6 6- 6- 6-
8- 8 8- 8- 8-
10- 10 10- 10- 10-12- 12 12- 12- 12-14- 14 14- 14- 14-
16- Duringearthq 16 16-
ing 16- 16-
18- 18 18- 18- 18-
20 - 20 20 - 20- 20-
22- 22 22 - 22- 22-
24 - 24 24- 24- 24-26 - 26 26 - 26- 26- d d
£ 28- £ 28 £ 28- 28- 28-
O 30 - 30- 30 -
Q
32 - 32 32 - 32- 32 -34- 34 34 - 34- 34-36 - 36 36- 36- 36-38 - 38 38- 38- 38 - ♦
40 - 40 40 - 40- 40 -
42- 42 42 - 42- 42 -44- 44
44- 44 _ 44-
46- 46 46 - 46- 46-
48- 48 48 - 48- 48-
50 - 50 50- 50-
52- & 52 52- 52 -
54 - 54 54- 54- 54 -56 - 56 56 - 56 56-
T
0 0.6 0 2 0 20 0 0.02 1.5 0.04 0.06
CRR&CSR Factor of safety Settlement (in)
Input parameters and analysis data F.S. color scheme
Depth to water table (erthq.): 15.00 ft
26 A-9 of 32
2m»mi ii
CLiq v.3.5.3.15 - CPT Liquefaction Assessment Software - Report created on: 7/30/2025, 3:02:30 PM Project file: C:\Users\jking\Yeh and Associates, Inc\223-400 Prado Road IC - General\3.2 CPT\223-400 Prado Road IC Liquefaction CPT-01 to 04.clq 50- >52- 3
Dry: 0.00
Wet: 0.07
O
Q
□□□■
O
C
LPI color scheme
■ Very high risk
• High risk
□ Low risk
Analysis method:

Fines correction method:Points to test:Earthquake magnitude M: Peak ground acceleration: Depth to water table (insitu):

Fill weight:

Transition detect, applied:

Kg applied:

Clay like behavior applied:

Limit depth applied:Limit depth:

N/A
YesYes
Sands onlyNoN/A
Almost certain it will liquefyVery likely to liquefy
Liquefaction and no liq. are equally likely
Unlike to liquefy
Almost certain it will not liquefy
Average results interval:

Ic cut-off value: Unit weight calculation: Use fill: Fill height:

52.40Based on SBTNoN/A
NCEER (1998)NCEER (1998)Based on Ic value

7.100.39

15.00 ft
2 30-
T
1 2
30 0
Displacement (in)
Li

0.4 Li
10 LPI
T"
15 Li

0.2 Li

0.5 T
5

This software is licensed to: Yeh and Associates CPT name: 25CPT-01 Liquefaction analysis summary plots
Illi 1 1 1 1 1 1 1 1 1,000 - 0.8
Analysis PGA: 0.39 ' Liquefaction 12.0-
7 Y 8 0.7 - 11.0-
- PA

10.0-
Cl
1 O

0.6-

9.0-
100 -

8.0-
r. 0.5-
-V

7.0- R.
a 0.4- F 6.0-
O
5 — 5.0-
ils &

0.3-
10 - U

4.0- 4
j

0.2- 3.0-

2.0-

0.1-
2 1.0-
No Liquefaction -
l 0 I I I I—n-1—Tun—r"|—I I I ।—I I I ।—I I I ।—I I I । I I I ।—I I I ।—I I I 0.0