HYDROLOGY & HYDRAULICS STUDY
The Related Companies
644-034-05 & 644-034-09
TPM-2025-118
LAGUNA BEACH, CALIFORNIA
Developer:
The Related Companies
18201 Von Karman Ste 900
Irvine, CA 92619
Contact: Craig Farmer
Development Manager
(949) 660-7272
Prepared For:
The Related Companies
18201 Von Karman Ste 900
Irvine, CA 92619
Contact: Craig Farmer
Development Manager
(949) 660-7272
Prepared By:
KES
1 Venture Ste 130
Irvine, CA 92618
Contact: Daryl Kessler
(949) 339-5331
February, 2025
Attachment 12
582
Executive Summary…………………………………………………….i
Acknowledgement and Signature Page…………………………………ii
I. Introduction……………………….…………………………………...1
II. Methodology…………………………………………………………...1
III. Design Assumptions…………………………………………………...2
IV. Conclusion……………………………………………………………..3
V. References……………………………………………………………..4
A. Hydrology Study (100-Year Storm Event)
B. Sub-Area Runoff Summary (Existing and Proposed)
C. Area Drain Pipe Capacity Calculations
D. Overflow Calculations
List of Exhibits:
1. Proposed Q100 Hydrology Map
2. Existing Conditions Q100 Hydrology Map
3. TPM
583
Hydrology Study and Hydraulic Analysis
For
TPM 2025-118
This Hydrology Study prepared by KES under the supervision of Ali Monshizadeh , P.E.
___________________________________ ____________
Ali Monshizadeh, PE 67674 Date
KES
ii
584
The purpose of this report is to provide quantitative information to verify preliminary storm drain infrastructure and hydrologic compliance of the project site. The values and statements within confirm the subject site is designed and planned in accordance to the Orange County Hydrology Manual and the City of Laguna Beach for Public and Private Drainage Facilities.
:
The proposed project is located at the northwest corner of Saint Anns Drive and Glenneyre Street and is located in the City of Laguna Beach bordered to the west and north by single family homes and is bordered along the north east boundary by Catalina Street.
The subject project site planned to be affordable housing on the western parcel and church sanctuary use to be done by others on the easterly parcel. The proposed housing development will be a podium style development with subsurface parking and all associated uses above grade on the concrete deck.
The proposed project will also incorporate fronting landscape space and community open space on the elevated deck. The community will install community utilized parking stalls, project frontage landscape. No car washing will be allowed on the subject site.
The subject housing site is proposed to be fully demolished and nothing will be saved. The existing site basically flows to the southwest direct into the right of way. There are no water quality devices that exist on the subject site. Catalina Right of way current flows against the northerly existing wall and directed to the west, this historical flow will remain in place post development. The proposed development will surface flow and catch flows within a small area drain system around the perimeter of the podium and within the structure itself. All water quality flows will be directed into a subsurface chamber within the lower level of the podium. The volume of the chambers are controlled based on the Vbmp requirement. Once flow enters the chambers the volume gets pumped to the upper level through a MWS unit for water quality. Flows above that required volume will be allowed to flow into the right of way via under walk drain/curb cores at a location to be determined by the MEP during final engineering. Because the time of concentration for the developed condition is similar than the existing condition the 100 year flow rates are less than 1% and do not require mitigation. The proposed and existing development both have a pervious area of 13%. / :
The proposed drainage area was analyzed by utilizing the Orange County Local Drainage Manual of Orange County. Each drainage area was divided as demonstrated on the hydrology map (Exhibit 1).
Each area was analyzed for acreage, impervious cover, and time of concentration according to the Rational Method. The flows, expressed in cubic feet per second (cfs), were totaled at connections to main storm drain lines. This information will in the future be used in conjunction with WSPG software during final engineering to validate the hydraulic grade line and other flow characteristics of each section of pipe.
585
- :
1. The onsite drainage area was analyzed for a 100-year storm event using Rational Method Analysis per the County of Orange Hydrology Manual.
2. The drainage area is located in Soil Groups A according to page 4-9 of the Hydrology Manual and geotechnical soils analysis. (Map Attached).
3. The rainfall intensity for a 100-year 1-hour storm varies according to Figure D-1 (page A4-4) of the Hydrology Manual.
4. The infiltration rate for the pervious area, Fp, is 0.40 inches/hour.
5. The impervious area has been calculated to be 87% for the subject project.
6. Storm drains and catch basins onsite will be designed for a 100-year storm event, which corresponds to the design requirements for the project.
7. All flows are based on the complete future development of land and roads.
8. The Hydrology Map attached to the back of this study is made part of the study. **Note: Additional Calculation Assumptions Have Been Noted Throughout Report** 586
:
The results from this hydrology and hydraulic analysis demonstrate the following:
• The drainage design for the “Project” has been designed to meet the County of Orange Flood Control Standards.
• The drainage system is designed to manage runoff from a 100-year storm. • Building pads will be protected and will be above the theoretical 100 year flood elevation as determined in this study
• Per FEMA the subject site is within Flood Zone X.
• The existing site conditions result in a predevelopment 100-year flow of 3.08 cfs to the right of way.
3
587
1. County of Orange, “Hydrology Manual” dated January 1999.
2. Water Surface and Pressure Gradient (WSPG) Hydraulic Analysis System Software, Los Angeles County Department of Public Works Program No. F0515P, April 1979.
3. Advanced Engineering Software, HELE1 Hydraulic Elements I for Street Flooding and Catch Basin Design, 1996 version.
4 588
Hydrology Study (100-Year Storm Event)
589
590
Sub-Area Runoff Summary
591
DATE: Feb 2025
DATE:
PAGE 1 OF 1
CONC. PT. SOIL DEV. Tt Tc I Fm Q FLOW SLOPE V HYDRAULICS AND (MAP AREA) SUBAREA TOTAL TYPE (Ap) MIN. MIN. in/hr in/hr TOTAL PATH, FT FT/FT FT/SEC NOTES Proposed Area
A1 0.66 A 0.13 6.6 5.28 0.052 3.10 287 Initial Area: L=287' H=1.5'
Existing Area
X1 0.66 A 0.13 6.7 5.23 0.052 3.08 348
RATIONAL METHOD STUDY FORM
CHECKED BY:
CALCULATED BY: DK
NOTES: I(t) = at^b a=15.560, b=-0.573 ; C = 0.90 ; Q = C*(I - Fm)*A; Fm=Ap*Fp; Fp=0.40 (Soil A, OC Soils Map)
AREA (ACRES)
Orange County
HYDROLOGY MANUAL
100-YEAR STORM RATIONAL METHOD STUDY
STUDY NAME: Laguna
592
Area Drain Pipe Capacities
593
4in
Manning Pipe Calculator
Given Input Data:
Shape ........................... Circular
Solving for ..................... Flowrate
Diameter ........................ 4.0000 in
Depth ........................... 4.0000 in
Slope ........................... 0.0050 ft/ft
Manning's n ..................... 0.0120
Computed Results:
Flowrate ........................ 0.1458 cfs
Area ............................ 0.0873 ft2
Wetted Area ..................... 0.0873 ft2
Wetted Perimeter ................ 12.5664 in
Perimeter ....................... 12.5664 in
Velocity ........................ 1.6706 fps
Hydraulic Radius ................ 1.0000 in
Percent Full .................... 100.0000 %
Full flow Flowrate .............. 0.1458 cfs
Full flow velocity .............. 1.6706 fps
Critical Information
Critical depth .................. 3.0719 in
Critical slope .................. 0.0094 ft/ft
Critical velocity ............... 2.8101 fps
Critical area ................... 0.0734 ft2
Critical perimeter .............. 8.4269 in
Critical hydraulic radius ....... 1.2544 in
Critical top width .............. 4.0000 in
Specific energy ................. 0.4005 ft
Minimum energy .................. 0.3840 ft
Froude number ................... 0.6721
Flow condition .................. Subcritical
594
6in
Manning Pipe Calculator
Given Input Data:
Shape ........................... Circular
Solving for ..................... Flowrate
Diameter ........................ 6.0000 in
Depth ........................... 6.0000 in
Slope ........................... 0.0050 ft/ft
Manning's n ..................... 0.0120
Computed Results:
Flowrate ........................ 0.4298 cfs
Area ............................ 0.1963 ft2
Wetted Area ..................... 0.1963 ft2
Wetted Perimeter ................ 18.8496 in
Perimeter ....................... 18.8496 in
Velocity ........................ 2.1891 fps
Hydraulic Radius ................ 1.5000 in
Percent Full .................... 100.0000 %
Full flow Flowrate .............. 0.4298 cfs
Full flow velocity .............. 2.1891 fps
Critical Information
Critical depth .................. 4.7575 in
Critical slope .................. 0.0084 ft/ft
Critical velocity ............... 3.5483 fps
Critical area ................... 0.1714 ft2
Critical perimeter .............. 12.9398 in
Critical hydraulic radius ....... 1.9075 in
Critical top width .............. 6.0000 in
Specific energy ................. 0.6154 ft
Minimum energy .................. 0.5947 ft
Froude number ................... 0.7191
Flow condition .................. Subcritical
595
8in
Manning Pipe Calculator
Given Input Data:
Shape ........................... Circular
Solving for ..................... Flowrate
Diameter ........................ 8.0000 in
Depth ........................... 8.0000 in
Slope ........................... 0.0050 ft/ft
Manning's n ..................... 0.0120
Computed Results:
Flowrate ........................ 0.9257 cfs
Area ............................ 0.3491 ft2
Wetted Area ..................... 0.3491 ft2
Wetted Perimeter ................ 25.1327 in
Perimeter ....................... 25.1327 in
Velocity ........................ 2.6519 fps
Hydraulic Radius ................ 2.0000 in
Percent Full .................... 100.0000 %
Full flow Flowrate .............. 0.9257 cfs
Full flow velocity .............. 2.6519 fps
Critical Information
Critical depth .................. 6.4843 in
Critical slope .................. 0.0077 ft/ft
Critical velocity ............... 4.1907 fps
Critical area ................... 0.3125 ft2
Critical perimeter .............. 17.5350 in
Critical hydraulic radius ....... 2.5667 in
Critical top width .............. 8.0000 in
Specific energy ................. 0.8360 ft
Minimum energy .................. 0.8105 ft
Froude number ................... 0.7544
Flow condition .................. Subcritical
596
Overflow Calculations
597
598
Exhibit
Proposed Hydrology Map
599
W W W W W W W W W W W W W W W W W W W W W W W W W W WWW W W W W W W W W W W W W W W W S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S 600
Exhibit
Existing Hydrology
601
S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S W W W W W W W W W W W W W W W WWW W W W W W W W W W W W W W W W W W W W W W W W W W W 602
Exhibit
TPM
603
’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ SITE LOT 11 LOT 9 LOT 7 LOT 5 LOT 3 LOT 1 LOT 12 LOT 10 LOT 8 LOT 6 LOT 4 LOT 2 LOT 24
LOT 25
LOT 26
LOT 27
LOT 20
LOT 19
LOT 18
LOT 22
LOT 23 LOT 21 LOT 99 LOT 17 LOT 16 LOT 15 LOT 14 LOT 13 PARCEL 2
PARCEL 3 PARCEL 4
PARCEL 1 PARCEL 1 LAGUNA TERRACE MM 4/80 TENTATIVE PARCEL NO. 2025-118 FOR LAND SUBDIVISION PURPOSES CITY OF LAGUNA BEACH COUNTY OF ORANGE STATE OF CALIFORNIA EXISTING MAPPING CONDITION PROPOSED MAPPING CONDITION 604
S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S W W W W W W W W W W W W W W W WWW W W W W W W W W W W W W W W W W W W W W W W W W W W 605
W
W W W W W W W W W W W W W W W W W W W W W W W W W W W WWW W W W W W W W W W W W W W S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S 606