Appendix J.3 - Drainage Master PlanAppendix J.3
Drainage Master Plan
Q3, 2021
Travertine SPA
Draft EIR
SCH# 201811023
Technical Appendices
October 2023
Travertine De veJopmenjt
DRAINAGE MASTER PLAN
City of La Quinta and County of Riverside, California
Regional Hydrology, Hydraulics, and Proposed Project Flood
Risk Mitigation
June 10, 2021
Prepared for:
Travertine Corporation
1380 Galaxy Way
Suite B
Concord, CA 94520
Prepared by:
r
Consulting
27042 Towne Centre Drive
Suite 110
Foothill Ranch, CA 92610
JN 40.001.000
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Travertine Development
Drainage Master Plan
Table of Contents
1 Introduction 1-1
1.1 Project overview 1-1
1.2 Project description 1-1
1.3 Goals and objectives 1-1
1.4 CVWD standards and policies 1-2
1.5 Document format 1-3
2 West Dike System 2-1
2.1 Dike No. 4 2-1
2.2 Guadalupe Creek Diversion Dikes 2-2
3 Geomorphic Watershed Assessment 3-1
3.1 Site description 3-1
3.2 Methodology 3-4
3.3 General findings 3-4
3.4 Landform mapping 3-6
3.5 Other Considerations 3-7
4 Regional Hydrology 4-1
4.1 Hydrologic goals and objectives 4-1
4.2 Hydrologic analysis — assumptions and general approach 4-1
4.3 Synthetic Unit Hydrograph Method 4-2
4.3.1 Watershed delineation, existing (baseline) conditions 4-2
4.3.2 Watershed delineation, project conditions 4-3
4.3.3 Precipitation 4-9
4.3.4 Precipitation losses (constant loss rate determination) 4-12
4.3.5 Unit hydrograph transform 4-25
4.4 Channel routing 4-28
4.5 HEC -HMS model development summary 4-32
4.6 Debris yield 4-32
4.7 Hydrologic analysis results 4-38
5 Flood conveyance and storage analysis 5-1
5.1 Goals and objectives 5-1
5.2 Two-dimensional flood routing 5-1
5.2.1 General model definitions 5-2
5.2.2 Topographic features 5-2
5.2.3 Levees 5-2
5.2.4 Hydraulic structures 5-3
5.2.5 Coral Mountain rock cutout at the terminus of upper Guadalupe Creek 5-3
5.2.6 Infiltration and transmission losses 5-5
5.2.7 Model inflow boundary conditions 5-6
5.2.8 Model exclusions 5-13
5.2.9 Model variations for flood pattern uncertainty 5-13
5.2.10 Model simulation results 5-14
6 Comparison to Previous Studies for West Side Dike No. 4 6-1
6.1 Regional hydrology 6-1
6.1.1 Model development comparison — PACE (2005) vs. Travertine 6-1
6.1.2 Precipitation comparison — PACE (2005) vs. Travertine 6-1
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6.2 Flood conveyance and impoundment 6-2
6.2.1 Flood runoff and debris comparison — PACE (2005) vs. Travertine 6-3
6.2.2 Flood stage comparison 6-5
7 Flood Hazard Impacts and Mitigation 7-1
7.1 General 7-1
7.2 Flood Hazard Mitigation Plan 7-1
7.2.1 Alluvial Fan Flood Protection Measures 7-1
7.2.2 Flood Protection System Selection 7-2
7.2.3 Conceptual Flood Protection System 7-2
7.3 Project Impacts 7-9
7.3.1 West Side Dike No. 4 7-9
7.3.2 Guadalupe Creek Diversion Dikes 7-9
7.3.3 California Drainage Law 7-10
7.4 Design Requirements 7-10
7.4.1 West and South Bank Protection 7-11
7.4.2 Guadalupe Creek Diversion Dikes 7-12
7.4.3 Jefferson Road, Avenue 62, and Madison Street Bridge Crossings 7-12
7.4.4 On -Site Drainage and Storm Water Retention 7-12
7.4.5 Operations and Maintenance Plan 7-13
8 References 8-1
Figures
Figure 1-1. Location map 1-4
Figure 1-2. Regional vicinity map 1-4
Figure 1-3. Local vicinity map 1-5
Figure 1-4. Travertine grading concept plan 1-6
Figure 2-1. Guadalupe Creek Diversion Dikes — as -built plan and profiles (CVCWD, 1968) 2-3
Figure 3-1. Location of Travertine on the eastern piedmont of the Santa Rosa Mountains 3-1
Figure 3-2. USGS topography showing a lack of radial fan contours on the upper piedmont 3-2
Figure 3-3. Recent aerial shows active/inactive fan areas and evidence of development activities 3-3
Figure 3-4. Geomorphic surfaces with flood hazard types overlain on USGS topography 3-9
Figure 3-5. Geomorphic surfaces with flood hazard types overlain on recent aerials 3-10
Figure 4-1. Baseline conditions regional hydrology map 4-5
Figure 4-2. Project conditions regional hydrology map 4-7
Figure 4-3. Southern California local storm depth -area relationships (Plate 4; USACE, 1980) 4-10
Figure 4-4. Baseline conditions composite soil map 4-13
Figure 4-5. Project conditions composite soil map 4-15
Figure 4-6. Baseline conditions land use map* 4-19
Figure 4-7. Project conditions land use map* 4-21
Figure 4-8. Baseline conditions HEC -HMS model schematic* 4-29
Figure 4-9. Project conditions HEC -HMS model schematic* 4-30
Figure 5-1 Conceptual arched bridge detail section (partial) 5-3
Figure 5-2 Selected cross sections for Coral Mountain rock cutout 5-4
Figure 5-3 Cross Section 1 (critical depth shown for 10,000 cfs) 5-5
Figure 5-4 Cross Section 2 (critical depth shown for 10,000 cfs) 5-5
Figure 5-5 infiltration area for model simulations focused on impoundment impacts to Dike No. 4 5-6
Figure 5-6 Travertine baseline 1 -percent annual chance maximum depths > 0.5 feet 5-17
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Figure 5-7. Travertine baseline 1 -percent annual chance maximum depths > 0.5 feet with DC1 forced split
in effect 5-19
Figure 5-8. Travertine composite baseline 1 -percent annual chance maximum depths > 0.5 feet 5-21
Figure 5-9. Travertine project 1 -percent annual chance maximum depths > 0.5 feet 5-23
Figure 5-10. Travertine project 1 -percent annual chance maximum depths > 0.5 feet with DC1 forced split
in effect 5-25
Figure 5-11. Travertine composite project 1 -percent annual chance maximum depths > 0.5 feet 5-27
Figure 5-12. Travertine change in composite 1 -percent annual chance maximum depths from baseline to
project conditions 5-29
Figure 5-13. Travertine baseline 1 -percent annual chance maximum velocities (maximum depths > 05
feet) 5-31
Figure 5-14. Travertine baseline 1 -percent annual chance maximum velocities (maximum depths > 05
feet) with DC1 forced split in effect 5-33
Figure 5-15. Travertine composite baseline 1 -percent annual chance maximum velocities (maximum
depths > 0.5 feet) 5-35
Figure 5-16. Travertine project 1 -percent annual chance maximum velocities (maximum depths > 0.5
feet) 5-37
Figure 5-17. Travertine project 1 -percent annual chance maximum velocities (maximum depths > 0.5
feet) with DC1 forced split in effect 5-39
Figure 5-18. Travertine composite project 1 -percent annual chance maximum velocities (maximum
depths > 0.5 feet) 5-41
Figure 5-19. Travertine change in composite 1 -percent annual chance maximum velocities (maximum
depths > 0.5 feet) from baseline to project conditions 5-43
Figure 5-20. Dike No. 4 baseline 1 -percent annual chance maximum depths > 0.5 feet 5-45
Figure 5-21. Dike No. 4 project 1 -percent annual chance maximum depths > 0.5 feet 5-47
Figure 5-22. Dike No. 4 change in 1 -percent annual chance maximum depths > 0.5 feet from baseline to
project conditions 5-49
Figure 5-23. Dike No. 4 baseline Standard Project Flood maximum depths > 0.5 feet 5-51
Figure 5-24. Dike No. 4 project Standard Project Flood maximum depths > 0.5 feet 5-53
Figure 5-25. Dike No. 4 change in Standard Project Flood maximum depths > 0.5 feet from baseline to
project conditions 5-55
Figure 5-26. Comparison of water surface and ground elevation profiles along Dike No. 4 5-57
Figure 5-27. 1 -percent annual chance water surface profiles adjacent to the North Guadalupe Creek
Diversion Dike 5-59
Figure 5-28. 1 -percent annual chance water surface profiles adjacent to the South Guadalupe Creek
Diversion Dike 5-60
Figure 5-29. 1 -percent annual chance water surface profiles along the centerline of Guadalupe Creek
Channel 5-61
Figure 5-30. 1 -percent annual chance flood depths and velocities adjacent to the North Guadalupe Creek
Diversion Dike 5-62
Figure 5-31. 1 -percent annual chance flood depths and velocities adjacent to the South Guadalupe Creek
Diversion Dike 5-63
Figure 5-32. 1 -percent annual chance flood depths and velocities along the centerline of Guadalupe Creek
Channel 5-64
Figure 5-33. Plan view of upper Guadalupe Creek Diversion Dikes 5-65
Figure 7-1. Flood protection plan 7-3
Figure 7-2. Flood conveyance typical sections- Guadalupe Diversion Dike 7-5
Figure 7-3. Flood conveyance typical sections- West and South banks 7-7
Figure 7-4. Onsite drainage plan 7-14
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Tables
Table 4-1. 1 -percent annual chance precipitation depths for selected durations 4-11
Table 4-2. Distribution of soil map units 4-17
Table 4-3. Hydrologic soil group composition for soil map units 4-18
Table 4-4. Distribution of land -use units 4-23
Table 4-5. Assigned percent imperviousness values for land use categories 4-24
Table 4-6. Summary of subbasin constant loss rates 4-25
Table 4-7. Lag formula hydraulic roughness n ("n -bar") 4-27
Table 4-8. Unit hydrograph lag parameter summary 4-28
Table 4-9. Muskingum routing parameter development summary 4-31
Table 4-10. Los Angeles District Debris Method (Table D-1; USACE, 2000) A -T factor guidelines4-35
Table 4-11. A -T factors estimated for each soil map unit 4-36
Table 4-12. Summary of A -T factors estimated for each subbasin 4-37
Table 4-13. 1 -percent annual chance hydrology and debris analysis results for the evaluation of the project
edge conditions 4-39
Table 4-14. 1 -percent annual chance debris analysis results for the evaluation of flood impoundment
adjacent to Dike No. 4 4-40
Table 4-15. SPF debris analysis results for the evaluation of flood impoundment adjacent to Dike No4 4-
41
Table 5-1. Summary of discharges versus critical depth at selected rock cutout cross sections 5-4
Table 5-2. Summary of inflow boundary conditions 5-7
Table 5-3. Baseline 1 -percent annual chance flood inflow distribution, no areal effects 5-8
Table 5-4. Baseline 1 -percent annual chance flood inflow distribution, areal effects 5-9
Table 5-5. Baseline SPF inflow distribution, areal effects 5-10
Table 5-6. Project 1 -percent annual chance flood inflow distribution, no areal effects 5-11
Table 5-7. Project 1 -percent annual chance flood inflow distribution, areal effects 5-12
Table 5-8. Project SPF inflow distribution, areal effects 5-13
Table 6-1. Precipitation comparison — PACE (2005) vs. Travertine 6-2
Table 6-2. Flood runoff and debris comparison — PACE (2005) vs. Travertine 6-4
Table 6-3. Dike No. 4 flood stage comparison — PACE (2005) vs. Travertine 6-5
Electronic Technical Appendix
Provided electronically
HEC -HMS Models
Excel spreadsheet — slope analysis
Excel spreadsheet — determination of precipitation losses
Excel spreadsheet — determination of debris yield A -T factors
Rating Table Hydraulics
ArcGIS files
FLO-2D PRO input and output files
Selected References
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1 INTRODUCTION
1.1 Project overview
The proposed Travertine Specific Plan Amendment is an 855.4 -acre mixed-use community in the City of
La Quinta and parts of unincorporated Riverside County, California. The Specific Plan Area is tucked
into one of the eastern piedmonts along the base of the Santa Rosa Mountains, above the flood
impoundment zone of West Dike System Dike No. 4 (BOR, 1947; Bechtel, 1991), and adjacent to the
Guadalupe Creek Diversion Dikes (CVCWD, 1968; Bechtel, 1991) to the north. Dike No. 4 and the
Guadalupe Creek Diversion Dikes were constructed circa 1967.
The purpose of the Drainage Master Plan is to determine the project -related impacts to existing
hydrology, floodplains, and drainage/flood control features, and identify appropriate flood control and
local drainage improvements necessary for the planned development. The Drainage Master Plan
addresses both regional and local impacts, flood hazard mitigation requirements, and design
constraints/features. The Drainage Master Plan is based on the requirements of the Coachella Valley
Water District (CVWD), County of Riverside, and the City of La Quinta. Travertine is shown in Figure 1-
1 (location map), Figure 1-2 (regional vicinity map), Figure 1-3 (local vicinity map), and Figure 1-4
(concept grading plan).
1.2 Project description
The Travertine Specific Plan Amendment encompasses approximately 855 acres in the City of La Quinta
at the northeastern base of the Santa Rosa Mountains in the Coachella Valley. The property is generally
bounded by Avenue 60 to the north; Avenue 64 and Bureau of Land Management land to the south;
Madison Street to the east; and Jefferson Street to the west. The property is located roughly one mile
south of PGA West and Lake Cahuilla, situated in Section 33, Township 6 south, Range 7 east; and in
Sections 3, 4 and 5 of Township 7 south, Range 7 east, San Bernardino Base and Meridian, County of
Riverside, California.
The Travertine Specific Plan proposes a variety of complementary land uses, including up to 1,200
residential units, proposed 100 villa resort, and associated commercial and recreational facilities.
Recreational opportunities include a 4 -hole golf practice facility, open -space areas, and private
recreational facilities provided in the individual residential developments.
1.3 Goals and objectives
The purpose of this document is to provide a detailed watershed assessment, including regional and local
hydrology, flood hazard analysis, hydraulics, and sedimentation in order to develop a drainage master
plan for the Travertine development. The overall goal of this study is to provide the appropriate level of
flood protection for the public, non-CVWD storm water facilities, and impacted CVWD storm water
facilities that are consistent with the requirements and guidelines instituted by the City of La Quinta,
CVWD, and the U.S. Bureau of Reclamation (Dike No. 4).
The primary objectives of this study include the following:
• Develop baseline ("without" project) and project conditions hydrology to establish peak flow
rates and flood volumes for use in the conceptual design of combined onsite/offsite flood
conveyances and temporary impoundments along the outer project edge of the planned
development (Travertine)
• Develop project conditions local hydrology for use in the conceptual design of on-site storm
water facilities
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• Identify and propose mitigation for any potentially significant development -related adverse flood
hazard impacts, including Dike No. 4 and the Guadalupe Creek Diversion Dikes
• Identify hydraulic, sedimentation, and erosion issues/design constraints associated with the major
flood conveyances, which extend through or around the proposed development, including the
Guadalupe Creek Diversion Dikes along the north edge of the Travertine boundary
• Formulate the conceptual design of regional and local storm water facilities
The drainage master plan includes the preparation of detailed technical studies for the regional watershed
and local onsite drainage areas leading to the identification of flood hazards, which may impact site
development. The technical studies included:
• Geomorphic assessment of the regional watershed, project site, and surrounding vicinity
• Regional hydrology, hydraulics, and sedimentation analysis for the Dike No. 4 watershed
• Dike No. 4 flood routing/impoundment and impact analysis
• Guadalupe Creek Diversion Dikes flood routing and impact analysis
• Local hydrology analysis and preliminary pipe sizing
The intended use of the drainage master plan is to (1) identify flood hazards within and in the vicinity of
the Travertine Specific Planning Area, (2) develop a regional approach to mitigate the flood hazards, (3)
identify local drainage facility requirements, and (4) evaluate development -related impacts to existing
facilities, including Dike No. 4, the Guadalupe Creek Diversion Dikes, and the CVWD deep aquifer
recharge basins.
1.4 CVWD standards and policies
The standards and policies described in the CVWD Development Design Manual (last revised February 3,
2020) were applied herein. The relevant sections considered are as follows:
• Section 8 — Design Criteria Stormwater Facilities, last revised January 2020
• Guideline K-3 — Scour Calculation Guidance, last revised December 11, 2019
• Guideline K-6 — Framework for Hydrologic Modeling, last revised January 14, 2020
• Guideline K-7 — Ordinance 1234.1, last revised February 20, 2020
The standard requirements for hydrologic studies applicable to the Travertine Development are as
follows:
• NOAA Atlas 14 (NWS, 2014) precipitation depth spatial datasets will be used in the computation
of the 1 -percent annual chance (100 -year) storm and flood
• CVWD recommends constructing a synthetic storm from 100 -year precipitation depths using
selected durations ranging from 5 minutes to 6 hours
• The Standard Project Storm (SPS) is based on the September 24, 1939 Indio Storm; and the
Standard Project Flood (SPF) is determined from hydrologic analysis based on the SPS
• For the analysis of the SPS/SPF and 1 -percent annual chance storm event, the precipitation depth -
area curve developed for the September 24, 1939 Indio Storm (Plate 4; USACE, 1980), will be
applied to watersheds with areas greater than 10 square miles
• CVWD recommends HEC -HMS for rainfall -runoff modeling
• CVWD recommends the Whitewater River dimensionless S -graph (USACE, 1980; RCFCWCD,
1978) for determining basin -specific unit hydrographs
• General advice on hydrologic loss rates is provided in Appendix K-5 of the Development Design
Manual
Ordinance 1234.1 states that levees shall be designed with a minimum of 4 feet of freeboard from the
levee crest elevation to the 1 -percent annual chance maximum flood stage and a minimum of one foot of
freeboard as measured from the levee crest elevation to the Standard Project Flood maximum flood stage.
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1.5 Document format
The document sections are set out to complete the primary objectives of this drainage master plan and
include the detailed discussion and technical analysis used for the study. Methodologies, technical
approaches, assumptions, design parameters, and result summaries used for the development of the
analyses, and identification of flood protection requirements as well as mitigation measures are included.
The detailed technical calculations, including spreadsheets and computer input/output files, are provided
electronically.
Submittal and Approval Process
The report is being submitted in three phases to better facilitate the review and approval of the document.
Each succeeding phase will expand on the previous submittal. The three phases are as follows:
1. Regional hydrology, baseline conditions
2. Regional and local hydrology, Project conditions
3. Final report including impact analysis and mitigation
This document is the complete submittal of Phases 1 through 3.
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Figure 1-1. Location map
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Figure 1-3. Local vicinity map
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Figure 1-4. Travertine grading concept plan
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2 WEST DIKE SYSTEM
2.1 Dike No. 4
Dike No. 4 is part of West Dike System, which also includes Dike No. 1 (Lake Cahuilla) and Dike No. 2
immediately to the north. This facility was originally constructed in the late 1960's by the Bureau of
Reclamation (BOR). This facility is currently owned by the BOR and maintained by CVWD.
There have been a number of studies in the past, which have reevaluated the hydrology and/or function of
the outlet works and interconnectivity of the West Dike System. Most recently, a Federal Emergency
Management Agency (FEMA) Letter of Map Revision (LOMR) application for the certification of Dike
No. 4 was prepared and last revised in 2005 by Pacific Advanced Civil Engineering (PACE) for CVWD,
the FEMA community responsible for this facility, on behalf of the Enclave at La Quinta (formerly
known as the Trilogy development).
As part of this FEMA LOMR application, the following documents were prepared:
• PACE, 2005, FEMA Application for Physical Map Revision: The Enclave at La Quinta — Dike
No. 4, prepared for the Enclave at La Quinta, LLC, April
• Sladden Engineering, 2001, Geotechnical Investigation of CVWD Dike No. 4 Flood Control
Levee, October
The analytical methods used were as follows:
• Flood hydrographs were developed based on the synthetic unit hydrograph method prescribed in
the Riverside County Hydrology Manual (RCFCWCD, 1978) and implemented using the HEC -1
v4.0 (USACE, 1990) computer model
• Debris/sediment yield was determined using the U.S. Army Corps of Engineers Los Angeles
District Method for Prediction of Debris Yield (2000).
• The Dike No. 4 storage analysis was performed using the Haested Methods PondPak v7.5 basin
routing model.
Flood hydrographs were developed for the 100 -year and Standard Project Flood events. The assumptions
applied in their development include the following:
• Dike No. 4 has a total drainage area of 27.7 square miles, divided among three subbasins (Devil,
Middle, and Toro Canyon areas)
• The Standard Project Flood 6 -hour storm pattern is based on the Indio Storm of September 24,
1939
• The 100 -year storm 6 -hour pattern was synthesized from 100 -year precipitation depths using
selected durations ranging from 5 minutes to 6 hours
• The 100 -year 6 -hour watershed -average maximum point precipitation depth is 2.90 inches,
estimated from NOAA Atlas 2; precipitation depths for shorter durations were determined from
the Cathedral City precipitation gauge and adjusted based on the 6 -hour depth ratio between both
sources (NOAA Atlas 2 and Cathedral City)
• The Standard Project Flood watershed -average maximum point precipitation depth is 6.45 inches,
based on the Indio Storm of September 1939
• A depth -area -reduction factor of 0.94, determined from the NOAA Atlas 2 depth -areal reduction
curves, was applied to the 100 -year 6 -hour storm, reducing the watershed -average maximum
point precipitation depth from 2.90 inches to 2.74 inches
• A depth -area -reduction factor of 0.82, determined from USACE (1980), was applied to the
Standard Project Storm, reducing the average -watershed maximum point precipitation depth from
6.45 inches to 5.29 inches
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• A constant loss rate of 0.20 inches per hour was applied to all subbasins to account for
precipitation losses
• A hydraulic roughness value of 0.035 and the Whitewater S -graph were applied in the
determination of the lag and unit hydrograph
The debris yield was computed based on the following assumptions:
• Equation 2 was used compute the debris yield for each individual subbasin and Equation 4 was
used to compute the debris yield for the combined drainage
• A fire factor of 3.0 was used since fuel for wildfires was considered minimal
• No Area -Transposition factor was applied
The adopted storage analysis was conducted using the following assumptions:
• A basin infiltration rate of 2.5 inches per hour was assumed for the SPF and no infiltration for the
100 -year storm;
• No pipe outflow;
• 50 percent of debris/sediment yield is transported to the basin for the Standard Project Flood and
100 percent for the 100 -year storm;
• Volume rating curve derived from aerial topographic mapping with minimum 2 -ft contour
intervals and spot elevations based on NGVD29, flown June 27, 2001 by R.J. Lung and
Associates and processed by Mainiero, Smith and Associates
Storage analysis conclusions:
• The Levee crest is to be maintained at elevation 25.0 feet NGVD29; the elevations were reported
to vary from 23.6 feet to 26 feet; an estimated 1,500 cubic yards of fill were required to raise the
crest to a minimum of 25.0 feet NGVD29
• The computed 100 -year maximum water surface elevation was 6.9 feet NGVD29 (18.1 feet of
freeboard)
• The computed SPF maximum water surface elevation was 20.3 feet NGVD29 (4.7 feet of
freeboard)
• Wave runup calculations resulted in 2 feet for 40 mph winds and 3 feet for 60 mph winds
2.2 Guadalupe Creek Diversion Dikes
As noted previously, the Guadalupe Creek Diversion Dikes are aligned parallel to northern Travertine
property boundary and direct flow to the east. Information related to the Guadalupe Creek Diversion
Dikes is sparse, only briefly being mentioned in previous studies (Bechtel, 1991) and presented in a
single -sheet as -built drawing of the plan and profiles (CVCWD, 1968) as shown in Figure 2-1.
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3 GEOMORPHIC WATERSHED ASSESSMENT
Geomorphic analysis was conducted to identify landform features and evidence of flooding and
sedimentation processes that would impact site development alternatives for the proposed Travertine
Development (Figure 3-1). This reconnaissance -level analysis focused on alluvial fans, as well as on
watercourses with severe lateral erosion potential. Areas subject to active (and inactive) alluvial fan
flooding, distributary flow path flooding, shallow sheet flooding, debris and mud flows, and ponding
were identified. Without adequate consideration of geomorphic processes operating in the study area,
future drainage improvements could be at risk of performance failure.
Figure 3-1. Location of Travertine on the eastern piedmont of the Santa Rosa Mountains
3.1 Site description
The Travertine Development is located on a piedmont bajada composed of moderately steep -sloped relict
(inactive) and active alluvial fans. This bajada extends eastward within an embayment of the Santa Rosa
Mountain front, and slopes toward the floor of the Coachella Valley and the Salton Sea. The portions of
the piedmont that have active alluvial fan areas do not have a strongly defined fan shape (Figure 3-2), but
the distributary channel pattern and surficial geology (Figure 3-3) suggests some potential for flow -path
uncertainty as well as relatively high rates of sediment transport. The lack of a defined radial fan shape
often is consistent with low rates of aggradation or even net degradation and dissection in places.
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Figure 3-2. USGS topography showing a lack of radial fan contours on the upper piedmont
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Development
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Figure 3-3. Recent aerial shows active/inactive fan areas and evidence of development activities
N.
S
Note: lighter tones are typical of active fan areas and darker (reddish) tones are typical of inactive fan areas
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Eight canyon drainages (subbasins) contribute runoff to the piedmont above Dike No. 4, which have been
identified as follows (from north to south):
• Devil Canyon
• unnamed canyon
• Middle North Canyon
• unnamed canyon
• Middle South Canyon
• Rock Avalanche Canyon
• unnamed canyon
• Toro Canyon
• unnamed canyon
• unnamed canyon
The major contributors are Devil Canyon, Middle North Canyon, Middle South Canyon, Rock Avalanche
Canyon, and Toro Canyon, which are identified as well in Figure 3-3. The unnamed canyons (not shown
in Figure 3-3) are generally shallow canyons along the mountain front. Devil Canyon has the largest
drainage of those tributary to the Travertine Development, with an area that extends to the ridgelines of
the Santa Rosa Mountains at elevations near 2,000 feet above sea level. Middle North, Middle South and
Rock Avalanche Canyons (collectively part of what is referred to as the Middle Canyons Area) are
smaller, but coalesce on the piedmont within the Travertine property boundaries. Toro Canyon is a
moderate-sized subbasin, which impacts only the southern edge of the Travertine property. There are
active alluvial fans associated with each of the ten subbasins, all varying in size and degree of fan activity.
3.2 Methodology
The geomorphic analysis was based on field observations, the interpretation of aerial photographs, the
evaluation of topographic maps, and a review of general soils and geologic information. Surficial
characteristics such as development of desert varnish, desert pavement, weathering of surface rock, color,
channel pattern, drainage network development, channel incision, topographic relief, and vegetative suites
were examined to identify active and relict fluvial processes. These surficial characteristics are indicative
of surface age, which in turn, is tied to the flood and erosional history of the surface. That is, old surfaces
become "old" by not being subject to flood inundation or to widespread erosion and sediment deposition
over very long time periods, typically hundreds or thousands of years. Using this methodology, active and
inactive areas on the piedmont were readily distinguished. Active areas are subject to potential flow -path
uncertainty. For inactive alluvial fan areas, the risk of flow -path uncertainty is very low or nonexistent
and can be set aside in the evaluation of flood hazards.
3.3 General findings
The study area for this geomorphic assessment consists of the area within and near the Travertine
property limits, and is focused on the watercourses and floodplains that drain to the development
boundaries, as indicated by the extents of Figure 3-4 and Figure 3-5. The following general findings and
conclusions apply to the entire study area:
• Debris flow potential. There is low potential for debris flows to impact the lands within the
development property limits. Debris flows are a type of flooding that consists of thick slurries of
mud, rock, sediment, water and debris that originate as mass movement on steep slopes or in
steep canyons. While debris flows can occur in the Santa Rosa Mountains, because the
mountains are low in elevation with generally thin soil mantles, debris flows tend to be limited to
the slopes of steep canyons, and tend not to run out beyond the canyon bottoms, with even less
potential to reach the mountain front. Also, the watershed is poorly vegetated, making it less
vulnerable to catastrophic wild -fire, which is a causative factor for many debris flows in Southern
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California. Finally, the Travertine Development boundaries are located nearly a mile from the
mountain front, making the possibility of debris flows reaching the project limits even more
remote. Therefore, whatever alluvial fan flooding impacts exist for the Travertine Development,
they are limited to fluvial processes (water floods).
■ Debris/sediment yield. All of the subbasins within the study area are likely to deliver relatively
high sediment loads, which is typical for floods on arid region streams. Sediment concentrations
are likely to be in excess of 10 to 20 percent, with a high proportion of coarse sand and gravel
conveyed as bed load. Flood control structures built for the Travertine Development should be
designed to accommodate, convey, or store sediment delivered from the off-site drainages. Much
of the sediment delivered from the mountainous portions of the upper drainages is deposited and
stored on the active alluvial fan surfaces upstream of the Travertine property limits.
■ Transmission losses. The surficial geology and channel morphology on the fan surfaces
upstream of the Travertine Development suggests that transmission losses are an important
process on the inundated portions of the active and inactive fan surface. The beds of the broad,
distributary channel systems that convey runoff over the fan surfaces are comprised of coarse
sand and gravel, which have high transmissivity and are capable of absorbing and storing
significant volumes of flow. This results in significant flood attenuation, particularly during
small floods. As floods spread out in the distributary channels on the fan surfaces, they not only
lose volume to the substrate, they lose stream power because of the massive flow expansion. As
they lose stream power, they drop their sediment load, which enhances the distributary flow
pattern as well as the potential for further flow attenuation and subsequent transmission losses.
Transmission losses should be accounted for in the routing of floods across the piedmont surfaces
prior to reaching the boundaries of the Travertine Development.
• On -fan flooding sources. The piedmont draining to the Travertine Development is large enough
that rainfall on the piedmont can generate significant flooding on its own, without contributions
from the mountain drainages. Runoff from on -fan precipitation should be accounted for in the
design of flood control and drainage facilities at the Travertine Development.
• Active/inactive alluvial fans. As described below, a large portion of the piedmont surface in the
vicinity of Travertine consists of readily identified inactive alluvial fans. It is likely that many of
the areas currently shown as active in Figure 3-4 and Figure 3-5 have not been active for
hundreds of years or are subject only to shallow sheet flooding. The most active alluvial fan
areas are limited in extent and located close to the mountain front upstream of the Travertine
Development.
• Past development impacts. There are development activities on the piedmont surface that
impact the natural, pre -development flood hazards to some degree. The piedmont is far from
pristine. Development impacts observed during the field reconnaissance and from inspection of
aerial photographs include mass grading and construction of flood control berms and recharge
ponds, channelization associated with agricultural development, sand and gravel mining
excavations, road construction, utility lines, a major aqueduct, residential development, and
construction of engineered and non -engineered diversion dikes and levees.
• Geologic history. While the piedmont surface may been formed by alluvial fan flooding and
debris flows in the distant geologic past, field evidence suggests that the geologic history over the
past 10,000 years has been dominated by erosion of the lower and mid-range of the piedmont,
with low rates of periodic aggradation due to fluvial processes in the upper piedmont. Field
evidence includes: (1) declining base level due to retreat of the Salton Sea during the late
Holocene, (2) exposed (unburied) shorelines of Lake Cahuilla, (3) drastic reduction in sediment
size (transport capacity and yield) between older and younger fan surfaces, and (4) overall
reduction of active portions of the fan surface relative to the size of the fan landform. Within
typical engineering time scales, net aggradation will be minimal, as will the effect of
sedimentation aggradation on drainage boundaries, and flow path uncertainty.
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• Fan toe. The toe of the fan landform (piedmont), or downstream end of the piedmont was defined
based on topographic contour pattern shown on the USGS topographic maps. The toe is located
east of Dike No. 4, and represents the geographic boundary between the piedmont slope and
valley floor.
3.4 Landform mapping
A reconnaissance -level map of geomorphic landforms in the study area was created to identify the types
of expected flood hazards in the Travertine Development watershed. The following geomorphic map units
are depicted on Figure 3-4 and Figure 3-5:
• Mountains/bedrock. The mountain/bedrock map unit consists steep mountain slopes, exposed
bedrock, and deep canyons. These areas are generally sources for runoff and sediment supply and
are located in the upper drainages well outside the limits of the Travertine Development property
lines.
• Active alluvial fans. Active alluvial fans are landforms that a composed of alluvial sediment
deposits (loosely compacted sand, gravel, cobbles, and boulders, with minor amounts of fine-
grained sediments). Active alluvial fans are subject to periodic flood inundation, active sediment
transport (erosion and deposition). However, the defining characteristics for active alluvial fans is
the potential for channel avulsions (sudden relocations of flood channels) and/or net aggradation
(progressive sediment deposition) that can lead to flood flow path uncertainty.
Design of flood control structures on or downstream of active alluvial fan should account for the
potential for flow path uncertainty and sedimentation. Included in this unit are weakly or
marginally active alluvial fans that may have low rates of aggradation and more stable channel
patterns.
Within the study area, active alluvial fans are located at and near the mountain front. The largest
subbasins have active alluvial fans that extend farther down the piedmont. However, the more
distal portions of the active alluvial fans are less subject to sediment deposition and are better
classified as transport rather than depositional (aggrading) surfaces, and typically are subject to
sheet flooding rather than channelized stream flow. In the case of the Travertine study area, the
lowest portions of the active alluvial fans have been completely altered by development to the
degree that the natural flood processes may no longer exist.
The following sub -units were also defined within the active alluvial fan category:
1. Active. These areas consist of the least disturbed, most active surfaces closest the mountain
front. Flood hazards in this map unit are the most severe, with the highest flow rates, depths,
and velocities and the highest rates of sediment deposition, erosion and avulsion.
2. Active — sheet flooding area. These areas consist of the mid- to distal portions of active
alluvial fans where flow has transitioned from single and distributary stream channels into
widely inundated areas of shallow sheet flow. Where there is some degree of flow path
uncertainty in sheet flooding areas, the floods tend to be relatively passive due to low flow
depths and velocities. Concentration of sheet flooding by development can lead to significant
erosion, channelization, headcutting, and downstream sedimentation.
3. Active — agricultural. These areas consist of probable active alluvial fans that have been
overlain by agricultural development that obscures and/or alters the natural flood regime.
Note that the geomorphic mapping is for the pre -development surface. Modern agricultural
development may alter the pre -development flood type and/or risk, which is discussed in
more detail later in this report.
4. Active — ponding. These areas consist of ponding areas upstream of the large aqueduct that
transects the piedmont downstream of the Travertine Development.
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5. Active — urbanized. These areas consist of the highly developed portions of the study area
located downstream and east of the aqueduct.
■ Inactive alluvial fans. Inactive alluvial fans are landforms that a composed of alluvial sediment
deposits (loosely compacted sand, gravel, cobbles, and boulders, with minor amounts of fine-
grained sediments). Inactive alluvial fans are essentially former active alluvial fans that have
been abandoned and are no longer subject to widespread flood inundation and are no longer
receiving sediment deposition from upper watershed sources and are not subject to channel
avulsions or flow path uncertainty. Inactive fans generally have tributary drainage patterns that
have developed over time from rainfall and erosion of the fan surface.
Design of flood control structures on inactive alluvial fans is similar to design of such structures
in riverine watersheds. On the piedmont surface below Devil Canyon, the mapped inactive area
includes erosional surfaces that may receive minor amounts of breakout flows from the active
alluvial fan area during the largest floods. It is unlikely that such breakouts have the flow
volume, frequency or sediment load to create avulsive flow paths, i.e., warrant inclusion in the
active alluvial fan flooding surface unit. Field observations indicate that such overflows are rare
and are primarily erosional in nature.
Within the study area, inactive alluvial fans are located in the upper piedmont away from the
largest mountain watershed sources, and along the margins of the active alluvial fans. Inactive
fans can be identified by their tributary drainage patterns, greater internal topographic relief, and
darker surface color due to surficial aging processes.
The following sub -units were also defined with the inactive alluvial fan category:
1. Inactive. These areas consist of primary undisturbed piedmont surfaces. Some of the inactive
alluvial fan surfaces, e.g. portions of the piedmont downstream of Devil Canyon, are cut by
stable channels that may convey overflows from the active portion of the piedmont (DC 1 and
DC2 in Figure 3-5). These overflows, in conjunction with on -piedmont runoff, contribute to
downstream flood hazards which should be considered in the design of flood control
measures for the proposed project. The geomorphic information collected for this
reconnaissance -level assessment suggests that the risk of avulsion is low along these
corridors.
2. Inactive — agricultural. These areas consist of probable inactive surfaces that have been
overlain by agricultural development, obscuring and/or altering natural flood processes to
some degree. Note that the geomorphic mapping is for the pre -development surface. Modern
agricultural development may alter the pre -development flood type and/or risk, which is
discussed in more detail later in this report.
3. Valley floor. The valley floor unit consists of area below the piedmont slope and is
comprised of former lake bed sediments. The valley floor unit is located entirely east and
downstream of the Travertine Development and has no impact on the project.
3.5 Other Considerations
Devil Canyon active alluvial fan. There are two areas where it appears the floodwaters within the active
portion of the Devil Canyon fan have overflowed onto areas considered inactive. The hydraulic and
hydrologic effects of the overflow flow splits or breakout flows are described in more detail in Sections 4
and 5 of this report. The breakout points are mapped as "DC 1" and "DC2" in Figure 3-5; however,
despite the appearance of these breakouts, the areas were not included in the active alluvial fan mapping
unit for the following reasons:
■ Mapping scale. At a reconnaissance level of mapping, the potential breakouts did not
warrant their own geomorphic map unit, particularly given the other factors identified below.
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• Field observations. Observations made during the field visit indicate that the potential
breakouts are only utilized during the largest discharges and are topographically separated
from the low flow conveyance areas within the active fan areas.
• Geologic context. The overall geologic context appears to be one of abandonment of the
"breakout" flow paths in favor of the active areas defined in Figure 3-4 and Figure 3-5.
• Surficial age. Field observations indicate that the "breakout" areas are significant older and
less active than the Devil Canyon active alluvial fan, even though they are not as old as the
adjacent inactive surfaces.
• Flood processes. The characteristics of the flood processes that occur during breakouts from
the active alluvial fan area (overflow at the peak of a hydrograph, minimal bedload transport)
are substantively different from flood and geomorphic processes that occur within an active
alluvial fan area (avulsion, aggradation, deposition). The "breakouts" are better classified as
stable distributary flow points rather than active alluvial fan flooding.
• High erosion hazard areas. The potential for lateral erosion exists along all of the flood
corridors in the study area due to the presence of high velocities and sand/gravel sediments.
The active alluvial fan surfaces are most vulnerable to lateral erosion due to the composition
of the sediment, as well as the general lack of compaction, cohesion, vegetative cover, and/or
cementation. In contrast, older inactive fan surfaces tend to be comprised of soils that are
compacted, cohesive, or armored by deflation and thus, are more resistant to lateral erosion.
Sheet flooding surfaces, if left undisturbed, are not subject to significant erosion hazards.
However, where sheet flooding is concentrated or channelized it can often cause head -
cutting, incision, and lateral erosion.
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Figure 3-4. Geomorphic surfaces with flood hazard types overlain on USGS topography
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Active Fan -Agricultural
Active Fan -Dike
Active Fan -P on di ng
Active Fan -Sheet Flood
Active Fan -Urbanized
Inadive Alluvial Fan
Inadive Fan -Agricultural
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Figure 3-5. Geomorphic surfaces with flood hazard types overlain on recent aerials
Legend
Geomorphic Map Units
Active Alluvial Fan
Active Fan -Agricultural
Active Fan -Dike
Active Fan -P an di ng
Active Fan -Sheet Flood
Active Fan -Urbanized
Inadive Alluvial Fan
Inadive Fan -Agricultural
MountainlHedrock
Valley Floor
Inactive Alluvial F an
Attire Alluvial Fan.9,
Mountain/Bedroth •
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4 REGIONAL HYDROLOGY
4.1 Hydrologic goals and objectives
The development of the regional hydrology for the planned development (Travertine) and affected
facilities, which includes the Guadalupe Creek Diversion Dikes, Dike No. 4, and the CVWD deep -aquifer
recharge basins, is intended to serve as the hydrologic basis for debris analysis, hydraulic modeling, and
sediment transport/scour computations conducted for site planning and design as well as for the
determination of impacts, mitigation requirements, and engineering constraints associated with the
following:
• Conveyance of floodwaters along the edge conditions and near vicinity of Travertine as it relates
to stream stability, flood and erosion protection, and consequences to adjacent properties and
existing infrastructure, including the integrity and performance of the Guadalupe Creek Diversion
Dikes
• Increased runoff volume and flow redistribution attributed to Travertine, which may impact the
integrity and performance of Dike No 4 as it relates to freeboard and embankment stability when
subjected to the temporary impoundment of floodwaters
• Displacement of impoundment storage and the disruption of impoundment connectivity that will
be incurred due to the proposed transportation infrastructure required to provide access to
Travertine
Flood hydrographs were developed for contributing drainages consisting of one or more subbasins, based
on the 1 -percent annual chance storm, for scenarios related to flood conveyance and/or the temporary
impoundment of floodwaters along project edge and near vicinity, including the Guadalupe Creek
Diversion Dikes, but excluding Dike No. 4. Precipitation areal effects were not considered since the
contributing drainage for any of these scenarios is less than 10 square miles.
For matters related to the impoundment of floodwaters along Dike No. 4, flood hydrographs were
developed for each subbasin, based on the 1 -percent annual chance storm and the Standard Project Storm
(SPS). Precipitation areal effects are expected to be significant since the entire watershed, which far
exceeds 10 square miles, will be contributing to the development of runoff. The SPS, which is based on
the September 24, 1939 Indio Storm, is the event required by the CVWD Development Design Manual to
develop the Standard Project Flood (SPF).
Hydrology was developed for the baseline ("without project") and project conditions to support the
determination of specific impacts, mitigation requirements, and design constraint related to Travertine.
4.2 Hydrologic analysis — assumptions and general approach
The HEC -HMS Hydrologic Modeling System Version 4.2 (USACE, 2016) was used for all hydrologic
model development and simulations performed herein.
The Riverside County Hydrology Manual (RCHM; RCFCWCD, 1978) Synthetic Unit Hydrograph
Method (SUHM) was used as the framework methodology for developing flood hydrographs.
Parameter development was performed using a combination of GIS and spreadsheet applications.
Concentration points were designated at or near canyon outfalls (above the Travertine property boundary)
and along the interior depression at the base of Dike No. 4.
The hydrologic parameters were determined using the following criteria, methods, and data resources:
• The 1 -percent annual chance storm was implemented using a hypothetical (synthetic) pattern
accomplished by nesting precipitation depths for duration ranging from 5 minutes to 6 hours
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• Frequency -duration point precipitation depths were extracted from the NOAA Atlas 14 spatial
datasets
• The SPS is based on September 24, 1939 Indio Storm, which produced a maximum total point
precipitation of 6.45 inches over 6.25 hours
• Areal effects were estimated for the SPS and the 1 -percent annual chance storm using the depth -
area relationship derived from the September 24, 1939 Indio Storm (Plate 4; USACE 1980) for
contributing drainages exceeding 10 square miles; precipitation depths for durations less than one
hour were not adjusted
• Constant loss rates were determined based on the method prescribed in the RCHM; however, the
low loss fraction (low loss rate) was not applied in conjunction with the constant loss rate, as
prescribed in the RCHM, which is consistent with CVWD development guidelines
• An initial abstraction was applied in the determination of precipitation losses based on typical
values used in similar environments (NHC, 2014; Bechtel, 1997)
• Topographic -based physical parameters, including drainage boundaries, lengths, and slopes were
based on 5 -meter digital terrain model developed from interferometric synthetic aperture radar
(IFSAR) topographic datasets (Intermap Technologies, 2005)
• The lag formula for southern California (USACE, 1962; RCFCWCD, 1978) was used in
conjunction with the Whitewater S -graph (RCFCWCD, 1978; USACE, 1980) to transform unit
hydrographs; a representative slope analysis was used to estimate the "effective" slope along the
longest watercourse; the basin factor (N) was computed based on the area weighting of
contributing terrain surfaces of varying hydraulic roughness (e.g., mountain/ hillslopes,
active/relic alluvial surfaces/piedmont, Travertine/developed areas)
The following outlines the general procedure used to develop the hydrologic models for simulation:
• Delineate the watershed, subbasins, and define the stream network to support the concentration
points required to satisfy the hydrologic objectives
• Identify the storm and storm pattern; estimate the applicable frequency -duration precipitation
depth(s) and areal adjustment to each contributing subbasin
• Determine the initial abstraction and constant loss rate for each subbasin for all
conditions/scenarios
• Determine the lag parameters and S -graph for each subbasin
• Determine the channel routing parameters
• Configure the watershed model, including basins, processes, and there ordered connectivity;
assign the required parameters as well as time -series and paired datasets
4.3 Synthetic Unit Hydrograph Method
The Synthetic Unit Hydrograph Method (SUHM; RCFCWCD, 1978) was used to develop flood
hydrographs for each delineated subbasin within the watershed tributary to Dike No. 4. The SUHM is
statistically based, assuming the watershed discharge is related to the total volume of runoff. The time
factors affecting the shape of the SUHM are dominant The watershed storm rainfall -runoff relationships
are characterized by watershed area, slope, and shape factors. The SUHM is used to estimate the time
distribution of watershed runoff in drainage basins where stream gauge information is not available. In
Riverside County, the SUHM is normally used to evaluate individual drainage areas in excess of 300 to
500 acres.
4.3.1 Watershed delineation, existing (baseline) conditions
Travertine is located within the lower extent of the watershed tributary to Dike No. 4, on the eastern
piedmont skirting the base of the Santa Rosa Mountains, generally situated on the southern terrace of the
active floodplain formed below the Devil Canyon outfall. The watershed tributary to Dike No. 4,
associated herein with the hydrologic node prefix of D4, encompasses just over 27 square miles as
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determined from the delineated watershed presented in Figure 4-1 (baseline conditions) and Figure 4-2
(project conditions) based on IFSAR topographic data (Intermap Technologies, 2005).
The Dike No. 4 watershed was subdivided into 10 canyon subbasins and three (3) piedmont subbasins.
Canyon subbasins have a corresponding hydrologic node (concentration point) located at or near each of
their respective outfalls and outside and above the Travertine property boundary. The piedmont subbasins
each have a concentration point located in the depression along the base of Dike No. 4. The delineated
subbasins are listed as follows with their respective downstream hydrologic nodes identified in
parentheses:
• Devil Canyon (D411)
• piedmont below Devil Canyon (D410)
• unnamed canyon (D422)
• Middle Canyon North(D423)
• unnamed canyon (D424)
• Middle Canyon South (D421A)
• Rock Avalanche Canyon (D421B)
• piedmont below the Middle Canyons (D420)
• unnamed canyon (D432)
• Toro Canyon (D431)
• piedmont below Toro Canyon (D430)
• unnamed canyon (D44)
• unnamed canyon (D45)
Middle Canyon South (D421A), Rock Avalanche Canyon (D421B), Middle Canyon North (D423), and
unnamed canyons (D422 and D424 collectively form the Middle Canyons Area. Toro Canyon (D431) and
the unnamed canyon (D432) collectively form the Toro Canyon Area.
4.3.2 Watershed delineation, project conditions
The planned development causes the following changes to the following interior drainage divides:
• The drainage divide separating subbasins D410 and D420 was adjusted to conform to the concept
grading proposed for the planned development shown in Figure 1-4
• The runoff produced by subbasin D422 is diverted from J42 to J41 as a result of the graded
footprint of the planned development
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Figure 4-1. Baseline conditions regional hydrology map
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Figure 4-2. Project conditions regional hydrology map
1
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4.3.3 Precipitation
The storm scenarios that were analyzed herein include the following:
• 1 -percent annual chance storm local analysis (local contributing drainages less than 10 square
miles; no areal effects)
• 1 -percent annual chance storm regional analysis (areal effects based on the entire watershed
contributing to the development of runoff)
• SPS/SPF regional analysis (areal effects based on entire watershed contributing to the
development of runoff)
4.3.3.1 Standard Project Storm
The SPF is based on the Indio Storm of September 24, 1939 (SPS), which produced a total precipitation
depth of 6.45 inches in approximately 6 hours. The SPS precipitation depth was adjusted using the depth -
area curve presented in Figure 4-3 (Plate 4; USACE, 1980) assuming the storm covers the entire
watershed at the same intensity, producing an adjusted value of 6 inches based on a watershed size of
27.07 square miles. The SPS was applied to the 6 -hour storm pattern presented in Plate E-5.9
(RCFCWCD, 1978), which is also based on the September 24, 1939 Indio Storm.
4.3.3.2 1 -percent annual chance storm
The 1 -percent annual chance storm was synthesized over a 6 -hour duration based on the hypothetical
storm, which is constructed from nested area -weighted average maximum precipitation depths for 5 -
minute, 15- minute, 60 -minute, 2 -hour, 3 -hour, and 6 -hour durations. These precipitation depths were
estimated from the NOAA Atlas 14 spatial datasets (NWS, 2014) and are presented in Table 4-1.
Although the depth -area relationship for the September 24, 1939 Indio Storm shown in Figure 4-3 is
specific to the areal nature and duration for this particular storm, CVWD guidance dictates that it be
applied to all storms and all durations; therefore, it was applied to each duration precipitation depth of the
1 -percent annual chance event. Depth -area -duration adjustments were not applied to individual or
combined drainage areas of less than 10 square miles.
The hypothetic storm pattern is balanced around the peak, with the maximum precipitation occurring two
thirds of the way through the 6 -hour storm period.
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Figure 4-3. Southern California local storm depth -area relationships (Plate 4; USACE, 1980)
CURVE
NUMBER
PRECIPITATION STATION
STORM
NAME
NUMBER
LOCATION
DURATION
DATE
1
SUNNY HILLS RANCH
8P98
FULLERTON, CALIF.
HR MIN.
2 0
MAR.14,1941
2
TOPANGA CANYON RANGER STATION
7077
TOPANGA CANYON, CAL IF.
3 0
FEB. 20,1941
3
AVALON
7P10
AVALON, CALIF.
3 15
OCT. 21,1941
4
SQUIRREL INN
8012
SOUIRREL INN, CALIF.
1 30
JULY 18,1922
5
SIERRA MADRE-CARTER
701338
SIERRA MADRE, CALIF.
3 0
MAR.3-4,1943
6
GARRET WINERY
—
CUCAMONGA,CALIF.
I 0
SEPT29,1946
7
SANTA BARBARA (FIRE STA it 3)
—
SANTA BARBARA, CALIF
1 10
FEB. 4, 1958
8
INDIO (REVISED 7MAR73)
9PI3
INDIO, CALIF.
6 0
SEPT. 24,I93
'.:PIT TIQN IN INCHES
DEPTH -AREA CURVES
1
i
I ! 1
r.€n r. u€ ;gifr.F I rcn 1
4.3.3.3 Storm centering
There is no guidance provided in the RCHM or by CVWD as it relates to the application of storm
centering and when it should be required. Current guidance assumes a storm covers the entire contributing
area at the same intensity, with a single depth -areal -reduction factor representing the entire contributing
area. This approach, referred to as "whole -basin" centering, is suitable for small basins or very large-
scale, frontal -type storms. The Dike No. 4 watershed is considered small enough where storm centering is
not expected to significantly change the hydrologic outcomes; therefore, additional storm centering
scenarios were not evaluated.
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Table 4-1. 1 -percent annual chance precipitation depths for selected durations
conditions
subbasin
precipitation depths_ in inches_ for selected durations
5rn
15rn
60m
2h
3h
6h
depth -areal reduction* =
0.93
093
0.93
0.93
0.93
093
baseline
410
0.47
0.81
1.67
2.08
239
101
{{
0.44
a�
0.76
1.55
7
1.73
y 55
2.22
5 a�
2.80
411
0.72
1/.5
169
118
149
413
0.67
1.16
2.50
2.95
3.25
393
420
0.48
014
1.72
2.15
2.47
111
0.45
0.78
1.60
2.00
2.29
2.89
421A
0.67
1.16
2.45
298
332
4.06
0.62
1.08
2.30
/77
3.08
17S
421E
011
123
2.64
117
152
431
0.66
1.14
2.46
2.95
3.27
4.00
422
0.56
0.97
/04
250
211
147
0.52
0.90
1.90
2.32
2.62
3.23
423
0.72
125
/69
322
3J5
433
0.67
1.16
2.50
2.99
3.30
4.03
424
0i3
092
193
238
2.69
334
0.49
0.86
1.80
2.21
2.50
111
430
0.47
0.81
1.66
2.10
2.43
3.07
0.44
0.76
1.55
195
2.26
2.85
431
038
1.00
2.12
2.61
295
165
0.54
0.93
1.97
2.4-3
2.74
33c.
432
0.5l
1.06
115
/40
163
329
0.47
0.99
152
2.23
2.45
3.0
44
0.49
015
136
222
2_55
320
0.45
0.79
L63
2.06
2.37
2.9S
45
0.47
0.82
1.68
2.13
2.46
112
0.4-4-
0.76
1.56
1.98
2.29
2.90
project
410
0.48
0.83
151
2.12
2.43
3.06
0.4-4
0.77
1.59
1.97
2.26
_. -
420
0.47
012
l_68
/11
143
3.07
0.44
0.76
1.56
1.95
2.26
2.85
*Depth -areal reduction factors were based on a total drainage area of 27.07 sq_ raiz;
values in red represent depth -areal reduced precipitation depths
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4.3.4 Precipitation losses (constant loss rate determination)
The following process was implemented to determine the constant loss rate for each delineated subbasin
within the Dike No. 4 watershed:
• The land use and hydrologic soils spatial datasets were intersected to determine the composition
of landuse/ hydrologic -soil -group combinations within each subbasin.
• The dimensionless runoff index value (RI) for pervious areas was determined for each land-
use/hydrologic-soil-group combination
• The pervious area constant loss rate (Fp), in inches per hour, was determined for each land-
use/hydrologic soil -group combination from the relationship between the pervious infiltration rate
for pervious areas versus runoff index values (Plate E-6.2; RCFC&WCD, 1978)
• The impervious fraction (Ai) for each land-use/hydrologic-soil group combination was assigned
based on the land -use percent imperviousness value (RTIMP)
• The adjusted constant loss rate (F) for each land-use/hydrologic-soil-group combination was
computed using the following equation:
F = Fp (1 - 0.9A)
• The adjusted constant loss rate computed for each land-use/hydrologic-soil-group combination
within each delineated subbasin was area weighted and averaged to determine the average
adjusted constant loss rate for each subbasin
• A low loss fraction (low loss rate) was not applied, which is consistent with CVWD guidance
In Riverside County, the NRCS detailed soil survey maps are typically used to estimate the spatial
variation of hydrologic soil groups within the drainage basin of interest. The detailed soil maps, which
provide coverage within the Dike No. 4 watershed are the Coachella Valley Area Soil Survey (CA680;
NRCS, 2008) and the San Bernardino National Forest Soil Survey Area (CA777; NRCS, 2008), roughly
encompassing a combined 12 percent of the total watershed. The U.S Generalized Soils Map (NRCS,
2004) was used to supplement soil information for the remainder of the watershed.
The NRCS soils datasets were used to prepare a composite map of detailed and generalized soil map units
for the Dike No. 4 watershed as presented in Figure 4-4 (baseline conditions) and Figure 4-5 (project
conditions); the percent distribution of soil map units for each subbasin and the watershed as a whole is
listed in Table 4-2. The percent distribution of hydrologic soil groups for each soil map unit are listed in
Table 4-3.
The land use dataset published by the Southern California Area Governments (SCAG, 2008) was used to
approximate the composition of land uses in the watershed tributary to Dike No. 4 as presented in Figure
4-6 (baseline conditions) and Figure 4-7 (project conditions). The percent distribution of land use map
units for each subbasin is depicted in Table 4-4. The land use categories and their respective percent
imperviousness are listed in Table 4-5. An average percent imperviousness for the Travertine developed
area was estimated from assumed land -use densities based on the current grading concept plan (Figure 1-
4).
Land cover was classified as poor -quality desert shrub (NRCS, 2004) for the entire watershed. The loss
rate parameterization for each subbasin is summarized in Table 4-6. The detailed loss rate calculation
worksheets for each subbasin are included as part of the Electronic Technical Appendix.
A watershed -average initial abstraction (IA) of 0.25 inches was used, derived from typical values
assumed for deserts and rangeland (0.15 — 0.35 inches) and vegetated mountains and hillslopes (0.25),
which is consistent with other studies conducted in the Coachella Valley region (NHC, 2014; Bechtel,
1997).
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Figure 4-4. Baseline conditions composite soil map
Legend
basin soils IMI
subbasin - CcC - Ip
subarea - CdC Is
0 hydrologic node - ChC - LR
— • — flow line DnE mLcF
o property line GbA MaB
GbB RO
RU
Rs
s1016
s1021
s991
Dike No. 2
0410/J41
DEVIL
CANYON
s1021
s1021
GbB Dike No. 4
D420/J42
s1021
s1016
O�
s1021
GA1`1YON
51021
D421A
D421B
s1021
MIDDLE
D430/J43
Cho"U N
CSNA
CdC Evacuation Channel
ChC
ChC 044
s991 M®
s991
M RU
C hC
RU RO
LR
s1021
s1021
s1021
s1021
s1021
0
0
2,750
5,500
Feet
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Figure 4-5. Project conditions composite soil map
Legend
basin
subarea
subbasin
0 hydrologic node
—•— flow line
o property line
Travertine grading limits
soils
CcC
CdC
ChC
DnE
GbA
GbB RO
Ip RU
Is Rs
LR s1016
LcF s1021
MaB s991
CANYON c,PN
s1016
Evacuation Channef
s1021 pREP1‘4Y014
s1021
s1021
CANYON AREA
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Table 4-2. Distribution of soil map units
NRCS soil
identifier
watershe d
drainage area
{acres}
subbasin drainage area {acres } ■
baseline conditions
pro ect
conditions
survev
area
MUSYM
baseline
conditions
project
conditions
D411
D410
D421A
D421B
D422
D423
D424
D420
D431
D432
D430
D44
D45
D410
D420
CA680
CcC
39
39
0
20
0
0
0
0
0
19
0
0
0
0
0
8
31
CdC
550
550
0
183
0
0
0
0
0
294
0
0
73
0
0
178
299
ChC
177
177
0
0
0
0
0
0
0
0
0
0
109
19
50
0
0
GbA
19
19
0
0
0
0
0
0
0
0
0
0
19
0
0
0
0
GbB
2
2
0
0
0
0
0
0
0
1
0
0
0
0
0
0
1
Ip
17
17
0
13
0
0
0
0
0
0
0
0
4
0
0
13
0
Is
4
4
0
4
0
0
0
0
0
0
0
0
0
0
0
4
0
LR
7
7
0
0
0
0
0
0
0
0
0
0
0
0
7
0
0
MaB
184
184
0
168
0
0
0
0
0
0
0
0
0
9
6
161
0
RO
78
78
0
52
0
0
0
0
0
0
0
0
0
0
25
52
0
RU
79
79
0
48
0
0
0
0
0
13
0
0
0
0
19
35
25
...-
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
CA777
DnE
0
0
0
0
0
0
0
0
0
0
0
0
0
0
LcF
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Rs
905
905
905
0
0
0
0
0
0
0
0
0
0
0
0
0
0
US
s991
3,661
3,661
0
341
16
1,445
0
0
9
481
323
165
771
94
16
346
476
s1016
1,451
1,458
1451
0
0
0
0
0
0
0
0
0
0
0
0
0
0
51021
10,053
10,053
2,628
361
1,463
723
250
756
223
165
2,901
19
22
365
176
431
95
total:
{acres}
17,328
17,328
5,015
1,190
1,479
2,161
250
756
232
974
3,224
184
999
487
300
1,235
921
{sgEli/
27.075
27.075
T946
1.859
2311
3317
0390
1.112
0362
1J22
5.038
0287
1.561
0.761
0.468
1.930
1.450
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Table 4-3. Hydrologic soil group composition for soil map units
NRCS soil
identifier
hydrologic soil
composition
survey
area
MUSYM
A
B
CD
CA6S9
CcC
100
0
0
0
CdC
100
0
0
0
ChC
100
0
0
0
GbA
100
0
0
0
GbB
100
0
0
0
Ip
100
0
0
0
Is
100
0
0
0
LR
0
0
0
100
\:aB
100
0
0
0
RO
0
0
0
100
RU
100
0
0
0
R'
0
0
0
100
CA777
DnE
100
0
0
0
LcF
100
0
0
0
Rs
0
0
0
100
CS
s991
100
0
0
0
s1016
6-
0
0
33
s1021
25
0
0
-`
June 2021
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Figure 4-6. Baseline conditions land use map*
Legend
basin
subbasin
subarea
Land Use
- communication facilities
regional parks and recreation
0 hydrologic node 1=regional park undeveloped
vacant
—•— low line
o property line
- vacant undifferentiated
water storage facilities
wildlife preserves and sanctuaries
DEVIL
CANYON
auezza
Evacuation Channef
O
0
2,750
5,500
Feet
*Based on SCAG (2008)
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Figure 4-7. Project conditions land use map*
Legend
basin
— subarea
subbasin
0 hydrologic node
— • — flow line
o property line
Travertine grading limits
Land Use
- communication TaciEities
regional parks and recreation
regional park undeveloped
vacant
vacant undifferentiated
water storage facilities
wildlife preserves and sanctuaries
60TH
DEVIL
ON
CANYON G PNS
a
Dike No. 4
CTDCZg
Evacuation Charm&
TORQ. CANYON AREA
440
•
0 2,750 5,500
}�
Feet 4'- r '464'
*Based on SCAG (2008)
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Table 4-4. Distribution of land -use units
land -use identifier
watershed
drainage area
{ares}
subbasin drainage area {acres}
baseline conditions
pro ect
conditions
baseline
conditions
project
conditions
D411
D410
D421A
D42111
D422
D423
D424
D420
D431
D432
D430
D44
D45
D410
D420
communication facilities
307
301
0
220
0
0
0
0
0
S6
0
0
0
0
0
220
81
golfcourses
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
multi -family residential
0
0
0
0
0
0
0
0
0
0
0
0
0
0
regional park undeveloped
102
102
0
0
0
0
0
0
0
0
10
92
0
0
reeionalparks and recreation
39
34
0
39
0
0
0
0
0
0
0
0
0
0
0
39
0
single family residential
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Travertine
0
445
0
0
0
0
0
0
0
0
0
0
0
0
0
109
337
under construction
0
0
0
0
0
.,
0
0
0
0
0
0
0
0
0
0
0
vacant
1.613
1.173
0
244
1
.,
138
58
193
701
0
0
278
0
0
172
334
vacant undifferentiated
15,195
15,195
5,040
682
1,479
2,,168
112
699
38
164
3,224
184
721
477
208
692
154
water
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
water storage facilities
261
261
0
3
0
0
0
0
0
23
0
0
0
0
0
3
23
wildlife preserves and sanctuaries
45
45
45
0
0
0
0
0
0
0
0
0
C
0
0
0
0
total:
{acres}
17,328
17,328
5,085
1,190
1,479
2,,168
250
756
232
974
3,224
184
.;"s"s
487
300
1,235
928
{sgmi}
27.075
27.073
7946
1.859
2111
3387
0190
1.182
0162
1522
5.038
0287
1.561
0.761
0.468
1.930
1150
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Table 4-5. Assigned percent imperviousness values for land use categories
land -use identifier
RTL\ 1P
{°o}
communication facilities
1
zolf courses
10
multi -family residential
c
regional park undeveloped
0
regional parks and recreation
single family residential
50
Travertine
42
under construction
'50
vacant
0
vacant undifferentiated
0
water
95
water storage facilities
50
wildlife preserves and sanctuaries
0
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Table 4-6. Summary of subbasin constant Toss rates
conditions
subbasin
Di
(acres)
RTL\:
{%}
117. -di olo i-io so 1 composition
F*
{inh}
A
B
C
D
baseline
410
1,190
0
69
1
3
27
0.350
411
5,085
0
32
0
0
63
0.243
420
974
1
S6
0
1
13
0.395
421A
1,479
0
26
0
0
74
0.225
421B
2,165
0
75
0
0
25
0.367
422
250
0
25
0
0
75
0.223
423
756
0
25
0
0
75
0.223
424
232
0
28
0
0
72
0.231
430
999
0
96
2
0
2
0.431
431
3,224
0
33
0
0
67
0.244
432
184
0
92
0
0
S
0.418
44
437
0
44
0
0
56
0.277
45
300
0
41
0
4
55
0.270
project
410
1,235
4
66
1
2
30
0.328
420
928
17
90
0
2
S
0.342
*maximum loss rate based on AMC II and sparse {poor quality} desert shrub pervious
4.3.5 Unit hydrograph transform
The transformation of unit hydrographs is a process that is integrated into the HEC -HMS model
definition. The lag formula used for Southern California watersheds (USACE, 1963; RCFCWCD, 1978)
is as follows:
where
LLcAl 0.38
lag (hours) = C
C = 2412 = basin factor or correlation coefficient
T1. = "n -bar" = mean hydraulic roughness of all collection streams and channels within
a watershed (dimensionless)
L = length of longest watercourse, in miles
LCA = length along longest watercourse, measured upstream to a point opposite the
centroid of the area, in miles
S = overall slope of the longest watercourse between headwaters and the collection
point, in feet per mile
The unit hydrograph lag parameters required for this transform were determined as follows:
Watercourse lengths. The length of the longest watercourse (L), in miles, and the length along the
longest watercourse from downstream to a line that intersects the area centroid and longest watercourse
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and is perpendicular to the longest watercourse (LCA), in miles, were computed for each delineated
subbasin based on IFSAR topographic data (Intermap Technologies, 2005).
Representative slope. The representative slope of the longest watercourse (S), in feet per mile, was
determined for each subbasin by balancing the area above and below a constant slope (representative
slope) formed between the longitudinal profile and the constant slope; in addition, representative slopes
were determined between each concentration point along the watercourse to support channel flood routing
calculations. All slope determinations were based on IFSAR topographic data (Intermap Technologies,
2005)
Basin factor. The basin factor (C) was determine for each subbasin based on the landform composition
consisting of some combination of Travertine/developed areas (n = 0.02), piedmont/alluvial surfaces (n =
0.03), and mountain/hillslope areas (n = 0.05). This is a conservative assumption given that more than 90
percent of the watershed will likely experience shallow flooding less than 0.5 feet in depth. Shallow
flooding n -values typically range from 0.05 to 0.3 (USACE, 1997), influenced by gradient, uniformity of
the terrain, soil texture, and vegetation. The derived lag hydraulic roughness values for each subbasin are
listed in Table 4-7.
S -graph. The Whitewater S -graph was assumed to represent the runoff response within the regional
watershed. The Whitewater S -graph is recommended by CVWD for use in the Coachella Valley and is
also the adopted Desert S -graph for Riverside County (RCFCWCD, 1978). The Whitewater S -graph was
developed by the USACE Los Angeles District by averaging the S -graphs constructed for nine gauged
watersheds located in southern California.
The lag parameters and computation is summarized in Table 4-8. The computed lag times were used in
conjunction with the Whitewater S -graph in the unit hydrograph transform
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Table 4-7. Lag formula hydraulic roughness n ("n -bar")
conditions
subbasin
DA
{acres}
hvdaulic roueness "n -bar"
distribution by percent
composite
n -bar
Travertine
developed
areas
{0.02}
piedmont
alluvial
surfaces
{0.03)
mountain
hillslope
areas
{0.05}
baseline
D411
5.05;
0.0
32.1
6'.9
0.044
D410
1,190
0.5
72.5
27.0
0.035
D421A
1,479
0.0
25.3
74.2
0.045
D421B
2,168
0.0
75.0
25.0
0.035
D422
250
0.0
25.0
75.0
0.045
D423
756
0.0
25.0
75.0
0.045
D424
232
0.0
27.9
72.1
0.044
D431
3,224
0.0
32.5
67.5
0.043
D432
1S4
0.0
92.4
7.6
0.032
D430
999
0.0
98.4
1.6
0.030
D44
4S7
0.0
43.8
56.2
0.041
D45
300
0.0
45.0
55.0
0.041
project
D410
1,235
4.2
66.7
29.1
0.036
D420
928
16.6
77.0
6.5
0.030
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Table 4-8. Unit hydrograph lag parameter summary
conditions
subbasin
drainage area
USACE lag equation parameters
lag
{hours}
{acres}
{sq mi}
L
{miles}
LCA
{miles}
S
{R'mi}
"n -bar"
basin
factor
C
baseline
D411
5.035
7.945
5.49
2.86
800.7
0.044
1.06
0.845
D410
1,190
1.859
2.79
1.13
289.6
0.035
0.84
0.442
D421A
1,479
2.311
4.27
1.82
1,056.0
0.045
1.07
0.6194
D421B
2,168
3.388
5.23 1
3.61
843.8
0.035
0.84
0.713
D422
250
0.391
1.49
0.7S
431.0
0.045
1.0S
0.361
D423
756
1.181
4.02
2.63
870.8
0.045
1.08
0.731
D424
232
0.363
1.50
0.32
529.9
0.044
1.06
0.346
D420
974
1.522
2.23
0.84
298.1
0.032
0.77
0.330
D431
3,224
5.033
5.1S
2.25
503.2
0.043
1.03
0.305
D432
184
0.288
1.31
0.63
799.4
0.032
0.77
0.200
D430
999
1.561
2.03
0.2S
373.2
0.030
0.72
0.139
D44
487
0.761
2.01
0.97
518.6
0.041
0.98
0.387
D45
300
0.469
1.37
0.57
630.7
0.041
0.93
0.260
project
D410
1,235
1.930
2.79
1.55
289.6
0.036
0.86
0.513
D420
92S
1.450
2.23
0.33
293.1
0.030
0.72
0.303
4.4 Channel routing
Reaches were defined for conveyances collecting flow from more than one subbasin, as shown in Figure
4-8 (baseline conditions) and Figure 4-9 (project conditions). Beyond the length and slope of the channel,
there is little information available to parameterize in -channel flow. The Muskingum routing approach
was selected because it is widely used, requires only two parameters that can be reasonably estimated
with limited data, and has been used in previous studies in the Coachella Valley (NHC, 2014; Bechtel,
1997; SLA, 2000).
The Muskingum K -parameter was estimated from the channel length divided by the flow velocity,
estimated using the Manning's formula; the width and depth of flow was approximated using stable
alluvial channel relationships; the longitudinal slope was estimated from IFSAR and the hydraulic
roughness from aerial photographic imagery.
A value of 0.15 was used for the Muskingum x -parameter, given the predominant non-riverine and
uncertain nature of the flood processes, which are expected on the piedmont
The Muskingum routing parameters are tabulated in Table 4-9. The hydrologic routing processes are not
expected to influence peak flow rates or runoff volumes resulting from the computation of the flood
hydrographs.
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Figure 4-8. Baseline conditions HEC -HMS model schematic*
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Figure 4-9. Project conditions HEC -HMS model schematic*
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Table 4-9. Muskingum routing parameter development summary
conditions
routing
ID
stable alluvial channel
relationships
length
{feet}
n
S
{fttft}
A
{sq ft}
P
{feet}
R
{feet}
V
{fps}
\;uskingum
parameters
Qloo
{cis}
width
{feet}
depth
{feet}
K
{hours}
x
no. of
subreaches
baseline
R41-1
10,512
;S6
2.84
12.013
0.045
0.047
1.097
392
2.30
14.27
0.23
0.15
2.S
R42 -1A
3,413
246
1.81
1,971
0.045
0.060
447
250
1.79
11.93
0.05
0.15
0.6
R42 -1B
4,577
277
2.04
2,43S
0.045
0.079
564
2S1
2.01
14.85
0.05
0.15
0.5
R42-1AB
7,795
342
2.52
7,727
0.045
0.044
864
347
2.49
12.67
0.17
0.15
2.0
R42-2
613
124
0.91
6,436
0.045
0.042
113
126
0.90
6.31
0.2S
0.15
3.4
R42-3
1,728
187
1.38
3,627
0.045
0.048
259
190
1.36
8.86
0.11
0.15
1.4
R42-4
534
117
0.36
1.924
0.045
0.041
101
119
0.35
6.03
0.09
0.15
1.1
R42-34
1,957
197
1.45
4,100
0.045
0.039
286
200
1.43
8.33
0.14
0.15
1.6
R42-234
2,361
212
1.56
1,27S
0.045
0.056
332
215
1.54
10.43
0.03
0.15
0.4
R43-1
5,349
294
2.17
3,776
0.045
0.036
639
299
2.14
10.37
0.10
0.15
1.2
R43-2
552
119
0.S7
5,115
0.045
0.029
104
120
0.56
5.12
0.2S
0.15
3.3
project
R41-1
10,512
386
2.84
8,787
0.045
0.041
1,097
392
2.80
13.36
0.18
0.15
2.2
R41-12
10.512
3S6
2.54
3.226
0.045
0.047
1.097
392
2.30
14.22
0.06
0.15
0.S
R42-2
613
124
0.91
5,862
0.045
0.015
113
126
0.90
3.74
0.44
0.15
5.2
R42-3
1,723
1S7
1.3S
2,747
0.045
0.039
259
190
1.36
S.02
0.10
0.15
1.1
R424
534
117
0.86
638
0.045
0.038
101
119
0.85
5.80
0.03
0.15
0.4
R42-34
1,957
197
1.45
6.410
0.045
0.042
236
200
1.43
3.53
0.21
0.15
2.5
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4.5 HEC -HMS model development summary
A summary of model development using HEC -HMS V4.2 (USACE, 2016) is as follows:
• The watershed, subbasins, streams, and subbasin centroids were determined from 5 -meter IFSAR
topographic data (Intermap Technologies, 2005).
• Subbasins and routing were defined and linked to accommodate selected concentration points at
major canyon outlets and along the depression at the base of Dike No. 4
• The model schematic constructed for the Dike No. 4 watershed is presented in Figure 4-8
(baseline conditions) and Figure 4-9 (project conditions).
• Precipitation for the 1 -percent annual chance storm was represented as a hypothetical storm using
the frequency storm method. Depth -areal reduction factors were applied externally to
precipitation depths prior to their implementation in HEC -HMS. The drainage area for the
frequency storm method was assigned a value of 0.1 to prevent HEC -HMS from applying an
additional depth -areal reduction factor. Also, the peak of the storm synthesized storm pattern was
defined to occur two thirds into the storm period.
• The Standard Project Storm was defined as a user-specified hyetograph linked to the 6 -hour storm
pattern based on the Indio Storm of September 24, 1939 (Plate E-5.9; RCFC&WCD, 1978)
defined as an incremental time series.
• The Whitewater S -graph was defined as a paired -data percentage curve and linked as a user-
specified S -graph for the unit hydrograph transformation in conjunction with the lag parameters
and coefficients
• Channel routing was performed using the Muskingum method based on hydraulic parameters
generalized from topographic mapping and aerial photographic imagery.
Data and worksheets used to parameterize the hydrologic models, including the models themselves, are
presented in the Electronic Technical Appendix.
4.6 Debris yield
The USACE Los Angeles District Debris Method (USACE, 2000) consists of a set of predictive
equations expressing the single event unit debris yield of a watershed as a function of physiographic,
hydrologic, and meteorologic parameters. These predictive equations were developed by multiple
regression analyses of single event debris data observed in the San Gabriel Ranges of southern California.
As defined in this method, the "total debris yield" is the total debris outflow from a watershed measurable
at a specific concentration point for a specified event. It may include clay, silt, sand, gravel, boulders, tree
stumps, and other organic materials. The "debris production" is the gross erosion within a watershed
while the "debris yield" is the quantity of debris actually delivered to a concentration point of interest.
The entire debris production of the watershed may not necessarily reach its outlet because it is stored
temporarily within the watershed due to the lack of transporting capacity of the conveyance system.
Predictive equations. There are five empirical equations that were derived on the basis of watershed size
ranging from 0.1 to 200 square miles. The multiple regression analyses indicated that the unit debris yield
(DY) for a watershed is highly correlated with the following basin parameters: relief ratio (RR) analogous
to watershed slope, drainage area (A), unit peak flow (Q), and the non -dimensional fire factor (FF).
Equation 2 is usually applied to drainages 3 to 10 square miles in area. Equation 1, which is a function of
precipitation rather than runoff, is used for basins 0.1 to 3; however, if frequency discharge information is
available, Equation 2 may be used for areas less than 3 square miles (USACE, 2002).
Equation 2 was applied herein to the drainages of interest less than 3 square miles in size since frequency
discharge information was available; thus, Equation 2 was applied to every subbasin:
Equation 2: logDY= 0.85logQ + 0.53logRR + 0.04logA + 0.22FF
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where
DY= unit debris yield (yd3/mi2),
RR = relief ratio (feet/mile),
A = drainage area (acres),
FF = non -dimensional fire factor, and
Q= unit peak flow (cfs/mi2)
Limitations. The general limitations related to the applications of the USACE Los Angeles District
Debris Method in the prediction of debris yield are as follows: (1) geographic constraints, (2) drainage
area constraints, (3) topographic constraints, (4) frequency constraints, and (5) input constraints. The
frequency and input constraints pertain to small events less than 20 -percent annual chance and low runoff
or precipitation. Since the recurrence interval in this study is 100 -year, only the geographic, drainage area
and topographic constraints remain. This method is intended to be used for the estimation of debris yield
mainly from coastal -draining mountainous watersheds located in southern California. Since the predictive
equations were derived from data observed in the San Gabriel Range, the use of these equations for
watershed conditions different from those of the San Gabriel Range must be specifically addressed. The
method is applicable only to watersheds with areas ranging from 0.1 to 200 square miles and with a high
proportion of their total area in steep, mountainous terrain. The use of this method to compute debris
yields for watersheds in mild -sloped valley areas with a high percentage of piedmonts and alluvial fans or
valley fill areas may result in estimates that are higher than actual yield. If the sediment transport capacity
is less than the statistical debris method results, the sediment transport capacity governs the debris yield.
Adjustment -Transposition (A -T) factor. The use of predictive equations developed from data
pertaining to watersheds, which historically demonstrate extremely high unit yields will result in
overestimates of debris yields when applied to areas with less erosional activity. Recognizing this
limitation, and the importance of uncertain geomorphic and geologic parameters, the USACE Los
Angeles District developed an Adjustment -Transposition (A -T) factor.
Since there are no debris or sediment records available for the Dike No. 4 watershed or nearby
watersheds, the USACE Los Angeles District suggests using Technique 4 (USACE, 2002) to estimate the
A -T factor. Technique 4, describes a method to determine the Adjustment -Transposition factor based on
four basin parameters: (1) parent material or surficial geology, (2) soils, (3) channel morphology, and (4)
hillslope geomorphology. A numerical factor ranging from 0.05 to 0.25 is assigned to each of these
parameters according to the characteristics of each of these parameters.
Guidelines were developed (Table D-1; USACE, 2002) to aid in the selection of these values. The
guidelines are also shown in Table 4-10. The A -T factor is equal to the sum of the individually assigned
numerical values for the four the A -T subfactor groups.
Observations that contributed to the basis for the A -T factor selection are summarized below:
• Parent material. The influence of folding, faulting, and fracturing on sediment production and
delivery was considered most severe on the steeper slopes of the Santa Rosa Mountains and
insignificant on the milder sloped alluvial surfaces. Weathering is sporadic, primarily a function
of chemical, thermal, and wind processes, and the infrequent and highly episodic nature of high
intensity rainfall. Overall, the contribution from weathering is minor relative to other parental
material factors.
• Soils. The influence of cohesion and clay colloids is considered increasingly more significant on
more developed portions of the piedmont and less so on the steep rocky canyon slopes of the
Santa Rosa Mountains. Active alluvial surfaces are not expected to be affected. The soil profile
was viewed as being most developed on the older surfaces of the piedmont, moderately
developed in areas on the slopes of the Santa Rosa Mountains, and minimally developed on the
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more active alluvial surfaces. Exposed rock can be seen as emulating the same behavior in that it
is resistant to erosion, but more due to its physical continuity.
• Channel morphology. Bedrock exposures and bank erosion are expected to have some
contribution along the edges of confined canyon beds and the more developed portions of the
piedmont. Vegetation is generally limited throughout and there is no significant evidence of
headcutting observed in the watershed; bed and bank materials are generally non -cohesive on
active portions of the piedmont and partially cohesive on the steeper slopes of the Santa Rosa
Mountains, and most significant along the edges of the more developed portions of the piedmont.
• Hillslope morphology. This subfactor group has little influence on the production and delivery of
sediment and debris within the watershed. There is no significant evidence of active rilling,
gulling, and mass movement. There are limited eroding deposits in the confined channel reaches.
A breakdown of A -T factors by soil map unit is shown in Table 4-11. The A -T factor computation for
each subbasin is presented in Table 4-12. The resultant A -T factors estimated for the each subbasin ranges
from 0.50 to 0.57.
Due to the low risk of wildfires occurring in this region due to sparse vegetation, the Fire Factor (FF)
used in the analysis of each subbasin was assigned a minimum value of 3.0 based on fire factor (Tables
A-1 and A-2; USACE, 2000).
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Table 4-10. Los Angeles District Debris Method (Table D-1; USACE, 2000) A -T factor guidelines
subfactor
roup
groupA-T
parameter
subfactor
0.25 :
_ : 0.15 0.10
0.05
parent
material
folding
severe
moderate
minor
faulting
severe
moderate
minor
fracturing
severe
moderate
minor
weathering
severe
moderate
minor
soils
cohesion
non -cohesive
partly cohesive
hl2hl• cohesive
profile
minimum soil profile
some soil profile
well-developed soil profile
cover
much bare soil in evidence
some bare soil in evidence
little bare soil in evidence
clay colloids
few clay colloids
some clay colloids
many clay colloids
channel
morphology
bedrock exposures
few se=menu in bedrock
some segments in bedrock
many segments in bedrock
bank erosion
> 30°o of banks eroding
10 - 30°o of banks eroding
< 10°0 of banks erodings
bed and bank materials
non -cohesive bed and banks
partly cohesive bed and banks
milds cohesive bed and banks
vegetation
poorly vegetated
some vegetation
much vegetation
headcutting
maw.- headcuts
few headcuts
no headcutting
hillslop e
erosion
rills and gullies
-
manv and active
some signs
few signs
mass movement
manv scars evident
few signs evident
no signs evident
debris deposits
many eroding deposits
some eroding deposits
few eroding deposits
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Table 4-11. A -T factors estimated for each soil map unit
XRCS soil
identifier
DA
{acres}
SO11a
RUMP__
{%}
parent material
soils
channel morphology
hillslope erosion
-
-
survey
area
MUSY24
•.
_
=
<_
_
_
=
_
=
_
-
mnsml1n
=
E.
a
clay colloidx
A -'t' nub tactor
e
c
-.
r
a
-
C
bcd and bank ncdcnalx
=
i
=
d
=
_
-
=
swill n'�' pnr 51111
3
r.
-
_
r
-
4
=
-
_
-.
C_ 6SO
CcC
39
0
0.05
0.04
0.05
0.05
0.05
0.25
0.15
0.25
025
0.23
0.25
0.05
0.25
0.25
0.05
0.17
0.10
0.05
0.25
0.13
0.53
CdC
:50
0
0.05
0.04
0.05
0.05
0.05
0.25
0.15
0.25
0.25
0.23
0.25
0.05
0.25
0.25
0.05
0.17
0.10
0.05
0.25
0.13
0.58
ChC
177
0
0.05
0.04
0.05
0.05
0.05
0.25
0.15
0.25
0.25
0.23
0.25
0.05
0.25
0.25
0.05
0.17
0.10
0.05
0.25
0.13
0.53
GbA
19
0
0.05
0.04
0.05
0.05
0.05
0.17
0.15
0.25
0.17
0.19
025
0.05
0.17
0.25
0.05
0.15
0.10
0.05
0.25
0.13
0.52
GbB
-
0
0.05
0.04
0.05
0.05
0.05
0.17
0.15
0.25
0.17
0.19
0.25
0.05
0.17
0.25
0.05
0.15
0.10
0.05
0.25
0.13
0.52
GP
0
0
0.05
0.04
0.05
0.05
0.05
0.05
0.15
0.00
0.05
0.06
025
0.00
0.05
0.00
0.00
0.06
0.10
0.00
0.25
0.12
0.29
Ip
1-
0
0.05
0.04
0.05
0.05
0.05
0.24
0.15
0.25
0.24
0.22
0.25
0.05
0.24
0.25
0.05
0.17
0.10
0.05
0.25
0.13
0.57
Is
4
0
0.05
0.04
0.05
0.05
0.05
0.24
0.15
0.25
0.24
0.22
0.25
0.05
0.24
0.25
0.05
0.17
0.10
0.05
0.25
0.13
0.57
LR
20
0.09
0.07
0.09
0.09
0.08
0.20
0.13
0.25
0.20
0.20
0.21
0.05
0.20
0.25
0.05
0.15
0.09
0.05
0.21
0.12
0.55
MaB
184
0
0.05
0.04
0.05
0.05
0.05
0.25
0.15
0.25
0.25
0.23
025
0.05
025
025
0.05
0.17
0.10
0.05
0.25
0.13
0.58
RA
0
0
0.05
0.04
0.05
0.05
0.05
0.25
0.15
0.25
0.25
0.23
0.25
0.05
0.25
0.25
0.05
0.17
0.10
0.05
0.25
0.13
0.5S
RO
7S
90
023
0.17
023
023
022
0.07
0.06
0.25
0.07
0.11
0.07
0.05
0.07
025
0.05
0.10
0.06
0.05
0.07
0.06
0.48
RI
79
0
0.05
0.04
0.05
0.05
0.05
0.25
0.15
0.25
0.25
0.23
0.25
0.05
0.25
0.25
0.05
0.17
0.10
0.05
0.25
0.13
0.5S
W
0
0
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
CA--
DnE
74
0
0.05
0.04
0.05
0.05
0.05
0.25
0.15
0.25
0.25
0.23
0.25
0.05
0.25
0.25
0.05
0.17
0.10
0.05
0.25
0.13
0.5S
LcF
19
25
0.10
0.08
0.10
0.10
0.09
0.20
0.13
0.25
020
0.19
020
0.05
020
025
0.05
0.15
0.09
0.05
0.20
0.11
0.55
Rs
905
S5
0.22
0.17
0.22
0.22
0.21
0.0S
0.07
0.25
0.03
0.12
0.03
0.05
OAS
0.25
0.05
0.10
0.06
0.05
0.0S
0.06
0.49
CS
s991
3,661
0
0.05
0.04
0.05
0.05
0.05
0.25
0.15
0.25
025
0.23
0.25
0.05
0.25
0.25
0.05
0.17
0.10
0.05
025
0.13
0.58
s1016
1.453
19
0.09
0.07
0.09
0.09
0.03
0.19
0.13
0.25
0.19
0.19
0.21
0.05
0.19
0.25
0.05
0.15
0.09
0.05
0.21
0.12
0.54
s1021
10,053
75
020
0.15
020
020
0.19
0.10
0.08
025
0.10
0.13
0.10
0.05
0.10
025
0.05
0.11
0.06
0.05
0.10
0.07
0.50
June 2021
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Table 4-12. Summary of A -T factors estimated for each subbasin
subfactor
group
group
parameter
subbasin
baseline conditions
project
conditions
D4l1
D410
D421A
D421B
D422
1)423
D424
D420
D431
D432
D430.
D44
D45
D410
D420
parent
material
folding
0.17
010
020
0.10
020
020
019
0.0B
0.18
0.07
C.:5
016
015
O.ii
0.07
faulting
013
0.08
015
0.08
015
015
015
0.06
014
0.05
0.C-
012
012
0.08
0.05
fracturing
017
010
020
0.1C
020
020
019
0.08
018
0.07
0.05
016
015
011
0.07
weathering
017
010
020
0.1C
020
020
019
0.08
018
0.07
0.05
016
015
011
0.07
A -T subfactor
0.16
0.10
0.19
0.0"s
0.14
0.19
0.18
0.07
0.17
0.06
0.05
0.15
0.14
0.11
0.06
soils
cohesion
013
020
010
020
0.1C
010
011
022
012
023
025
0.14
015
019
023
profile
0.09
012
0.08
012
0.08
0.08
0.08
014
0.08
014
015
0.09
010
012
014
cover
0.25
025
025
025
025
025
025
025
025
025
025
0.25
025
025
025
clay colloids
0.13
020
010
020
0.1C
010
011
022
012
023
025
0.14
015
019
023
A -T subfactor
015
019
013
019
013
013
013
021
014
022
022
015
016
019
021
channel
morphology
bedrock exposures
013
020
010
C.2C
010
010
011
022
012
023
025
C.1'
0.15
9.19
023
bank erasion
0.05
0.05
0.05
C.C5
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
C.C5
Cr'. 05
0.05
be d and bank materials
013
020
010
020
010
010
011
022
012
023
025
014
015
019
023
vegetation
025
025
025
025
025
025
025
025
025
025
025
025
025
025
025
headcutting
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.30
0.05
0.05
0.05
A -T subfactor
012
015
011
015
011
011
011
016
012
016
017
v.13
013
015
016
hillslope
erosion
rills and gullies
0.07
0.09
0.06
0.04
0.06
0.06
0.06
0.09
0.07
010
010
0.07
0.07
0.0S
0_l0
mass movement
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
debris deposits
013
020
010
020
0.1C
010
011
022
012
023
025
014
015
019
023
A -T subfactor
0.0&
0.11
0.07
011
0.07
0.07
0.07
012
0.08
013
013
0.09
0.09
011
013
A -T factor
051
0.55
0.50
0.55
0.50
0.50
050
0.56
0.51
057
057
057
0.52
0.54
0.57
June 2021
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Q3 Consulting
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Drainage Master Plan
4.7 Hydrologic analysis results
All hydrologic models were analyzed using a 24-hour simulation time to ensure the flood hydrograph
recessions and total runoff volumes for the 6 -hour storm are reported.
The 1 -percent annual chance hydrologic model and debris analysis results focused on conveyance and
temporary impoundment along the project edge and near vicinity, including the Guadalupe Creek Dike
Diversions are summarized in Table 4-13. The contributing drainages for each area of interest is less than
10 square miles; therefore, areal effects were not applied. Flood hydrographs were developed and debris
analysis performed for each individual subbasin for each set of conditions (baseline and project). The
subbasins associated with hydrologic nodes D410 and D420 are the only drainages, which change
characteristics going from baseline to project conditions.
The 1 -percent annual chance and SPS/SPF hydrology and debris analysis results focused on the
impoundment of floodwaters along the base of Dike No. 4 are summarized in Table 4-14 and Table 4-15,
respectively. Areal effects were based on the entire watershed tributary to Dike No. 4 (27.07 square
miles) contributing. Flood hydrographs were developed and debris analysis performed for each individual
subbasin for each set of conditions (baseline and project).
June 2021 4-38 Q3 Consulting
Travertine Development
Drainage Master Plan
Table 4-13. 1 -percent annual chance hydrology and debris analysis results for the evaluation of the project edge conditions
conditions
subbasin
drainage
area
(acres)
relief
ratio
{ft nu}
fire
factor
A -T
factor
Qp
{cfs}
flood
volume
{ac -ft}
CIP
{cfs'mi2}
debris
yield
{ac -ft}
bulked
volume
{ac -ft}
bulking
factor
Qpburged
{cfs}
baseline
D411
{Devil Canyon}
5,035
500.7
3.0
0.51
10,505
1,192
1,322
251
1,443
1.21
12,720
D410
1.190
289.6
3.0
0.55
2,032
137
1.093
30
167
1.22
2,473
J41
6,275
-
-
-
10,413
1,329
1,062
281
1,610
1.21
12,615
D121
(Middle Canyon South}
1,479
1117.9
3.0
0.50
3,420
336
1,430
90
425
1.27
4,332
D421B
{Rock Avalanche Canyon}
2.16S
543.3
3.0
0.55
4,577
441
1,351
117
553
1.27
5,791
D422
250
431.0
3.0
0.50
613
45
1,573
9
54
1.20
734
D423
{Middle Canyon North}
756
370.3
3.0
0.50
1.730
139
1,463
39
227
1.21
2,034
D424
232
529.9
3.0
0.50
535
39
1,477
9
48
1.22
655
D420
974
29S.1
3.0
0.56
1,953
111
1,236
29
140
1.26
2,462
J42
5,859
-
-
-
9,955
1,161
1,087
292
1,453
1.25
12,454
D431
{Toro Canyon)
3.224
'
503.2
3.0
0.51
5.319
601
1.062
102
705
1.17
6.249
D432
134
799.4
3.0
0.57
554
24
1,932
12
36
1.51
S39
D430
999
373.2
3.0
0.57
2,574
105
1,649
42
146
1.40
3,597
J43
4,407 1
-
-
-
5893
732
856
155
888
1.21
7,143
D44
487
518.6
3.0
0.57
1,006
70
1,321
19
S9
1.2S
1,286
D45
300
680.7
3.0
0.52
719
41
1,536
14
55
1.34
964
total
17,327
--
-
-
3,333
-
761
4,094
-
-
2.422
°ject
{changes only}
1 Ai
D410
1,235
239.6
3.0
0.54
2,054
151
1,064
27
17S
1.1S
D422
{moved from J42}
250
431.0
3.0
0.50
613
45
1.573
9
54
1.20
734
J41
6,570
-
-
-
10,934
1,333
1,065
237
1,675
1.21
13,196
D420
923
293.1
3.0
0.57
1,997
111
1.3--
19
129
1.17
2,335
J42
total
5,563
-
9,269
1,115
1.055
273
749
1,383
4,095
1.24
11,536
17,327
3,347
Note: Contributing drainages are less than 10 square miles; therefore hydrology was not subjected to areal effects
June 2021
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Travertine Development
Drainage Master Plan
Table 4-14. 1 -percent annual chance debris analysis results for the evaluation of flood impoundment adjacent to Dike No. 4
conditions
subbasin
drainage
area
{acres}
relief
ratio
{ft mi)
fire
factor
A -T
factor
Qp
{cfs}
flood
volume
{ac -ft}
Qp
{cfs'mi2}
debris
yield
{ac -ft)
bulked
volume
{ac -ft}
bulking
factor
Qpbutked
{cfs}
baseline
D411
{Devil Canyon}
5,085
300.7
3.0
0.51
9.650
1,07S
1,213
234
1,313
1.22
11,784
D410
1.190
239.6
3.0
0.55
1.572
123
1.007
23
150
1.23
2,293
J41
6,275
-
-
-
9,564
1:201
975
262
1,463
1.22
11,651
D421
{Middle Canyon South}
1,479
1117.9
3.0
0.50
3,152
303
1,364
S4
387
1.2S
4,022
D421B
{Rock Avalanche Canyon}
2,163
343.8
3.0
0.55
4,211
400
1,243
109
509
1.27
5,356
D422
250
431.0
3.0
0.50
566
41
1,452
S
49
1.20
682
D423
{Middle Canyon North}
756
870.3
3.0
0.50
1.596
171
1.350
36
207
1.21
1.933
D424
232
529.9
3.0
0.50
495
35
1,367
S
43
1.23
610
D420
974
298.1
3.0
0.56
1.795
100
1,132
27
127
1.27
2.273
J42
5,859
-
-
-
9,141
1,050
999
272
1,322
1.26
11,508
D431
{Toro Canyon}
3,224
503.2
3.0
0.51
4,923
543
977
95
637
1.17
5,781
D432
184
799.4
3.0
0.57
510
21
1,777
11
33
1.54
733
D430
999
373.2
3.0
0.57
2,333
94
1,527
39
133
1.41
3,371
J43
4,407
-
-
-
5390
658
783
145
803
1.22
6,578
D44
487
518.6
3.0
0.57
922
63
1,211
18
81
1.29
1,188
D45
300
680.7
3.0
0.52
663
37
1,417
13
50
1.36
899
total
17,327
-
-
-
-
3,009
-
710
3,719
-
-
project
{changes only)
D410
1,235
289.6
3.0
0.54
1,879
136
974
25
161
1.18
2,226
D422
{moved from J42}
250
431.0
3.0
0.50
566
41
1,452
S
49
1.20
6S2
141
6,570
-
-
-
10,048
1,255
979
265
1,522
1.21
12,193
D420
928
298.1
3.0
0.57
1,336
99
1,266
17
116
1.13
2,159
J42
total
5,563
--
--
-
-
8,510
-
1,008
979
-
254
69S
1,262
1.25
10,657
17,327
3,020
3,718
-
-
Note: Hydrology subjected to areal effects assuming the entire watershed (27.07 square miles) is contributing
June 2021
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Q3 Consulting
Travertine Development
Drainage Master Plan
Table 4-15. SPF debris analysis results for the evaluation of flood impoundment adjacent to Dike No. 4
conditions
subbasin
drainage
area
{acres}
relief
ratio
{ft mi)
fire
factor
A -T
factor
Qp
{cfs}
flood
volume
{ac -ft}
Qp
{cfs'mi2}
debris
yield
{ac -ft}
bulked
volume
{ac -ft}
bulking
factor
Qpbutked
(cfs)
baseline
D411
{Devil Canyon}
5,085
300.7
3.0
0.51
9,031
1,882
1,137
221
2,103
1.12
10,092
D410
1.190
239.6
3.0
0.55
2,550
384
1,372
36
420
1.09
2,739
J41
6,275
-
-
-
9,766
2,266
996
257
2,523
1.11
10,873
D321
(Middle Canyon South}
1,479
1117.9
3.0
0.50
3,020
559
1,307
81
640
1.14
3,456
D421B
(Rock Avalanche Canyon)
2,163
343.8
3.0
0.55
3,334
684
1,135
101
785
1.15
4,410
D422
250
431.0
3.0
0.50
609
95
1,562
9
103
1.09
667
D423
(Middle Canyon North}
756
870.3
3.0
0.50
1.439
287
1,217
33
320
1.12
1,605
D424
232
529.9
3.0
0.50
571
37
1,573
9
96
1.11
632
D420
974
298.1
3.0
0.56
2.277
296
1.496
33
323
1.11
2,527
J42
5,859
-
-
-
9588
2,007
1,047
265
2,272
1.13
10,855
D431
{Toro Canyon}
3,224
503.2
3.0
0.51
5,869
1,192
1,165
110
1,302
1.09
6,410
D432
184
799.4
3.0
0.57
491
54
1,710
11
65
1.20
591
D430
999
373.2
3.0
0.57
2,635
253
1,720
43
331
1.15
3,033
J43
4,407
-
-
-
7523
1,533
1,093
164
1,697
1.11
8,334
D44
487
518.6
3.0
0.57
1,137
173
1,393
22
195
1.12
1,278
D45
300
680.7
3.0
0.52
783
107
1,673
15
122
1.14
393
total
17,327
--
-
-
6,087
-
723
6,810
-
-
project
{changes only)
D410
1,235
289.6
3.0
0.54
2,563
411
1,328
33
444
1.08
2,766
D422
{moved from J42}
250
431.0
3.0
0.50
609
95
1,562
9
103
1.09
667
131
6,570
-
-
-
10,366
2,387
1,010
262
2,650
1.11
11,506
D420
928
298.1
3.0
0.57
2,245
303
1,551
21
324
1.07
2,402
J42
total
5,563
--
--
-
-
8,776
-
1,920
6,121
1,010
-
244
70S
2,164
6,829
1.13
9,943
17,327
-
-
Note: Hydrology subjected to areal effects assuming the entire watershed (27.07 square miles) is contributing
June 2021
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June 2021 4-42 Q3 Consulting
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Drainage Master Plan
5 FLOOD CONVEYANCE AND STORAGE ANALYSIS
The proposed Travertine Development is situated on the piedmont, which skirts along the eastern base of
the Santa Rosa Mountains. The upper piedmont is comprised of a number of active fan areas stemming
from the canyons above. The active fan areas associated with the larger collective of canyons referred to
as Devil, Middle, and Toro Canyon Areas, are physically segregated by areas of significant soil
development, identified as inactive fan areas, except on the more distal portions of the piedmont.
The piedmont experiences a complex mix of flood processes, which can be generally categorized as
shallow "non-riverine" flooding, except within the impoundment area along Dike No. 4, where deep
ponding can occur during more extreme events. Shallow flooding is typically more confined at or near the
canyon outfalls and transitions to flood processes of a distributary nature followed by sheet flooding on
the more distal portions of the piedmont. Past agricultural activities have resulted in areas elevated on fill,
which cause a significant disruption in the natural flood processes on the northern section of the
piedmont.
Evaluating flood conveyance on the piedmont surface and flood storage along the upstream side of Dike
No. 4 are the key focal points of this study as these two flood -related phenomena are expected to
influence (1) site planning and design in terms of providing sustainable flood protection around and/or
through the development footprint and (2) mitigation of flood hazard impacts to adjacent properties and
facilities, including the Guadalupe Creek Diversion Dikes, Dike No. 4, and the deep aquifer recharge
basins, as a consequence of the planned development.
Given the nature of the flood environment on the piedmont, a two-dimensional flood routing model was
selected in lieu of a more conventional one-dimensional hydraulic modeling scheme in order to avoid
over -simplifying the complexities that are typical of such an environment. In addition, a two-dimensional
flood routing model provides an improved measure for evaluating the transient behavior of the water
surface profile along Dike No. 4 caused by the unbalanced delivery of floodwaters, as compared to
conventional level -pool storage analysis, which might underestimate the maximum water surface at some
locations along Dike No. 4.
Floodwaters temporarily impounded by Dike No. 4 typically percolate into the ground, but during
extreme flood stages, may discharge to a functioning evacuation channel maintained by CVWD via an
overflow outlet structure.
5.1 Goals and objectives
The primary goal of conducting two-dimensional flood routing is to approximate existing (baseline) and
project -influenced flood patterns to use as a base for future development planning; it is not intended as a
regulatory floodplain evaluation.
Objectives including: (1) spatial mapping of 1 -percent annual chance flood depths, velocities, and flow
rate distributions above, around, within, and below the Travertine property limits; (2) computing the 1 -
percent annual chance flood and Standard Project Flood maximum water surface elevation profiles along
Dike No. 4.
5.2 Two-dimensional flood routing
The bulked (sediment/debris loaded) 1 -percent annual chance flood and Standard Project Flood were used
to determine the freeboard along Dike No. 4 as well as estimate the behavior of flood conveyance on the
piedmont based on the IFSAR topographic dataset (Intermap Technologies, 2005) using FLO-2D PRO
(Flo -2d, Inc., 2013), a two-dimensional, finite -difference scheme, flood routing model. The FLO-2D PRO
model development includes the following aspects:
June 2021 5-1 Q3 Consulting
Travertine Development
Drainage Master Plan
• General model definitions
• Topographic features
• Levees
• Hydraulic structures
• Infiltration and transmission losses
• Inflow boundary conditions
5.2.1 General model definitions
The model domain was defined to include the piedmont confined by Dike No. 4 to the east, the mountain
front to the west and south, and the Guadalupe Creek Diversion Dikes and rock outcroppings to the north.
The following information describes the general model definition:
• Domain of 101,833 grid elements
• 24-hour simulation time
• 50' x 50' grid element size
• Grid element elevations were interpolated from IFSAR topographic dataset (Intermap
Technologies, 2005)
• A constant floodplain n -value of 0.045 was assigned to the entire domain
• A shallow n -value of 0.100 was assigned to the entire domain
• A limiting Froude number of 0.95 was assigned to the entire domain
5.2.2 Topographic features
The IFSAR topographic dataset (Intermap Technologies, 2005), which was used to determine the grid
element elevations across the model domain, captures in some measure the influence of the following
anthropogenic (human -made) features/disturbances:
• Guadalupe Creek Diversion Dikes (3 in all)
• Fill slope/berm/channelization along the southern edge of the vineyard
The following human -made features/disturbances are not significantly represented by the model domain
elevations:
• Fill slope/berm along the west edge of the vineyard
• Recharge ponds and associated berms
• Rock outcrop cutout area below Guadalupe Creek Diversion Dike Nos. 1 and 2
No significant man-made disturbances were observed (in the field or on aerial imagery) on the piedmont
upstream of the Project site that would potentially influence flood patterns.
5.2.3 Levees
The following levee definitions were applied to the model domain:
• Dike No. 4. The domain boundary was defined along the top of Dike No. 4 to serve as a levee of
infinite height
• Guadalupe Creek Diversion Dikes. Levees were defined along each of the three alignments with
the assumption that overtopping will not occur for all conditions and all flood events up to and
including the Standard Project Flood; the domain boundary was defined for a portion along the
top of Guadalupe Creek Diversion Dike No. 1 (north dike) to emulate the leveed conditions
• Development footprint edge conditions. A levee was defined around the entire edge of the
development footprint to preclude run-on from offsite flows for the Project conditions
• Avenue 62 and Jefferson Street bridge crossings. Both bridges were leveed along their upstream
and downstream faces to limit flow through the structure via a series of defined hydraulic
structures
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• Devil Canyon breakout locations. A levee was defined to divert floodwaters onto the overbank
areas at a selected breakout location
5.2.4 Hydraulic structures
The following hydraulic structures were defined in the model domain•
■ Avenue 62 and Madison bridge crossing. The proposed Avenue 62 and Madison crossings were
modeled using the FHWA culvert equations in the FLO-2D PRO computer program. The
crossings were modeled as 8 — 20 -ft wide by 8 -feet height reinforced concrete box culverts.
• Jefferson Street bridge crossing. The proposed Jefferson Street crossing consists of a bridge and
14 arched pier walls with a thickness of 1.33 feet, spaced 21.33 feet from centerline to centerline,
and 9 feet from the finish grade to the highest point along the low chord, whose rating curve was
approximated using HEC -RAS v4.1 (see Technical Appendix) assuming a constant slope of 0.001
ft/ft and uniform cross sections to represent the channel section; a typical bridge crossing detail is
shown in Figure 5-1.
The final design configuration for each proposed bridge crossing is unknown at this time; therefore, the
rating curves were conceptually and simplistically approximated based on the assumption the openings,
grades, and elevations would be constant along the span of each bridge to allow for the determination and
application of a unit width rating curve. Updated hydraulic models should be prepared with the final
design of the bridge crossings which shall incorporate the final grades and bridge configuration.
Figure 5-1 Conceptual arched bridge detail section (partial)
3011 -300-3011-3011-3011-300-3011-3011-3011-3011-3011-3011-3011- •
11111111111111111::---------
incon
---er---_o o FC
If If II II (TYP)
5.2.5 Coral Mountain rock cutout at the terminus of upper Guadalupe Creek
A hydraulic rating table was determined for the Coral Mountain rock cutout, which separates the upper
and lower segments of Guadalupe Creek, assuming the water surface functions at critical depth despite
the steep slopes through this section, which would normally result in supercritical flow.
The hydraulic rating table was constructed from the higher critical depth resulting from the two cross
sections for each analyze discharge. In the plan view, cross section one (1) is curvilinear along the 150'
elevation (invert) and cross section two (2) is more linear across the cutout where the invert is at the 144'
elevation (see Figure 5-2). Critical depths were computed for each cross section using the Hydraulic
ToolBox V4.2 (FHWA, 2014).
The resultant critical depths for selected discharges are shown in Table 5-1 with the governing depths
highlighted in green. The critical depths for cross section 1 are relative to the 150' elevation whereas the
critical depths for cross section 2 are relative to the 144' elevation. The critical depths for cross section 1
were increased 6 feet (150' — 144') so that the critical depths for both cross sections are relative to the
same elevation. The section profile for cross section 1 in depicted in Figure 5-3 and the section profile for
cross section 2 is presented in Figure 5-4.
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Figure 5-2 Selected cross sections for Coral Mountain rock cutout
Table 5-1. Summary of discharges versus critical depth at selected rock cutout cross sections
Q
{cfs}
critical depth, in feet,
relative to invert elevation
cross
section
cross
section
2
EL 150'
EL 144'
EL 144'
10
0.39
6.39
1.23
50
0.85
6.85
2.32
100
1.16
7.16
3.08
500
2.41
8.41
6.16
1,000
3.29
9.29
8.33
5,000
7.32
13.32
15.78
10,000
10.30
16.30
19.33
15,000
12.34
18.34
22.09
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165
Figure 5-3 Cross Section 1 (critical depth shown for 10,000 cfs)
t 160-
0
CI) 15 5 —
W —
150 T I 1 1 I 1 1 1 I 1 1 1 I 1 1 1 I 1 1 1 I 1 1 I
0 20 40 60 80 100 120
Station (ft)
Figure 5-4 Cross Section 2 (critical depth shown for 10,000 cfs)
165
145—
r
0 20
40 60 80
t a t i o n (ft)
5.2.6 Infiltration and transmission losses
Infiltration was defined along the base of Dike No. 4 as shown in Figure 5-5, similar to PACE (2005), for
the impoundment analysis of the Standard Project Flood only. The Green-Ampt infiltration method was
used and parameters were adjusted to produce an average infiltration rate over the 24-hour simulation
period that does not exceed the constant infiltration rate of 2.5 inches per hour originally assumed by
PACE (2005).
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Figure 5-5 infiltration area for model simulations focused on impoundment impacts to Dike No. 4
Legend
infiltration footprint
o property Line
5.2.7 Model inflow boundary conditions
The definition of the inflow boundary conditions were subjected to combinations of the following
elements and there possible variations as summarized in Table 5-2:
• Event: 1 -percent annual chance flood or Standard Project flood
• Conditions: baseline or project
• Areal effects
The flood conditions along the project edge and near vicinity, including the Guadalupe Creek Dike
Diversion System, were only analyzed for the 1 -percent annual chance flood; and because the
contributing drainage for anyone contiguous area or alignment of interest was less than 10 square miles,
areal effects were not applied.
The flood conditions along Dike No.4 were analyzed assuming the entire watershed (27.07 square miles)
is contributing; and therefore, areal effects were used to adjust precipitation depths. The 1 -percent annual
chance flood and Standard Project Flood were both analyzed to determine whether or not freeboard
requirements are met.
For each model simulation focus, the baseline and project conditions were analyzed to facilitate the
determination of impacts and related mitigation.
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Table 5-2. Summary of inflow boundary conditions
inflow
boundary
conditions
scenario
development
conditions
simulation
focus
flood
event
areal
effects
1
baseline
project edge
and
contributing
drainages
project
near vicinity
1 -percent
annual chance
< 10 sgmr
]
baseline
flood
entire
4
project
watershed
Dike No. 4
{21.01 sq mid
5
baseline
Standard
contributing
Project
»» 10 sq mi
6
project
Flood
Inflow hydrographs were defined at or near the canyon outfalls outside the Travertine property boundary.
The definition of these inflow hydrographs are based on the translation of the combined hydrographs at
hydrologic nodes J41, J42, J43 to the nodes located at or near the canyon outfalls (D411, D421A, D421B,
D422, D423, D424, D431, D432, D441, and D451). D441 and D451 were not defined in the hydrologic
model, but were added to identify the inflow locations representing hydrologic nodes D44 and D45.
The distribution of hydrographs were weighted by volume and include the runoff developed on the
piedmont (D410, D420, and D430).
Inflow hydrographs were defined at or near each canyon outfall as follows:
• Baseline conditions only
o The combined flood hydrograph at node
o The combined flood hydrograph at node
D422, D423, and D424
• Project conditions only
o The combined flood hydrograph at node
o The combined flood hydrograph at node
D423, and D424
• Baseline and project conditions
o The combined flood hydrograph at node J43 was proportioned to nodes D431 and D432
• The individual flood hydrograph at node D44 was assigned to node D441
• The individual flood hydrograph at node D45 was assigned to node D451
Inflow flood hydrographs were depth proportioned across one up to several lateral grid elements based on
a common critical water surface elevation across the applicable grid elements. All inflow flood
hydrographs were bulked based on debris yield estimations.
J41 was assigned to node D411
J42 was proportioned to nodes D421A, D421B,
J41 was proportioned to nodes D411 and D422
J42 was proportioned to nodes D421A, D421B,
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Summaries of this translation/distribution of the combined hydrographs to the inflow locations at or near
the canyon outfalls are summarized as follows:
• Table 5-3 (Baseline 1 -percent annual chance flood, no areal effects)
• Table 5-4 (Baseline 1 -percent annual chance flood, areal effects)
• Table 5-5 (Baseline Standard Project Flood, areal effects)
• Table 5-6 (Project 1 -percent annual chance flood, no areal effects)
• Table 5-7 (Project 1 -percent annual chance flood, areal effects)
• Table 5-8 (Project Standard Project Flood, areal effects)
Table 5-3. Baseline 1 -percent annual chance flood inflow distribution, no areal effects
combined
flow
node at
Dike
No. =
subbasin
node
flood
volume
qac -ft}
bulking
factor
bullied flood
volume [ac -ft}
redist.
fraction of
combined
flow
initial
redist.
341
D411
1,192
1.21
1,443
1,610
1.00
D410
137
1.21
167
0
0.00
J41
1,329
1.21
1,610
1,610
-
j_:2
D421A
336
1.27
425
471
0.32
D4218
441
1.27
55S
618
0.42
D422
45
1.20
54
60
0.04
D423
189
121
227
252
0.17
D424
39
1.22
43
53
0.04
D420
111
1.26
140
0
0.00
J42
1,161
1.25
1,453
1,453
-
D431
604
1.17
705
S44
0.95
D432
24
1.51
36
43
0.05
D430
105
1.40
146
0
0.00
J43
732
1.21
888
888
-
D44
D44
70
118
89
89
-
D45
D45
41
1.34
55
55
-
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Table 5-4. Baseline 1 -percent annual chance flood inflow distribution, areal effects
combined
flow
node at
Dike
No. 4
subbasin
node
flood
volume
{ac -ft}
bulking
factor
bullied flood
volume {ac -ft}
redist.
fraction of
combined
flow
initial
redist.
J41
D411
1,078
1.22
1,313
1,463
1.00
D410
123
1.22
150
0
0.00
J41
1,201
1.22
1,463
1,463
-
J42
D421A
303
1.23
337
428
0.33
D421B
400
1.27
509
563
0.42
D422
41
1.20
49
54
0.04
D423
171
1.21
207
229
0.18
D424
35
1.23
43
43
0.04
D420
100
1.27
127
0
0.00
342
1,050
1.26
1,322
1,322
-
343
D431
543
1.17
637
764
0.95
D432
21
1.54
33
39
0.05
D430
94
1.41
133
0
0.00
343
65S
1.22
803
803
-
i==
D;�
63
1.29
S 1
SI
-
D=5
DL5
37
1.36=
_
50
-
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Table 5-5. Baseline SPF inflow distribution, areal effects
combined
flow
node at
Dike
No. 4
subbasin"
node
flood
volume
{ac -ft}
bulking
factor
bulked flood
volume {ac -ft}
redist.
fraction of
combined
flow
initial
redist.
J41
D411
1,SS2
1.12
2,103
2,523
1.00
D410
384
1.09
420
0
0.00
J41
2,266
1.11
2,523
2,523
-
J42
D421A
559
1.14
640
74S
0.33
D421B
6S4
1.15
785
918
0.40
D422
95
1.09
103
121
0.05
D423
287
1.12
320
374
0.16
D424
S7
1.11
96
112
0.05
D420
296
1.11
328
0
0.00
J42
2,007
1.13
2,272
2,272
-
J43
D431
1.192
1.09
1,302
1,617
0.95
D432
54
1.20
65
81
0.05
D430
288
1.15
331
0
0.00
J43
1,533
1.11
1,697
1,697
-
D44
D44
173
1.12 [195
195
-
D45
D45
107
1.14
122
122
-
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Table 5-6. Project 1 -percent annual chance flood inflow distribution, no areal effects
combined
flow
node at
Dike
No. 4
subbasin
node
flood
volume
{ac -ft}
bulking
factor
bull:ed flood
volwne (ac -ft}
redist.
fraction of
combined
flow
initial
redist.
j..:1
D411
1.192
1.21
1,443
1,615
0.96
D422
45
1.20
54
61
0.04
D410
151
1.1S
173
0
0.00
J41
1,338
1.21
1,675
1,675
-
r_2
D421A
336
1.27
425
469
0.34
D421B
441
1.27
558
615
0.44
D423
139
1.21
227
251
0.13
D424
39
1.22
48
53
0.04
D420
111
1.17
129
0
0.00
J42
1,115
1.24
1,388
1,388
-
j....;
D431
604
1.17
705
S44
0.95
D432
24
1.51
36
43
0.05
D430
105
1.40
146
0
0.00
343
-32
1.21
SSS
SSS
-
D--
D44
0
1.2S
S.9
St
D41'
D45
=1
1.3:
- -
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Table 5-7. Project 1 -percent annual chance flood inflow distribution, areal effects
combined
flow
node at
Dike
No.
subbasin
node
flood
volume
{ac -ft}
bulking
factor
bulked flood
volume (ac -ft}
redist.
fraction of
combined
flow
initial
redist.
T. 1
D411
1.07S
1.22
1,313
1,467
0.96
D422
41
1.20
49
55
0.04
D410
136
1.1S
161
0
0.00
J41
1,255
1.21
1,522
1,523
-
r_2
D421A
303
1.2S
3S7
426
0.34
D421B
400
1.27
509
561
0.44
D423
171
1.21
207
22S
0.13
D424
35
1.23
43
48
0.04
D420
99
1.18
116
0
0.00
J42
1,008
1.25
1,262
1,262
-
J.:;
D431
543
1.17
637
764
0.95
D432
21
1.54
33
39
0.05
D430
94
1.41
133
0
0.00
343
65S
1.22
803
S03
-
J==
D44
5
1.29
SI
S1
-
D-:5
D45
;-
1.36
50
50
-
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Table 5-8. Project SPF inflow distribution, areal effects
combined
flow
node at
Dike
No. 4
subbasin
node
flood
volume
{ac -ft}
bulking
factor
bulked flood
volume (ac -ft}
redist.
fraction of
combined
flow
initial
redist.
J41
D411
1,882
1.12
2,103
2,526
0.95
D422
95
1.09
103
124
0.05
D410
411
1.0S
444
0
0.00
J41
2,387
1.11
2,650
2,650
-
J42
D421A
559
1.14
640
752
0.35
D421B
684
1.15
785
923
0.43
D423
287
1.12
320
376
0.17
D424
87
1.11
96
113
0.05
D420
303
1.07
324
0
0.00
J42
1,920
1.13
2,164
2,164
-
D431
1.192
1.09
1,302
1,617
0.95
D432
54
1.20
65
81
0.05
D430
2SS
1.15
331
0
0.00
J43
1,533
1.11
1,697
1,697
-
D-
D44
173
1.12
195
195
-
D45
D45
107
1.14
122
122
-
5.2.8 Model exclusions
The Dike No. 4 outlet structure was not defined thereby eliminating any outflow from the impoundment.
For the exclusion of topographic features, see Section 5.2.2.
5.2.9 Model variations for flood pattern uncertainty
Given the uncertainty in flood pattern behavior on and along the edges of the active areas, one model
variation was simulated to determine a worse -case composite flood environment as it relates to the
aggregate of maximum flood depths and velocities as well as the distribution of flood rates along the edge
conditions and in near vicinity of the planned development. This variation considers the upper breakout
location (DC1) on the southern bank/terrace of the Devil Canyon active floodplain previously identified
in Figure 3-5. This model variation was implemented by obstructing the Devil Canyon active floodplain
at DC1 to force floodwaters onto the southern overbank/terrace.
The results from this model variation is not intended for the purpose of mapping the flood hazard, but
rather, to provide a depiction of flood patterns based on recent digital topographic mapping for the
purpose of conceptualizing viable flood protection and conveyance alternatives for the planned
development.
No variations were considered for the Middle Canyon Area, since the flood conveyance below the canyon
outfalls is generally confined with a preferred direction on a portion of the piedmont/fans, which is
considered inactive, due partly to the substantial amount of soil development that has occurred over time.
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No flow path variations were considered for the Toro Canyon Area outfalls since no development is
proposed near this region.
5.2.10 Model simulation results
In regard to the graphical depiction of simulation outcomes, the maximum flood depths and velocities
were displayed based on a minimum depth threshold of 0.5 feet.
The simulated maximum flood depths produced by the 1 -percent annual chance flood routing models
focused on conveyance along the edge conditions and near vicinity of the planned development are
presented as follows:
• Baseline conditions (Figure 5-6)
• Baseline conditions with forced split at breakout location DC 1 previously identified in Section 3
(Figure 5-7)
• Composite of baseline conditions above (Figure 5-8)
• Project conditions (Figure 5-9)
• Project conditions with forced split at breakout location DC1 previously identified in Section 3
(Figure 5-10)
• Composite of project conditions above (Figure 5-11)
• Change in composite maximum flood depths from baseline to project conditions (Figure 5-12)
The simulated maximum flood velocities produced by the 1 -percent annual chance flood routing models
focused on conveyance and temporary impoundment along the edge conditions and near vicinity of the
planned development are presented as follows:
• Baseline conditions (Figure 5-13)
• Baseline conditions with forced split at breakout location DC 1 previously identified in Section 3
(Figure 5-14)
• Composite of baseline conditions above (Figure 5-15)
• Project conditions (Figure 5-16)
• Project conditions with forced split at breakout location DC1 previously identified in Section 3
(Figure 5-17)
• Composite of project conditions above (Figure 5-18)
• Change in composite maximum flood velocities from baseline to project conditions (Figure 5-19)
The simulated maximum flood depths produced by the 1 -percent annual chance flood routing models
focused on impoundment along the interior of Dike No. 4 and are presented as follows:
• Baseline conditions (Figure 5-20)
• Project conditions (Figure 5-21)
• Change in flood depths from baseline to project conditions (Figure 5-22)
The simulated maximum flood depths produced by the Standard Project Flood routing models focused on
impoundment along the interior of Dike No. 4 are presented as follows:
• Baseline conditions (Figure 5-23)
• Project conditions (Figure 5-24)
• Change in flood depths from baseline to project conditions (Figure 5-25)
5.2.10.1 Dike No. 4 freeboard evaluation
A profile comparison of ground elevations and maximum water surface elevations along Dike No. 4,
including past results determined as part of the FEMA Physical Map Revision Application (PACE, 2005),
are presented in Figure 5-13. A portion of each ground elevation profile is missing due to spatial gaps in
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topographic mapping. In addition, the 2011 LiDAR ground elevation profiles show a significant amount
of variability, which may suggest there are mapping irregularities.
A comparison of the follow water surface profiles are presented in Figure 5-26:
• 1 -percent annual chance flood, baseline conditions
• 1 -percent annual chance flood, project conditions
• 1 -percent annual chance flood (PACE, 2005)
• Standard Project Flood, baseline conditions
• Standard Project Flood, project conditions
• Standard Project Flood (PACE, 2005)
5.2.10.2 Guadalupe Creek Diversion Dikes
The "conveyance" models identified above were also used to determine the aggregate 1 -percent annual
chance maximum flow rate as measured from floodplain cross sections defined across the conveyance
area between the Guadalupe Creek Diversion Dikes:
• Baseline conditions: 7,000 cfs
• Baseline conditions with forced split at breakout location DC1: 0 cfs
• Project conditions: 13,704 cfs
• Project conditions with forced split at breakout location DC1: 13,790 cfs
Profile comparisons of ground elevations and 1 -percent annual chance maximum water surface elevations
for the upper Guadalupe Creek Diversion Dikes are presented as follows:
• Baseline (no breakout) and project (with forced split at breakout location DC1) conditions
maximum water surface profiles adjacent to the Northern Guadalupe Creek Diversion Dike
(Figure 5-27)
• Baseline (no breakout) and project (with forced split at breakout location DC1) conditions
maximum water surface profiles adjacent to the Southern Guadalupe Creek Diversion Dike
(Figure 5-28)
• Baseline (no breakout) and project (with forced split at breakout location DC1) conditions
maximum water surface profiles along the centerline between the upper Guadalupe Creek
Diversion Dikes (Figure 5-29)
Profile comparisons of flood depths and velocities adjacent to the upper Guadalupe Creek Diversion
Dikes are presented as follows:
• Baseline (no breakout) and project (with forced split at breakout location DC1) conditions flood
depth and velocity profiles adjacent to the Northern Guadalupe Creek Diversion Dike (Figure 5-
29)
• Baseline (no breakout) and project (with forced split at breakout location DC1) conditions flood
depth and velocity profiles adjacent to the Southern Guadalupe Creek Diversion Dike (Figure 5-
30)
• Baseline (no breakout) and project (with forced split at breakout location DC1) conditions flood
depth and velocity profiles along the centerline between the upper Guadalupe Creek Diversion
Dikes (Figure 5-31)
For reference, a plan view of the upper Guadalupe Creek Diversion Dikes, as interpreted from the as -built
drawing (Figure 2-1), is shown in Figure 5-32.
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0.505y<1.00
1.005y<2.00
2.00sy{3.00
3.005y<4.00
4.00sy<5.00
5.00sy<6.00
6.005y<7.00
7.00sy<9.00
9.00sy<12.00
12.00sy<15.00
15.00 +
0 Inflow Node
= Property Line
100 -foot Contours
20 -foot Contours
Figure 5-6 Travertine baseline 1 -percent annual chance maximum depths > 0.5 feet
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Figure 5-7. Travertine baseline 1 -percent annual chance maximum depths > 0.5 feet with DC1 forced split in effect
Legend
depth , y (ft)
0.50 y <1.00
1.00 y <2.00
2.00 <y < 3.00
3.00 y <4.00
4.00 s y < 5.00
-
-
5.00 y < 6.00 Q Inflow Node
6 00 s y < 7.00 = Property Line
7.00< y < 9.00 100 -foot Contours
9 00 s y < 12.00 20 -foot Contours
12.00 y < 15.00
15.00 +
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Figure 5-8. Travertine composite baseline 1 -percent annual chance maximum depths > 0.5 feet
Legend
depth , y (ft)
0.50<y<1.00
1.00<y<2.00
2.00sy<3.00
5.005ya6.00 0 Inflow Node
6.00 s y < 7.00 o Property Line
7.00 s y < 9.00 100 -foot Contours
9.00 s y < 12.00 20 -foot Contours
3.005y <4.00 n 12.005y< 15.00
FT 4.00sy<5.00 15.00+
1
•
wp& ■1
•
a CANYON
•
•
SCJ. 1 f
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Figure 5-9. Travertine project 1 -percent annual chance maximum depths > 0.5 feet
Legend
depth, y (ft)
0.50. y<1.00
1.00 . y < 2.00
2.005y<3.00
3.005y<4.00
4.00 y45.00
▪ ! 1 1- - '. -
L_m
5.40sy<6.00 0 Inflow Node
6.005y<7.00 'Property Line
7.00<ya9.00
9.00<y<12.00
12.005ya 15.00
15.00 +
100 -foot Contours
20 -foot Contours
Project Grading
y
✓ 1 -
ir
16.110111t z ,s: 1
II 44E4
proposed access
culvert crossing
•
t
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Figure 5-10. Travertine project 1 -percent annual chance maximum depths > 0.5 feet with DC1 forced split in effect
Legend
depth , y (ft)
0.50Ey<1-00
1.00<y<2.00
1 12.00 s y < 3-00
3.00<y<4 -00I
5.00 5 y < 6.00 0 Inflow Node
6.00 y <7.00 =Property Line
7.00 5 y c 9.00 100 -foot Contours
9.00 s y < 12.00 20 -foot Contours
112.00 s y < 15.00 Project Grading
�4.O0sy<5.00nr15.00+
% to /)
a it
N + cr
w
N
'--� -��-
EVIL
CANYON
proposed access
Avenue 62
culvert crossing
ai
CANYON
REA
r
600 1,200
Feet
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Figure 5-11. Travertine composite project 1 -percent annual chance maximum depths > 0.5 feet
Legend
depth , y (ft) 5.00 5 y < 6.00 0 Inflow Node
0.50sy<1.0Q 6.005y<7,00 'Property Line
1.00 s y < 2.00 7.00 5 y < 9.00 - 100 -foot Contours
2.00 s y < 3.00 9.00 5 y < 12.00 20 -foot Contours
3.00 S y < 4.00 12.00 5 y < 15.00 Project Grading
FT 4.00sy<5.00 ® 15.00+
1
CANYON
ftoposect access
Averiiute'62
culvert crossing
MIDDLE
r
4.
CANYON
600 1,200
Feet
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Figure 5-12. Travertine change in composite 1 -percent annual chance maximum depths from baseline to project conditions
1
Legend
depth, y (ft) -0.50 5 y < 0.50 0 inflow Node
y < -26.00 n 0.50 5 y a 1.00 ' Property Line
-26.00 5 y < -9.00 17 1.00 5 y < 3.00 100 -foot Contours
-9.00 5 y < -7.00 3.00 s y < 5.00 20 -foot Contours
-7.005y<-5.00 0 5.005y<7.00 Project Grading
-5.005y<-3.00 - 7.00sy<9.00
-3.005y<-1.00 - 9.005y< 10.00
-1.00 y<-0.50 - 10.00+
r
,•f t1.1."1.1."W t
i .'
Via:• ,
;
ti .,
�91.\:lir.
1
600 1,200
Feet
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Figure 5-13. Travertine baseline 1 -percent annual chance maximum velocities (maximum depths > 0.5 feet)
Legend
flood velocity (v) in fps
0.50 s v < 1.00
1.00 v < 2.00
2.00 s v < 3.00
3.00=_v<4.00 <v
4.00 s v < 5.00
-
5.00 V < 6.00 0 Inflow Node
6.00 v < 7.00 = Property Line
7.00 s v < 9.00 100 -foot Contours
9.00 s v < 12.00 20 -foot Contours
12.00 v < 15.00
15.00 +
1.1
r
=Im
• •
I • •.1.
)
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Figure 5-14. Travertine baseline 1 -percent annual chance maximum velocities (maximum depths > 0.5 feet) with DC1 forced split in effect
Legend
flood velocity (v) in fps
0.50
1.00
2.00
3,00
4.00
v <1.00
< v <2.00
s v < 3 00
s v <4,00
< 5 00
< v
5.00 v < 6.00
6,00 v < 7,00
7.00 sv< 9.00
g 00 s v < 12.00
12.00 s v <15,00
15.00 +
27.
• 111,01j.
0 Inflow Node
= Property Line
100 -foot Contours
20 -foot Contours
DC1
•
MIDDLE
CANYON
0
0 600 1,200
Feet
F.
•
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Figure 5-15. Travertine composite baseline 1 -percent annual chance maximum velocities (maximum depths > 0.5 feet)
Legend
flood velocity (v) in fps 5.00sv<8.00 0 Inflow Node
0 50 Sv<1.0O
F--|100sv<2l0
6.00 v«r.0o ===== Property Line
7.00sv<9.00 100 -foot Contours
200sv< 3.00 8%0sv<12D0 20 -foot Contours
3U0s,<4.00 I I1%.00sv«15.00
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Figure 5-16. Travertine project 1 -percent annual chance maximum velocities (maximum depths > 0.5 feet)
Legend
flood velocity (v) in fps
0.50 v<1.00
1.005v<2.00
5.00 5 v < 6.00 0 Inflow Node
6-00 5 v < 7.00 = Property Line
7.00 5 v < 9.00 100 -foot Contours
2.005v <3.00 _ 9.00 5v< 12-00
Wil 3.005v<4.00 _ 12.005va 15.00
4.005v<5.00 15.00+
20 -foot Contours
Project Grading
t
.411.11"
•
r y
1100
proposed access
culvert crossing
nu-
,_•�u
J �� `i j ••`
•
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Figure 5-17. Travertine project 1 -percent annual chance maximum velocities (maximum depths > 0.5 feet) with DC1 forced split in effect
Legend
flood velocity (v) in fps 5.00 5 v < 6.00 0 Inflow Node
—7
[ 0.50 5 v < 1_00 6_00 5 v < 7.00 . Property Line
j 1.00 5 v <200 7.00 5 v <9.00 100 -foot Contours
T1 2.00 5 v < 3.00 9.00 5 v < 12.00 20 -foot Contours
WW1 3.00 s v 4_00 12.00 5 v < 15.00 Project Grading
ri 4.00 5 v < 5_00 J 15.00 +
DC1
proposed access
culvert crossing
_ 4 orm....A.Apmemorp.iimmi
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Figure 5-18. Travertine composite project 1 -percent annual chance maximum velocities (maximum depths > 0.5 feet)
Legend
flood velocity (v) in fps 5.00 5 v < 6.00 0 Inflow Node
I0.50<v<1.00 6.005v<7.00 = Property Line
1.00 s v < 2.00 7.00 5 v < 9.00 100 -foot Contours
2.00 5 v < 3.00 9.00 5 v < 12.00 20 -foot Contours
3.00 s v < 4.00 12.00 5 v < 15.00 Project Grading
4.00sv<5.00 MI 15.00+
„16a
• :51st. .. ,
IN I
CANYON
;imposed access
culvert crossing
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Figure 5-19. Travertine change in composite 1 -percent annual chance maximum velocities (maximum depths > 0.5 feet) from baseline to project conditions
P
L
Legend
flood velocity (v) in fps [ -0.50 5 v < 0.50 0 Inflow Node
v < -12.00 0.50 5 v 1.00 = Property Line
-12.00 5 v < -9.00 1.00 5 v < 3.00 100 -foot Contours
-9.00 5 v < -7.00 3.00 5 v < 5.00 20 -foot Contours
-7.00 5 v < -5.00 n 5.00 5 v < 7.00 Project Grading
FT -5.005v<-3.00 n 7.005v<9.00
-3.005v<-1.00 9.005v ¢ 11.00
FT -1.005v<-0.50 11.00+
''►� t _fir._ _ :.� �j
CANYON
•
MIDDLE
_. .
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Legend
depth, y (ft)
0 50 5 y < 1 00
1.005y<2.00
2 00 5 y < 3 00
' • .- - • ••••- •L•-• •
Figure 5-20. Dike No. 4 baseline 1 -percent annual chance maximum depths > 0.5 feet
5.00 y < 6.00 0 Inflow Node
6.00 y < 7.00 = Property Line
7.00 y < 9.00
9.00 <y < 12.00
3.00 y < 4.00 I -I 12.00 y < 15.00
4.00 5 y < 5.00 15.00
100 -foot Contours
20 -foot Contours
1179gamai)
Ir.
TORO CANYON AREA
/.021•11
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Figure 5-21. Dike No. 4 project 1 -percent annual chance maximum depths > 0.5 feet
Legend
depth, y (ft) 5.00 s y < 6.00 0 Inflow Node
0.50 s y < 1.00 6.00 s y 7.00 ' Property Line
1.00 s y < 2.00 7.00 s y a 9.00 - 100 -foot Contours
2.00 s y < 3.00 9.00 y < 12.00 20 -foot Contours
. 3.00sy<4.00 n 12.00< y < 15.00 Project Grading
• -4.00sy<5.00®15.00+
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Figure 5-22. Dike No. 4 change in 1 -percent annual chance maximum depths > 0.5 feet from baseline to project conditions
•.-_l - . - e ,.
Legend
depth, y (ft)
y < -26.00
-26-00 5 y < -9.00
- -9-00 5 y < -7.00
-700sy<-5.00
FT -5.00 s y < -3.00
-3.00sy<-1.00
1-1-1.005y<-0.50
-0.505y<0.50 0 Inflow Node
0.50 5 y < 1.00 o Property Line
1.005y=3.00
3.005y<5-00
n 5.00 5 y < 7.00
nToo 5y<9-00
-9.005y<10.00
10.00 +
100 -foot Contours
20 -foot Contours
Avenue
eSZOrITO
1
CANYO
` 1IDDLE
1.�
CANYON
AREA
Avenue
TORO CANYON AREA
w
900 1,800
Feet
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Figure 5-23. Dike No. 4 baseline Standard Project Flood maximum depths > 0.5 feet
Legend
depth, y (ft)
0.50Syc1.00
5.00 s y < 6.00 0 Inflow Node
6.00 5 y a 7.00 = Properly Line
1.00 sy <2.00 TOO 5ya9.00
2.00sy<3.00 9.005ya 12.00
3.00sy<4.00 n 12.005ya15.00
F14.00sy<5.00- 15.00+
100 -foot Contours
20 -foot Contours
1'500 7300
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Figure 5-24. Dike No. 4 project Standard Project Flood maximum depths > 0.5 feet
Legend
depth, y (ft)
0.505y<1,00
1.00<y<2.00
� 7.fly fl
5.00sy<6.00
0 Inflow Node
6.00 s y < 7.00 o Property Line
7.005y<9.00 —
2.00sy<3.00 9.00Sya12.00
3.005y<4.00 n 12.00<y<15.00
TT4.00sy<5.00-15.00+
100 -foot Contours
20 -foot Contours
Project Grading
fr re".
CANYO
MIDDLE
CANYON.
AREA
0421A
04216
TORO CANYON AREA
900 1,800
Feet
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Figure 5-25. Dike No. 4 change in Standard Project Flood maximum depths > 0.5 feet from baseline to project conditions
Legend
depth, y (ft)
y < -26.00
--26.005y<-9.00
--9.005y<-7.00
-7.00 5 y < -5.00
-5.005y<-3.00
-3.005y<-1.00
n-1.005ye-0.50
-0.505y<0.50 0 Inflow Node
0.50 s y < 1.00 o Property Line
1.00 5 y < 3.00 100 -foot Contours
3.005y<5.00
n 5.00sy<7.00
F-1 7.00 5 y < 9.00
-9.00 y<10.00
- 10.00 +
20 -foot Contours
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3S
30
25
1u
15
10
-10
-15
20
-25
-30
-35
Figure 5-26. Comparison of water surface and ground elevation profiles along Dike No. 4
r
1-
i PACE (2005) profiles were converted from 7
r NGVD29 to NAVD88 with an adjustment of
+2.28 feet
_ 1 J
r ---.c-.._.... rt ._...._...,.,
1 1 f
I
L▪ O I
—I
-1-
- --• levee crest {PACE, 2005)
— — — SPF maximum flood stage, project, infil € 2.5 inlh
SPF maximum flood stage, baseline, infil a 2.5101
SPF maximum flood stage {PACE, 2005)
— — — 1%AC maximum flood stage, project
1%AC maximum flood stage, baseline
1%AC maximum flood stage (PACE, 2005)
1f
1
0+00
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50+00 100+00
Dike No. 4 station in feet
150+00 200+00
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Figure 5-27. 1 -percent annual chance water surface profiles adjacent to the North Guadalupe Creek Diversion Dike
top of dike; LUOAR
WSEL baseine
- ---- WSEL project
- ---• baseof dike; LiDAR
4.4
a
x�l
O
•'1
Rr
0_
1 '
3,544
260
250
240
230
220
L
210 o
anan
dJ
240
190
180
170
160
DD0 2,540 2,000 1,540 1,000 540
station in feet
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Figure 5-28. 1 -percent annual chance water surface profiles adjacent to the South Guadalupe Creek Diversion Dike
ti
tin titer- *�
-61
r
0
w
91
oId
7# •• t�
ti�
- tap of dike, LiDAR
WSEL, baseine
- ---- WSEL, project
- ---- base of dike, LiDAR
• N.
ti
0_
f
1,600 1.400 1200 1J1111 800 600 400 200 0
station in feet
210
200
190
180
C
C
0
W
170
160
150
140
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Figure 5-29. 1 -percent annual chance water surface profiles along the centerline of Guadalupe Creek Channel
3,500 3,000 2500 2,000 1,500
station in feet
1,000
500
0
250
240
230
220
210
200
190
180
170
160
150
140
130
120
110
100
el evsti on i n feet
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yy#
Ih4
1
"N.,
I
..3
D
T_11
rson St crossi ng
k
'''r,�
+.
_
WSEL, baseine
WSEL,
project
I
----• ground, LiDAR
'8I
w
0
a_
i7
a
'I
I
I
1
ii
t1
I
4.
3,500 3,000 2500 2,000 1,500
station in feet
1,000
500
0
250
240
230
220
210
200
190
180
170
160
150
140
130
120
110
100
el evsti on i n feet
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Figure 5-30. 1 -percent annual chance flood depths and velocities adjacent to the North Guadalupe Creek Diversion Dike
depth, baseline
- --- depth, project
I/elo[ty, baseline
- ---- VeIOCiy, project
re .1▪ /
t.
I
4
1 1 '\
t x
/ % Ir
i Raj
0. +
x;
.4
+a 111
f r �
J t
1
r{ r
—
4—r
3000 2500 2,000
station in feed
1,500
LAO 500
14
12
10
8
6
4
2
0
depth infeet, vel ocityinft%c
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Figure 5-31. 1 -percent annual chance flood depths and velocities adjacent to the South Guadalupe Creek Diversion Dike
1600
1440
1200
1000
Station in feet
Edd
400
200
0
20
18
16
14
12
10
8
6
4
2
0
depth infee vel in city. inft/sec
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I I I I I I I
depth, baseline
--- -• depth, project
Al
r
I
veloc ky, baseline
i#
o
-----velocLy, proles
i
II
1
tr
'}+r
%
e
i
i
t
}
+# of
i�
0
4.
f'''',....4\#�
{%4
r�
\
�t{\{fix}•
}#
l���\
I
4...
............
••yl
ear
•-.-
•
1600
1440
1200
1000
Station in feet
Edd
400
200
0
20
18
16
14
12
10
8
6
4
2
0
depth infee vel in city. inft/sec
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Figure 5-32. 1 -percent annual chance flood depths and velocities along the centerline of Guadalupe Creek Channel
3,500
3,000
2_,5100
2,000
Station infect
1,500
1,000
500
0
45
40
35
30
25
20
15
10
5
0
depth infee, vel ocityinfVsec
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depth,
baseline
�o-1
ci
-----depth,
project
u
n
cr
sc
r
yeloLOy,
baseline
LJ
r
L
—
I,
-----velocty,
pfelkr:
r —
t
Si
I
15
i —
r
—
IS
I
1_I
—
or_
—
I
—
I
r
i
.--
r
-}
a
•- i.i
1
+ ••�
1-
a �•'S
. •h?
.
,' F
,f
3,500
3,000
2_,5100
2,000
Station infect
1,500
1,000
500
0
45
40
35
30
25
20
15
10
5
0
depth infee, vel ocityinfVsec
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Figure 5-33. Plan view of upper Guadalupe Creek Diversion Dikes
DIKE NO. 4
GUADALUPE CREEK
NORTHERN DIKE
PROPERTY BOUNDARY
13+12.90+ CHANNEL
8.0.W.
f
-1--1 —F-1— -1-1— 1 I 1 I I i---1
..----__A
�
------.4------n O H-
_,
+00 1$+00 16+00 14+00 12+00 10+00 8+00 6+00 4+00 2+52.73
ter`
_� 24x00 X 0x0
x00 I I— 1 + I - i� —1 I 1 I 1— ' �'
/ x 26 1 20+00 8+015+00 14+00 12+00 10+00 8+00 6+00 4+00
2$x00 /�+0p 2 13+14.441
/�,C2"3 �xoa 24 GUADALUPE CHANNEL r� oo �I 12+00 1 10+00 a ioo Ii a 1 4+o rz+a o+oa
2 CREEK CHANNEL 1-
31+79.20
X T.6 13+15.98+ I13+15.98+ CHANNEL SOUTHERN DIKE
CP R.O.W.
,y" t 5+20
30+53.54
250 125
0
250
500
750
SCALE: 1"=250'
PROPERTY BOUNDARY
-0+50.05
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6 COMPARISON TO PREVIOUS STUDIES FOR WEST SIDE DIKE No. 4
6.1 Regional hydrology
The hydrologic models developed as part of this study in support of the flood hazard evaluation
performed for the proposed Travertine Development and effected resource facilities was used to analyzed
the 1 -percent annual chance storm event and SPS/SPF using the framework of the Synthetic Unit
Hydrograph Method prescribed in the Riverside County Hydrology Manual (RCFCWCD, 1978),
accompanied by the following implemented hydrologic processes and parameterization assumptions:
• Watershed delineation. Drainage divides were determined from IFSAR topographic data
(Intermap Technologies, 2005)
• Precipitation. The 1 -percent annual chance storm was represented using the 6 -hour USACE
hypothetical (synthetic) storm based on NOAA Atlas 14 spatial precipitation data; the SPS/SPF
precipitation depth and storm pattern were based on the Indio Storm of September 24, 1939; the
depth -area relationship based on the September 24, 1939 Indio Storm (USACE, 1980) was
applied in the determination of the 1 -percent annual chance flood and SPS/SPF for contributing
drainages in excess of 10 square miles
• Infiltration. Precipitation losses were based on an initial abstraction and constant loss rate, but
excluded the use of a low loss fraction (low loss rate) that is typically applied in Riverside
County, but commonly ignored in the Coachella Valley.
• Unit hydrograph. Runoff response was determined in part using the lag formula developed for
Southern California (RCFCWCD, 1978; USACE, 1962), which involved the following aspects:
1. Topographic -based lag parameters were determined from IFSAR topographic data (Intermap
Technologies, 2005)
2. The basin factor, which has been historically related to hydraulic roughness was estimated
from assumed correlations between hydraulic roughness and identifiable terrain
characteristics (Travertine/developed areas, Mountain and hillslopes, and alluvial/relict
surfaces/piedmont)
3. The Whitewater S -graph (RCFCWCD, 1978; USACE, 1980) was used in conjunction with
the lag to transform the unit hydrograph
Flood hydrographs were produced for the 1 -percent annual chance storm event and Standard Project
Flood at concentration points located at or near canyon outfalls above the Travertine property and along
the base of the dike using HEC -HMS Version 4.2 (USACE, 2016).
6.1.1 Model development comparison — PACE (2005) vs. Travertine
Notable differences related to the hydrologic models developed for Travertine and PACE (2005) are as
follows:
• PACE (2005) developed single -area flood hydrographs (no channel routing); the hydrology
developed for Travertine relied on linked node models segregating major canyon subbasins from
the piedmont drainage
• PACE (2005) globally assigned a lag basin roughness ("n -bar") value of 0.035 to all subbasins;
for Travertine, the computed "n -bar" value for each subbasin, which ranged from 0.030 to 0.045
with an average value of 0.040.
6.1.2 Precipitation comparison — PACE (2005) vs. Travertine
The precipitation data used by PACE (2005) to develop flood hydrographs for the Dike No. 4 watershed
was compared to the precipitation data used to develop the flood hydrographs for Travertine in Table 6-1.
There is very little difference in the parameterization for the SPS/SPF; however, for the 1 -percent annual
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chance storm, PACE (2005) relied on NOAA Atlas 2 (RCFCWCD, 1978; NWS, 1973) frequency -
duration precipitation mapping in conjunction with the Cathedral City precipitation gauge record to
estimate the precipitation depths for the watershed, which were substantially less than what was estimated
from the NOAA Atlas 14 (NWS, 2014) frequency -duration precipitation spatial datasets used for
Travertine. NOAA Atlas 14 was not available until 2006, which followed the completion of the LOMR
for Dike No. 4 (PACE, 2005).
Table 6-1. Precipitation comparison — PACE (2005) vs. Travertine
parameter
PACE
{2005}
Travertine
baseline
project
drainage area
{sq mi}
17 7
_�_ 0_
SPF
P
{inches }
6.45
DAR
Bechtel {1997}
USACE {1980)
0 S2
0.93
pD'
{inches }
529
6.00
store
pattern
September 24, 1939 Indio 6 -hour storm
100 -year
storm
p
{inches }
NA2
{RCFCWCD, 1978)
NA14
{NWS, 2014)
2.91
3.83
DAR
{RCFC\VCD, 1973)
USACE (1930)
0.94
0.93
pc`
{inches}
2.74
3.56
storm
pattern
6 -hour hypothetical
storm based on
Cathedral City gauge
synthetic
6 -hour storm based on
NA14 (\SVS, 2014)
loss rate
{in'h}
0200
0.286
0.278
6.2 Flood conveyance and impoundment
Two-dimensional flood routing model simulations were performed, using FLO-2D PRO, to evaluate the
flood intensities and patterns on the piedmont as well as impoundment of floodwaters along Dike No. 4.
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The baseline and project conditions along Dike No. 4 satisfy the minimum freeboard requirements for the
Standard Project Flood (one foot) and the 1 -percent annual chance flood event (four feet) as stated in
Ordinance 1234.1. No outflow was permitted from the impoundment. Storage loss due to sedimentation
was accounted for by bulking flood hydrographs for 100 percent of the computed debris yield. For the
Standard Project Flood simulations, the Green-Ampt parameters were adjusted to produce an average
infiltration rate over the 24-hour simulation period such that the constant infiltration rate of 2.5 inches per
hour originally assumed by PACE (2005) is not exceeded along the base of Dike No. 4. The resultant
average infiltration rate over the 24-hour simulation period was approximately 2.4 inches per hour for
each set of conditions modeled.
The map of 1 -percent annual chance flood depths is generally consistent with the geomorphic mapping of
active and inactive fan surfaces shown previously in Figure 3-4 and Figure 3-5. Portions of the mapped
active areas did not flood or were limited to very shallow flooding less than 0.5 feet in depth and is of a
non-erosive nature, which is consistent with the geomorphic observations indicating that portions of
active fans have not been exposed to significant flood processes in hundreds of years. Some portions of
the inactive fan below Devil Canyon were subject to overflow; the most impactful "breakout" location
(DC1) was further evaluated by forcing all flows within the active floodplain onto the overflow terrace.
Flood depths and velocities for the baseline and project conditions were determined and mapped to
support site planning and the design of flood conveyances required to provide flood protection for the
planned development. These maps are not intended for regulatory floodplain evaluation.
6.2.1 Flood runoff and debris comparison — PACE (2005) vs. Travertine
The computed runoff volume and debris as determined by PACE (2005) was compared to the computed
runoff volume and debris as determined for Travertine and is presented in Table 6-2.
There is a 2.6 percent increase in the SPS/SPF net bulked volume for the Travertine baseline conditions
relative to the results reported by PACE (2005). There is less than a 0.3 percent increase in the net bulked
volume going from baseline conditions to project conditions.
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Table 6-2. Flood runoff and debris comparison — PACE (2005) vs. Travertine
parameter
PACE
{2005}
Travertine
baseline
project
fire factor
3.0
A -T factor
1.00
0.52
SPF
water volume
{ac -ft}
6.10S
6.087
6,121
debris yield
{ac -ft}
1.060
723
703
delivery efficiency
{%}
50
100
net debris yield
{ac -ft}
530
723
70S
net bulked volume
{ac -ft}
6.63S
6,810
6.829
100 -year
storm
water volume
{ac -ft}
1.639
3.009
3,020
debris yield
{ac -ft}
509
710
698
delivery efficiency
{%}
100
net debris yield
{ac -ft}
509
-10
698
net bulked volume
{ac -ft}
2.15S
3,719
3,71S
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6.2.2 Flood stage comparison
The results of the storage analysis performed by PACE (2005) were compared to the results of a similar
analysis conducted for Travertine, as shown in Table 6-3. For Travertine, a two-dimensional flood routing
model was used to analyze the impoundment of floodwaters along Dike No. 4. This scheme captures the
effects related to the unbalanced delivery of floodwaters to the base of Dike No.4, resulting in a variable
maximum water surface profile along the dike; PACE (2005), on the other hand, previously evaluated the
flood storage along Dike No. 4 based on a level -pool analysis, which produces a single maximum water
surface elevation for the entire length of the dike.
Table 6-3. Dike No. 4 flood stage comparison — PACE (2005) vs. Travertine
parameter
?AC?
; , : ,
Travertinr
baseline
project
levee crest
{feet}
2-.2S
S?:
infiltration
{in h}
2.4
maximum \VSEL
{feet}
, _ S
23.55
24.13
average \VSEL
{feet}
22.fS
23.49
23.S2
min. freeboard
{feet}
-•
3.15
100 -year
storm
infiltration
{in h}
0.0
maximum R -SEL
{feet}
:S
: S
15.53
average \VSEL
{feet}
'.15
1_.1:
15.47
min. freeboard
{feet}
:S : .
Note: all elevations based on NA\DSS
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7 FLOOD HAZARD IMPACTS AND MITIGATION
7.1 General
This chapter includes a summary of the impacts associated with the planned project and a discussion of
the mitigation measures proposed to address the project impacts and provide flood risk management to
protect the project improvements. A detailed flood hazard assessment has been prepared to identify the
expected flood hazards at the project site and affected vicinity (adjacent properties and regional facilities),
resulting from the 100 -year and SPF storm events. The geomorphic conditions, expected flow rates,
depths, and velocities for the assessment of the Project impacts have been identified in the previous
chapters. The purpose of this chapter is to identify and discuss the project impacts and develop the
necessary mitigation measures and conceptual flood protection systems for the Project to convey the
floodwaters around the site and avoid significant flood hazard impacts to adjacent properties and
downstream facilities.
The Specific Plan Area is located on one of the eastern piedmonts along the base of the Santa Rosa
Mountains, above the flood impoundment zone of West Side System Dike No. 4 (BOR, 1947; Bechtel,
1991), and adjacent to the Guadalupe Creek Diversion Dikes (CVCWD, 1968; Bechtel, 1991) to the
north. The piedmont bajada on which the site is located is composed of moderately steep -sloped relict
(inactive) and active alluvial fans. These site conditions and existing flood control infrastructure are key
considerations used in the development of the drainage master plan.
7.2 Flood Hazard Mitigation Plan
7.2.1 Alluvial Fan Flood Protection Measures
Three general approaches are typically used for flood management on an alluvial fan. These approaches
are:
1. Whole Fan Protection
2. Subdivision or Localized Protection
3. Single Lot/Structure Protection
Whole fan protection would generally be considered as a regional flood protection system undertaken by
a government agency or collection of landowners. Whole fan protection can be achieved through the use
of levees, channels, detention basins and/or dams. This method includes large-scale structural measures
appropriate to use on extensively developed fans and are more cost-effective in high-density situations.
Structures must be designed to intercept watershed flow and debris at the apex and transport the flow
around the entire urbanized fan. These structures are most often financed through federal or state sources,
but can also be financed through special regional districts, local governments, or developers.
Subdivision or localized protection can be provided to protect projects in the absence of whole fan
protection. These measures may include; local dikes, conveyance channels/swales, site plans to convey
flow, streets design to convey flow, or elevation on armored fill. These are smaller scale measures that
can be used for moderate density development on alluvial fans and are designed to convey water and
debris around or through the individual development.
Single lot or structure protection measures are for protection of isolated lots or structures. These
measures may include elevated or properly designed foundations, or floodwalls and berms. The measures
are most effective when used for low-density developments.
The Project is located on active and inactive alluvial fan surfaces, and subject to the requirements to
convey offsite flow through or around the site development. Therefore, alluvial fan flood protection
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measures need to be incorporated into the project to convey the anticipated flood flows, and prevent
adverse floodplain impacts to adjacent properties and downstream facilities.
Since the development area of the project is only a portion of the piedmont bajada of active and inactive
alluvial fans, localized subdivision protection is proposed to protect the project in the absence of any
whole fan protection system. Mitigation measures for the site development will also be identified to
address any project related impacts on the existing flood protection systems including the West Side Dike
System No. 4, and the Guadalupe Creek Diversion Dikes.
7.2.2 Flood Protection System Selection
The Travertine project is the only currently planned development upstream of the West Side Dike No. 4.
Currently, no whole fan (regional) flood protection systems exist in this area. The Project is an isolated
development on the piedmont bajada, therefore, a regional flood protection system of improvements from
the fan apex to the base of the dike would not be practical or appropriate as it would result in greater
environmental impacts. Single lot or structure protection is also not appropriate due to the size of the
planned development. As such, subdivision or localized protection is necessary for the Project, which
includes collection, conveyance, and redistribution of flood flows.
Physical and legal constraints also govern the types of flood protection measures that can be used for the
site development. The Project site is located along a poorly defined drainage corridor near the outlet of
the Devil, Middle (North and South), and Rock Avalanche Canyons, and conveys runoff from the
canyons through the project site to Dike No. 4. The Project is bounded by the Guadalupe Creek
Diversion Dike No. 2 to the north, and the CVWD Infiltration Ponds and Dike No. 4 to the east. The west
and south sides of the project are subject to active and inactive alluvial fan flows. Based on the available
tools and project constraints, the proposed regional flood protection measures include a combination of
perimeter embankments and drainage swales along the west and south site development boundaries, and
improvements to the Guadalupe Creek Diversion Dikes on the north side. The on-site plan will be
designed to capture and convey on-site runoff and discharge to water quality treatment facilities prior to
releasing upstream of Dike No. 4.
7.2.3 Conceptual Flood Protection System
A conceptual flood protection system has been identified and incorporated into the proposed Travertine
site plan to intercept flood waters along the west and south boundary and convey the floodwaters around
the site development area. The Project proposes to use a protected embankment, elevated fill, and a
graded swale along the west boundary to collect and convey the unconfined alluvial fan flows (Devil and
the small un -named canyon) to the north side of the site and into the Guadalupe Creek Diversion Dikes.
The dikes are proposed to be improved to accommodate the design flows rates and upgraded to meet
Federal requirements for a levee system. It is not anticipated that the existing Guadalupe Creek Diversion
Dikes would meet Federal criteria for an accredited levee system.
The runoff from the Middle North and South, and Rock Avalanche Canyons would be intercepted along
the south edge of the planned development. A protected embankment and elevated fill would be used to
convey flows easterly along the south boundary to Dike No. 4.
The Conceptual drainage plan for the Travertine development ensures that all residents of the community,
as well as downstream facilities and properties, will be protected from periodic flooding that is
experienced in the region. Figures 5-8 (composite 1 -percent annual chance event maximum depth) and 5-
15 (composite 1 -percent annual chance event maximum velocities) depicted the existing flow conditions
that come on to the project site and were used for the conceptual design of the flood protection system.
The Project site plan with the proposed flood protection system is shown on Figure 7-1, Flood Protection
Plan. Typical sections along the perimeter facilities are shown in Figures 7-2 and 7-3.
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Figure 7-1. Flood protection plan
Guadalupe Dike !6
va North Bank `-' ti
p s 1Guadalupe Dike South Bank
z
Diversion Dike
Road/Bridge
Crossing
West Edge
Protection
Travertine
Boundary
AVE 60
'10
South Edge
Protection
Road/Bridge
Crossing
Dike#4
Road/Bridge
Crossing
62
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1
2
Figure 7-2. Flood conveyance typical sections- Guadalupe Diversion Dike
20'
4
/
Varies Below Invert
Bank Protection (4') Freeboard
Existing WSE ((boo) L
Bank Protection —\
Existing
--
mayi \alis 741111D1 ID Ir
L�I _J1
Scour W742
'IIII„„\\`` 1
1
4 14 14
NATURAL LEVEE NATURAL
North Levee
1r
1
Guadalupe Dike
SECTION A -A
SLOPE
9141 lli%li. —
Varies Below Invert
4
South Levee
PAD
m.
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Figure 7-3. Flood conveyance typical sections- West and South banks
Existing
Freeboard + Wave Runup
WSE (Ouo► \‘
Sedimentation
Scour Depth
Varies
NATURAL
Vanes Below Innen
SLOPE
PAD
West Edge
SECTION B -B
Bank Protection
2 Existing —\
Vanes Below Invert J
SLOPE 'I"PAD
(3' min) Freeboard
404/11KMp/n %NV
WSE (0u0)
Scour
PAD
SLOPE
South Edge
SECTION C -C
NATURAL
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7.3 Project Impacts
7.3.1 West Side Dike No. 4
The proposed project will have little to no impact on the runoff volumes generated from the watershed
tributary to the Dike No. 4. Table 6-2 provides a summary of the net bulked runoff volume tributary to
Dike No. 4. The net bulked volume for the 1 -percent annual chance event is effectively the same in the
existing and project conditions. The increase in clear -water runoff volume associated with the site
development is effectively neutralized by the resultant reduction in sediment yield associated with the
development. Therefore, the net bulked volume is essentially the same at 3,718 acre-feet. During an SPF
event, the net bulked runoff volume is increased from 6,810 acre-feet to 6,829 acre-feet in the project
condition. This is an increase of only 0.3%.
The project will include the extension of Avenue 62 and Madison Street over Dike No. 4, and a minor re-
direction of flow from the unnamed canyon (Node 422) to the Guadalupe Dikes. These project elements
will have a minor impact on the maximum flood stage profile along the Dike. The results of the flood
routing analysis and potential impacts are summarized in Table 6-3. In the SPF event, the maximum
water surface depth is increased from 23.55 feet to 24.13 feet in the project condition. During the 1 -
percent annual chance event, the maximum water surface depth increases from 15.18 to 15.53 feet,
resulting in a minimum freeboard of 11.75 feet. The increased depth still provides for a minimum
freeboard of 3.15 feet which far exceeds the prior criteria of one foot adopted by CVWD for the SPF
event, and the 1 -percent annual chance event freeboard of 11.75 feet also far exceeds to current standard
of 4 -feet. In addition, the flood routing analysis was prepared using the total runoff volume from the
existing and project conditions. The onsite improvements will include storm water retention and
infiltration to meet the water quality requirements. This storage volume will reduce the runoff volume
generated in the project condition and mitigate some of the impact to the water surface profile. The
remaining impact is not significant in terms of the function and operation of the Dike No. 4.
The final design of the Avenue 62 and the Madison Street crossings of the dike shall be evaluated to
ensure that a significant change in the water surface profile along the dike does not occur. The final
design shall also review the geotechnical analyses used to certify the dike to ensure that the change in
water surface elevation does not adversely impact the stability or seepage analyses.
7.3.2 Guadalupe Creek Diversion Dikes
The Guadalupe dikes were constructed in 1968. No documentation for the design was available,
however, it is reasonable to assume that the facility was designed to handle the total flow from the Devil
Canyon watershed. The construction of the proposed project will also result in additional flow from the
unnamed canyon being diverted to the Guadalupe dikes. The 1 -percent annual chance peak flow rate
(bulked) to the dike from Devil Canyon was determined to be 12,615 cfs at node J41 (Table 4-13). With
the proposed improvements, the total peak flow rate (bulked) tributary to the dike was determined from
the flood routing analysis to be 13,196 cfs. This is an increase of less than 5 percent. The resultant
change in the water surface profile, flood depths, and flow velocities are shown on Figures 5-24 through
5-30. The impacts to the dike are generally located downstream of the proposed Jefferson Road crossing,
where the flow diversion occurs. Above this location, the flow depths and velocities along the northern
dike are similar between the existing and project conditions.
The Guadalupe Creek Diversion Dikes downstream of the diversion are proposed to be improved as a part
of the project. This will mitigate any adverse impacts to the dikes associated with the project. The dikes
will be designed to convey the new flow rates with the freeboard and scour protection as required by
CVWD, and in accordance with Federal standards for levee certification.
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7.3.3 California Drainage Law
California Drainage Law states that property owners have the right to protect themselves from flooding as
long as they do not unreasonably increase flood risk for adjacent property owners. To accomplish this,
CVWD has identified that flows must be reasonably received and released in the historical flow paths at
the historical flow depths and velocities (CVWD, 2020).
The 2-dimensional hydraulic analysis completed for the project was used to evaluate the drainage impacts
to the adjacent parcels. An impact analysis of the 1 -percent annual chance storm event was prepared
using the results of the hydraulic modeling. The baseline (pre -project) flooding depths and velocities
were compared with the project conditions to identify the change in flow depth and velocities as a result
of the proposed improvements. The project impacts are illustrated on Figures 5-12 (depth) and 5-19
(velocity).
The primary impacts from the project are on the adjacent parcels owned by the United States Bureau of
Land Management (BLM) along the West Bank, and the United States Bureau of Reclamation (BoR)
lands along the Guadalupe Dike and Dike No. 4. The project team is in discussions with both agencies to
permit the proposed improvements and associated drainage impacts on the governmental lands. Minor
impacts were also identified to a few parcels along the eastern property line south of 62 Avenue. These
impacts include a minor increase in the flow depths and velocities. The majority of the properties along
the eastern property line will see a significant reduction in the potential flood hazard as a result of the
project. These include parcels owned by CVWD, BoR, and a private property owner.
The final impacts will be identified and coordinated with the property owners during the Final Map
stages.
7.4 Design Requirements
The conceptual design and layout for the proposed flood protection for the project has been developed
and evaluated as a part of this master plan. More detailed engineering and design, consistent with design
standards established by the City and the Coachella Valley Water District, will be completed at the Final
Map stages of development, resulting in the precise location, alignment, and sizing of all regional
drainage facilities. The objectives for the flood control and drainage facilities throughout the Travertine
properties are:
• Protect all buildings from damage from the 100 -year storm in any of the drainage areas that cross
or are within the property.
• Safely discharge all flows leaving the property.
• Control and manage runoff and sediment flow around the site.
• Mitigate adverse impacts to existing facilities.
• Assure the reliable operation of each drainage feature through a full range of flow events.
• Where levees, channels, bridge, or embankments are used, provide adequate freeboard and scour.
• Assure that embankment, levee, and channel lining or stabilization is used to control scouring of
channel side slopes or inverts.
The following summarizes the requirements and criteria to be evaluated as a part of the more detailed
facility design. The Regional Drainage System is assumed to include the West and South Bank
Protection, Guadalupe Creek Diversion Dikes, and the Jefferson, Avenue 62 and Madison Street Bridge
crossings.
Regional Drainage System Design Requirements:
1. All facilities shall be designed in accordance with the latest version of the CVWD Development
Design Manual.
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2. The regional hydrology analysis identified in Chapter 4 — Regional Hydrology of this report is
acceptable for use in the final design. Regional facilities shall be designed using the bulked 1 -
percent annual chance event.
3. Updated hydraulic analyses utilizing a refined grid -cell size and detailed topography, grading and
facility alignments shall be prepared to determine design water surface elevations and flow
velocities along the perimeter flood barriers and Guadalupe Diversion Dikes.
4. Evaluate flow depths and velocities on a reach by reach basis to determine: a) water surface
elevations, b) freeboard requirements, c) lining requirements in terms of materials and lining
thickness, d) scour depths, e) potential for deposition of sediments, and f) the need for channel
stabilization to control degradation or bed incision.
5. Adjust flood protection system configuration (in terms of barrier and levee heights/scour depths
and bridge crossing configurations) based on the refined hydraulic analysis. Determine the
optimum configuration of channels, barriers, and levees with necessary containment and erosion
control structures which will provide the 100 -year flood protection.
6. Bridges at the Jefferson Road crossing of the Guadalupe Dike and the Avenue 62 and Madison
Street crossings of Dike No. 4 shall be designed in accordance with the scour requirements in
Section K-3.11 of the Development Design Manual.
7. Prepare detailed designs and specifications for facilities including levee improvements, erosion
protection (natural appearing where possible), and channel stabilization structures for the required
facilities.
8. Prepare an Operations and Maintenance (O&M) plan for the regional flood protection system
facilities in conformance to the requirements in Section 8, Design Criteria Stormwater Facility of
the Development Design Manual.
9. Obtain a Conditional Letter of Map Revision (CLOMR) from the FEMA for the areas of the site
within the mapped floodplain areas prior to the start of grading operations. Obtain a Letter of
Map Revision (LOMR) to remove the areas of the site within the Special Flood Hazard Areas
(SFHA) prior to occupancy.
Consideration of re -naturalization, preservation of natural features, and reduction of visual impacts will
be made during the various stages of the final design. In addition, all drainage facilities for on-site
drainage will be designed following the same process.
The following sections provide additional details and information for the design of the individual regional
and local drainage facilities.
7.4.1 West and South Bank Protection
The west and south banks are subject to active and inactive alluvial fan flows. The volume and peak flow
rates tributary to these boundaries have been determined as a part of the hydrology and hydraulic analysis
completed for this master plan. The worst-case scenarios along these edges are shown on Figure 5-8 and
Figure 5-15. The final design should consider the use of a more detailed flood routing analysis using a
refined grid -cell size, and the latest topographic mapping and grading plans
The West Bank is subject to direct impingement flows as a result of the unpredictable flow patterns on the
active alluvial fan. The scour analysis for the determination of the scour protection limits shall consider
direct impingement in addition to general scour associated with flows parallel to the embankment fill.
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The location and orientation of the West Bank may also result in the deposition of sediment along the
bank during certain flow events. The determination of the top of lining or embankment fill height shall
consider the potential for sediment deposition and wave runup. Flows from D423 are currently shown to
have 2 flow paths on the alluvial fan. Future design studies shall consider the potential for flows to
concentrate into only one of the two shown flowpaths and its impact on the design of the West Bank.
The South Bank is subject to flows from the Middle Canyons and Rock Avalanche Canyon. The bank is
proposed to be roughly parallel to the direction of flow and should be designed as a standard channel
bank. The top of bank shall provide a minimum of 3 feet of freeboard above the 1 -percent annual chance
storm event flow depths or water surface profile. The final grading for the South Bank shall be reviewed
with CVWD to ensure that the bank is considered an incised channel and not a levee. Scour shall be
determined in accordance with Guideline K-3. Flow from D421A may have the potential to impact the
South Bank further west than shown in the current analysis. The final design of the South Bank shall
consider this potential migration west of flood flows and the impact on the final design. Similar to the
West Bank design, flows from D423 are currently shown to have 2 flow paths on the alluvial fan. Future
design studies for the South Bank shall consider the potential for flows to concentrate into only one of the
two shown flowpaths.
7.4.2 Guadalupe Creek Diversion Dikes
The final design for the dikes shall include more detailed 1D and 2D hydraulic models prepared in
conjunction with the design of the adjacent embankment fill and Jefferson Road bridge crossing. The
models should be prepared using a refined grid -cell size and the latest topographic mapping and detailed
plans
The north and south Guadalupe Creek Diversion dikes shall be designed to meet FEMA requirements as
stipulated in Title 44, Code of Federal Regulations, Chapter 1, Section 65.10 (44CFR65.10) and all
current engineering manuals and engineering technical letters of the USACE related to levee design and
construction that are referred to in the Federal Code. Ownership and maintenance of the levees is a
CVWD responsibility. The engineer shall consult with CVWD prior to preparation of the final design
and technical studies.
7.4.3 Jefferson Road, Avenue 62, and Madison Street Bridge Crossings
The Jefferson Road, Avenue 62, and Madison Street roadway extensions into the project site will require
crossings of the Guadalupe Creek Diversion Dikes and Dike No. 4. The conceptual design for these
crossings include the use of multiple arch bridges. The bridge configuration and sizing shall be
determined during the final design and incorporated into the hydraulic models. The final design shall
address freeboard and scour calculations as well as impacts to the dikes based on the updated hydraulic
modeling.
The Avenue 62 and Madison Street crossings have the potential to impact the exiting CVWD recharge
ponds directly adjacent to the crossings. The final design shall include a detailed analysis of the impacts
to the ponds and identify any adverse impacts and mitigation measures.
7.4.4 On -Site Drainage and Storm Water Retention
The onsite drainage system is designed to capture, convey, and mitigate storm water runoff from within
the site development. The system is designed to provide protection for the 1-perecent annual chance
event through a combination of street flow and a storm drain pipe system. All runoff shall receive water
quality treatment in accordance with the City ordinance and MS -4 permit requirements. Two onsite storm
water detention basins are designed to reduce the project condition peak runoff flow rates prior to being
released to Dike #4. The basins will also provide dead storage to retain and infiltrate the required
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stormwater quality volume. The onsite drainage system of storm drain pipes and basins is illustrated on
Figure 7-4.
The onsite analysis is provided in the report titled, Travertine Project, Preliminary Hydrology Study,
Tentative Tract Map 37387, prepared by Proactive Engineering Consultants, Inc., dated October 12, 2020.
7.4.5 Operations and Maintenance Plan
In general, the ownership and maintenance of the flood control facilities is proposed to be split between
the development association and CVWD. The West and South Bank protection system along with the on-
site drainage system and detention basins would be maintained by the development association. The
improvements to the Guadalupe Creek Diversion Dikes and the existing Dike #4 would continue to be
maintained by CVWD.
Sediment is anticipated to deposited along the West Bank of the project site as a result of the potential 90 -
degree change in flow path direction. It is anticipated that the O&M plan will include provisions to
monitor and remove sediment along the West Bank to maintain the required conveyance and freeboard
conditions. Other aspects of the bank maintenance shall be identified based on the final design
configuration of the systems. A Flood Control Facilities Operations and Maintenance Manual for the
proposed improvements shall be prepared and submitted to CVWD for review and approval. The manual
shall meet the requirements of Section 5.8.9 of the Development Design Manual.
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Travertine Development
Drainage Master Plan
z>.
Figure 7-4. Onsite drainage plan
7
Storm Water
Detention Basins
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/ 4
Storm Drain Systems
Water Quality Basins
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Q3 Consulting
Travertine Development
Drainage Master Plan
8 REFERENCES
CVCWD, 1968, Guadalupe Creek Diversion Dikes Plan and Profiles, as -built drawing, Coachella Valley
County Water District, All-American Canal System — California, Boulder Canyon Project,
Bureau of Reclamation, U.S. Dept. of the Interior, Denver, Colorado, June 24.
CVWD, 2020, Development Design Manual, Coachella Valley Water District (CVWD), Coachella,
California, last revised February 3.
FLO-2D, Inc. 2013. FLO-2D PRO Computer Program, Nutrioso, AZ.
NOAA, 2012, NOAA Atlas 14 Precipitation -Frequency Atlas of the United States, Volume 6: California,
Version 2, National Oceanic and Atmospheric Administration, U.S. Department of Commerce,
Silver Springs, MD, June.
NRCS, 2008a, Soil Survey Geographic (SSURGO) Database for Riverside County, Coachella Valley
Area, California, CA680, Natural Resources Conservation Service, Fort Worth, Texas.
NRCS, 2008b, Soil Survey Geographic (SSURGO) Database for Riverside County, San Bernardino
National Forest, California, CA777, Natural Resources Conservation Service, Fort Worth, Texas.
NRCS, 2006, Soil Survey Geographic (SSURGO) Digital General Soil Map of United States, Natural
Resources Conservation Service, Fort Worth, Texas.
NRCS, 2004, National Engineering Handbook, Part 630 — Hydrology, Chapter 9 — Hydrologic Soil -
Cover Complexes, Natural Resources Conservation Service (NRCS), U.S. Dept. of Agriculture,
Washington D.C.
NHC, 2014, North Cathedral City and Thousand Palms Stormwater Management Plan, Morongo Wash
Watershed Hydrology and Hydraulics, prepared for the Coachella Valley Water District, Palm
Desert, CA, April 25.
PACE, 2005, FEMA Application for Physical Map Revision, The Enclave at La Quinta — Dike No. 4,
prepared for the Enclave at La Quinta, LLC, April.
Proactive Engineering Consultants, Inc., 2020, Travertine Project, Preliminary Hydrology Study,
Tentative Tract Map 37387, prepared by Proactive Engineering Consultants, Inc., October 12.
RCFCWCD, 1978, Hydrology Manual, Riverside County Flood Control and Water Conservation District
(RCFCWCD), Riverside County, April.
USACE, 2017, Hydrologic Modeling System (HEC -HMS), Version 4.2.1, Hydrologic Engineering Center,
Institute for Water Resources, U.S. Army Corps of Engineers, Davis, CA, March.
USACE, 2010, River Analysis System (HEC -RAS), Version 4.1.0, Hydrologic Engineer Center, U.S.
Army Corps of Engineers, Davis, CA, January.
USACE, 1994, Flood-RunoffAnalysis, EM 1110-2-1417, U.S. Army Corps of Engineers (USACE),
Washington D.C., August 31.
USACE, 1980, Whitewater River Basin Feasibility Report for Flood Control and Allied Purposes, San
Bernardino and Riverside Counties, California, Appendix 1 — Hydrology, U.S. Army Corps of
Engineers, May.
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Drainage Master Plan
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