North Cathedral City and Thousand Palms Stormwater Management Plan Morongo Wash and Thousand Palms Watersheds Alternatives Analysis Report
September 30, 2013
DRAFT
North Cathedral City and Thousand Palms Stormwater Management Plan Thousand Palms and Morongo Wash Watersheds Alternatives Analysis Report
September 30, 2013
Prepared for:
Coachella Valley Water District Palm Desert Operations 75 – 525 Hovley Lane East Palm Desert, CA 92211
Contact: Tesfaye Demissie, P.E.
DRAFT
Prepared by:
northwest hydraulic consultants 3950 Industrial Blvd, #100c West Sacramento, California 95691 Phone: 916.371.7400
Contact: Ken Rood
File 500058
Report Prepared by:
______
Brady McDaniel, PE, Project Engineer
______
Andrey Shvidchenko, Project Hydraulic Modeler
______
Ken Rood, Principal-in-Charge
DISCLAIMER
This document has been prepared by Northwest Hydraulic Consultants, Inc in accordance with generally accepted engineering practices and is intended for the exclusive use and benefit of the Coachella Valley Water District and their authorizedDRAFT representatives for specific application to stormwater management in North Cathedral City and Thousand Palms, CA. The contents of this document are not to be relied upon or used, in whole or in part, by or for the benefit of others without specific written authorization from Northwest Hydraulic Consultants, Inc. No other warranty, expressed or implied, is made.
Northwest Hydraulic Consultants, Inc and its officers, directors, employees, and agents assume no responsibility for the reliance upon this document or any of its contents by any parties other than the client for whom the document was prepared.
EXECUTIVE SUMMARY
Coachella Valley Water District (CVWD) issued a task order to Northwest Hydraulic Consultant (NHC) to develop a regional stormwater master plan for North Cathedral City and the community of Thousand Palms. Earlier studies by NHC examined hazards in North Cathedral City and Thousand Palms from floods from Morongo Wash, Long and Wide Canyons and from Willow Hole (referred to as the “riverine flows”) and evaluated the hazard reduction benefits of CVWD’s Thousand Palms Flood Control Project. The general conclusion of the earlier studies was that stormwater management in the North Cathedral and Thousand Palms planning units required an integrated approach that addressed all the sources of flooding in order to have appreciable benefits.
The objective of this report was to develop concept-level details and costs for three stormwater management alternatives for North Cathedral City and Thousand Palms and evaluate their benefits in reducing areas of flooding and peak flows. The Thousand Palms FCP is the only alternative that CVWD is considering to manage 100-year floods from the Thousand Palms Watershed. As a result, the alternatives developed in this report all included the Thousand Palms FCP as one component of the design and cost.
The alternatives evaluated in the report were:
• Alternative 1: Thousand Palms FCP and a flood channel to convey flows from the I-10 culverts beneath the SPRR and to the Whitewater River Stormwater Channel (WWRSC); • Alternative 2: Thousand Palms FCP and a flood channel that collected 100-year floods from Morongo Wash fan and Willow Hole and conveyed them to the Sun City Palm Desert flood channels; and • Alternative 3: Thousand Palms FCP and a new bridge beneath I-10 to convey the 100-year flood from Morongo Wash fan to the WWRSC.
Alternative 1 reduced the area of inundation in the two planning units from the 100-year riverine flood by about 1,900 acres and also reduced peak flows crossing properties along the corridor, at a cost of about $98 million. Alternative 2 eliminated about 6,500 acres of flooding in the planning units from the riverine flows; costs ranged fromDRAFT $305 to $350 million, depending on the alignment of the flood channel. Alternative 3 reduced the area of flooding by 5,000 acres and greatly reduced peak flows crossing properties near I-10, at a cost of about $120 million.
North Cathedral/Thousand Palms SMP i September 30, 2013 Alternatives Analysis
TABLE OF CONTENTS
List of Tables ...... iii List of Figures ...... iii List of Appendices ...... iii
1. INTRODUCTION ...... 1 1.1 Background ...... 1 1.2 Development of Alternatives ...... 4 1.3 Objectives and Approach ...... 4 1.4 Sources of Information ...... 5 1.5 Report Organization ...... 5
2. BACKGROUND ...... 6 2.1 Study Area ...... 6 2.2 Flood Control Structures ...... 6 2.3 Hydrology ...... 8 2.4 Hydraulic Modeling ...... 8
3. DESCRIPTION OF THE ALTERNATIVES ...... 9 3.1 Introduction ...... 9 3.2 Alternative 1: Flood channel and Thousand Palms FCP ...... 9 3.2.1 General Features ...... 9 3.2.2 Design Hydrology ...... 9 3.2.3 Hydraulic Performance ...... 11 3.2.4 Future Modifications ...... 11 3.2.5 Concept Level Costs ...... 11 3.3 Alternative 2: Conveyance to SCPD and Thousand Palms FCP ...... 11 3.3.1 General Features ...... 11 3.3.2 Design Hydrology ...... DRAFT 13 3.3.3 Hydraulic Analysis ...... 14 3.3.4 Future Modifications ...... 14 3.3.5 Costs ...... 14 3.4 Alternative 3: New I-10 Bridge and Thousand Palms FCP...... 14 3.4.1 General Features ...... 14 3.4.2 Design Hydrology ...... 16 3.4.3 Hydraulic Analysis ...... 16 3.4.4 Future Modifications ...... 17 3.4.5 Costs ...... 17
North Cathedral/Thousand Palms SMP ii September 30, 2013 Alternatives Analysis
4. FLOOD HAZARDS WITH THE ALTERNATIVES...... 17 4.1 Introduction ...... 17 4.3 Areas of Inundation ...... 24 4.2 Peak Flows ...... 24 4.4 Discussion by Alternative ...... 25 Alternative 1: Flood control channel through SPRR Bridge ...... 25 Alternative 2: Flood channel to Sun City Palm Desert ...... 26 Alternative 3: New Bridge at Willow Wash ...... 26
5. SUMMARY AND CONCLUSIONS ...... 26
6. REFERENCES ...... 29
List of Tables
Table 2-1: 100-Year Whole Basin Centering Peak Flows (NHC 2013a) Table 2-2: Hydraulic Model Parameters Table 4-1: Areas of Flooding Along I-10 Simulated by MIKE FLOOD Table 4-2: Maximum Depths of Flooding Along I-10 Simulated by MIKE FLOOD Table 4-3: 100-Year Peak Flows Along I-10 Simulated by MIKE FLOOD Table 5-1: Costs and Benefits for the Three Alternatives List of Figures
Figure 1-1: CVWD Watersheds Figure 1-2: The Thousand Palms Flood Control Project Figure 2-1: Study Area Figure 3-1: Alternative 1 Layout Figure 3-2: Alternative 2 Layout Figure 3-3: Alternative 3 Layout Figure 4-1: 100-Year Maximum Depths for Alternative 1 Figure 4-2: 100-Year MaximumDRAFT Depths for Alternative 2 Figure 4-3: 100-Year Maximum Depths for Alternative 3 List of Appendices
Appendix A: Alternative 1 Hydraulic Analysis Appendix B: Alternative 2 Hydraulic Analysis Appendix C: Alternative 3 Hydraulic Analysis Appendix D: Preliminary Cost Estimates
North Cathedral/Thousand Palms SMP iii September 30, 2013 Alternatives Analysis
1. INTRODUCTION 1.1 Background
Coachella Valley Water District (CVWD) is responsible for regional stormwater planning and development of regional facilities within their Stormwater Unit. CVWD is now focusing on developing alternatives for stormwater management in the North Cathedral City and Thousand Palms planning units. The North Cathedral City planning unit is the portion of the North Cathedral City Watershed (Figure 1-1) that lies within the CVWD Stormwater Unit. It is on the north side of the Coachella Valley, mostly north of Interstate 10 (I-10). The North Cathedral Watershed consists of Morongo Wash, Long and Wide Canyons and Willow Hole subwatersheds. Similarly, the Thousand Palms planning unit is the portion of the Thousand Palms Watershed that lies within the stormwater boundary. The Thousand Palms Watershed consists of Thousand Palms Canyon and the small washes and canyons that flow from the Indio Hills.
Northwest Hydraulic Consultants (NHC 2013a) previously prepared the “Morongo Wash Watershed Existing Conditions Report” for CVWD. This report updated the 100-year hydrology in the Morongo Wash Watershed and developed a hydraulic model that determined areas of inundation and peak flows along the bottom of the Coachella Valley in the North Cathedral City and Thousand Palms planning units. The study area for the analysis extended from about Palm Drive southeast along the I-10 corridor to Adams Street. These flows are referred to by CVWD as “riverine flows”.
In North Cathedral City, the 100-year riverine flows would inundate a corridor about 5,000 feet wide, from Morongo Wash to about the community of Thousand Palms, roughly centered on I-10. Downstream of Thousand Palms, flooding is mostly north of I-10 and the riverine flows are directed towards Sun City Palm Desert (SCPD). Depths of inundation range from less than 1 to more than 10 feet.
Recently, NHC (2013b) prepared a second report for CVWD titled “Thousand Palms Watershed and the Thousand Palms Flood Control Project”. The Thousand Palms Flood Control Project (FCP) was developed by the US Army Corps of Engineers (USACE) to protect this planning unit from 100-year floods from small canyons and washes in the Indio Hills and from Thousand Palms Canyon. It has now been taken over by CVWD. The FCP consistsDRAFT of levees and channels on the fan surfaces north of Thousand Palms that collect flows from the washes and canyons and direct them through the existing flood channels in the Classic Club Golf Course (CCGC), into a proposed channel, and then into the southern entrance to the Sun City Palm Desert (SCPD) flood channels (Figure 1-2).
The Thousand Palms report (NHC 2103b) updated the original hydrology and hydraulics for the Thousand Palms FCP and evaluated the flood reduction benefits in the Thousand Palms planning unit of the project. The benefits were identified by combining the area inundated by the 100-year riverine flows with the area inundated uphill from the Thousand Palms FCP. This showed that the Thousand Palms FCP would only remove about 3 or 4 square miles from the fan hazard zone, mostly north of Ramon Road near the community of Thousand Palms.
North Cathedral/Thousand Palms SMP 1 September 30, 2013 Alternatives Analysis DRAFT
Figure 1-1 CVWD Watersheds, North Cathedral/Thousand Palms Stormwater Plan
North Cathedral/Thousand Palms Stormwater Plan
CP9 Figure 1-2 CP13 Thousand Palms Flood Control Project CP8 Scale - 1:48,000 1 inch = 4,000 feet CP10 0 2,000 4,000 8,000 Feet © CA State Plane, Zone VI horz. datum: NAD 83 horz. units: feet CP11 northwest hydraulic consultants project no. 500058 September 2013 Reference Map CP14
CP12
CP15 CP21 Reach 1 Levee
Reach 2 Levee Sources: Esri, DeLorme, NAVTEQ, USGS, Intermap, iPC, NRCAN, Esri Japan, METI, Esri Francis Way Channel Sun City Palm Desert China (Hong Kong), Esri (SCPD) (Thailand), TomTom, 2013
Legend Inflow Locations Northern Entrance to SCPD Reach 3 Levee and Channel 2 Excavated Channel (L&C) Alignments
Southern Entrance to SCPD Channel 2
Classic Course Golf Club (CCGC) SCPD Channel 1 DRAFT(Mirasera Channel) SCPD Channel 1A
Reach 4 Levee and Excavated Channel (L&C)
Copyright:© 2013 Esri, DeLorme, NAVTEQ, TomTom Data Sources: NAIP Orthorectified Ccolor Aerial Imagery, 2010. nhc
The general conclusion from the two previous studies was that stormwater management in the North Cathedral and Thousand Palms planning units required an integrated approach that addressed all the sources of flooding in order to have appreciable benefits.
1.2 Development of Alternatives
In the Thousand Palms area, the Thousand Palms Flood Control project is the only alternative that is being considered for stormwater management by CVWD. As noted earlier, the project was taken over by CVWD in 2012 and CVWD is now proceeding through environmental permitting and project design.
Consequently, the alternatives developed for the North Cathedral City and Thousand Palms units all include the Thousand Palms FCP plus concepts to manage flooding from the riverine flows. A preliminary review identified several broad options for managing the riverine flows. These were to convey the riverine flows in flood channels to Sun City Palm Desert, divert them to the Whitewater River Stormwater Channel (WWRSC) or store part of them. Following a meeting with CVWD, three alternatives were selected for further development in this report. They were:
• Alternative 1: With the Thousand Palms FCP, construct a flood channel to collect flows from the culverts or bridges beneath I-10 and convey them through the existing, but unfinished, SPRR Bridge at Morongo Wash to the WWRSC. The design of this project has been partly completed. • Alternative 2: With the Thousand Palms FCP, construct a flood control channel to collect the Morongo Wash and Willow Hole flows and convey them through North Cathedral City and Thousand Palms and to the Sun City Palm Desert flood channels. • Alternative 3: With the Thousand Palms FCP, construct a new bridge beneath I-10 near Morongo Wash and a flood channel to connect to the SPRR Bridge to convey Morongo Wash fan 100-year peak flows to the WWRSC. 1.3 Objectives and Approach
The main objectives of this report are to develop concept-level details and costs and determine areas of inundation and peak flows at various locations in North Cathedral City and Thousand Palms for the three alternatives. DRAFT The preliminary design and costs of the Thousand Palms FCP were developed by Parsons Brinckerhoff for CVWD from earlier USACE studies. NHC provided hydrology and hydraulics for the preliminary design in their 2013(b) report. The preliminary hydraulic design of the flood channel for Alternative 1 was prepared in NHC (2012; refer to Appendix A). The HEC-RAS model for the preliminary design of Alternative 3 is described in Appendix C. Preliminary design for Alternative 2 was based on uniform flow calculations; details are in Appendix B.
Inundated areas and peak flows at various locations with the alternatives in place were calculated with the MIKE FLOOD model developed for existing conditions, with suitable modifications to structures, topography, or inflows for each alternative (refer to NHC 2013a for model descriptions).
North Cathedral/Thousand Palms SMP 4 September 30, 2013 Alternatives Analysis
1.4 Sources of Information
Study area topography was provided by CVWD, consisting of FEMA Riverside County LiDAR data collected in February and March of 2011 (Digital Mapping Inc 2011). The LiDAR data were provided in feet in the State Plane Zone VI, North American Datum of 1983 (NAD83) and North American Vertical Datum of 1988 (NAVD88). Check point surveys for the FEMA LiDAR were provided by Summit Engineering Corp (2011). Vertical elevations quoted in this report refer to the North American Vertical Datum of 1988 (NAVD88).
Flood control channel dimensions for Alternative 1 were obtained from the preliminary design prepared by Krieger & Stewart, Inc (2010). The geometries of existing culverts or bridges beneath I-10 were obtained from Caltrans as-built plans and survey data provided by CVWD.
The 100-year hydrographs and peak flows were obtained from NHC (2013a) “Morongo Wash Watershed Existing Conditions Study”.
1.5 Report Organization
Chapter 2 provides a brief summary of the study area characteristics and 100-year hydrology and describes the general nature of the MIKE FLOOD hydraulic model used in the alternative analysis. Please refer to NHC (2013a; 2013b) for a detailed discussion of the study area and the analytic procedures.
Chapter 3 describes the three alternatives and Chapter 4 summarizes areas of inundation and peak flows along the I-10 corridor for each alternative. Appendices A, B and C provide the preliminary hydraulic analyses that were completed to help develop the alternatives; Appendix D provides concept- level costs. Chapter 5 compares the three alternatives and provides a summary and conclusions.
DRAFT
North Cathedral/Thousand Palms SMP 5 September 30, 2013 Alternatives Analysis
2. BACKGROUND 2.1 Study Area
The study area includes the lower part of the Morongo Wash fan, the portion of Morongo Wash fan that is south of I-10 and SPRR, and a 2 to 3 mile wide zone along the I-10/SPRR corridor, from Palm Drive southeast as far as Adams Street near Sun City Palm Desert (Figure 2-1). The alternatives analysis assumes that the Thousand Palms Flood Control project is in place and functioning to collect and convey the 100-year floods from the Thousand Palms Watershed to SCPD. The Thousand Palms FCP forms the northern boundary of the study area near SCPD.
The valley bottom along the I-10 corridor slopes to the southeast. Valley bottom slopes near Morongo Wash are about 1% or so; near Sun City Palm Desert they are 0.2% or so. From Morongo Wash to the community of Thousand Palms, there is little development north or south of the I-10 corridor. The area is largely devoid of vegetation; exposed sediments primarily consist of sand, with small amounts of silt and gravel. Flood channels are visible on the fans and slopes, along the north side of I-10 to the southeast of Date Palm Drive, and between I-10 and the SPRR. Construction of I-10 and other highway features has obscured flood channels along the valley bottom.
Southeast of Thousand Palms, the valley bottom has been developed on both sides of the I-10 corridor. Flood channels in this part of the study area have been obscured by development.
2.2 Flood Control Structures
The primary flood control structures in the study area are the three bridges (often referred to as “culverts”) constructed to convey flows from Morongo Wash fan beneath I-10. From west to east, they are called Salvia Wash, Edom Wash, and Willow Wash Culverts (Figure 2-1). Flood waters on the Morongo Wash fan are directed to the culverts by excavated channels and training dikes constructed on the north side of I-10.
SPRR has constructed a bridge beneath their rail line to convey Morongo Wash flows to the Whitewater River Stormwater Channel but the channel that connects the I-10 culverts to the bridge has not been built and the bridge opening is blockedDRAFT by a berm. Under existing conditions, flows that pass through the I-10 culverts are directed southeast between I-10 and SPRR, with some overtopping of the SPRR grade. Non-engineered training dikes have been built along the north side of SPRR, presumably to protect the grade from flooding and erosion.
Further downstream, there are no significant flood control or conveyance structures. The I-10 grade, SPRR grade, fills and bridges for entrance and exit ramps from I-10, buildings, and other structures control the direction and ponding of flows. NHC (2013a) provided an analysis of existing condition flooding patterns along the corridor.
North Cathedral/Thousand Palms SMP 6 September 30, 2013 Alternatives Analysis West Wide Canyon!. Dam
M North Cathedral/Thousand Palms Stormwater Plan
o
r
o
n
g Colorado River Aqueduct
o
W Figure 2-1
Bob Hope Dr Bob Hope n o a y
s n Study Area a MissionCreek h C e n d o i y W n t a North Cathedral/Thousand Palms Morongo Wash Inflow Long Canyones !( W C !( e Stormwater Plan id Seven Palms W Long/Wide Canyon Inflow t Valley s Scale - 1:84,000 1 inch = 7,000 feet a E 0 4,000 8,000 16,000 Willow Feet Hole © ¨¦§10 CA State Plane, Zone VI horz. datum: NAD 83 horz. units: feet SP northwest hydraulic consultants project no. 500058 September 2013 RR Reference Map Salvia Wash
Edom Wash Flat Top Mountain Willow Hole Inflow Willow Wash !(
SPRR Bridge
Vista Chino Vista Chino St Adams N Gene N Gene TrailAutry
Landau Blvd Landau Varner Rd Date Palm Dr Palm Date Whitewater River Da Vall Dr 30th Ave Sources: Esri, DeLorme, Palm NAVTEQ, USGS, Intermap, iPC, Springs NRCAN, Esri Japan, METI, Esri China (Hong Kong), Esri Thousand (Thailand), TomTom, 2013 Ramon Road Ramon Road Palms LEGEND
!( Dinah Shore Dr Inflow Locations Da Vall Dr Montgomery Montgomery Ave Model Boundary
Washington St Washington Roads General Ford Dr Portola Ave Sun City Railroads Palm Desert DRAFT St Cook Frank Sinatra Dr
Cathedral City St Adams ¨¦§10
Country Club Dr Dr El Dorado Oasis Club Dr Oasis Club Cook St Cook
Data Sources: NAIP Orthorectified Color Aerial Imagery, 2010. County of Riverside Roads, 04/2013. nhc
Palm Desert
2.3 Hydrology
NHC (2013a) defined 100-year hydrographs at concentration points for the Morongo Wash, Long and Wide Canyons, and Willow Hole subwatersheds (Figure 2-1) and these hydrographs were selected as the appropriate upstream boundary condition in the MIKE FLOOD model for the alternatives analysis. The inflow hydrographs were based on the 100-year whole-basin storm centering described in NHC (2013a); 100-year peak flows are summarized in Table 2-1. Table 2-1: 100-year Whole Basin Centering Peak Flows (NHC 2013a) Concentration Point 100-year peak flow (cfs) Morongo Wash 28,300 Long/Wide Canyons 7,860 Willow Hole 3,980
Peak flows for the Thousand Palms watershed are not required to evaluate flood hazards with the alternatives in place because it is assumed that the Thousand Palms FCP is in place and that it intercepts 100-year floods and directs them to the SCPD flood channels. Flooding is restricted to the area uphill from the Thousand Palms FCP.
2.4 Hydraulic Modeling
MIKE FLOOD, a coupled one dimensional (1-d)/two dimensional (2-d) hydraulic software package, was used to simulate the flooding near Morongo Wash and along the I-10 and SPRR corridor, southeast to Adams Street, under existing conditions (NHC 2013a). It was chosen because it is the best model to distribute shallow flows over the complex terrain. The same model was used for the evaluation of flood hazards with Alternatives 1 and 3 in place (Alternative 2 intercepts and conveys the peak flows from Morongo Watershed and eliminates 100-year flood hazards from the riverine flows).
The existing conditions model was used as the base geometry from which the alternative models were developed. The existing condition and alternatives used the same model parameters, roughness, grid cell size and hydraulic boundaries. Details are provided in NHC (2013a). The model parameters for Alternative 1 were specified in accordanceDRAFT with the NHC’s previous Morongo Wash Flood Control Project modeling study (NHC 2012). The main model parameters are summarized in Table 2-2.
Table 2-2: Hydraulic Model Parameters Parameter MIKE FLOOD HEC-RAS 2-d model 1-d models 1-d model
Grid cell size 10 m ------Manning roughness coefficient 0.05 0.015-0.04 0.015-0.04 Inflow 100-yr hydrograph 100-yr hydrograph 100-yr peak flows Simulation time step 1 s 0.5 s Steady state Simulation period 36 hrs 36 hrs ---
North Cathedral/Thousand Palms SMP 8 September 30, 2013 Alternatives Analysis
For Alternative 1, the culverts at I-10, the flood control channel, and the bridge beneath SPRR were modeled in one-dimension (MIKE 11) and coupled to the 2-d model domain. The performance of the MIKE11 model was confirmed with a steady state HEC-RAS model (Appendix A). The HEC-RAS model used the peak inflows to the flood channel, including those passing through the I-10 culverts and over I- 10, as computed by MIKE FLOOD, and was used to calculate 100-year water surface elevations and other hydraulic characteristics through the SPRR Bridge opening and channel. Results are discussed in Appendix A.
3. DESCRIPTION OF THE ALTERNATIVES 3.1 Introduction
The following sections provide a brief description of the alternatives. Hydraulic analyses are included in Appendices A, B and C; concept level costs in Appendix D. The Thousand Palms FCP is common to all the alternatives and is not described in detail below but is included in the alternative costs.
3.2 Alternative 1: Morongo Creek Channel and Thousand Palms FCP
3.2.1 General Features This alternative is based on the design of the Morongo Creek Channel by Krieger & Stewart, Inc (2010; included in Appendix A). It includes a flood control channel that connects the three culverts under I-10 to the SPRR Bridge, a drop structure and channel beneath the bridge, an excavated flood channel and concrete bank protection downstream of the bridge. The flood channel passes around two tight bends upstream and downstream of the SPRR Bridge (refer to Appendix A). The left bank of the channel towards the WWRSC is concrete-lined for about 5,000 feet or so to protect the Verona Subdivision.
The original concept was for a natural bottom and concrete banks in the upper part of the flood channel but given the presence of a high-pressure natural gas line beneath the channel, the high flood velocities, and the fine sediments in the bed of the flood channel, a concrete-lined channel was assumed to be required. The concrete lining extendsDRAFT to about 50 feet downstream of the bridge. Figure 3-1 shows the proposed concept; Appendix A provides the preliminary plans from Krieger & Stewart that were incorporated into the hydraulic model.
3.2.2 Design Hydrology Based on the revised 100-year peak flows for Morongo Wash and Long/Wide Canyons and the MIKE FLOOD model (NHC 2013a), the new peak inflows from the I-10 culverts to the flood channel are 6,300 cfs from the Salvia Wash Culvert, 2,700 cfs from the Edom Wash Culvert, and 4,600 cfs from the Willow Wash Culvert. An additional flow of about 2,300 cfs overtops I-10 and is conveyed to the flood channel. The peak outflow beneath the SPRR Bridge is about 15,900 cfs. A small flow overtops the SPRR grade.
North Cathedral/Thousand Palms SMP 9 September 30, 2013 Alternatives Analysis Willow Hole
¨¦§10
North Cathedral/Thousand Palms Stormwater Plan
Figure 3-1 Alternative 1 Layout
North Cathedral/Thousand Palms Stormwater Plan ¨¦§10 Scale - 1:13,703 1 inch = 1,142 feet Salvia Wash 6,900 cfs 0 500 1,000 2,000 Feet © CA State Plane, Zone VI horz. datum: NAD 83 horz. units: feet northwest hydraulic consultants project no. 500058 September 2013 Reference Map Edom Wash 2,700 cfs
Willow Wash SP 5,100 cfs RR N Gene Autry Trail N Gene Autry
Sources: Esri, DeLorme, NAVTEQ, USGS, Intermap, iPC, NRCAN, Esri Japan, METI, Esri China (Hong Kong), Esri Flood Control Channel (Thailand), TomTom, 2013
LEGEND
SPRR Bridge Model Boundary
10 Roads Excavated Channel ¨¦§ Left Bank Protection 5,000 ft Railroads
Discharge (Q) Drop Structure 16,000 cfs DRAFT
Data Sources: NAIP Orthorectified Color Aerial Imagery, 2010. County of Riverside Roads, 04/2013. nhc
3.2.3 Hydraulic Performance The performance of the flood channel was analyzed with the HEC-RAS model originally developed by NHC (2012) for preliminary design. The Manning’s n for the concrete-lined flood channel was assumed to be 0.025. This is greater than the typical value of 0.015 for a concrete bed to account for transport of sand through the I-10 culverts and into the flood channel. Appendix A provides the results of the HEC- RAS model, showing the variations in flow depths, velocities, Froude numbers, and freeboard along the channel (Figures A1 to A5). Flow is supercritical at the Salvia Wash Culvert inlet and in the vicinity of the drop structure and SPRR Bridge. The freeboard analysis for the HEC-RAS water surface profile (Figure A5) shows a minimum freeboard of more than 3 feet in the channel and several feet of clearance at the SPRR Bridge. However, the HEC-RAS profile does not include superelevation of the water surface in the supercritical reach near the bridge.
Figure A5 shows the increases in the water surface elevation on each bank due to superelevation and standing waves. (Superelevation is a transverse rise in water surface that occurs around a channel bend due to centrifugal forces. Standing waves form in curved rapid flows and persist for long distances downstream.) The rise in water surface due to superelevation and standing waves was calculated outside of HEC-RAS using the procedures and equations in USACE (1991). The calculated rise in water surface in the sharp curves in the vicinity of the SPRR Bridge is very large, up to 17 ft. This large rise results from the high flow velocities combined with the small radii of channel curvature in the bends. With this superelevation, the current freeboard to the top of the flood channel banks would be exceeded and water surface elevations would be above the bridge soffit on the left bank.
3.2.4 Future Modifications It is likely that the calculated superelevation is conservative since that height is twice the flow depth at the bridge and flow patterns through the bends are complicated by the drop structure. Further analysis will be needed to modify the alternative to reduce superelevation. Such modifications may consist of re- grading the profile, adding walls in the channel to reduce superelevation at the bends, revising the position and height of the drop structure, modifications to the bends, or other features.
One improvement would be to re-design the concrete-lined channel for supercritical flow, steepen the slope, reduce the cross section area substantially and re-align the channel to reduce the tightness of the existing bends. This improvementDRAFT would also reduce construction costs. 3.2.5 Concept Level Costs Appendix Table D.1 provides concept level costs for the above features of the alternative and includes the cost established by CVWD for the Thousand Palms Flood Control Project.
3.3 Alternative 2: Conveyance to SCPD and Thousand Palms FCP
3.3.1 General Features Alternative 2 would construct a berm and flood channel that collects the Morongo Wash and Long and Wide canyon floods on the lower Morongo Wash fan and conveys them to Sun City Palm Desert (Figure 3-2). The berm or diversion structure would intercept and collect flows from Morongo Wash and convey them into the flood conveyance channel.
North Cathedral/Thousand Palms SMP 11 September 30, 2013 Alternatives Analysis Desert Hot Springs
North Cathedral/Thousand Palms Stormwater Plan
Figure 3-2 West Wide Canyon Dam !. Alternative 2 Layout Long Canyon North Cathedral/Thousand Palms Stormwater Plan North Palm Springs on ny Colorado River Aqueduct Scale - 1:96,000 1 inch = 8,000 feet Ca e id 0 4,000 8,000 16,000 W n t yo Feet s an © e C W e MissionCreek id CA State Plane, Zone VI horz. datum: NAD 83 horz. units: feet Morongo Wash Morongo W t s September 2013 a northwest hydraulic consultants project no. 500058 Seven Palms E Valley Reference Map
Whitewater River ") Collection Levee 10 ¨¦§ Willow Hole ") SP RR Alignment 1 (250' wide channel)
") Flat Top Collection Basin Mountain (Willow Hole) Concrete Channel
N Gene N Gene TrailAutry Alignment 2 (250' wide channel) ") Levee 1 Vista Chino Vista Chino Varner Rd Sources: Esri, DeLorme, Date Palm Dr Palm Date
Landau Blvd Landau NAVTEQ, USGS, Intermap, iPC, Da Vall Dr NRCAN, Esri Japan, METI, Esri China (Hong Kong), Esri 30th Ave (Thailand), TomTom, 2013 ") Levee 2 Palm Springs Thousand ") Palms LEGEND
Ramon Road Ramon Road ") ") ")")")")")")")")")")")")")")") ") ") ") ") Levee 3 Thousand Palms Project
") TPFCP Levees
Bob Hope Dr Bob Hope ") Da Vall Dr ")") Avenue 38 Channel Dinah Shore Dr ")
Montgomery Montgomery Ave Washington St Washington North Cathedral Project ") Portola Portola Ave General Ford Dr ") ") Sun City Road Crossings ") Levee 4
Cook St Cook Palm Desert Collection Basin DRAFT") Alignment 1 Frank Sinatra Dr
Cathedral St Adams Alignment 2 City Collection Levee Avenue 38 Country Club Dr Channel Roads Oasis Club Dr Oasis Club El Dorado Dr El Dorado Cook St Cook ¨¦§10
nhc Data Sources: NAIP Orthorectified Ccolor Aerial Imagery, 2010.
Palm Desert
Indio
Inspection of the study area indicates that the flood conveyance channel would work better on the north side of I-10 than on the south. The north alignment would avoid crossing beneath the I-10 and SPRR and then back to the north to join the Sun City Palm Desert flood channels. The north alignment would avoid more development than the southern one, and also provide an alignment where flood flows from Willow Hole could be conveyed to the flood channel. The north alignment would not avoid existing development and it would require constructing bridges for road crossings of the channel and acquisition of property along the corridor.
Two general alignments were considered for a north conveyance channel, as follows:
• Alignment 1 would convey the flow in a 60,000-foot long channel that lies just north of I-10 and joins to the Avenue 38 Channel of the Thousand Palms FCP. This alignment would require 5 major bridge crossings (Date Palm Drive, Monterey Ave, Ramon Road, Bob Hope Drive and Cook Street), multiple re-alignments of freeway access ramps and acquisition of residential and commercial properties along I-10, particularly southeast of Thousand Palms. • Alignment 2 would convey the flow in a channel on the north side of I-10 as far as the community of Thousand Palms. The channel would then be directed east along Ramon Road to deliver flows to Thousand Palms FCP Levee 2. From here, floods would pass through the Classic Club Golf Course to Mirasera Channel and into the Sun City Palm Desert flood channels.
Alignment 2 is shorter (45,000 ft) and avoids much of the development along I-10. It would require 3 major bridge crossings (Date Palm Drive, Bob Hope Drive and Ramon Road) of the channel, numerous surface road crossings along Ramon Road, and acquisition of properties on one side or the other of Ramon Road. It may also require upgrades to the Thousand Palms project levees in order to convey the flows to SCPD.
Ground slopes at the western end of the flood channels are around 1% and concrete-lined supercritical flow channels have been proposed for these parts of the two alignments. Soil-cement lined channels might work equally well and be less expensive. Ground slopes are shallower at the western ends of the alignments and flow would be subcritical in concrete-lined channels. Sediment carried in by flows from Morongo Wash and Long and Wide Canyons will need to be considered in the design of any supercritical sections of the conveyance channelDRAFTs and a sediment collection basin may be required to reduce maintenance.
The two alignments would also include a collection basin, or sediment basin, in the vicinity of Varner Road and Date Palm Drive, bridges or other features near the road intersection, and a connecting channel to divert the flows from Willow Hole into the main flood conveyance channel. As discussed in NHC (2013a), the hydrograph from Willow Hole peaks well in advance of that from Morongo Wash and Long and Wide canyons so no additional channel capacity is required to accommodate these flows.
3.3.2 Design Hydrology The combined 100-year peak flow from Morongo Wash and Long and Wide Canyons on the Morongo Wash fan is 36,200 cfs when the two 100-year hydrographs are added. Assuming efficient collection of
North Cathedral/Thousand Palms SMP 13 September 30, 2013 Alternatives Analysis
flows on the fan and little attenuation of peak flows during conveyance, the peak discharges at the outlet of Alignment 1 and 2 would not be much less than the combined peak on the fan.
For Alignment 1, such a discharge would exceed the design capacity of the southern entrance to the SCPD flood channels and of Flood Channels 1 and 1A. There is no practical alternative to increase capacity at SCPD so reducing the peak flows into the channel is the only option. For Alignment 2, the peak flows at the outlet would exceed the design capacity of Levees 2 and 3 and the levee 3 channel and result in flooding downstream of the Thousand Palms FCP. In order for Alternative 2 to be practical, it will be necessary to either reduce the peak flow into the conveyance channel or upgrade the capacity of the Thousand Palms Flood Control project.
Combining Alternative 2 with the previous Alternative 1, which diverts a maximum of about 15,900 cfs to the WWRSC through the I-10 culverts and the SPRR Bridge, could reduce the peak inflow to the proposed flood channels to about 20,300 cfs. Such a peak flow may be practical to convey through the SCPD channels without flooding near Washington Street or in SCPD. The design of a collection structure that splits the flows on Morongo Fan above I-10 is expected to be complex and the structure will require maintenance to prevent sediment deposition.
3.3.3 Hydraulic Analysis The hydraulic analyses for this alternative consisted of sizing the conveyance channels for the two alignments under the assumption that Alternative 1 is in place. A constant bottom width of 150 ft was used for both alignments, with flow depths varying with bed slopes. Appendix B provides longitudinal profiles of the two proposed alignments, typical cross-sections and average hydraulic properties. The total channel footprint, including maintenance roads of about 20 feet on each bank, is about 250 feet wide (Figure 3-2).
3.3.4 Future Modifications Both alignments would require further hydraulic analysis to confirm that the peak flows in the channels are consistent with design capacities for the Thousand Palms FCP and for the flood channels through Sun City Palm Desert. Such analyses may indicate that some further reduction in peak flows into the conveyance channels will be required so that the alternative is feasible. 3.3.5 Costs DRAFT Appendix Table D.2 and D.3 provide concept level costs for the two alignments described above. The tables include the cost for Alternative 1 (Table D.1) and the cost established by CVWD for the Thousand Palms Flood Control Project. Land acquisition costs are very uncertain for both of these alignments.
3.4 Alternative 3: New I-10 Bridge and Thousand Palms FCP
3.4.1 General Features Alternative 3 would collect the Morongo Wash, Long and Wide Canyon flows in the Salvia and Edom Culverts and a new Willow Wash Culvert and convey them to the WWRSC through the SPRR Bridge (Figure 3-3). This alternative is designed to convey the Morongo Wash, Long and West Wide Canyon
North Cathedral/Thousand Palms SMP 14 September 30, 2013 Alternatives Analysis ¨¦§10
North Cathedral/Thousand Palms Stormwater Plan
Figure 3-3 Alternative 3 Layout
North Cathedral/Thousand Palms Stormwater Plan
Salvia Wash Scale - 1:12,000 1 inch = 1,000 feet 0 500 1,000 2,000 ¨¦§10 Feet © CA State Plane, Zone VI horz. datum: NAD 83 horz. units: feet northwest hydraulic consultants project no. 500058 September 2013 Reference Map
Edom Wash Graded Area to Direct Flow
Discharge (Q) SP 27,200 cfs RR
Willow Wash
Concrete Channel Widen Willow Wash 200 ft Discharge (Q) Sources: Esri, DeLorme, 9,000 cfs NAVTEQ, USGS, Intermap, iPC, NRCAN, Esri Japan, METI, Esri Berms China (Hong Kong), Esri (Thailand), TomTom, 2013
Concrete Channel 200 ft Wide, LEGEND
N Gene Autry Trail N Gene Autry 1.5:1 Side Slopes
Concrete Channel SPRR Bridge 200 ft Wide, Model Boundary 1.5:1 Side Slopes Roads
Discharge (Q) Railroads 36,200 cfs Left Bank Protection ¨¦§10 DRAFT5,000 ft
Data Sources: NAIP Orthorectified Color Aerial Imagery, 2010. County of Riverside Roads, 04/2013. nhc
flows to the WWRSC. Under this alternative, the flooding source to North Cathedral City and Thousand Palms would be the inflows from Willow Hole.
The main components of this alternative are a new (or modified) bridge at Willow Wash Culvert beneath I-10 that maintains the current highway grade, a concrete-lined channel that extends from Willow Wash Bridge through the SPRR Bridge, a concrete channel downstream of SPRR that would transition to existing grade and a concrete channel to collect flows from Salvia and Edom Culverts and convey them to the channel joining Willow Wash and the SPRR Bridges.
The channel that collects flows from Salvia and Edom culverts would be similar to Alternative 1. The left bank downstream of the SPRR Bridge, adjacent to Verona subdivision, would be concrete-lined as in Alternative 1.
Two levees or berms would extend north on the east side of the SPRR Bridge to I-10 and from I-10 to Flat Top Mountain. These berms would direct flows into the new Willow Wash Bridge and prevent overflows to the southeast along the I-10/SPRR corridor. The alternative will also require earthwork, berms or other structures on the Morongo Wash fan to partition flows to the three culverts or bridges beneath I-10.
3.4.2 Design Hydrology The 100-year peak flow on Morongo Wash fan north of I-10 was calculated to be 36,200 cfs. The existing conditions MIKE FLOOD model showed Salvia and Edom Culverts convey a combined 9,000 cfs during the 100-year peak flow (NHC 2013a). If these flows continue to be conveyed through the two culverts, the peak flow that would be conveyed through the new Willow Wash Bridge would be 27,200 cfs. The peak flow through the concrete connecting channel and SPRR Bridge would be 36,200 cfs.
3.4.3 Hydraulic Analysis The Willow Wash Culvert was selected as the best site for a new bridge because it is better aligned with the SPRR Bridge than the other two culverts. This eliminates the need for a tight curve to pass flows through the SPRR Bridge and the superelevation discussed for Alternative 1. Adding capacity at one bridge site was preferred to increasing the capacity at all three culverts. It was thought to be less expensive to construct one larger bridge and also that construction at only one site would reduce road closure delays and traffic managementDRAFT costs. Willow Wash is also the best site because it is adjacent to Flat Top Mountain which acts as a natural barrier to guide flood flows towards the new bridge. It is also the furthest downstream of the culverts and thus provides the best opportunity to capture flood flows that pond against the I-10 grade upstream. Re-contouring of the upstream basin is likely to be required to direct the major part of the peak flow through the expanded Willow Wash Culvert. Modification of existing guide berms or adding new guide berms may be necessary north of I-10 and between I-10 and the SPRR.
Hydraulic analysis for the bridges and flood channel was prepared in HEC-RAS. The goal of the simulation was to determine a minimum size of opening for Willow Wash to convey the peak flow and
North Cathedral/Thousand Palms SMP 16 September 30, 2013 Alternatives Analysis
confirm that the peak flow would pass through the existing SPRR Bridge opening with adequate clearance. A description of the hydraulic model and the results are in Appendix C.
Inflows through the Salvia and Edom culverts were not modeled in HEC-RAS but their peak flows were added to the HEC-RAS model between the I-10 and SPRR Bridges. The Krieger and Stewart Flood Control Channel dimensions were used for the channel that conveys the Salvia and Edom Flows to the east. The SPRR Bridge structure and opening width were not modified in this alternative. The channel connecting the Willow Wash and SPRR Bridges was assumed to be 200 feet wide and concrete-lined.
A minimum width of 200 feet for the Willow Wash Bridge, with a lower bed elevation than in the Willow Wash culvert, would be adequate to convey the peak flow. The model confirmed that the SPRR Bridge opening would be able to pass the peak flow with clearance below the bridge deck.
3.4.4 Future Modifications The channel alignment and profile connecting the two bridges will require further hydraulic design. Potential issues to consider include superelevation in the channel and the required extension of the channel downstream of SPRR to minimize scour.
3.4.5 Costs Appendix Table D.4 provides concept level costs for the features described above, including the cost established by CVWD for the Thousand Palms Flood Control Project.
4. FLOOD HAZARDS WITH THE ALTERNATIVES 4.1 Introduction
As described earlier, maximum water surface elevations, depths, and velocities were re-computed with MIKE FLOOD and combined with the Thousand Palms FCP results to show the flood hazards associated with each alternative. The 100-year maximum depths and peak flows at various locations along the I-10 corridor are shown on Figures 4-1 to 4-3. The figures also show maximum depths uphill of the levees and channels of the Thousand PalmsDRAFT Flood Control Project. Alternative 2 conveys the Morongo Wash fan and Willow Hole 100-year floods to the WWRSC or SCPD so no flooding occurs along the I-10 corridor. Alternative 2 does have flooding uphill from the Thousand Palms FCP and on the Morongo Wash fan north of I-10.
The two sections that follow the Figures summarize the reduction of areas of flooding, depths of flooding, and peak flows at various points along the I-10 corridor for each of the alternatives relative to existing conditions. A third section discusses the flooding associated with each alternative in more detail.
North Cathedral/Thousand Palms SMP 17 September 30, 2013 Alternatives Analysis M North Cathedral/Thousand Palms Stormwater Plan o r o n g o Figure 4-1a W a s Alternative 1 h Long Canyon anyon e C 100-Year Maximum Depth West Wi d Seven Palms Valley North Cathedral/Thousand Palms Stormwater Plan Edom Hill Conservation Area Scale - 1:42,000 1 inch = 3,500 feet
0 1,750 3,500 7,000 n Willow o Feet © y
Hole n
a Mission Creek CA State Plane, Zone VI horz. datum: NAD 83 horz. units: feet
C
e northwest hydraulic consultants project no. 500058 September 2013
d
i
W
t Reference Map s
SP a
R E R ¨¦§10 Edom Hill Conservation Area
Peak flow North of I-10 8,100 cfs Edom Hill Peak outflow to WWR Flat Top Conservation Area 15,900 cfs Mountain N Gene Autry Trail N Gene Autry
Sources: Esri, DeLorme, Katrina Henrich NAVTEQ, USGS, Intermap, iPC, NRCAN, Esri Japan, METI, Esri !( China (Hong Kong), Esri Varner Rd (Thailand), TomTom, 2013 Peak flow North of I-10 LEGEND Peak flow between I-10 and SPRR 1,500 cfs 9,000 cfs !(
PA4 - Marvin Family Ltd. Model Boundary Vista Chino Vista Chino Roads PA1 - Messenger
PA3 - Lazar Depth (in feet) 0 - 1 Peak flow between I-10 and SPRR Peak flow North of I-10 1 - 2 1,300 cfs Rd Sol Del Rio DRAFTDr Palm Date 4,600 cfs 2 - 3 Peak flow South of SPRR 3 - 5 30th Ave PA2 -
17,900 cfs VallDa Dr Lazar/Messenger 5 - 10 10 - 15 Whitewater River Landau Blvd Landau 15 - 20 20 + Peak flow between I-10 and SPRR 5,200 cfs
Peak flow South of SPRR Thousand 8,200 cfs Palms Ramon Road Ramon Road
Data Sources: NAIP Orthorectified Color Aerial Imagery, 2010. County of Riverside Roads, 04/2013. nhc !( !( North Cathedral/Thousand Palms Stormwater Plan
Thousand Palms Figure 4-1b Alternative 1 Ramon Road 100-Year Maximum Depth
LOT- 142 North Cathedral/Thousand Palms Stormwater Plan
Scale - 1:42,000 1 inch = 3,500 feet
0 1,750 3,500 7,000
Bob Hope Dr Hope Bob Feet © CA State Plane, Zone VI horz. datum: NAD 83 horz. units: feet northwest hydraulic consultants project no. 500058 September 2013
Washington St Washington Reference Map Peak flow North of I-10 11,600 cfs
Montgomery AveMontgomery Ivey Ranch Portola Portola Ave
Sun City Palm Desert
Peak flow North of I-10 3,300 cfs
Frank Sinatra Dr
Cook St Cook Sources: Esri, DeLorme, NAVTEQ, USGS, Intermap, iPC, NRCAN, Esri Japan, METI, Esri China (Hong Kong), Esri (Thailand), TomTom, 2013 10 ¨¦§ St Adams LEGEND Peak flow North of I-10 2,300 cfs Model Boundary Roads Country Club Dr El Dorado Dr El Dorado Peak flow North of I-10 1,200 cfs Depth (in feet) 0 - 1
Oasis Club Dr Club Oasis 1 - 2 DRAFT 2 - 3 3 - 5 5 - 10 10 - 15 15 - 20 20 +
nhc Data Sources: NAIP Orthorectified Color Aerial Imagery, 2010. County of Riverside Roads, 04/2013.
Palm Desert M
o r o North Cathedral/Thousand Palms Stormwater Plan n g o W a Figure 4-2a sh Long Canyon anyon e C Alternative 2 West Wid 100-Year Maximum Depth Seven Palms Valley North Cathedral/Thousand Palms Edom Hill Conservation Area Stormwater Plan
Scale - 1:42,000 1 inch = 3,500 feet n Willow o 0 1,750 3,500 7,000 y Feet © Hole n
Mission Creek a
C
e CA State Plane, Zone VI horz. datum: NAD 83 horz. units: feet d i
W northwest hydraulic consultants project no. 500058 September 2013
t s
SP a R E Reference Map R ¨¦§10 Edom Hill Conservation Area
Flat Top Edom Hill
N Gene Autry Trail N Gene Autry Mountain Conservation Area
Katrina Henrich Sources: Esri, DeLorme, NAVTEQ, USGS, Intermap, iPC, Varner Rd NRCAN, Esri Japan, METI, Esri China (Hong Kong), Esri (Thailand), TomTom, 2013
LEGEND PA4 - Marvin Family Ltd. Vista Chino Vista Chino Model Boundary PA1 - Messenger Roads
PA3 - Lazar Depth (in feet)
Date Palm Dr Palm Date 0 - 1 Rio Del Sol Rd Sol Del Rio DRAFT 1 - 2
Da VallDa Dr 2 - 3 30th Ave PA2 - 3 - 5 Lazar/Messenger 5 - 10 Whitewater River
Landau Blvd Landau 10 - 15 Palm 15 - 20 Springs 20 +
Thousand Ramon Road Ramon Road Palms
Data Sources: NAIP Orthorectified Color Aerial Imagery, 2010. County of Riverside Roads, 04/2013. nhc North Cathedral/Thousand Palms Stormwater Plan
Figure 4-2b Thousand Alternative 2 Palms Ramon Road 100-Year Maximum Depth
LOT- 142 North Cathedral/Thousand Palms Stormwater Plan
Scale - 1:42,000 1 inch = 3,500 feet
0 1,750 3,500 7,000 Feet Bob Hope Dr Hope Bob © CA State Plane, Zone VI horz. datum: NAD 83 horz. units: feet northwest hydraulic consultants project no. 500058 September 2013
Washington St Washington Reference Map Washington St Washington Montgomery AveMontgomery Ivey Ranch Portola Portola Ave
Sun City Palm Desert
Frank Sinatra Dr
Cook St Cook Sources: Esri, DeLorme, NAVTEQ, USGS, Intermap, iPC, NRCAN, Esri Japan, METI, Esri China (Hong Kong), Esri (Thailand), TomTom, 2013 ¨¦§10 St Adams Adams St Adams LEGEND
Model Boundary Country Club Dr Roads El Dorado Dr El Dorado
Depth (in feet) 0 - 1 DRAFT Dr Club Oasis 1 - 2 2 - 3 3 - 5 5 - 10 10 - 15 15 - 20 20 +
Data Sources: NAIP Orthorectified Color Aerial Imagery, 2010. County of Riverside Roads, 04/2013. nhc
Palm Desert M
o r o North Cathedral/Thousand Palms Stormwater Plan n g o W a Figure 4-3a sh Long Canyon anyon e C Alternative 3 W id est W 100-Year Maximum Depth Seven Palms Valley North Cathedral/Thousand Palms Edom Hill Conservation Area Stormwater Plan
Scale - 1:42,000 1 inch = 3,500 feet n Willow o 0 1,750 3,500 7,000 y Feet © Hole n
Mission Creek a
C
e CA State Plane, Zone VI horz. datum: NAD 83 horz. units: feet d
i
W northwest hydraulic consultants project no. 500058 September 2013
t s
SP a Reference Map R E R ¨¦§10 Edom Hill Conservation Area
Flat Top Edom Hill Mountain N Gene Autry Trail N Gene Autry Conservation Area
Katrina Henrich Sources: Esri, DeLorme, NAVTEQ, USGS, Intermap, iPC, Varner Rd NRCAN, Esri Japan, METI, Esri Peak flow North of I-10 China (Hong Kong), Esri 1,500 cfs (Thailand), TomTom, 2013
LEGEND PA4 - Marvin Family Ltd. Vista Chino Vista Chino Model Boundary PA1 - Messenger Roads
PA3 - Lazar Depth (in feet) Peak flow between I-10 and SPRR Peak flow North of I-10 Date Palm Dr Palm Date 0 - 1 1,300 cfs Rd Sol Del Rio DRAFT 950 cfs 1 - 2
Peak flow South of SPRR VallDa Dr 2 - 3 100 cfs 30th Ave PA2 - 3 - 5 Lazar/Messenger 5 - 10 Whitewater River
Landau Blvd Landau 10 - 15 Palm 15 - 20 Peak flow between I-10 and SPRR Springs 800 cfs 20 +
Peak flow South of SPRR 100 cfs Thousand Ramon Road Ramon Road Palms
Data Sources: NAIP Orthorectified Color Aerial Imagery, 2010. County of Riverside Roads, 04/2013. nhc North Cathedral/Thousand Palms Stormwater Plan
Figure 4-3b Thousand Palms Alternative 3 Ramon Road 100-Year Maximum Depth
LOT- 142 North Cathedral/Thousand Palms Stormwater Plan Peak flow North of I-10 350 cfs Scale - 1:42,000 1 inch = 3,500 feet 0 1,750 3,500 7,000 Feet Bob Hope Dr Hope Bob © CA State Plane, Zone VI horz. datum: NAD 83 horz. units: feet northwest hydraulic consultants project no. 500058 September 2013
Washington St Washington Reference Map Washington St Washington Montgomery AveMontgomery Ivey Ranch Portola Portola Ave
Sun City Palm Desert
Frank Sinatra Dr
Cook St Cook Sources: Esri, DeLorme, NAVTEQ, USGS, Intermap, iPC, NRCAN, Esri Japan, METI, Esri China (Hong Kong), Esri (Thailand), TomTom, 2013 ¨¦§10 St Adams Adams St Adams LEGEND
Model Boundary Country Club Dr Roads El Dorado Dr El Dorado
Depth (in feet) 0 - 1
Oasis Club Dr Club Oasis 1 - 2 DRAFT 2 - 3 3 - 5 5 - 10 10 - 15 15 - 20 20 +
Data Sources: NAIP Orthorectified Color Aerial Imagery, 2010. County of Riverside Roads, 04/2013. nhc
Palm Desert
4.2 Areas and Depths of Inundation
Table 4-1 summarizes the total area inundated in North Cathedral City and Thousand Palms planning units under existing conditions and with the three alternatives in place. The areas in Table 4-1 include flooding on Morongo Wash upstream of I-10 but do not include the inundated areas uphill of the Thousand Palms Flood Control Project.
Table 4-1: Areas of Flooding along I-10 Simulated by MIKE FLOOD Alternative Inundated Area (acres) by planning unit North Cathedral City Thousand Palms Both Units Existing Conditions 1 3,100 4,300 7,400 Alternative 1 2,700 2,800 5,500 Alternative 2 930 2 0 930 Alternative 3 1,900 600 2,400 1. Areas for Existing (no breach) scenario described in NHC (2013a) 2. Inundated area on Morongo Wash fan north of I-10
The dividing line between North Cathedral City and Thousand Palms planning units is just upstream of the community of Thousand Palms near Bob Hope Road. The areas of inundation include all grid cells with depths greater than 0.002 feet.
Inspection of Figures 4-1 through 4-3 shows that the depth of flooding, compared to existing conditions, also decreases for the three alternatives. Table 4-2 summarizes the area of flooding for different maximum depth categories for each alternative.
Table 4-2: Maximum Depths of Flooding along I-10 simulated by MIKE FLOOD Alternative Inundated Area (acres) by maximum depth of flooding <1 ft 1 to 3 ft 3 to 5 ft 5 to 9 ft >9 ft Existing Conditions 1 1,980 2,690 1,600 870 270 Alternative 1 1,850 2,160 950 410 130 Alternative 2 2 320 410 170 40 4 Alternative 3 1,310 850 230 80 20 1. Area for BreachedDRAFT Condition described in NHC (2013a) 2. Inundated area on Morongo Wash fan north of I-10
The flooded area with maximum depths greater than 1 foot is significantly reduced by Alternative 1. These deeper flows have a greater risk of damage than those less than 1 foot. The total area of maximum depths greater than 1 foot is reduced from about 5,400 acres under existing conditions to 3,700 acres under Alternative 1. Alternative 3 further reduces the area with maximum depths greater than 1 foot to 1,200 acres. Alternative 2, where the flood hazards occur on Morongo Wash upstream and downstream of I-10 results in about 600 acres of inundation where maximum depths are greater than 1 foot.
North Cathedral/Thousand Palms SMP 24 September 30, 2013 Alternatives Analysis
4.3 Peak Flows
Table 4-3 summarizes 100-year peak flows for existing conditions and for each alternative, computed at various locations near Morongo Wash and along the I-10 corridor. Peak flows are assumed to be zero along the I-10/SPRR corridor for Alternative 2.
Table 4-3: 100-year peak flows along I-10 simulated by MIKE FLOOD Location Peak Flows (cfs) for Existing Alternative Alternative Alternative conditions 1 2 3 Peak Flows near Morongo Wash Salvia Wash Culvert 6,300 6,300 6,300 6,300 Edom Wash Culvert 2,700 2,700 2700 2,700 Willow Wash 4,600 4,600 4,600 27,200 Culvert SPRR Bridge 0 15,900 15,900 36,200 to Whitewater River 2,000 15,900 15,900 36,200 Peak flows along I-10/SPRR corridor near Verona 32,500 17,100 0 0 d/s of Date Palm Dr 34,200 20,700 0 2,900 u/s Bob Hope Dr 31,300 18,000 0 1,900 Portola Avenue 26,800 11,600 0 350 d/s Cook St 17,100 3,300 0 0 d/s Oasis Club Dr 11,500 2,300 0 0 Washington St 11,300 1,200 0 0
Table 4-3 shows a significant reduction of peak flows along the I-10 corridor for all the alternatives, compared to existing conditions. It also shows that storage of flood waters downstream of Portola Avenue result in a rapid decrease of peak flows further southeast towards Washington Street. This storage reduces peak flows to the Sun City Palm Desert flood channels at Washington Street to about 1,200 cfs for Alternatives 1 and to zero for Alternative 3. 4.4 Discussion by AlternativeDRAFT Alternative 1: Flood control channel through SPRR Bridge For Alternative 1, the extent of inundation in the North Cathedral City planning unit is not much reduced from existing conditions but a greater portion of the flood area has depths less than 1 foot (Tables 4-1 and 4-2). The Date Palm Drive Overpass and ramps still divert flow south into the developments around the intersection of Vista Chino and Date Palm Drive with Alternative 1 in place. In this part of the corridor, the primary benefit of the Alternative 1 diversion is in lower depths and velocities within the inundated areas. On the north side of the corridor, from Date Palm towards the community of Thousand Palms, flooding is caused by the peak flows from Willow Hole. These peak flows and the corresponding inundation are not altered by Alternative 1.
North Cathedral/Thousand Palms SMP 25 September 30, 2013 Alternatives Analysis
In the Thousand Palms area, the extent of inundation and overtopping of I-10 is reduced for Alternative 1 compared to existing conditions. Inundation to the south of I-10 and SPRR is mostly eliminated, except for a small area between Cook Street and Eldorado Drive. On the north side of I-10 the area of inundation is about the same as for existing conditions except at the downstream end of the study area, close to Washington Street, and extends to the southern limits of the Thousand Palms FCP inundation. Depths and velocities are reduced from existing conditions.
Alternative 2: Flood Channel to Sun City Palm Desert Under this alternative, inundation would occur on the Morongo Wash fan upstream of the I-10 culverts, through the culverts and downstream to the WWRSC and uphill from the Thousand Palms FCP (Figure 4- 2).
Alternative 3: New Bridge at Willow Wash Under this alternative, the 100-year flood on the Morongo Wash fan is conveyed to the WWRSC and flooding occurs on the Morongo Wash fan, through I-10 and SPRR, and downstream to WWRSC. Flooding also occurs downhill from where the 100-year inflows from Willow Hole enter the MIKE FLOOD model. Figure 4-3 shows that flows split to the east and west of Date Palm Road on the fan surface. The flows on the west are ponded by Date Palm Drive overpass and ramp fills, overflow the SPRR and cause shallow flooding in the subdivisions near Vista Chino and Date Palm Drive. The resulting flood depths are mostly less than 1 foot.
The flows on the east side of Date Palm Drive continue southeast between 1-10 and Varner Road, and cause shallow flooding in the community of Thousand Palms, mostly within 1,000 feet north of I-10. Further downstream the floodwaters are stored in various depressions and no flows pass Cook Street.
5. SUMMARY AND CONCLUSIONS
CVWD is preparing stormwater management plans for the North Cathedral City and Thousand Palms planning units. As the first step in plan preparation, NHC prepared an existing conditions report for the flooding that results from 100-year floods from the Morongo Watershed (called “riverine flows”), identifying areas of inundation and peak flows along the I-10 corridor downstream to Adams Street. A second report revised the hydrologyDRAFT and hydraulics for the Thousand Palms Flood Control Project based on new hydrologic and hydraulic models that met the policies and standards of CVWD. This second report also evaluated the benefits of this project with no management of the riverine flows.
The general conclusion of the earlier studies was that stormwater management in the North Cathedral City and Thousand Palms planning units required an integrated approach that addresses all sources of flooding in order to have appreciable benefits. In the Thousand Palms planning unit, the Thousand Palms Flood Control Project is the only alternative that CVWD is considering to manage 100-year floods from the Thousand Palms Watershed. As a result, the alternatives developed in this report all included the Thousand Palms FCP as a component of the design and cost.
North Cathedral/Thousand Palms SMP 26 September 30, 2013 Alternatives Analysis
This report developed three concepts to be implemented with the Thousand Palms FCP. They are:
• Construct a flood channel to convey flows from the existing I-10 culverts beneath the SPRR Bridge and to the Whitewater River Stormwater Channel (WWRSC); • Construct a flood channel to collect 100-year floods from Morongo Wash fan and Willow Hole and convey them to the Sun City Palm Desert flood channels; and • Construct a new bridge beneath I-10 to convey the entire 100-year flood on Morongo Wash fan to the WWRSC.
This report estimated preliminary or concept-level costs for the alternatives and evaluated their benefits by comparing the area of flooding with the alternative in place to that for existing conditions. The results are summarized in Table 5-1.
Table 5-1: Costs and Benefits for the Three Alternatives Alternative Flooded Area Concept Level Costs ($ millions) (acres) Thousand Palms Other Features Total Existing 7,400 - - - 1 5,500 $85 $13 $98 2 (Alignment 1) 900 1 $85 $265 $350 2 (Alignment 2) 900 1 $85 $220 $305 3 2,400 $85 $35 $120 1. Flooding occurs on Morongo Wash fan north of I-10 culverts
Table 5-1 shows that eliminating flood hazards along the I-10 corridor would cost between $305 and $350 million, depending on the selected alignment. A substantial reduction in the inundated or flooded area can be achieved by Alternative 3 at a cost of around $120 million. Alternative 1 provides some reduction in the areas of inundation and a larger reduction in peak flows crossing properties near I-10 for a cost just below $100 million. For Alternative 1, the reduction in the area inundated by the 100-year flood occurs mostly where depths of flooding are greater than 1 foot, where the potential damage from flooding is greatest.
There are some uncertainties for the costs. The most uncertain cost component is for the acquisition of property, which will have the greatestDRAFT effect on the cost estimates for the two alignments for Alternative 2. Property acquisition costs are thought to be a less significant component of the costs for the other two alternatives.
There are several hydraulic and other design issues that will need to be addressed during further development of the alternatives. For Alternative 1, reducing superelevation in the tight bends near the SPRR Bridge will be required to meet bridge clearances and freeboard. A variety of approaches are thought to be practical, including re-grading the channel, splitter walls in the channel, altering the position of the drop structure or other potential actions.
For Alternative 2, the main design issue would be to manage the peak inflows into the conveyance channels so that they match design capacities of the flood channels in SCPD or the capacity behind the
North Cathedral/Thousand Palms SMP 27 September 30, 2013 Alternatives Analysis
levees in the Thousand Palms FCP, depending on the alignment that is considered. The best approach to managing the peak inflows is to split them on the Morongo fan, sending some to the Whitewater River Stormwater Channel by incorporating Alternative 1 with both the selected alignment for Alternative 2. The splitting of the peak flows is expected to be a significant design challenge.
For Alternative 3, the main design issue will be to modify the Morongo Wash fan or add guide berms or other structures to ensure that peak flows on the fan are directed to the existing culverts and the new Bridge and that flooding of I-10 is avoided. The other issue will be to develop an alignment that avoids superelevation.
DRAFT
North Cathedral/Thousand Palms SMP 28 September 30, 2013 Alternatives Analysis
6. REFERENCES
Bechtel Corporation. 1996. Morongo Wash Flood Control Project – Hydraulic Design Report. Prepared for CVWD. July. 88 p.
Bechtel Corporation. 1997. “Without Project” Hydrology Report, Thousand Palms Area, Whitewater River Basin, Riverside and San Bernardino Counties, CA. US Army Corps of Engineers, Los Angeles District. March 20. 149 p.
Bechtel Corporation. 2008. Morongo Wash Flood Control Project: Final Hydraulic Design Report. Prepared by Bechtel Infrastructure Corporation, submitted to CVWD, May 26, 2008.
DHI (2011). MIKE 21 Flow Model, Hydrodynamic Module, User Guide.
Digital Mapping Inc., 2011. LiDAR Dataset for Riverside, California. Acquired for FEMA Region 9.
FEMA. 2008. Flood Insurance Study for Riverside County and Incorporated Areas. Volume 1 of 4. August 28.
Northwest Hydraulic Consultants. 2012. Morongo Wash Flood Control Project: Hydraulic Design Studies. Prepared for CVWD. September 25.
Northwest Hydraulic Consultants. 2013a. North Cathedral and Thousand Palms Stormwater Management Plan: Morongo Wash Watershed Existing Conditions Report. Prepared for CVWD. July 29.
Northwest Hydraulic Consultants. 2013b. North Cathedral and Thousand Palms Stormwater Management Plan: Thousand Palms Watershed and Thousand Palms Flood Control Project. Prepared for CVWD. September 19.
Simons, Li and Associates, Inc. (SLA). 2000. Hydraulic Appendix Whitewater River Feasibility Study. Report prepared for Los Angeles District, Corps of Engineers by Simons, Li and Associates, Inc., Irvine, California, 73 p.
Summit Engineering Corporation. 2011. FEMA Checkpoint Surveys for Riverside, California. Reno, NV. 227 p. DRAFT US Army Corps of Engineers (USACE). 1991. Hydraulic Design of Flood Control Channels. Engineering and Design Manual EM-1110-2-1601. Washington, D.C.
North Cathedral/Thousand Palms SMP 29 September 30, 2013 Alternatives Analysis
APPENDIX A
Alternative 1 Hydraulic Analysis
DRAFT
APPENDIX A: ALTERNATIVE 1 HYDRAULIC ANALYSIS
A.1 Introduction
The hydraulic characteristics within the Morongo Wash flood control project were simulated with a 1-d HEC-RAS model based on inflow hydrographs computed by MIKE FLOOD. The HEC-RAS model is a modified version of the one developed in NHC (2012). The following sections summarize the development of the HEC-RAS model, derivation of input data, key assumptions, computational parameters, and model results.
A.2 Model Development
Introduction The Hydrologic Engineering Center’s River Analysis System (HEC-RAS, Version 4.1, 2010) was used for the hydraulic analysis. The model geometry was developed from the Krieger & Stewart, Inc (2010; follows figures in this appendix)) drawings for the proposed flood control channel and from Whitewater River channel topography. Altogether, 64 cross-sections were specified in the model (34 between I-10 and SPRR and 30 downstream of SPRR). The cross-sections were generally about 100 to 200 ft apart. A narrower spacing was used near hydraulic structures.
The model included the proposed drop structure upstream of SPRR and the existing SPRR Bridge. The drop structure was modeled as an inline weir with a weir coefficient of 3.0 (default value). Dimensions and elevations of the SPRR Bridge deck and piers were taken from as-built plans provided by Krieger & Stewart. Flow through the bridge opening was computed using the energy (standard step) approach.
Accumulation of debris on the bridge piers was not included in the HEC-RAS model nor was an ineffective area defined for the bridge opening.
Manning’s Roughness A Manning’s n of 0.025 was adopted for the concrete-lined sections of the flood channel and 0.025 for sections with a sand bed. Contraction and expansion coefficients of 0.1 and 0.3, respectively, were specified for all the model cross-sections (default values for channels with gradually varying cross- sections). DRAFT
Hydraulic Boundary Conditions Given the brief duration of the 100-year flood, the short length of conveyance channel, and the similar timing of peak inflows from the Salvia Wash, Edom Wash, and Willow Wash Culverts and from over I-10, the HEC-RAS model of the Morongo Wash flood control channel was run in a steady state mode. Results from the most recent MIKE FLOOD simulations were used to specify 100-year peak inflows to the conveyance channel (Figure A1). Upstream and downstream boundary conditions were determined from normal depth computations.
A.3 Model Results
Introduction Figures A2 to A5 provide the results of the HEC-RAS model, showing the variations in flow depths, velocities, Froude numbers, and freeboard along the channel. Flow is supercritical at the Salvia Wash Culvert inlet and in the vicinity of the drop structure and SPRR Bridge. Flow depths range from about 4 to 5 ft upstream of the SPRR Bridge and from 5 to 8 ft immediately downstream of the drop structure and downstream of the bridge. Flow velocities are generally around 10 ft/s upstream of the drop structure, 18-21 ft/s in the vicinity of the SPRR Bridge, and 6-13 ft/s in the downstream portions of the conveyance channel. Figure A2 also shows the maximum depth with superelevation in the bends near the SPRR Bridge, calculated as described below.
Significant variations in depth occur because of lateral inflows from the culverts and overbank inflows, the drop structure, varying channel widths, frequent transitions between subcritical and supercritical flow and superelevation around bends.
Superelevation Superelevation is a transverse rise in water surface that occurs around a channel bend due to centrifugal forces. Bends also produce other conditions that affect hydraulic performance. They create secondary flows (helical or helicoidal flow) from the shifting of the maximum velocity from the channel center line and these flows may persist for many channel widths downstream. There may be flow separation near the inner bank, particularly for very sharp bends. A particular problem in channels designed for rapid flow is the formation of large standing waves in the curved flow that also persist for long distances downstream.
The potential rise in water surfaces due to superelevation and standing waves is an important process when designing top of bank elevations for high speed man-made channels. Bechtel (1996) estimated superelevation for the initial channel design of about 0.5 ft in the curved reach in the upper part of the channel and 2 ft in the curved reach between the drop structure and the SPRR Bridge. Bechtel (2008) reported that superelevation in the channel bend downstream from the drop structure would be 0.69 to 1.08 ft.
For this study, the rise in water surfaceDRAFT due to superelevation and standing waves was calculated using the procedures and equations in USACE (1991). The calculated water surface rise in the curved reaches is about 1.0 ft in the upstream part of the project channel, 9 ft between the drop structure and SPRR Bridge, 15 ft immediately downstream of the SPRR Bridge, and 1.7 ft approximately 300 to 400 ft downstream of the bridge.
The large rise in water surface elevation in the curved reaches immediately upstream and downstream of the SPRR Bridge results from the high flow velocities (18 to 20 ft/s) combined with small radii of curvature at the two bends. With superelevation, the current freeboard to the top of levees upstream of the SPRR Bridge and downstream of the bridge and the clearance to the bridge soffit would be exceeded.
Freeboard Analysis CVWD requires a minimum freeboard of 3 ft below adjacent ground for incised channels and a minimum freeboard of 4 ft from the top of levee to the 100-year water surface elevation for channels with levees. According to Bechtel (2008), the SPRR clearance requirements at railroad bridges are: (1) the energy grade line at the upstream side of the bridge should be at least 2 ft lower than the base of rail elevation for the 100-year flood peak discharge; and (2) the water level should be lower than the soffit elevation of the bridge for the 50-year flood peak discharge.
Figure A5 shows the freeboard (vertical distance between top of banks and water surface elevation) for the left and right banks based on the average water surface from HEC-RAS and the maximum water surface elevation with superelevation added. The freeboard meets the 3 foot criteria for an incised channel based on the average water surface elevation and also meets the SPRR clearance requirements. As is apparent on the figure, freeboard is not met in the vicinity of the SPRR Bridge when superelevation is considered.
A.4 Recommendations
The primary issue for the next stage of hydraulic design would be to reduce superelevation in the channel near the SPRR Bridge. There are a variety of options to address this issue. For the existing alignment, performance through the two curves could be improved with spiral transition curves (with or without a banked invert), dividing walls to reduce the channel width, invert sills in the curve, or reducing the channel curvature. USACE (1994a) provides detailed information on each of these methods. Alternatively, the current channel widths could be substantially reduced and the channel slope and alignment altered to improve performance.
The general features of the two options are described below:
• Maintain the existing alignment and provide dividing walls in the curved reaches upstream and downstream of the SPRR Bridge. The walls should extend continuously from about 400-450 ft upstream of the bridge to 400-450 ft downstream of the bridge. Spacing between the dividing walls would be 30-50 ft. These walls would reduce superelevation in the bends by a factor of 4. DRAFT • Narrow the channel and revise the alignment so that the curvature of the upper and lower bends is reduced to meet USACE recommendations for minimum radius of 2,800 ft upstream and 2,200 ft downstream of the SPRR Bridge. Essentially, this would require straightening the upstream bend so that the channel is shifted to the left (east) downstream of the bridge. The bend to re-join the downstream channel alignment would also be straightened to increase its radius of curvature to about 2,200 ft. These adjustments would reduce superelevation by a factor of 15.
Morongo Wash flood control channel
20,000 100-year flood 18,000 Flow direction
16,000
14,000
12,000
10,000 SPRR Bridge Drop structure
Discharge (cfs) 8,000
6,000
Willow Wash 4,000 Edom Wash Culvert Total inflow (MIKE FLOOD) Culvert 2,000 Salvia Wash Culvert Inflow from culverts (MIKE FLOOD)
0 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Longitudinal distance (ft)
Figure A1: 100-year peak flows in conveyance channel (from MIKE FLOOD).
Morongo Wash flood control channel
24
22 100-year flood Flow direction
20 Salvia Wash Willow Wash Culvert Culvert 18 Edom Wash Culvert 16
14 Depth (HEC-RAS steady) 12 DRAFTDepth (HEC-RAS steady) + superelevation
Depth (ft) Depth 10
8
6
4
2 SPRR Bridge Drop structure 0 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Longitudinal distance (ft)
Figure A2: 100-year flow depths in channel with and without superelevation (from HEC-RAS).
Morongo Wash flood control channel
24
22 100-year flood Flow direction
20 Salvia Wash Willow Wash Culvert Culvert 18 Edom Wash Culvert 16
14
12
10 Velocity (ft/s)
8
6
4 Velocity (HEC-RAS steady)
2 Drop structure SPRR Bridge
0 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Longitudinal distance (ft)
Figure A3: 100-year flow velocities in conveyance channel (from HEC-RAS).
Morongo Wash flood control channel
3
100-year flood Flow direction
Salvia Wash Willow Wash Culvert Culvert Edom Wash Drop structure Culvert 2 DRAFTFroude number (HEC-RAS steady) Froude number Froude
1
SPRR Bridge
0 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Longitudinal distance (ft)
Figure A4: 100-year Froude number in conveyance channel (from HEC-RAS).
Morongo Wash flood control channel
12 Flow direction 10 100-year flood
8
6
4
2 FEMA freeboard 0 requirement Salvia Wash -2 Freeboard (ft) Culvert Left bank (HEC-RAS steady) -4 Edom Wash Willow Wash Culvert Culvert Left bank (HEC-RAS steady) + superelevation -6
-8
-10 Drop structure SPRR Bridge -12 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Longitudinal distance (ft)
12 Flow direction 10 100-year flood
8
6
4
2 FEMA freeboard requirement 0
-2 Freeboard (ft) Salvia Wash DRAFTWillow Wash Right bank (HEC-RAS steady) -4 Culvert Culvert Right bank (HEC-RAS steady) + superelevation -6 Edom Wash Culvert -8
-10 Drop structure SPRR Bridge -12 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 Longitudinal distance (ft)
Figure A5: Left bank (top) and right bank (bottom) freeboards in conveyance channel for 100-year peak flow with and without superelevation (from HEC-RAS).
APPENDIX B
Alternative 2 Hydraulic Analysis
DRAFT
APPENDIX B: ALTERNATIVE 2 HYDRAULIC ANALYSIS
B.1 Introduction
Uniform flow calculations were carried for the two potential alignments of Alternative 2 in order to establish typical channel dimensions for concept-level cost estimates.
B.2 Channel Profiles
Figures B.1 and B.2 show ground profiles cut from the LiDAR topography along the alignments shown on Figure 3.2. The two profiles show that construction of a channel near ground level is reasonably practical. Alignment 2 will have considerably more excavation of overburden than Alignment 1 in order to maintain consistent bed slopes.
Both profiles show steeper slopes near Morongo Wash Fan than in the downstream 3 miles of the alignments. For hydraulic calculations the profiles were divided into two parts and typical slopes calculated (Table B1).
Table B1: Average Ground Slopes along the Two Alignments Alignment Stationing Average Slope (ft/ft) No. 1 d/s end 0 to 286+85 0.31% No. 1 u/s end 286+85 to 609+51 0.95% No. 2 d/s end 0 to 175+55 0.2% No. 2 u/s end 175+55 to 44+252 1.02%
B.3 Channel Cross Section
A constant bed width of 150 feet was adopted for both alignments. The channels were assumed to be concrete-lined (6-inchesDRAFT thick) to withstand abrasion and erosive effects of the super- critical flow. Side slopes were set to 1.5:1 and an allowance of 20 ft was assumed for access roads, shoulder and fencing on each side. The typical footprint for each channel was about 250 feet wide. (Refer to the cross section drawing at the end of this Appendix.)
Normal flow depths were calculated for each segment of the flood channel alignment based on a peak flow of 20,300 cfs, the above design cross section, and a Manning’s roughness of 0.025 (fine sand). This roughness was adopted to account for sand in the channel and sand in transport.
Alignment 1 Profile 600 550 500
450 400 350 300 250 Elevation (ft) NGVD29 (ft) Elevation 200 150 100 0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 55000 60000 65000 Distance (DS to US), ft
Alignment 2 Profile 550
500
450
400 350 DRAFT
Elevation (ft) NGVD29 (ft) Elevation 300
250
200 0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 Distance DS to US (ft)
Figures B1 and B2: Ground Profiles along Alignments 1 and 2
A table on the typical cross section drawing (following page) summarizes the hydraulic characteristics for each alignment. The flood channel in the upper part of each alignment will flow supercritical; the downstream reaches with the shallower slopes will have subcritical flow. Froude numbers are typical of those required for design of supercritical and subcritical channels.
Excavation volumes for channel construction were based on the typical depths quoted on the following page plus a freeboard of 3 feet, which assumes that the top of the channels banks will be near existing ground elevations. An average overburden of 3 feet was assumed as part of excavation.
DRAFT
APPENDIX C
Alternative 3 Hydraulic Analysis
DRAFT
APPENDIX C: ALTERNATIVE 3 HYDRAULIC ANALYSIS
C.1 Introduction
The hydraulic characteristics for this alternative were simulated with a 1-d HEC-RAS model. Inflows to the model consisted of the peak flows through Edom and Salvia Culverts computed by MIKE FLOOD and an inflow for the proposed Willow Wash Bridge or Culvert that was calculated by subtracting the flows through Edom and Salvia Culverts from the combined 100-year peak flow on Morongo Wash fan. This is a conservative estimate of the peak flow at Willow Wash. Flows through the two culverts and the bridge were then added for the peak flow through the SPRR Bridge.
The HEC-RAS model is a modified version of the one developed in NHC (2012). The following sections summarize the development of the HEC-RAS model, derivation of input data, key assumptions, computational parameters, and model results.
C.2 Model Development
Introduction The Hydrologic Engineering Center’s River Analysis System (HEC-RAS, Version 4.1, 2010) was used for the hydraulic analysis. The model geometry was designed for full conveyance of the 100-yr Morongo Wash 100-year peak flow of 36,200 cfs to the WWRSC with minimum modifications to existing culverts and bridges. The SPRR Bridge structure and Edom and Salvia Culverts were not modified in the HEC-RAS model.
The model included a concrete-lined flood channel of varying slopes with a bottom width of 200ft, side slopes of 1.5:1, and a bank height of 12 ft between Willow Wash Bridge and the SPRR Bridge. The top of the channel banks were set near ground level to match existing grade where possible.
The new Willow Wash Culvert included in the model has a bottom width of 200 ft, 1.5:1 side slopes and an invert elevation that was 5 ft lower than the existing culvert. The area directly upstream of the Willow Wash Culvert was graded with a 200ft wide channel to guide the flow under I-10. The section of the Krieger and StewartDRAFT Morongo Creek Channel, between Edom and Willow Wash Culverts, was used in the model to represent the inlet conditions and convey flows from the two upstream culverts. A transition region where the flood channel expanded to 250 ft was added at the confluence of Edom and Salvia channel and the new Willow Wash Flood Channel.
The SPRR Bridge was not changed. The 200 ft wide concrete-lined channel would fit between the SPRR Bridge abutments. The invert elevation at the bridge would be 494.8 ft. This would create a drop of 15 feet over the 1,200 ft long channel, from the upstream edge of the Willow Wash Culvert to the upstream edge of the SPRR Bridge, creating a slope of 1.25% between the two bridges. Downstream of the SPRR Bridge the flood control channel flattens to a slope of 1% until it meets existing grade.
Accumulation of debris on the bridge piers was not included in the HEC-RAS model nor was an ineffective area defined for the bridge opening.
Manning’s Roughness A Manning’s n of 0.025 was adopted for the concrete-lined flood channels. Contraction and expansion coefficients of 0.1 and 0.3, respectively, were specified for all the model cross-sections (default values for channels with gradually varying cross-sections). A Manning’s value of 0.04 was used for the area outside of the constructed channel and for the natural materials at the downstream boundary of the model.
Hydraulic Boundary Conditions Given the brief duration of the 100-year flood, the short length of conveyance channel, and the similar timing of peak inflows to Salvia and Edom culverts and the new Willow Wash Bridge, the HEC-RAS model was run in a steady state mode. Results from the most recent MIKE FLOOD simulations were used to specify 100-year peak inflows to the Edom and Salvia Culverts. The peak flow at Willow Wash Culvert (27,200cfs) was computed by subtracting the peak discharges of the two upstream culverts (9,000cfs) from the peak Morongo Wash Flow (36,200cfs). Upstream and downstream boundary conditions were determined from normal depth computations.
C.3 Model Results
Introduction Figures C1 to C5 provide the results of the HEC-RAS model, showing the 100-year water surface profile and the variations in flow depths, velocities, Froude numbers, and freeboard along the channel. Flow is supercritical through nearly all the Willow Wash channel, except for a jump where the flows from Edom and Salvia culverts enter. Flow depths are 6 to 7 ft upstream of the SPRR Bridge but rise to 10 feet at the jump to subcritical flow. Depths are about 8 ft immediately downstream of the drop structure and downstream of the bridge. Flow velocities range from 16 to 22 ft/s. Significant variations in depth occur where the lateral inflows from the culverts join the flood channel.
Superelevation Superelevation is a transverse rise in water surface that occurs around a channel bend due to centrifugal forces. Bends also produce otherDRAFT conditions that affect hydraulic performance. They create secondary flows (helical or helicoidal flow) from the shifting of the maximum velocity from the channel center line and these flows may persist for many channel widths downstream. There may be flow separation near the inner bank, particularly for very sharp bends. A particular problem in channels designed for rapid flow is the formation of large standing waves in the curved flow that also persist for long distances downstream.
The potential rise in water surfaces due to superelevation and standing waves is an important process when designing top of bank elevations for high speed man-made channels. The flood control channel for Alternative 3 is not at the level of design to assess superelevation at this time. However, the large superelevation calculated for Alternative 1 shows that this is a design concern moving forward.
Freeboard Analysis CVWD requires a minimum freeboard of 3 ft below adjacent ground for incised channels and a minimum freeboard of 4 ft from the top of levee to the 100-year water surface elevation for channels with levee. According to Bechtel (2008), the SPRR clearance requirements at their bridges are: (1) the energy grade line at the upstream side of the bridge should be at least 2 ft lower than the base of rail elevation for the 100-year flood peak discharge; and (2) the water level should be lower than the soffit elevation of the bridge for the 50-year flood peak discharge.
Figure shows the freeboard (vertical distance between top of banks and water surface elevation) for the left and right banks based on the water surface elevation from the steady HEC-RAS model. The freeboard meets the 3 foot criteria for an incised channel based on the average water surface elevation. Given the high velocities, the 100-year energy grade may not be 2 feet below base of rail and some modifications to the channel may be required to meet this criterion.
C.4 Next Steps
Alternative 3 was designed to test if the Morongo Wash peak flow could be conveyed to the WWRSC through a new bridge at Willow Wash and the existing SPRR Bridge. There are a few issues that would need to be examined further before the next stage of design. These issues include the following:
• The extent and design of modifications required to direct peak flows into the new Willow Wash Culvert will be examined through MIKE FLOOD simulations. These simulations will also revise the 100-year design flow to Willow Wash and through the SPRR Bridge. • The bed width in the Krieger and Stewart Flood Control channel could be substantially reduced and the channel slope and alignment altered to improve performance and reduce costs. • The junction between the channels from the Edom and Salvia Culverts and from the new Willow Wash Bridge will need further design to eliminate the hydraulic jump. • Superelevation may be an issue, depending on the curvature of the flood control channels. There are a variety of options to address superelevation, as discussed for Alternative 1.
DRAFT
Alternative 3 100-Yr Water Surface Profile 530
9,000 cfs Inflow 525 From Edom and Salvia Culverts 520
515
510 27,200 cfs 505 Morongo Wash Inflow
500
Elevation (ft) NGVD29 S =1.25%
495
490
485 S= 1.0%
480 6500 7000 7500 8000 8500 9000 9500 10000 Station (ft)
Levee El Min Ch El W.S. Elev SPRR Bridge Willow Wash Bridge
Figure C1: Water surface profile for flood control channel (from HEC-RAS).
Willow Wash Replacement flood control channel
12
11 100-year flood Flow direction
10 Willow Wash Culvert 9
8
7 6 DRAFT Depth (ft) Depth 5 SPRR Bridge 4
3
2 Depth (HEC-RAS steady) 1 Without superelevation in curved reaches 0 0 500 1,000 1,500 2,000 2,500 3,000 Longitudinal distance (ft)
Figure C2: 100-year flow depths in channel with and without superelevation (from HEC-RAS).
Willow Wash Replacement flood control channel
30
100-year flood Flow direction 28
26 Willow Wash Culvert 24
22
20
Velocity (ft/s) 18
16 SPRR Bridge
14 Velocity (HEC-RAS steady)
12
10 0 500 1,000 1,500 2,000 2,500 3,000 Longitudinal distance (ft)
Figure C3: 100-yr velocity in channel (from HEC-RAS).
Willow Wash Replacement flood control channel
3
100-year flood Flow direction
Willow Wash Culvert 2 DRAFTFroude number (HEC-RAS steady) Froude number Froude
1
SPRR Bridge
0 0 500 1,000 1,500 2,000 2,500 3,000 Longitudinal distance (ft)
Figure C4: 100-yr Froude numbers in channel (from HEC-RAS)
Willow Wash Replacement flood control channel
12
11 100-year flood Flow direction
10 Willow Wash 9 Culvert Without superelevation in curved reaches
8
7
6
5 Freeboard (ft)
4
3
2 Left bank (HEC-RAS steady) 1 SPRR Bridge Right bank (HEC-RAS steady) 0 0 500 1,000 1,500 2,000 2,500 3,000 Longitudinal distance (ft)
Figure C5: Left bank and right bank (bottom) freeboards in conveyance channel for 100-year peak flow (from HEC-RAS).
DRAFT
APPENDIX D
Preliminary Cost Estimates
DRAFT
Table D.1: Preliminary Cost Estimate for Alternative 1
Item Quantity Unit Unit Cost Subtotal Mobilization/De-Mobilization 2 LS $50,000 $100,000 Upstream of SPRR Bridge – Concrete-lined channel (4,340 feet long) Concrete volume (160 ft bottom, 4 ft deep) 19,800 CY $250 $4,900,000 Excavation volume 280,000 CY $12 $3,400,000 Property footprint (assumed CVWD owned) 0 Acres $30,000 $0 Downstream of SPRR Bridge – Bank Lining (4,900 feet long) Concrete Volume (20 foot vertical, 1.5:1 slope) 2,800 CY $250 $700,000 Excavation volume 70,000 CY $5 $500,000 Property footprint (assumed CVWD owned) 0 LS $30,000 $0
Subtotal $9,600,000 Design and Construction Supervision $400,000
Contingency 25% $2,500,000 ALTERNATIVE SUBTOTAL $12,500,000 Thousand Palms FCP $85,000,000 TOTAL $98,000,000 1. Channel depth is flow depth plus 3 feet of freeboard. Bank slopes are 1.5H:1V 2. Excavation volumes assume the channel cross section plus 3 feet of overburden on the total top width. 3. Concrete for channel lining and bank protection is assumed to 6 inches thick and include rebar and forming. Thicker concrete may be required where velocities exceed 10 ft/s. 4. Property footprint assumes channel top width plus 20 foot roadway on each bank. 5. Concrete and excavation unit costs are from the Jefferson Street Grade Control and Sewer line Replacement construction cost estimates. DRAFT
Table D.2: Preliminary Cost Estimate for Alternative 2 Alignment 1
Item Quantity Unit Unit Cost Subtotal Mobilization/De-Mob 2 LS $250,000 $500,000 Collection Structure on Fan Rough estimate 1 LS $5,000,000 $5,000,000 Main Conveyance Channel (60,000 ft) Concrete volume (150 ft bottom width, 8.5 ft 283,000 CY $250 $71,000,000 deep) Excavation volume (assumes 3 ft of overburden) 5,600,000 CY $12 $66,600,000 Property footprint 310 Acres $50,000 $16,000,000 Willow Hole Connecting Channel (3,000 ft) Collection Basin 1 LS $1,000,000 Concrete volume (40 ft bottom width, 5 ft depth) 5,100 CY $250 1,300,000 Excavation volume (assumes 3 ft of overburden) 69,000 CY $12 830,000 Property footprint 7 Acres $50,000 210,000 Bridge Crossings Major Bridges 5 LS $4,800,000 $24,000,000 Smaller Bridges 7 LS $1,900,000 $13,300,000 Alternative 1 to Convey Flows to WWRSC Refer to Table D.1 1 LS $10,000,000 Subtotal $210,000,000 Design and Construction Supervision $2,000,000
Contingency 25% $53,000,000 CONCEPT COST $265,000,000 Thousand Palms FCP DRAFT $85,000,000 TOTAL $350,000,000 1. Channel depth is flow depth plus 3 feet of freeboard. Bank slopes are 1.5H:1V 2. Excavation volumes assume the channel cross section plus 3 feet of overburden on the total top width. 3. Concrete for channel lining and bank protection is assumed to 6 inches thick and include rebar and forming. Thicker concrete may be required where velocities exceed 10 ft/s. 4. Property footprint assumes channel top width plus 20 foot roadway on each bank. 5. Concrete and excavation unit costs are from the Jefferson Street Grade Control and Sewer line Replacement construction cost estimates.
Table D.3: Preliminary Cost Estimate for Alternative 2 Alignment 2
Item Quantity Unit Unit Cost Subtotal Mobilization/De-Mob 2 LS $250,000 $500,000 Collection Structure on Fan Rough estimate 1 LS $5,000,000 $5,000,000 Conveyance Channel (45,000 ft) Concrete volume (150 ft bottom width, 8.5 ft 210,000 CY $250 $53,000,000 depth) Excavation volume (assumes 3 ft of overburden) 4,200,000 CY $12 $50,000,000 Property footprint 232 Acres $50,000 $11,600,000 Willow Hole Connecting Channel (3,000 ft) Collection Basin 1 LS $1,000,000 Concrete volume (40 ft bottom width, 7 ft depth) 4,800 CY $250 1,300,000 Excavation volume (assumes 3 ft of overburden) 61,000 CY $12 830,000 Property footprint 7 Acres $30,000 210,000 Bridge Crossings Major Bridges 3 LS $4,800,000 $14,400,000 Smaller Bridges 14 LS $1,900,000 $26,600,000 Alternative 1 to Convey Flows to WWRSC Refer to Table D.1 1 LS $10,000,000
Subtotal $174,000,000 Design and Construction Supervision $2,000,000
Contingency 25% $44,000,000 CONCEPT COST $220,000,000 Thousand Palms FCP $85,000,000 TOTAL DRAFT $305,000,000 1. Channel depth is flow depth plus 3 feet of freeboard. Bank slopes are 1.5H:1V 2. Excavation volumes assume the channel cross section plus 3 feet of overburden on the total top width. 3. Concrete for channel lining and bank protection is assumed to 6 inches thick and include rebar and forming. Thicker concrete may be required where velocities exceed 10 ft/s. 4. Property footprint assumes channel top width plus 20 foot roadway on each bank. 5. Concrete and excavation unit costs are from the Jefferson Street Grade Control and Sewer line Replacement construction cost estimates.
Table D.4: Preliminary Cost Estimate for Alternative 3
Item Quantity Unit Unit Cost Subtotal Mobilization/De-Mob 2 LS $250,000 $500,000 New Willow Wash (I-10) Bridges Two Bridges (75 ft wide by 200 ft long) 30,000 SF $250 $7,500,000 Traffic Management, etc 1 LS $3,750,000 Grading upstream of Bridge 300,000 CY $5 $1,500,000 Property Acquisition 0 Acres $30,000 $0 Channel Downstream of Willow Wash (2,600 ft) Concrete volume (200 ft bottom; 10 ft depth) 15,100 CY $250 $3,800,000 Excavation volume 280,000 CY $12 $3,000,000 Property footprint (assumed CVWD owned) 0 Acres $30,000 $0 Channel from Edom and Salvia Culverts(3,140 ft) Concrete volume (160 ft bottom width, 4 ft depth) 14,300 CY $250 $3,600,000 Excavation volume 200,000 CY $12 $2,400,000 Property footprint (assumed CVWD owned) 0 Acres $30,000 $0 Bank Lining Downstream of SPRR (5,000 ft) Concrete Volume (30 foot vertical height at 1.5:1) 4,200 CY $250 $1,000,000 Excavation volume 100,000 CY $5 $500,000 Property footprint (assumed CVWD owned) 0 LS $30,000 $0
Subtotal $27,600,000 Design and Construction Supervision Fees $500,000
Contingency 25% $7,000,000 CONCEPT COST $35,000,000 Thousand Palms FCP $85,000,000 TOTAL DRAFT $120,000,000 1. Channel depth is flow depth plus 3 feet of freeboard. Bank slopes are 1.5H:1V 2. Excavation volumes assume the channel cross section plus 3 feet of overburden on the total top width. 3. Concrete for channel lining and bank protection is assumed to 6 inches thick and include rebar and forming. Thicker concrete may be required where velocities exceed 10 ft/s. 4. Property footprint assumes channel top width plus 20 foot roadway on each bank. 5. Concrete and excavation unit costs are from the Jefferson Street Grade Control and Sewer line Replacement construction cost estimates.