HomeMy WebLinkAboutDune Palms Hydrologic and Hydraulic Analysis_8-26-2015
Hydrology & Hydraulic Study
For
The Replacement of the Dune Palms Road Low-Water Crossing
at the Coachella Valley Stormwater Channel
In La Quinta, California
Federal Aid Project No. BLRKS-5433(014)
Prepared For
The City of La Quinta
BY
August 16, 2015 (Revised)
250 Big Sur Drive, Goleta, CA 93117 Phone: (805) 563-0788
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page i
Bengal Engineering, Inc. August 16, 2015 (Revised)
This Hydrology & Hydraulic Study has been prepared under the direction of Mohammed
Wahiduzzaman, Registered Civil Engineer, who attests to the technical information contained
herein and the engineering data upon which the recommendations, conclusions, and decisions
are based.
08/16/15 (Revised)
REGISTERED CIVIL ENGINEER Date
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page ii
Bengal Engineering, Inc. August 16, 2015 (Revised)
Contents
EXECUTIVE SUMMARY................................................................................................................................................. 1
Scope ................................................................................................................................................................. 1
Introduction ......................................................................................................................................................... 1
Results ................................................................................................................................................................ 3
KEY FACTORS OF THE PROJECT ............................................................................................................................. 4
WATERSHED CHARACTERISTICS ............................................................................................................................ 6
HYDRAULIC ANALYSIS ................................................................................................................................................ 6
Analysis of Proposed Bridge ............................................................................................................................. 7
Scour Analysis ................................................................................................................................................. 10
CONCLUSIONS AND RECOMMENDATIONS ......................................................................................................... 15
ATTACHMENTS: ........................................................................................................................................................... 17
Project Photos .................................................................................................................................................. 17
Figure 1: Vicinity Map ...................................................................................................................................... 19
Plate 1 - Watershed Map ................................................................................................................................. 20
Plate 2: Storm Frequency vs Discharge Graph .............................................................................................. 21
Appendix A: HEC-RAS Output ................................................................................................................................ 22
CVSC HEC-RAS Alignment at the Project Site .............................................................................................. 23
Hydraulic Table for Proposed Condition - QSPF & Q100 (FEMA) ........................................................................... 24
Hydraulic Table for Existing & Proposed Conditions - QSPF ........................................................................... 25
Hydraulic Profile for QSPF ................................................................................................................................. 26
Cross Section Upstream of Dune Palms Bridge – Proposed Condition ........................................................ 27
Dune Palms Bridge X-Sections – Proposed Condition .................................................................................. 27
Appendix B: Equilibrium Slope Calculations ...................................................................................................... 28
Appendix C: Bridge Scour Calculations ............................................................................................................... 34
Appendix D: CVSC Hydraulic Profiles .................................................................................................................. 49
Appendix E: Advance Planning Study Bridge Plan ............................................................................................... 51
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 1
Bengal Engineering, Inc. August 16, 2015 (Revised)
EXECUTIVE SUMMARY
Scope
This document presents a Hydrology and Hydraulic Study for the proposed Dune Palms Road
Low-Water Crossing Replacement Project, at the Coachella Valley Stormwater Channel (CVSC),
in the City of La Quinta. The location of the bridge is shown in the Figure 1: Vicinity Map.
This limited study was undertaken using information available to the City from the previous
studies prepared for the CVSC. These previous studies include design discharge, scour potential,
and channel / capacity improvement plans.
This Hydrology & Hydraulic Study is not a comprehensive study of all aspects which may be
addressed in the ultimate development of the CVSC. This analysis has been undertaken with
limited time and budget to provide hydraulics data required for the Structure Type Selection, the
development of the bridge plans and the development of the necessary slope protection plans.
This project is proposed to be constructed with the assistance of the FHWA - Highway Bridge
Program (HBP).
Introduction
The purpose of this project is to replace the existing Dune Palms Road Low-Water (“at grade”)
crossing with a bridge at the CVSC in the City of La Quinta, California at the location shown on
Figure 1: Vicinity Map. The channel crossing is located north of Highway 111 between Adams
Street and Jefferson Street.
This report has identified the following key objectives in developing a comprehensive technical
analysis of the hydraulics associated with the Dune Palms Road crossing of the CVSC;
1. Perform supporting water surface profile hydraulic analysis of the CVSC crossing to verify
that the minimum freeboard requirements and flood protection levels provided are
consistent with local and federal jurisdiction requirements. Water surface profiles will
examine the 100-year and Standard Project Flood (SPF) Conditions.
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 2
Bengal Engineering, Inc. August 16, 2015 (Revised)
2. Determine the preliminary bridge configuration to maximize flow, provide minimum
freeboard requirements, and the flood protection levels which are consistent with local and
federal jurisdiction requirements.
3. Evaluate the toe-protection depths for the revetment sections based upon the
application of standard design criteria for the channel.
4. Evaluate the general scour depths, including long-term scour and local pier scour
based upon the application of standard design criteria for the channel.
5. Provide recommendations for the foundation types for the proposed bridge.
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 3
Bengal Engineering, Inc. August 16, 2015 (Revised)
Results
The results of the analyses are summarized in the following tables which define the project
hydrology, hydraulics and the performance of the CVSC at the proposed bridge site.
Table A: Hydrology Summary
Table B: Water Surface Profile Data
Flood
Frequency
Cross Section
Location
Existing
HGL
(ft)
Proposed
HGL
(ft)
QSPF Bridge
Upstream 62.2 57.5
Q100 (FEMA) Bridge
Upstream 57.0 51.7
Existing HGL: Hydraulic Grade Line elevation (NAVD88 Datum) for the existing condition
Proposed HGL: Hydraulic Grade Line elevation (NAVD88 Datum) anticipated after
replacement of the existing low-water crossing
Table C : Bridge Performance Data
Key Criteria Proposed Bridge
Freeboard to bridge soffit for SPF flood event ±1.6 ft
Freeboard to Levee for FEMA 100-yr flood event ±8.3 ft
Overtopping Flow 110,000 ft3/sec
Channel Slope : 0.2%
Design Flood, QSPF : 82,000 ft3/sec
Design Flood, Q100 (FEMA) : 43,000 ft3/sec
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 4
Bengal Engineering, Inc. August 16, 2015 (Revised)
KEY FACTORS OF THE PROJECT
• The City of La Quinta is proposing to replace the existing low-water crossing at the
Coachella Valley Stormwater Channel (CVSC) with an all-weather bridge.
• The bridge type is proposed to be a Cast-in-Place Pre-stressed Concrete Box Girder,
supported by large-diameter caissons at the piers.
• The proposed conveyance capacity of the new bridge will convey Standard Project Flood
(SPF), plus a minimum of 1.0 foot of freeboard, as set forth by the Coachella Valley
Water District (CVWD) for the CVSC.
• This report was prepared for the City of La Quinta as part of the project design
requirements set forth by the FHWA – Highway Bridge Program (HBP), administered by
Caltrans Local Assistance.
• The proposed project will require CVWD approval of this report and all improvement plans
within the CVSC right of way. Following approval of the study and plans, CVWD will issue both
a permanent encroachment and temporary construction permit.
• This proposed project will be constructed with the assistance of the FHWA - Highway
Bridge Program (HBP).
• CVWD set the Standard Project Flood (SPF) discharge of 82,000 ft3/sec as a design flow
requirement for the channel at the project site.
CVWD Design Requirements
CVWD is the local agency responsible for the regional flood control facilities, including the
CVSC, within the immediate project limits. CVWD has developed the following design
requirements for improvements within the subject reach of the CVSC:
• Standard Project Flood (SPF) discharge is 82,000 ft3/sec .
• The minimum freeboard under the bridge for the SPF discharge is 1-foot.a
• The minimum levee freeboard for the SPF discharge is 1-foot.b
• The minimum levee freeboard for the 100-year FEMA discharge is 4-foot c.
• Maximum scour depths for bridge are to be calculated for the SPF d.
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 5
Bengal Engineering, Inc. August 16, 2015 (Revised)
• CVWD has adopted the Blench regime equation for calculating scour depths for bank
protection e.
This study followed the CVWD design requirements for the CVSC with the following
assumptions:
• The existing low flow channel crossing at the Dune Palms Rd. will be removed following
construction of the bridge.
• The channel invert at the crossing will degrade once the low water crossing is removed.
However, the channel thalweg will aggrade immediately downstream of the crossing,
after removal of the hydraulic drop condition.
• Bengal Engineering updated the CVWD WWRSC – CVSC HEC-RAS model. The model
update was limited to the immediate vicinity of the project.
• The minimum channel invert at the bridge is set to elevation 40.0-feet for the HEC-RAS
analysis to provide conservative HGL profile.
• Fbo = 1, zero-bed factor was used to calculate dfo (Eqn K3.1) for Blench regime equation.
• Z-factor = 1 is recommended for the calculation of ds instead of Z =1.25 (Eqn K3-2) for
scour at the bridge, since the channel bank protections will have minimum alignment
intrusion in to the channel. Also, due to the proposed accommodation of the CVLink
Trail at the south bank near south abutment, the contraction scour at the bridge will be
negligible. A Z=1.25 value will increase the calculated scour depth and might interfere
subsurface flow of the channel if implemented in the design.
• No grade control structure was modeled or is proposed to be installed at the project site.
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 6
Bengal Engineering, Inc. August 16, 2015 (Revised)
WATERSHED CHARACTERISTICS
The Whitewater River Basin is located approximately 100 miles east of Los Angeles. The
watershed drains to the Salton Sea located about 23 miles south of the project site. The
tributary area of the watershed is made up of a broad desert valley (Coachella Valley) between
two mountain ranges; the San Bernardino and Little San Bernardino Mountains form the
northeast boundary of the watershed, the San Jacinto and Santa Rosa Mountains form the
southeast boundary.
Upstream from the vicinity of Washington Street (Point Happy), the channelized section of the
Whitewater River is referred to as the Whitewater River Stormwater Channel (WWRSC).
Downstream of Point Happy to the Salton Sea, this channelized section is referred to as the
Coachella Valley Stormwater Channel (CVSC).
The drainage area tributary to the CVSC at the proposed Dune Palms Road Bridge is
approximately 788 sq. mi. (USCOE 1980)f. The mean seasonal precipitation in the area
tributary to the Dune Palms Road crossing varies from 44 inches at San Gorgonio Mountain
to about 3 inches at the crossing. The watershed is shown in Plate 1 - Watershed Map. The
channel discharge-frequency graph is shown on Plate 2: Storm Frequency vs Discharge Graph.
HYDRAULIC ANALYSIS
The hydraulic analysis of the CVSC at the Dune Palms Road Low-Water Crossing was made using
the HEC-RAS g (Version 4.1.0) River Analysis System computer model for calculating water surface
profiles in rivers (US Corps of Engineers, January 2010).
The vertical datum for the analysis is NAVD88. The NGVD 1929 datum elevation can be obtained
at the project site by subtracting 2.37 feet from the NAVD 1988 datum elevation. The California
Coordinate System Zone VI, NAD83 was followed for the project survey.
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 7
Bengal Engineering, Inc. August 16, 2015 (Revised)
Analysis of Proposed Bridge
The existing Dune Palms Road crossing is a 60-foot wide, three lane facility which is classified
as a “major collector” by the City of La Quinta through it’s General Plan. The road crosses the
CVSC at a skew of approximately 18 degrees. The top width of the channel is approximately
460 feet. The channel bottom is earthen and comprised of mostly fine-grained, sandy alluvial
material.
Concrete slope protection exists at the southwest and northeast corners of the crossing. The
concrete slope protection at the northwest corner ends approximately 200 feet upstream of
the crossing and at the southeast corner the slope protection ends approximately 340 feet
downstream of the crossing. Photos 1- 4 show various views of the existing channel crossing
at Dune Palms Road. The following table shows the existing location and elevation of the slope
protection cut off walls.
Crossing
Corner
Dist. From
Crossing
Cut-off Wall
Elev
(NGVD29)
Cut-off Wall
Elev
(NAVD88)
CVWD
Plan #
Northwest 200’ west 22.16 24.53 39069
Northeast At crossing 29.90 32.27 19514
Southwest At crossing 28.38 30.75 25854
Southeast 340’ east 26.06 28.43 35788
Channel Morphology
The fluvial geomorphology of a river channel is a function of a number of processes and
environmental conditions, including the composition and erodibility of the bed and banks (e.g.,
sand, clay, bedrock); vegetation and the rate of plant growth; the availability of sediment; the size
and composition of the sediment moving through the channel; the rate of sediment transport
through the channel and the rate of deposition on the floodplain, banks, bars, and bed; and regional
aggradation or degradation due to subsidence or uplift.
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 8
Bengal Engineering, Inc. August 16, 2015 (Revised)
The CVSC fluvial geomorphology is dynamic and is influenced by the land use and development
taking place in the watershed. The CVWD is actively monitoring, managing, and maintaining the
channel bed, flood control levee, and grade control structures.
Existing Channel Condition
There are two permanent grade control structures within the channel reach, located at
the following locations:
1) Downstream of the Washington Street Bridge
2) Downstream of the Jefferson Street Bridge
The existing Dune Palms Road low-water crossing is currently preventing the channel bed to adjust
through normal fluvial process. Through time an 8-foot grade difference in elevation between the
upstream and downstream of the crossing has developed. The low-water crossing will be removed
once the new bridge is constructed. Once the crossing is removed, the channel profile will go
through gradual fluvial adjustments, based on the flow volume, flood frequencies, channel
vegetation, sediment loads, and maintenance activities.
During our study, we compared our current topographic survey with the existing HEC-RAS model
provided by the CVWD. It appears that the channel grade between Washington Street and Dune
Palms Road crossing is still adjusting as a result of the removal of the Adams Street h low-water
crossing. Similarly, due to the recent construction of the grade control structure at the Jefferson
Street Bridge, the channel reach between the Jefferson Street and the Dune Palms Road crossing
is aggrading, starting from downstream towards upstream. However, once the Dune Palms Road
crossing is removed, the channel reach between the Washington Street and Jefferson Street grade
control structures will adjust and will eventually reach a fluvial equilibrium.
We considered stable part of the channel reaches where it slopes are not immediately influenced
by the localized conditions would be appropriate and relevant to calculate the average channel
slopes for the hydraulic analysis.
The average slope of the channel below the Dune Palms Road crossing is 0.001 (between stations
1261+43 and 1271+83). The average slope of the channel above the Dune Palms Rd. crossing is
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 9
Bengal Engineering, Inc. August 16, 2015 (Revised)
0.0021 (between stations 1287+69 and 1306+93). The channel slope immediately downstream of
the Dune Palms Rd. crossing was ignored due to the local scour developed as a result of the 8-
foot channel grade difference. The existing channel invert elevation is about 42.9-feet at immediate
upstream of the crossing and 31.9-feet at immediate downstream of the crossing.
The average slope between the top of the Jefferson Street grade control structure and the bottom
of Washington Street grade control structure is approximately .0024.
The calculated stable slope for 5-year channel flow (Q5), controlled by zero or negligible transport
forming the bed of the stream channel, is 0.0001i. See Appendix B: Equilibrium Slope
Calculations for details.
In order to evaluate the proposed bridge hydraulics in our hydraulic model, the existing Dune Palms
Road low-water crossing was removed, and conservative invert elevations of 40-feet at the
upstream side and 39.5-feet at the downstream side were used to adjust the channel invert at the
bridge site. The assumed elevation is 1.87-feet higher than the projected elevation from the
downstream Jefferson Street grade control structure with a slope of .0024. The assumed channel
elevations are 2.92-feet lower at the upstream and 8.07-feet higher than the downstream of the
existing channel. The channel grade coming into the bridge used in our analyses is flatter than the
condition will be following removal of the crossing. As such, the assumed channel elevations at the
bridge used in our analyses are conservative when calculating the high water elevations.
Following the construction and subsequent removal of the existing low-water crossing, the channel
will lower (degrade) to a fluvial equilibrium, and thus will be several feet lower than the assumed
elevation at the bridge for the HEC-RAS analysis.
Bengal Engineering updated the HEC-RAS WWRSC - CVSC model with the latest topographic
survey information and replaced the low water crossing with the proposed Dune Palms bridge
model. Also, the channel invert at the bridge was conservatively adjusted to account for the removal
of the existing crossing.
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 10
Bengal Engineering, Inc. August 16, 2015 (Revised)
The proposed low-water crossing replacement structure is proposed to be a four-span 480-foot
long, cast-in-place, pre-stressed concrete box girder bridge supported by 5-foot diameter caissons
at the piers. The analysis considered 7-foot-wide full height debris load on the piers. The bridge
layout, elevation, and typical sections are shown in Appendix E: Advance Planning Study Bridge
Plan (APS). Note, the proposed 16-foot wide CV Link Trail opening under south bridge abutment
is shown in the APS Plan.
The calculated hydraulic grade line (HGL) of the water surface elevation at the upstream bridge
entrance is at an elevation of 57.5-feet (NGVD29 elev. 55.1-feet). The minimum soffit elevation of
the bridge will be 59.1-feet (NGVD29 elev. 56.7-feet), located at the bridge north abutment. The
bridge will convey the design flood (QSPF) plus a minimum of 1.0 foot of freeboard. The calculated
minimum freeboard at the bridge abutments will be 1.6 feet.
Scour Analysis
The following components of scour were considered for the proposed Dune Palms Bridge:
1) Long-term degradation or aggradation
2) Bend scour
3) Contraction scour
4) Local pier scour
5) Abutment scour
Long-term degradation or aggradation
The long-term degradation of the channel at the project site will be limited by the permanent grade
control structures (GCS) located at the Jefferson Street and Washington Street bridges. After the
removal of the Dune Palms at-grade crossing, the channel reach primarily upstream of the crossing
is expected to degrade. The maximum channel degradation is not expected to drop below elevation
34-feet at the project location, which is based on the assumed 0.1% slope projection from the top
of the Jefferson Street grade control structure to the existing crossing. The assumed slope of 0.1%
was the average of the observed channel slope similarities between the Jefferson Street and
Washington Street GCS and the calculated equilibrium slope for 5-year flow. The existing channel
and future profiles are shown in Appendix D: CVSC Hydraulic Profiles. Estimation for the long-term
degradation would be best studied by conducting a detailed sediment transport analysis, which is
beyond the scope of this study.
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 11
Bengal Engineering, Inc. August 16, 2015 (Revised)
Bend scour
The channel flows easterly on a tangent at the project location. As such, no bend scour is expected
at the project site.
Contraction scour
Contraction scour equations are based on the principle of the conservation of sediment
transport (continuity). In the case of live-bed scour, the fully developed scour in the bridge
cross section reaches equilibrium when sediment transported into the contracted section
equals sediment transported out.
For clear-water scour, the sediment transport into the contracted section is essentially zero
and maximum scour occurs when the shear stress reduces to the critical shear stress of the
bed material in the section. Normally, for both live-bed and clear-water scour the width of the
contracted section is constrained and depth increases until the limiting conditions are reached.
The channel is relatively wide (about 460-feet) at the project location. The proposed bridge will have
3 rows of 5-feet wide piers in the channel. The project will accommodate a 16-feet wide recreational
trail under the bridge near the south abutment. The channel cross section area will be consistent
through the project site. As such, the channel is not expected to develop contraction scour. The
calculated contraction scours for 5.0-foot, 5.5-foot, 6.0-foot, and 7.0-foot diameter caissons are
shown in Appendix C: Bridge Scour Calculations.
Local pier scour
Local scour at piers is a function of bed material characteristics, bed configuration, flow
characteristics, fluid properties, and the geometry of the pier and footing.
The FHWA recommends using the Hydraulic Engineering Circular No. 18 j (HEC 18) pier scour
equation, which is based on the Colorado State University (CSU) equation for both live-bed and
clear-water pier scour.
The bridge scour computations were performed by using the Hydraulic Design Functions of the
HEC-RAS computer program. The computation of scour at bridges within HEC-RAS is based upon
the methods outlined in HEC 18. In addition to HEC-RAS built-in scour analysis, a detail Pier Scour
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 12
Bengal Engineering, Inc. August 16, 2015 (Revised)
Calculation per HEC 18 guidelines were performed and the findings are presented in Appendix C:
Bridge Scour Calculation.
The results from both approaches were reviewed and the most conservative scour values were
recommended for the structure. The design pier scour for 5-foot diameter shaft will be 16.4-feet and
the top width of the scour hole will be 70.7-foot wide.
A simplified scour summary table has been presented in "The Scour Summary for Dune Palms
Bridge" table on the Conclusions and Recommendations section of the report. The table was
developed per AASHTO 2.6.4.4, 3.4.1, 3.7.5 and CA Amendments to LRFD BDS Sixth edition,
Section 3.7.5. Guidelines. It presents design scour and scour elevations for four different diameter
pier sizes and the corresponding design states scour and scour elevations. Scour per se is not a
force effect, but by changing the conditions of the substructure it alter the consequences of force
effects acting on structures. The information is required for the structural and foundation design of
the bridge piers.
Bank Protection
The CVWD requires Blench regime equation to be used for calculating scour depths for the Bank
Protection k. Per CVWD requirement, the channel SPF flow was used for the analysis. The zero-
bed factor, Fbo = 1 and Z-factor, Z =1.25 were used for the analysis. Since there were no change in
the projection of the channel lining through the bridge reach of the channel, we recommend to
modify the Z-factor = 1. However, the calculation shows ds applying Z =1.25 (Eqn K3-2) to compare
the scour at the bridge using Eqn K3-2 and Eqn K3-3.
We recommend to use Eqn K3-3 through the bridge reach including both upstream and
downstream of the bridge. Based on the scour calculations, the toe of the channel lining cut-off wall
is recommended to be at elevation 24-feet under the bridge and extend both upstream and
downstream at a 0.2% slope. The new and replacement channel linings are recommended to
extend 300-feet beyond the bridge edges.
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 13
Bengal Engineering, Inc. August 16, 2015 (Revised)
Abutment Scour
A typical bridge waterway crossing creates a complex set of flow/boundary interactions. The
boundary materials of the main channel, the floodplain, and the embankment components of
a bridge-waterway usually constitute different zones of alluvial sediments and soil. Abutment
scour usually occurs within several zones of sediment and soil, leading to different erosion
processes and varying rates of erosion.
The abutments of the proposed Dune Palms Road Bridge will be placed behind the concrete bank
revetments. As such, abutment scour will not be an issue at the project site.
Lateral Shifting
Streams are dynamic. Areas of flow concentration continually shift banklines, and in meandering
streams the channel moves both laterally and downstream.
As bridge remains static, it fixes the stream at one place in time and space. A meandering
stream whose channel moves laterally and downstream into the bridge reach can erode the
approach embankment and can affect contraction and local scour because of changes in flow
direction.
Factors that affect lateral shifting of a stream and the stability of a bridge are the
geomorphology of the stream, location of the crossing on the stream, flood characteristics, the
characteristics of the bed and bank material, and wash load. The channel lateral shift may be
gradual or the result of a single major flood event.
The slope protection proposed for this project will consists of a concrete revetment extending
from the top of the channel bank or levee to the elevation of the lowest point of the channel
bed (based on the original channel design); with a cutoff wall extending from that point to the
maximum scour depth or minimum scour elevation.
It is recommended that concrete slope revetment be constructed at the northwest, southeast
and southwest corners of the proposed bridge. The existing slope revetment at the southwest
corner will be reconstructed to accommodate future channel access ramp and CVLink trail. The
toe of the slope paving shall be set at elevation 34-feet at the bridge and at the northwest and
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 14
Bengal Engineering, Inc. August 16, 2015 (Revised)
southeast corners, the protection will be extended to termini of the existing concrete protection
at a slope of 0.2%. The slope of the revetment should be 1V:1.5H. The cut-off walls shall be 10-
feet deep with a 1V:1H slope. The cutoff elevation under the bridge is recommended to be set
at elevation 24-feet.
The elevation of the bottom of the existing channel lining at the northeast corner of the
intersection of Dune Palm Road and the CVSC is 32.3-feet, which is fairly close to the current
thalweg elevation of 31.9-feet. Although, it is expected that the channel will aggrade downstream
of Dune Palms Road after removal of the existing crossing, we recommend augmenting toe of
this existing channel lining to bolster the scour protection in the future.
One option for augmenting the existing channel slope protection include installation of sheet pile
buried along the toe of the channel lining. Another option for scour protection could be “Launchable
Toe of Riprap” slope protection buried along the toe of the channel lining. The design of the riprap
shall be performed per EM 1110-2-1601 (USACE 1991) and CVWD Guideline K-2. Any augmented
slope protection option shall be installed to the thalweg elevation of 24-feet and extend a distance
of 150 feet beyond the edge of the bridge.
Since the 16-feet opening for the CV Link trail under the bridge will offset the flow obstruction by
the bridge piers, no additional scour depth protection is recommended under the bridge.
Adequate surface drainage measures shall be constructed for proper discharge of the surface run-
off to avoid ponding and undermining of the slope protection measures.
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 15
Bengal Engineering, Inc. August 16, 2015 (Revised)
CONCLUSIONS AND RECOMMENDATIONS
1. The project will convey a Standard Project Flood (SPF) of 82,000 ft3/sec with required 1-foot
freeboard.
2. Concrete slope revetments should be constructed under the bridge and at the NW, SW
and SE corners of the structure. The revetments are recommended to extend 300-feet
beyond the bridge edges.
3. The revetment cutoff shall be set at elevation 24-feet under the bridge and extend both
upstream and downstream at a 0.2% slope.
4. The existing slope protection at the NE corner should be augmented a distance of 150-feet
beyond the bridge edge.
5. Adequate roadway surface drainage shall be constructed to protect the slope-protection
measures.
6. The proposed structure shall be supported by deep pile foundations, both at the piers and
the abutments.
7. The bridge scour potential and limit state scour elevations per AASHTO LRFD bridge design
for the alternate pile shaft diameters at the pier locations are shown in the table below:
8. The minimum bridge soffit elevation shall be 59.1-feet (NAVD88).
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 16
Bengal Engineering, Inc. August 16, 2015 (Revised)
a CVWD Design Criteria Stormwater Facilities, Section 8.4.3
b CVWD Ordinance No. 1234.1 Sect. 2 (i)(d)
c CVWD Ordinance No. 1234.1 Section 2 (ii)(d)
d CVWD Guideline K-3; Scour Calculation Guidance; K-3.4
e CVWD Guideline K-3; Scour Calculation Guidance; K-3.6
f USACE-Whitewater River Basin Feasibility Report for Flood Control and Allied Purposes, San
Bernardino and Riverside Counties, California, Appendix 1 Hydrlogy, May 1980
g Corps of Engineers. 2010. User’s Manual HEC-RAS. River Analysis System Version –
4.1.0., Hydrologic Engineering Center, US Army Corps of Engineers, Davis, CA
h RBF Consulting – Basis of Design Report; Whitewater River Crossing at Adams Street, La
Quinta, CA Hydrology and Hydraulics, May 21, 2010
i DIBR, Computing Degradation and Local Scour, January 1984
j Federal Highway Administration. April 2012. Evaluating Scour at Bridges, Fifth Edition,
FHWA Hydraulic Engineering Circular No. 18, Publication No. FHWA-HIF-12-003
k Coachella Valley Water District – Guideline K-3; Scour Calculation Guidance, July 2013
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 17
Bengal Engineering, Inc August 16, 2015 (Revised)
ATTACHMENTS:
Project Photos
Photograph No. 1 - CVSC Crossing at Dune Palms Rd. looking south.
Photograph No. 2 - CVSC Crossing at Dune Palms Rd. looking north.
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 18
Bengal Engineering, Inc August 16, 2015 (Revised)
Photograph No. 3 – Looking downstream towards Dune Palms Rd. crossing, from NW bank.
Photograph No. 4 – Looking downstream from Dune Palms Road towards
Jefferson Street Bridge.
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 19
Bengal Engineering, Inc August 16, 2015 (Revised)
Figure 1: Vicinity Map
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 20
Bengal Engineering, Inc August 16, 2015 (Revised)
Plate 1 - Watershed Map
Project Location
No Scale
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 21
Bengal Engineering, Inc. August 16, 2015 (Revised)
Plate 2: Storm Frequency vs Discharge Graph
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 22
Bengal Engineering, Inc. August 16, 2015 (Revised)
Appendix A: HEC-RAS Output
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 23
Bengal Engineering, Inc. August 16, 2015 (Revised)
CVSC HEC-RAS Alignment at the Project Site
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 24
Bengal Engineering, Inc. August 16, 2015 (Revised)
Hydraulic Table for Proposed Condition - QSPF & Q100 (FEMA)
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 25
Bengal Engineering, Inc. August 16, 2015 (Revised)
Hydraulic Table for Existing & Proposed Conditions - QSPF
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 26
Bengal Engineering, Inc. August 16, 2015 (Revised)
Hydraulic Profile for QSPF
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 27
Bengal Engineering, Inc. August 16, 2015 (Revised)
Cross Section Upstream of Dune Palms Bridge – Proposed Condition
Dune Palms Bridge X-Sections – Proposed Condition
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 28
Bengal Engineering, Inc. August 16, 2015 (Revised)
Appendix B: Equilibrium Slope Calculations
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 29
Bengal Engineering, Inc. August 16, 2015 (Revised)
Variation of d50 with distance along the Whitewater River
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 30
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 31
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 32
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 33
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 34
Bengal Engineering, Inc. August 16, 2015 (Revised)
Appendix C: Bridge Scour Calculations
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 35
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Bridge Scour Calculation for 5’-0” diameter piers
Hydraulic Design Data
Contraction Scour
Left Channel Right
Input Data
Average Depth (ft): 11.08
Approach Velocity (ft/s): 17.63
Br Average Depth (ft): 14.88
BR Opening Flow (cfs): 82000.00
BR Top WD (ft): 419.45
Grain Size D50 (mm): 0.05
Approach Flow (cfs): 82000.00
Approach Top WD (ft): 419.81
K1 Coefficient: 0.690
100 200 300 400 500 600 70020
30
40
50
60
70
80
Bridge Scour RS = 127943
Station (ft)Elevation (ft)Legend
WS SPF
Ground
Levee
Bank Sta
Contr Scour
Total Scour
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 36
Bengal Engineering, Inc. August 16, 2015 (Revised)
Results
Scour Depth Ys (ft): 0.00
Critical Velocity (ft/s): 0.92
Equation: Live
--------------------------------------------------------------------------------------------------------------
Pier Scour
Pier: #1 (CL = 274.76)
Input Data
Pier Shape: Round nose
Pier Width (ft): 5.00
Grain Size D50 (mm): 0.25000
Depth Upstream (ft): 16.06
Velocity Upstream (ft/s): 12.29
Projected Width (ft): 6.00
Pier shape Coeff: 1.00
Results
Scour Depth Ys (ft): 10.93
Froude #: 0.54
Equation: Froehlich's equation
Pier: #2 (CL = 403.16)
Input Data
Pier Shape: Round nose
Pier Width (ft): 5.00
Grain Size D50 (mm): 0.25000
Depth Upstream (ft): 17.37
Velocity Upstream (ft/s): 12.14
Projected Width (ft): 6.00
Pier shape Coeff: 1.00
Results
Scour Depth Ys (ft): 11.09
Froude #: 0.51
Equation: Froehlich's equation
Pier: #3 (CL = 531.56)
Input Data
Pier Shape: Round nose
Pier Width (ft): 5.00
Grain Size D50 (mm): 0.25000
Depth Upstream (ft): 16.01
Velocity Upstream (ft/s): 12.90
Projected Width (ft): 6.00
Pier shape Coeff: 1.00
Results
Scour Depth Ys (ft): 10.99
Froude #: 0.57
Equation: Froehlich's equation
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 37
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Bridge Scour Calculation for 5’-6” diameter piers
Hydraulic Design Data
Contraction Scour
Left Channel Right
Input Data
Average Depth (ft): 11.08
Approach Velocity (ft/s): 17.63
Br Average Depth (ft): 14.88
BR Opening Flow (cfs): 82000.00
BR Top WD (ft): 419.45
Grain Size D50 (mm): 0.05
Approach Flow (cfs): 82000.00
Approach Top WD (ft): 419.81
100 200 300 400 500 600 70020
30
40
50
60
70
80
Bridge Scour RS = 127943
Station (ft)Elevation (ft)Legend
WS SPF
Ground
Levee
Bank Sta
Contr Scour
Total Scour
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 38
Bengal Engineering, Inc. August 16, 2015 (Revised)
K1 Coefficient: 0.690
Results
Scour Depth Ys (ft): 0.00
Critical Velocity (ft/s): 0.92
Equation: Live
------------------------------------------------------------------------------------------------------------------
Pier Scour
Pier: #1 (CL = 274.76)
Input Data
Pier Shape: Round nose
Pier Width (ft): 5.50
Grain Size D50 (mm): 0.25000
Depth Upstream (ft): 16.06
Velocity Upstream (ft/s): 12.29
Projected Width (ft): 6.00
Pier shape Coeff: 1.00
Results
Scour Depth Ys (ft): 11.43
Froude #: 0.54
Equation: Froehlich's equation
Pier: #2 (CL = 403.16)
Input Data
Pier Shape: Round nose
Pier Width (ft): 5.50
Grain Size D50 (mm): 0.25000
Depth Upstream (ft): 17.37
Velocity Upstream (ft/s): 12.14
Projected Width (ft): 6.00
Pier shape Coeff: 1.00
Results
Scour Depth Ys (ft): 11.59
Froude #: 0.51
Equation: Froehlich's equation
Pier: #3 (CL = 531.56)
Input Data
Pier Shape: Round nose
Pier Width (ft): 5.50
Grain Size D50 (mm): 0.25000
Depth Upstream (ft): 16.01
Velocity Upstream (ft/s): 12.90
Projected Width (ft): 6.00
Pier shape Coeff: 1.00
Results
Scour Depth Ys (ft): 11.49
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 39
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Bridge Scour Calculation for 6’-0” diameter piers
Hydraulic Design Data
Contraction Scour
Left Channel Right
Input Data
Average Depth (ft): 11.08
Approach Velocity (ft/s): 17.63
Br Average Depth (ft): 14.88
BR Opening Flow (cfs): 82000.00
BR Top WD (ft): 419.45
Grain Size D50 (mm): 0.05
Approach Flow (cfs): 82000.00
Approach Top WD (ft): 419.81
100 200 300 400 500 600 70020
30
40
50
60
70
80
Bridge Scour RS = 127943
Station (ft)Elevation (ft)Legend
WS SPF
Ground
Levee
Bank Sta
Contr Scour
Total Scour
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 40
Bengal Engineering, Inc. August 16, 2015 (Revised)
K1 Coefficient: 0.690
Results
Scour Depth Ys (ft): 0.00
Critical Velocity (ft/s): 0.92
Equation: Live
-----------------------------------------------------------------------------------------------------------------------------------
Pier Scour
Pier: #1 (CL = 274.76)
Input Data
Pier Shape: Round nose
Pier Width (ft): 6.00
Grain Size D50 (mm): 0.25000
Depth Upstream (ft): 16.06
Velocity Upstream (ft/s): 12.29
Projected Width (ft): 6.00
Pier shape Coeff: 1.00
Results
Scour Depth Ys (ft): 11.93
Froude #: 0.54
Equation: Froehlich's equation
Pier: #2 (CL = 403.16)
Input Data
Pier Shape: Round nose
Pier Width (ft): 6.00
Grain Size D50 (mm): 0.25000
Depth Upstream (ft): 17.37
Velocity Upstream (ft/s): 12.14
Projected Width (ft): 6.00
Pier shape Coeff: 1.00
Results
Scour Depth Ys (ft): 12.09
Froude #: 0.51
Equation: Froehlich's equation
Pier: #3 (CL = 531.56)
Input Data
Pier Shape: Round nose
Pier Width (ft): 6.00
Grain Size D50 (mm): 0.25000
Depth Upstream (ft): 16.01
Velocity Upstream (ft/s): 12.90
Projected Width (ft): 6.00
Pier shape Coeff: 1.00
Results
Scour Depth Ys (ft): 11.99
Froude #: 0.57
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 41
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Bridge Scour Calculation for 7’-0” diameter piers
Hydraulic Design Data
Contraction Scour
Left Channel Right
Input Data
Average Depth (ft): 11.08
Approach Velocity (ft/s): 17.63
Br Average Depth (ft): 14.88
BR Opening Flow (cfs): 82000.00
BR Top WD (ft): 419.45
Grain Size D50 (mm): 0.05
Approach Flow (cfs): 82000.00
Approach Top WD (ft): 419.81
K1 Coefficient: 0.690
100 200 300 400 500 600 70020
30
40
50
60
70
80
Bridge Scour RS = 127943
Station (ft)Elevation (ft)Legend
WS SPF
Ground
Levee
Bank Sta
Contr Scour
Total Scour
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 42
Bengal Engineering, Inc. August 16, 2015 (Revised)
Results
Scour Depth Ys (ft): 0.00
Critical Velocity (ft/s): 0.92
Equation: Live
-------------------------------------------------------------------------------------------------------------------------
Pier Scour
Pier: #1 (CL = 274.76)
Input Data
Pier Shape: Round nose
Pier Width (ft): 7.00
Grain Size D50 (mm): 0.25000
Depth Upstream (ft): 16.06
Velocity Upstream (ft/s): 12.29
Projected Width (ft): 6.00
Pier shape Coeff: 1.00
Results
Scour Depth Ys (ft): 12.93
Froude #: 0.54
Equation: Froehlich's equation
Pier: #2 (CL = 403.16)
Input Data
Pier Shape: Round nose
Pier Width (ft): 7.00
Grain Size D50 (mm): 0.25000
Depth Upstream (ft): 17.37
Velocity Upstream (ft/s): 12.14
Projected Width (ft): 6.00
Pier shape Coeff: 1.00
Results
Scour Depth Ys (ft): 13.09
Froude #: 0.51
Equation: Froehlich's equation
Pier: #3 (CL = 531.56)
Input Data
Pier Shape: Round nose
Pier Width (ft): 7.00
Grain Size D50 (mm): 0.25000
Depth Upstream (ft): 16.01
Velocity Upstream (ft/s): 12.90
Projected Width (ft): 6.00
Pier shape Coeff: 1.00
Results
Scour Depth Ys (ft): 12.99
Froude #: 0.57
Equation: Froehlich's equation
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 43
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 44
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 45
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 46
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 47
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 48
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 49
Bengal Engineering, Inc. August 16, 2015 (Revised)
Appendix D: CVSC Hydraulic Profiles
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 50
Bengal Engineering, Inc. August 16, 2015 (Revised)
Dune Palms Road Low-Water Crossing Replacement Project
Hydrology & Hydraulic Study
Page 51
Bengal Engineering, Inc. August 16, 2015 (Revised)
Appendix E: Advance Planning Study Bridge Plan