1989 LQ Stormwater Project Design ReportLA QUINTA STORMWATER PROJECT
DESIGN REPORT
TABLE OF C014TENTS
Section Prage
1.0 INTRODUCTION 1
2.0 BACKGROUND
2.1 Origianl Studies 2
2.2 Alternative Studies in 1983 3
�.3 Selected Project Arrangement 5
2.4 Heritage Club 6
2.5 Area South of Calle Tecate 6
2.6 Domestic WaterSystem Facilities 7
3.0 PROJECT HYDROLOGY
3.1 Design Floods 9
Debris Production 13
Confluente of CVSC and LQEC 13
4.0 BEAR CREEK SYSTEM
4.1
System Description
15
4.2
Upper Bear Creek Training Dike
15
4.3
Upper Bear Creek Detention Basin
20
4.4
Bear Creek Channel
25
4.5
Oleander Reservoir
37
4.6
La Quinta Evacuation Channel Capacity
38
5.0 EAST
LA QUINTA SYSTEM
5.1
System Description,
40
-5.2
Upper Training DikeT
40
5.3
Calle Tecate Detention.Basin
43
5.4
East La Quinta Channel
46
5.5
Avenida Bermudas Detention Basin
49
5.6
Heritage Club
51
5.7
60-inch Diameter Buried Stormwater Conduit-
52
6.0 PRESENTLY -DEVELOPED AREA OF LA QUINTA
6.1 Introduction 54
6.2 Runoff from Areas Contributing to the East La Quinta System 54
6.3 Runoff from Areas Contributing to Bear Creek System 55
7.0 INSPECTION AND MAINTENANCE CRITERIA
General 57
7.2 Channels and Training Dikes .57
7.3 Detention Basins and Side Drainage Inlets 59
7.4 Buried Conduits 61
REFERENCES 62
TABLES
FIGURES
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LA QUINTA STORMWATER PROJECT DESIGN REPORT
1.0 INTRODUCTION
The La Quints. Stormwater Project (Project) was designed by Bechtel for
the Coachella Valley Water District (District) to protect currently
developed and potentially developable areas of the City of La Quints. from
damage during a major rainflood event. The Project, as finally designed,
was based on a flood control plan for the general area developed by
Bechtel for the District in 1970. Design was completed in April 1985 and
a construction contract for the work was awarded to the E. L. Yeager
Construction Company in September 1985. Construction was completed in
November 1986.
Additional flood control facilitie's needed to complete the eastern
portion of the Project, which are located in an area proposed for private
development, were designed by the developer's engineer, with the design
reviewed by Bechtel. Construction of these facilities was completed in
mid-1988, also by Yeager.
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2.0 BACKGROUND
2.1 Original Studies In 1970, the District retained Bechtel to develop
a flood control plan for the La Quinta area, located about 5 miles southwest
of Indio below the Santa Rosa Mountains. The results of this work are
contained in the Bechtel "Engineering Report on Preliminary Design and Cost
Estimate for Flood Control Works for the La Quinta Area", issued in September
1970. The report provided a recommended flood control plan to protect against
a Standard Project Flood (SPF) event.. This plan was used by the District to
guide subsequent phased development of staged flood control facilities in the
area.
The basic plan comprised:
0 improvements to the existing Bear Creek channel
0 construction of a reservoir (Oleander Reservoir) at the end of an
improved Bear Creek channel, with facilities to direct runoff from
the adjacent drainage areas located to the north and west into the
reservoir
o construction of a reservoir (Cove Reservoir) to the east of the -
developed area, with a training dike to lead runoff from the
drainage areas east of the developed area into the reservoir
0 construction of a flood evacuation channel, the La Quinta Evacuation
Channel (LQEC), from Oleander Reservoir to the existing Coachella
Valley Stormwater Channel (CVSC), with a connecting buried conduit
providing an outlet from the Cove Reservoir.
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Oleander Reservoir and the LQEC were constructed in the early 1980's, based
.upon designs developed by Bechtel.
2.2 Alternative Studies in1983 - In July 1983, the District authorized
Bechtel to update and review three alternative flood control plans for the La
Quinta area, with the objective of selecting a plan to serve as the basis for
final design for the remaining aspects of the basic flood control plan. The
three alternates were:
Scheme A. Improvement of the Bear Creek channel upstream from Oleander
Reservoir to the mouth of Bear Creek Canyon. Construction of diversion
facilities to direct runoff from the canyon immediately east of Bear
Creek into the Bear Creek Channel. Provision of detention storage east
of the presently developed area of La Quinta, with an upstream training
dike, and with an outlet conduit leading into the existing LQEC.
Scheme B. Similar to Scheme A, except diversion facilities above La
Quinta would be more extensive and direct essentially all the runoff from
the drainage areas south of the present La Quinta development into the
Bear Creek Channel. With this arrangement, requirements for detention
sto rage east of La Quinta (which would.need to be located on valuable
land) could be reduced, or possibly -eliminated. This scheme would
include facilities to the east of La Quinta as needed to protect the area
from runoff from the contiguous foothills, with or without detention
storage, and to convey flood flows safely into the existing LQEC.
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Scheme C. Construction of a diversion dike across the mouths of the
canyons above La Quinta, including Bear Creek, and excavation of an open
cut.channel through an existing saddle to the southeast. These
facilities would be sized to divert all flood flows reaching them to an
area south of Lake Cahuilla. Construction or improvement of facilities
south from Lake Cahuilla to convey these flood flows safely to the
southeast into the CVSC. This scheme would also include any needed
improvements to Bear Creek Channel to accommodate remaining local inflows
and provision of adequate flood control facilities to the east of La
Quinta, which would convey remaining flood flows into the existing LQEC.
About midway through the study, Scheme C was eliminated, as it became apparent
that it was not economically competitive with Schemes A and B. Eighteen
alternative combinations of Schemes A & B were studied and the results
presented to the District in early September 1983. These alternatives assumed
full concrete lining for any improvements to Bear Creek Channel and bank
protection on the west side only for channel facilities to the east of the
presently developed La Quints, area.
Scheme B-2/E-7, which provided 97% SPF level protection, was preferred by the
District. Based on comments received from them, the scheme was modified and
identified as "Layout for Final Design". This information was reported to the
District in a letter dated 23 September 1983. The basic modifications were:
0 to provide lining only along the east bank of the Bear Creek Channel
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I t
0 to add flood detention capacity to the eastern project facilities
able to handle the volume of SPF runoff from the presently developed
area of La Quinta south of Calle Durango
2.3 Selected Project Arrangement - In May 1984, the District authorized
Bechtel to proceed with final design of the Project. The "Layout for Final
Design" developed in Septem. ber 1983 was updated and modified at the District's
request to provide full SPF protection and to reflect preliminary plans for a
proposed golf course/ condominium development (Heritage Club, see Section 2.4)
which would affect the Project facilities east of the presently developed area
of La Quinta. A draft of Basic Design Criteria was furnished the District in
August 1984. (Reference 1)
The Project was divided into two systems, the Bear Creek System (comprising
the Upper Bear Creek Detention Basin and the facilities'draining to it, and
the Bear. Creek Channel), and the East La Quinta System (comprising the Calle
Tecate Detention Basin and the facilities draining to it, the East La Quinta
Channel, the Avenida Bermudas Detention Basin, the flood control facilities
within the Heritage Club Development area and a buried conduit outletting to
the LQEC).,
Three alternative locations were investigated for training dikes in the area
south of Calle Tecate to direct runoff to the Bear Creek System facilities. A
letter report on these preliminary studies was sent to the District,on July 6,
1984, and on July 16 the District selected Alternate No. 1, with the training
dike located at approximately El. 480, as the basis for proceeding with final
design.
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2.4 Heritage Club - A golf course/condominium type development is
proposed for the open area in Section 7 east of the presently developed area
of La Quinta. The development was originally referred to as "Sand Pebbles",
then "Crystal Canyon", and later changed to "Heritage Club". Project
facilities are located in this area, principally detention works and a channel
to convey Project flows through the area from south to north. The arrangement
selected by the District in July 1984 as the basis for final design, consisted
of three detention basins and a channel alignment in the Heritage Club area
that had been worked out in coordination with the developer's engineer, J. F.
Davidson Associates, Inc.
Directions from the District regarding work in this area were that design was
to be done by the developer's engineer.in coordination with Bechtel's work on
the overall Project. Bechtel was to review all of Davidson's work pertinent
to the Project prior to District approval.
There were several major changes in the golf course/condominium development
layout during Bechtel's design of the Project. These are described in Section
5.6.
Construction of the Project stormwater facilities in the proposed Heritage
Club development area was completed in mid-1988.
2.5 Area South of Calle Tecate - The large open area south of Calle
Tecate was very critical to the Project, since the location and orientation of
Project facilities in that area would determine the distribution of runoff
between the Bear Creek System and the East La Quinta System, as well as
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significantly effect the amount of area protected by the Project. This area
-was also assumed to be available for the economic disposal of large quantities
,of surplus material to be excavated from the adjacent detention basins.
As discussed previously, alternate layouts for diversion dikes in this area
were investigated and a final design arrangement was developed with the Upper
Bear Creek Training Dike at approximately E1.480. This arrangement was used
in the bid documents. However, the District was not able to reach a
reasonable R/W settlement with the principal landowner in this area. Because
of this, shortly after the construction.contract was awarded, the District
determined that it was in their best interests to acquire all the property
from this.owner and to have Bechtel revise the design of Project facilities in
this area. The objectives of the revised designs were to minimize
construction costs and also to relocate any Project facilities off an adjacent
parcel owned by the U.S. Burea u of Reclamation (USBR), where problems on
timely R/W acquisition also had developed. It was also decided by the
District that the revised,design would include a required grading plan for the
excavated material to be placed in this area, and that the material would be
compacted. The revised design was developed and used as the basis for a major
change order to the contractor.
. 2.6 Domestic Water System Facilities - In addition to the basic
stormwater work, the District included some domestic,water system facilities
in the Project construction contract. These originally consisted of.two water
pipelines, a new 18-inch diameter line along Eisenhower Drive at the outlet to
Oleander Reservoir, and a 24 inch diameter line along the.east side of the
Calle Tecate Detention Basin to replace an existing line to be eliminated by
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the construction. This work also included grading and appurtenant work for a
water tank site east of the Avenida Bermudas Detention Basin. The water
pipelines and tank site grading designs were done by others and incorporated
,by Bechtel in the bid documents.
In the major change order discussed in Section 2.5, the District added grading
for two more water tank sites and changed the single 24 inch diameter water
pipeline in the Calle Tecate Detention Basin area to two 18 inch diameter
pipelines.
I/
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3.0 PROJECT HYDROLOGY
3.1 Design Floods The Project, as shown on Figure 1, was designed to
protect against an SPF event, which comprises the runoff from a 6-hour
Standard Project Storm (SPS) occurring over the Bear Creek basin and other
smaller drainage areas tributary to the Project. However, there were cases
where the 100-year flood.event governed the design. The methodology and
assumptions used to develop these design flood conditions are'discussed below.
3.1.1 Design Flood Hydrograph and Peak Flow Derivations As shown
on Figure 1, the Project consists of two major sub -systems:
0 the Bear Creek System, which conveys -run-off from the areas to the
south (except sub -drainage area, P3) and west of the presently
developed area of the City of La Quinta (City) into Oleander
Reservoir.
0 the East La Quinta System, which receives run-off from a portion of
the presently developed area of.the City and sub -drainage areas P3,
P4 and Ql through Q7.
The Project was designed to protect against flood runoffs from a 6-hour SPS
occuring over the contributing drainage areas. The 6-hour SPS is defined by
the U.S. Army Corps of Engineers (COE) (Reference 13) for the Whitewater River
Basin. It is based on the observed thunderstorm that occurred at Indio,
California on September 24, 1939. During that storm, 6.45 inches of rain fell
over a 6-hour period.
However, for small drainage areas, short -duration rainfall intensities higher
than that of the 6-hour SPS are possible. Therefore, for some sub -drainage
areas, the 100-year storm event results in a higher peak discharge than that
for the SPS, and thus governs the design of related Project facilities. The
100-year storm event data, therefore, was also evaluated. The 100-yeat
rainfall duration/depth data are presented in Table 1.
Flood hydrographs for the Bear Creek System have been derived by the COE
(Reference 13) for the SPF conditions. However, no SPF data was developed for
the East La Quinta System, nor were 100-year flood hydrographB computed by the
COE for either system. Peak discharge values for a 100-year event were
developed by the COE at selected locations along the Bear Creek System. These
100-year peak discharges were derived, according to the COE (Reference 13),
from a generalized peak discharge versus drainage area relationship developed
for the Whitewater River Basin. However, data used to develop this
relationship was derived from drainage areas greater than 8 square miles, and
may,not be applicable for smaller -size watersheds. Therefore, Bechtel
developed 100-year flood event data as needed for the design.. In addition,
because the preliminary facility layout analyzed by the COE was not the s ame
as the final layout of the Project, some flood hydrographs for the Bear Creek
System designs had to be re -derived by Bechtel.
Floods for the latter cases were estimated by applying basin rainfall excesses
(rainfall less infiltration), to unit hydrographs derived from the regional
average S-graph given by the COE (Reference 13). In all cases, the storm was
.. assumed to center over the drainage area for which the flood peak discharge
was being derived.
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Unit hydrographs were derived using the average S-graph for the Whitewater
River.Basin given by the COE (Reference 13). Basin lag was also estimated
according to the procedures suggested by the COE (Reference 13), assuming an
average Manning's roughness "n" value equal to 0.035 for the drainage area.
For developed areas, and areas subject to future developments, an average
basin roughness factor "n" of 0.015 was used to reflect an urbanized
condition. Watershed lengths and average basin slopes were obtained from
topographic data developed for the Project design and from U.S. Geological
Survey topographic maps (1:24,000 scale). Sub -drainage area characteristics
are summarized in Table 2.
A uniform rainfall loss of 0.20 in./hr. was adopted for design (Reference
13). Drainage areas presently developed and those planned for future
development, such as P3, P4, Q6 and Q7, were assumed to be 50% impervious.
Flood peak discharges and runoff volumes from all sub -drainage areas, based on
the indicated data and assumptions, were computed with the COE's HEC-1
computer program (Reference 15) and are given in the Table 3. These results
indicate:
0 The 100-year peak discharges are larger than the SPF peak flows for
drainage areas less than about 0.5 m12. Therefore, for these
smaller drainage areas, the 100-year flood peak flow rates were used
for designing the affected Project facilities. (See Section 3.1.3
for discussion of 100 year peak flows in the presently developed
area of La Quinta.)
0 The total surface runoff volume from the SPF is always larger than
that from a 100-year flood event. Therefore, for detention basin
design where flood volume considerations arecritical, the SPF
hydrographs derived from contributing drainage areas were used.
Design flood peak discharges at selected concentration points along the Bear
Creek and East La Quinta systems are given in Table 4. These values were
derived by routing the design flood hydrograph, SPF or 100-year as
appropriate, through the individual system. The flood routing studies
performed are discussed in detail in Sections 4.0 and 5.0. As stated earlier
in this section, in the derivation of the design flood hydrograph at each
point of concentration, the design storm was assumed to center over the
drainage areas contributing to that point.
3.1.3 Presently Developed Area of the City of La Quinta. In
deriving the run-off from the the presently developed areas of City, it was
assumed that only the area south of Calle Sonora would contribute runoff to
the East La Quints, System. Areas to the north of Calle Sonora are too low to
drain by gravity into the East La Quinta System facilities. Therefore, as
depicted on Figure 1, only the runoff from LQ1, I;Q2, LQ3, and LQ4A were
considered in the designs of the East La Quints. System.
We were advised by the District to assume that the capacity of the future
storm drain system being planned by the City for the presently developed areas
in the City would be designed for a 100-year storm event, using Riverside
County Flood Control District criteria (Reference 16). Therefore, the SPF
hydrographs for sub -drainage areas LQ1, LQ2, LQ3 and LQ4A have been truncated
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at a discharge rate equal to the 100-year flood peak derived from Riverside
County's criteria, for the determination.of inflows to the Project facilities
east of Avenida Bermudas. Any runoff volumes in excess of the 100-year peak
were assumed to flow northward into the lower area of the City adjacent to the
LQEC.
The 100-year values developed by Bechtel based on Riverside County criteria
were higher than those developed by Dav idson (who also used the Riverside
County design data) due to a difference in determination of applicable slopes.
3.2 Debris Production Debris production was estimated using the Tatum
method (Reference 17) for all sub -drainage areas except those within the
presently developed area of the City and the areas occupied by the detention
basins. Estimates were made assuming that the.SPS occurs 10 years after a
fire over the watershed. The Tatum method of estimating debris production and
the assumption of a watershed condition equivalent to that 10-years after a
burn were used by COE in their evaluation of debris production potential in
the Coachella Valley area (Reference 13). Drainage densities, average basin
slopes and hyps ometric indices were derived from U.S. Geological Survey
topographic maps (1:24,000 scale). Debris production parameters and the
estimated volumes are shown on Table 5.
3.3. Confluence of CVSC and LQEC As.shown in Figure 1, surface runoff
collected by the Project facilities will be discharged to the CVSC via the
existing 3.5-mile long LQEC. The hydraulic boundary condition at the
confluence of CVSC and LQEC is important to the design of the Project. The
design of the Project assumed thatan SPF event would occur over the Project
drainage area simultaneously with a 100-year flood event in the adjacent Deep
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Canyon drainage area. It was also assumed that there would be no significant
flow in the CVSC upstream of the Deep Canyon channel confluence. Based on
this, the flood peak discharge in the CVSC just upstream from its confluence
with LQEC would be 19,000 cfs (Reference 13). This discharge, together.with
the flood flows in LQEC, determine the downstream hydraulic boundary
conditions of the Project. The flood peak discharge in LQEC under the SPF
conditions was estimated to be 7370 cfs. If both peaks were coincidental, the
maximum flood discharge at the confluence of CVSC and LQEC governing the
design of the Project would be 26,370 cfs, equivalent to a water level of
Elev. 39.4 feet at this location. However, since these flood peaks are not
coincidental, a constant water level of Elev. 39 feet was assumed at the
confluence of CVSC and LQEC for the design of the Project, as discussed in
Section 4.6.
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4.0 BEAR CREEK SYSTEM
4.1 System Description The Bear Creek System, as shown on Figure 1,
intercepts and detains runoff originating from 12.8 m12 of foothill drainage
area southwest and west of La Quinta. The system has also been designed to
handle runoff from 1.7 m12 of drainage area located due south of La Quinta and
diverted to the Bear Creek System by the Upper Bear Creek Training Dike. The
Bear Creek System, as shown on Figure 1, consists of the following features:
• Upper Bear Creek Training Dike
• Upper Bear Creek Detention Basin
• Bear Creek Channel
• Side Drainage Inlets (SDI) No. 1, 2, 3, and 4
The system conveys storm runoff past the presently developed western limits of
La Quinta.to the existing Oleander Reservoir. Stormwater outflows from
Oleander Reservoir are conveyed by the existing LQEC to the CVSC, which
discharges to the Salton Sea.
4.2 Upper Bear Creek Training Dike
4-2*-1 General Description The Upper Bear Creek Training Dike
diverts stormwater runoff from 1.7 m12 of drainage area lying south of it, to
Bear Creek and thence to the Upper Bear Creek Detention Basin. Historically,
runoff from this area flowed north in abraided channels on the terrace south
of Calle Tecate and was partially diverted from the developed area of La
Quinta by ditches and training dikes to a natural channel running along the
eastern limits of La Quinta. This runoff reached the low area northeast of La
Quinta between Ave. 52, the LQEC, Avenida Bermudas, and Calle Ronda and
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ultimately flowed southerly toward the Coachella Canal. Diversion of the
runoff from this drainage area to the Bear Creek System reduced the required
size of the detention and conveyance facilities in the East La Quinta System,
while requiring only a relatively small increase in the capacities of the
affected Bear Creek System facilities. The location of the Upper Bear Creek.
Training Dike was adjusted several times during design to respond to economic
and right-of-way considerations discussed in Section 2.5. The final alignment
was established in accordance with the following criteria:
0 Outlet (western) end located at the southern tip of a large rock
outcrop (Shipwreck Rock) to minimize rock excavation while at the
same time using the existing rock to provide a stable outlet down
into the natural Bear Creek channel.
0 Alignment selected to minimize excavation and to be clear of USBR
property limits.
0 A mild invert grade (0.001) was selected along the training dike to
.limit the design velocity to 3 fps, when inflow is relatively small
and sediment deposition along the dike is not significant. However,
as discussed below, during an SPF event, the maximum channel
velocities could be as high as 16 fps and dike protection is
required. This design was selected to provide a reasonable balance
between erosion protection and sediment deposition considerations..
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0 Upper (eastern) end of dike located to take advantage of a "natural"
detention area created by the dike and an existing swale adjacent to
the foothills
The dike is designed to contain the runoff from the design storm (SPF),
including an allowance for storm related sediment deposits, with a minimum
freeboard allowance of one foot. Riprap slope protection is provided to
prevent erosion of the embankment. Existing depressions south of the dike
were required to be filled to prevent development of areas of standing water
after a storm event.
4.2.2 Detention Provided by Dike and Outlet. An important
design aspect was to most effectively use the runoff detention capacity
available along the Upper Bear Creek Training Dike to attenuate the peak
flow discharging at the outlet of the dike into Bear Creek, and thus
minimize the impact of this inflow on the required capacity of the Bear
Creek Detention Basin while maintaining an efficient dike height. This was
achieved by providing a 12-foot wide control notch at the outlet to Bear
Creek. For the design storm this created about 145 AF of detention capacity
along,the dike with a- maximum water surface at E1.421.
With this constriction in place, a hydrograph with the design storm
centering over sub -drainage areas Pl, P2, and 02 (D.A. = 1.69 m12) was used
to route the runoff through the longitudinal detention basin thus formed.
The resulting peak outflow (1840 cfs) to Bear Creek is about 68% of the peak
inflow (2700 cfs) along the dike.
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4.2.3 Sediment Loads and Deposition Along Dike. During an SPF
event, about 13 A.F. of debris may reach the dike from sub -drainage areas Pl,
P2 and 02. Drainage from sub -drainage area P2 is poorly defined in the.
vicinity of the dike alignment and potentially can shift anywhere along about
2600 feet of the dike length during a major storm. Due to the uncertainty of
the location of the side inflow, it was assumed that side inflows and
associated sediment could impinge on the dike at any location along this
2600 -foot re ach. From the soil gradation data, a median sediment size (d50)
of 0.09 Pm was used for the sediment routing. The sediment routing analysis
showed that during an SPF event, due to the flat slope of the flow line along
the dike (S = 0.001), sediment deposition.will occur. As a result of such
deposition, the channel slope and the associated sediment transport capacity
downstream from the side inflow will increase until the transport capacity
equals the rate of sediment supply. The net increase in the maximum water
level along the dike resulting from sediment deposition varies from 0.5-foot
at locations near both ends of the dike to one foot near the middle.
4..2.4 Channel Hydraulics and Dike Height Using the 12-foot wide
outlet notch described in Section 4.2.2, the design objective was to determine
dike heights that would contain the SPF runoff. The following factors
affecting the water level in the channel along the dike were considered for
determining dike heights:
0 Normal depth (Yn): Normal depth is defined as the computed maximum
depth along the dike for a peak outflow of 1840 cfs at the
downstream outlet control. The computations assumed a Manning's "n"
of 0.025, a 30-foot bottom width trapezoidal channel, with the dike
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forming the north bank, with a 2.5:1 side slope protected with
riprap, and with a 3:1 side slope in natural material for the south
bank.
0 Sediment deposition effect (Ysd): As discussed above, sediment
deposition resulted in an increase in water level along the dike
ranging from 0.5 to 1.0-foot.
0 Roughness effect (Yr): With riprap protection provided along most
of the dike length, it was estimated that the Mann ing's "n" may vary
from 0.025 to 0.034. However, due to the backwater effect induced
by the downstream outlet control, the net roughness effect was only
about 0.2-foot.
0 Side inflow effect (Ys): It was estimated the side inflows will
induce about 0.2-foot of additional water depth due to wave action.
This could occur along the entire dike.
0 Freeboard (Yf): One -foot of additional freeboard was provided in
determining the required total dike height.
Table 6 summarizes the required dike height and the amount of each of the
these factors at various locations along the dike.
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4.2.5 Dike Slope Protection Without sediment deposition effects,
the computed average design flow velocity in the channel along the dike was
about 2 fps. However, since the side inflows may impinge on the dike at any
location, it was computed that, during an SPF event, the maximum transient
bottom slope along the dike resulting from sediment deposition could vary from
0.005 in the upper 1000 feet, to 0.014 in the lower 1000"feet. The
corresponding maximum flow velocities due to these slopes were about 11 fps
and 16 fps, respectively. Therefore, during any major storm event, the actual
channel bottom slope could be steeper than the constructed slope of 0.001 as a
result of sediment inflow and deposition, and bank protection should be
provided. Rock for erosion protection was specified in accordance with
Caltrans Standard Specifications (Reference 19). Facing class (d50 = 12"),
light class (d5O 16") and 1/4-ton class W50 24") riprap bank protection
were provided for the upper, middle and lower reaches along the dike,
respectively.
4.3 Upper Bear Creek Detention Basin
4.3.1 General Description In the early stages of the design of
the Project, alternative concepts were considered for a single large basin
(at the upstream end of the Bear Creek Channel) or two smaller size basins
(one at.the upstream end and one near the downstream end). It was found
that the single large basin at the beginning of the channel was the more
effective arrangement.
This basin is located at the mouth of the natural Bear Creek southwest of La
Quinta and contains a total of 752 AF of storage for temporary detention of
storm runoff and detention of debris. Basin side slopes vary from 2.5 to 1
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(horizontal to vertical) in soil to about 1.5 to 1 along the existing rock
surface exposed adjacent to Shipwreck Rock. Flows from Bear Creek will enter
the basin via a 5:1 sloped inlet protected with 1/4 ton to one ton riprap
(Reference 19). Attenuated by temporary basin storage, outflows from the
basin will enter the Bear Creek Channel via a rectangular concrete spillway in
the basin embankment. A notch is provided in the ogee crest of the spillway
.to permit complete draining of the basin, without.the need for a low level
outlet structure and a relatively long outlet conduit. After a storm event,
detained stormwater will continue to drain from the basin to the Bear Creek
Channel until the basin is empty. The bottom of the basin is sloped at about
0.5% toward the notch outlet to promote complete draining. Debris deposited
in thebasin during a storm event would raise the bottom grade in varying
degrees but drainage of retained stormwater through the notch would still
occur.
4.3.2 Basin Capacity The purpose of the Upper Bear Creek
detention basin is two fold, i.e.:
0 to attenuate the peak flow from the 11.05 m12 contributing drainage
area, comprised of sub -drainage areas Pl, P2, 01, 02, and Ml. A
total of about 752 A.F., to E1.357.0, of storage volume is
provided. About 202 A.F. of this is for debris storage. The
remaining 550 A.F. is for flood runoff detention to attenuate the
peak flow rate from the basin into the Bear Creek Channel and,
thereby limit the maximum water level in the downstream Oleander
Reservoir to El. 54.0 (See Section 4.5). This will provide a
minimum freeboard of one foot below the existing top of the
reservoir embankment.
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0 to trap debris produced from sub -drainage areas 01 and Ml.. Debris
from sub -drainage areas Pl, P2, and 02 is to be detained along the
Upper Bear Creek Training Dike. Debris storage is determined as the
volume in the basin starting at the spillway crest with a surface
extending upstream in the basin at a slope equal to half of the
average natural slope in that area.
The basin is about 700 feet wide and 1350 feet long, with the bottom set at
about El-320. From the soil gradation data (0 to 10-foot deep), the median
sediment size, d5O, is about 1.5 mm, with less than 5% of the sediment finer
than 0.1 mm. As a result, it was estimated that, except for the debris from
side drainage area Ml, the majority of the debris will deposit within the
upper 700 feet of the basin. Therefore, the spillway crest was set at E1.323,
with a 3-foot wide rectangular notch with a flow line at E1.320 to drain the
basin. Between El-323 and E1.320, about 23 AF of dead storage volume was
provided to accommodate the SPF debris production from sub -drainage area Ml.
Therefore, in the SPF flood routing, it was assumed that the effective water
storage capacity was above E1.323.
As indicated in Section 3.2, a hydrograph with the design storm centering over
the sub -drainage areas of Pl, P2, 01, 02 and Ml (D.A. 11.05 m12) was used to
route the runoff from Bear Creek and the discharge from the Upper Bear Creek
Training Dike through the basin. The resulting basin shape and capacities are
shown in Figure 2. During an SPF event the peak outflow (9540 cfs) will be
about 82% of the peak inflow (11,630 cfs).
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4.3.3 Inlet Hydraulics The inlet, located at the southern end of
the basin, is designed to handle the run-off from sub -drainage areas Pl, P2,
01, and 62. The overflow rockfill spillway criteria proposed by Knauss
(Reference No. 10) was used to design the inlet. An inlet channel with a 5:1
slope was used to bring the run-off from the natural Bear Creek grade (EL.390)
to the invert of the basin. The unit discharge down the inlet slope was
limited to 30 cfs per foot maximum so that the required riprap sizing would be
within a practical range. In order to adjust to the rock outcrop on the east
side, the width of the riprapped inlet was gradually converged from 400 feet,
to 150 feet. From Knauss's study, for uniform non -turbulent flows, the
minimum required riprap size is about 25-inch WO). However, from hydraulic
computations, it was found that either a high velocity (up to 20 fps) flow or
a hydraulic jump will occur along the inlet slope between EL.370 and 350 under
design conditions. Therefore, it was decided to use 1-ton class riprap W50
34 inches) for the slope between EL.370 and 350 and use 1/4-ton class WO
24 inches) for the remainder (Reference 19). A 6-foot deep riprap cut-off is
provided at the entrance of the slope to secure the inlet.
Runoff.from sub -drainage area Ml will enter along the west bank of the basin
with a peak inflow of about 1770 cfs. When Knauss's criteria was applied,
light classriprap WO = 16 inches) (Reference 19) was found suitable for
slope protection at this inlet.
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4.3.4 Spillway Hydraulics The spillway was designed to constrict.
the basin outflow in order to develop temporary storage in the basin and
attenuate the peak flow rate entering Bear Creek Channel. A 16-foot wide ogee
spillway crest with vertical side walls was designed to limit the maximum
water level in the basin to E1.357. This provided an embankment with a
maximum height of about 20 feet, which would blend well with the surrounding
terrain. A rounded entrance to the spillway was used to minimize entrance
losses. The crest of the spillway was set at E1.323, which is 3-feet above
the bottom of the basin. A 3-foot wide slot was provided in the spillway
crest extending down to thebottom of the basin to ensure complete drainage
following a storm event. The spillway rating curve is shown on Figure 3.
To protect the embankment adjacent to the entrance from erosion, 12-inch D50
riprap protection was provided within 20-feet of the entrance, and 8-inch D50
riprap was used for the area between 20 to 40 feet from the entrance.
The spillway is connected to the trapezoidal Bear Creek Channel by a 312-foot
long c oncrete lined trapezoidal transition channel. Six-inch high concrete
blocks, located at 25-feet intervals, are installed along this transition to
provide artificial roughness. This roughness will ensure that the velocity at
the end of the transition will not exceed 35 fps (Reference No. 8). A USBR
design procedure for determining spillway freeboard (Reference No. 9) was used
to determine the freeboard requirement for the transition.
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4.4 Bear Creek Channel
4.4.1 General The 2.5 mile long Bear Creek Channel is a soil
cement lined, trapezoidal channel. As shown in Figure 4, the upper 2.0 mile s
has a steep gradient of about 0.028, starting from the spillway of the Upper
Bear Creek Detention Basin. The lower 0.5 mile is on a mild gradient of
0.0015, and contains a drop structure upstream of the outlet into the Oleander
Reservoir. Four side drainage inlets are provided to collect and introduce
run-off from the adjacent sub -drainage areas M2, Ll, L2, Kl and K2 into the
channel. The effect of these local side inflows was incorporated in the
channel routing from the Upper Bear Creek Detention Basin to Oleander
Reservoir.
4.4.2 Bear Creek Channel Lining In the early stages of Project
design, lining of only the east bank of the channel was considered. During
preliminary design, it was found that about 20 large check structures would be
required to limit the bank lining cut-off depth to a reasonable range, i.e.,
15 feet or less. In addition, a channel withonly one bank lined also creates
other problems relative to the design and maintenance of the system. These
are:
0 Channel Meandering: Potential channel meandering and armoring
effect make the determination of scour depths and embankment heights
very uncertain. The existence of secondary currents in flows around
bends is a principal cause of meandering. Armoring results from a
thin layer of coarse material being left at the bed surface after
the finer material is transported away by the flow.
-25-
Meandering could result in a channel flow alignment quite different
from that designed, with peak discharges flowing in channels which
would be narrower and with tighter curve radii than designed. The
resulting maximum scour depths andwater depths could.be different
from the values computed from an assumed prismatic channel. Also,
the coarse material armoring effe ct could reduce general scour while
increasing local scour.
0 Antidune: In a supercritical flow regime, antidunes will form in an
alluvial channel. Antidunes are bed forms that change with flow and
the sediment characteristics. The longitudinal profiles vary from
triangular to a sinusoidal shape. The troughs of these antidunes
will result in an additional 3 -foot scour depth in the Bear Creek
channel, and the crests will develop greater waveheights, which for
the Bear Creek Channel ranged up to 6 feet.
0 Sedimentation: After a major storm, the sediment eroded from the
steep upper reach would deposit in the flatter lower reach. Since
the sediment storage capacity of the lower reach would be limited,
there was concern that a build-up of sediment could occur and
possibly cause flows to overtop the channel banks. Large volumes of
deposited sediment would also require significant maintenance work.
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Because of these factors., the one -side bank protection concept was abandoned.
Three types of fully -lined channel were subsequently considered:
cast -in -place concrete, roller compacted concrete (RCC) and soil cement.
Soil cement was selected for the.design on the basis of economic and aesthetic
considerations.
Literature related to maximum permissible velocities for soil cement -lined
channels is limited. A study by Simons & Li Associate (Reference 6) indicated
that a soil cement -lined channel can withstand up to about 35 fps of flow
velocity for about 8 hours without experiencing damage. Research by the
Portland Cement Association (PCA) on the abrasion resistance of various
combinations of cement content and gravel content in soil cement indicated
that good abrasion resistance could be obtained (Reference 18).
A 2-foot channel bottom.thickness was used for the entire channel except as
discussed below. The selection of the 2-foot thickness was based on
consideration of potential cumulative and short term erosion and uplift on the
invert lining. From laboratory data developed by the PCA (Reference 18), it
is expected that some erosion of the lining will take place during major flood
flows in the channel. The amount of erosion will vary with sediment volumes
and gradation, velocity, storm duration, cement content, soil -cement mix ture
gradation, and surface roughness and irregularities. Many of these factors
cannot be closely defined, nor can the effects of potential combinations of
these factors.
However, from the PCA research it appears that the principal factors
contributing to erosion or erosion resistance of.soil-cement are the presence
-27-
of abrasive sediment in flood flows and the cement content and soil gradation
in the soil -cement.
Since debris basins are provided at all principal flow inlets to the channel,
the amount of sediment in the channel flows will be minimal. Sediment in the
channel flows will derive principally from ravelling of the excavated slopes
along the channel, wind blown deposits and suspended sediment. PCA data on
cement content (8%) and soil gradation (A-1-b) were used to design an erosion
resistant soil -cement channel lining.
Considering the above, an allowance was made for erosion of up to 12 incheslin
localized areas as a result of the accumulative effects of the design storm
and antecedent storms, leaving a.minimum residual lining thickness of 12
inches to protect the channel until the invert was restored to design
thickness. The 2-foot thickness, together with the longitudinal underdrains
will also effectively resist potential uplift forces which may develop
adjacent to the side drain inlets orother areas of ponded water along the
channel.
A 3-foot bottom thickness was used for three reaches listed below, to provide
additional protection against erosion and uplift, where either the design flow
velocity will exceed 35 fps or a hydraulic jump will occur:
0 Reaches with Velocity In Excess of 35 fps:
Sta. 72+00 to Sta. 82+00 and
Sta. 89+00 to Sta. 101+00
0 Reach with Hydraulic Jump:
Sta. 32+50 to sta. 35+50
"28-
4.4.3 Bear Creek Channel Geometry For both economic and hydraulic
considerations, a trapezoidal channel section was selected over a rectangular
section. The results of the flood routing indicated that the variation in
peak flow rates (9,600 cfs to 12,500 cfs) along the length of the channel
allowed the use of a 40-foot constant bottom width for the entire channel,
except for the last 400 feet as discussed in Section 4.4.7. For safety and
economic reasons, a 2:1 side slope was selected for the soil -cement lined
channel.
For construction reasons the horizontal width of the soil -cement along the
channel banks was set at 8 feet, which gave a thickness normal to the slope of
about 3.6 feet.
In the last 400 feet of the channel, a 70-foot bottom width with 1.5:1 side
slopes was used to discharge the run-off into the grass -lined golf coursearea
(Oleander Reservoir) at the outlet. The selected geometry also resulted.in an
embankment height design compatible with the surrounding physical constraints.
4.4.4 Bear Creek Channel - Hydraulics and Embankment Height
Channel bank heights were selected to contain the SPF flood within the
channel. Determination of bank heights took into account all factors that
could affect -the water depth in the channel. Factors considered were:
0 Normal depth (Yn): The normal depth was computed for each sub -reach
using Manning's "n" = 0.020
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0 Superelevation (Yb): In curved channel reaches, Yb is the banking
height for the outer bank, provided to minimize the cross wave
effect in the local area. Yb for the inner bank is zero.
0 Roughness-(Yr): Assuming a 4 to 8-inch surface roughness for the
soil cement lined side slopes, the corresponding Manning's "n"
ranges from 0.028.to 0.035. It was assumed that the soil cement
lining in the channel bottom is fairly smooth with "n" = 0.015.
Based on this, the composite Manning's "n" for the soil cement lined
channel was estimated to range from 0.020 to 0.025. The computed
design flow characteristics were determined using an "n" value of
0 .020. An allowance, Yr, of an additional 0.5,to 1.0 foot of water
depth was provided to.account for the possible higher "n" of 0.025.
The amount of the allowance is greater for reaches of sub -critical
flow than for reaches of supercritical flow.
0 Side Inflow Effect (Ys): Based on model test data for the Palm
Valley Stormwater Channel (Reference No. 7), an extrapolation was
made to derive wave heights in the main channel which could be
caused by side inflows with flow in the main channel at an average
velocity of 35 fps. It was found that about 3 feet of wave height
may be generated for a side inflow design rate of 5 cfs per foot of
weir length.
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o Freeboard (Yf): One foot of additional freeboard was included in
the design of the bank heights.
Tables 7 and 8, respectively, summarize the calculated required bank heights
and.the amount of each of the above factors at various locations along the
upper and lower reaches.of channel. As shown, the design embankment heights,
Yt, are equal to, or greater than, those calculated.
4.4.5 Upper Bear Creek Channel and Energy Dissipator As depicted
on Figure 4, the upper reach of the Bear Creek Channel is about 2 miles long,
with an average slope of about 2.8%. The steep slope will result in
supercritical flow and high velocities. The horizontal and vertical
alignments of the channel were designed in accordance with the following:
0 Horizontal Alignment:
COE (Reference -5)
Rmin 7 4V2 T
gy
where Rmin = minimum required radius of
curvature (ft)
V - average flow velocity (fps)
T - channel top water surface width (ft)
g = acceleration due to gravity
32.2 (ft/sec2)
y = average water depth (ft),
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-AW
0 Vertical Alignment: In the initial design, an effort was made to
keep the design water surface in the channel at or below the top of
the existing Avenida Montezuma roadway east of the channel. This
was found to be uneconomic in the lower reaches of the channel due
to right-of-way constraints and heavy rock excavation. However, the
channel design in the reacheslabove Station 70+00 basically met this
criteria.
As indicated on Figure 4, a 100-foot wide, 150-foot long flat reach within the
lower end of the channel was provided to dissipate the energy from the high
velocity upstream flows. This energy dissipating basin will also receive the
inflow from Side Drain Inlet No. 4.
4.4.6 Bear Creek Channel - Lower Reach and Drop Structure Three
principal reasons led to the decision to provide a subcritical flow channel in
the last 0.5-mile reach of the Bear Creek Channel. They are:
0 The curving horizontal alignment of the channel required by
topography and right-of-way constraints,isnot compatible with
supercritical flows.
6 Savings in rock excavation costs resulting from the mild slope.
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0 A request from the District to limit channel outlet velocities and
resultant shear stresses at the channel outlet to avoid significant
damage to the grassed areas in Oleander Reservoir.
As -shown on Figure 4, there was about a 10-foot existing drop in elevation in
this short reach, and the resulting average natural slope of 0.6% was too
steep to ensure a subcritical flow for the expected channel roughness.
Therefore, a 7.2-foot deep drop structure, located in rock cut, was provided
to develop a mild slope of 0.15% for the reach above the drop structure and a
0.04% slope for the reach below the drop. The resulting backwater from the
drop structure is sufficient to contain a hydraulic jump in the upstream
energy dissipating "basin" locatedin the channel a short distance upstream.
The vertical drop structure is about 410 feet upstream from the outlet and was
designed in accordance with the criteria in COE-HDC-623 (Ref. No. 4).
4.4.7 Bear Creek Channel Outlet to Oleander Reservoir The
Oleander Reservoir area also serves as a golf course. The Bear Creek Channel
outlet was designed to minimize damage to the well -maintained grassed golf
course area for discharges up to those resulting from a 100-year storm. From
prior hydraulic model test results for grass lined channels (Reference No. 2),
it was found that the maximum permissible shear stress in a reach with uniform
flow is about 7 lb/ft2 for unreinforced grassed areas, and about 8.5 lb/ft2
for grassed areas reinforced with soil reinforcement matting, such as
Enkamat. During a 100-year storm the water level in the reservoir will rise
to about E1.44. Depending upon the reservoir elevations at the time of the
peak inflow.from the Bear Creek Channel, a weak hydraulic jump can occur in
the grass lined area of the outlet between reservoir water surface E1.38 and
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E1.41. In the vicinity of the hydraulic jump, the local shear stress caused
by turbulence could be 150% higher than that in the reach upstream of the jump
(Reference No. 3). A 70-foot bottom width channel with .1.5:1 side slopes was
designed for the reach of the Bear Creek Channel from the drop structure to
the outlet into Oleander Reservoir. The resulting maximum shear stresses from
a 100-year storm discharge are about 7 lb/ft2 with a hydraulic jump
occurrence, and 4.5 lb/ft2 without a jump. As an added protective measure,
embedded Enkamat was also installed in the 230-foot long reach immediately
downstream from the end of the soil -cement lined channel where hydraulic jumps.
may occur. In addition, buried concrete slope protection was provided in the
east bank of the outlet to protect this embankment if there was erosion of the
grassed earth bank.
4.4.8 Side Drain Inlets As located on Figure 1 and shown on
Figure 5 through 8, four side drain inlets (SDI) were designed along the west
bank of the channel to store debris produced during the SPF storm and to
control the introduction of the runoff fromthese areas into the channel. No
credit for storm flow attenuation was taken at these basins. Locations,
debris production and design flows for the SPF are given below:
SDI No. Location Design Flow
(Sta) (cfs)
1 109+00
1770
2 84+70
1990
3 44+00
340
4 32+00
1480
Debris Production
(A. F. )
14.3
28.1
1.9
21.7
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,The COE procedure for Debris Basin Design (Ref. No. 5) was used to estimate
the slope of the surface of the deposited debris and to determine the debris
capacity of the basins. The weir crest elevation of each inlet was set at a
minimum of 0.5-foot above the ma,ximum design water level in the Bear Creek
Channel. A broad crested weir equation, with a unit discharge of 5 cfs/ft.,
was used to design the weirs. A minimum freeboard of one foot was used to
design the embankments for the basins.
4.4.9 Bear Creek Channel - Minor Drainage Inlets Small drainage
ditches and inlets were designed along both sides of the main channel to
intercept the run-off from minor contiguous drainage areas and convey it to
the channel. Low areas adjacent to the embankment, which would allow
undrained pockets of water to form, were required to be filled level with the
top of the embankment and graded to drain. On the west side of the channel,
two small (10 feet to 15 feet wide) side ditches were provided to bring the
local run-off into SDI's No. 1 and No. 2.
Runoff from part of thepresently developed area of La Quinta previously
flowed into the original Bear Creek channel where Avenida Obregon made a grade
crossing of the channel. The limits of the related drainage area are not
clearly defined but it appears to cover about 0.20 m12 west of Avenida
Carranza and north of Calle Nogales. This runoff is to be handled by a 60
inch diameter RCP drain which will intercept storm flows near the intersection
of Calle Obregon and the original Bear Creek channel alignment. Also a double
36 inch diameter CSP flapgated inlet to Oleander Reservoir was provided near
Calle Tampico east of the Bear Creek Channel outlet. This is to drain runoff
which otherwise would, pond in this area.due to Project construction. The
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intent of these facilities is to maintain or improve the previous drainage
situation until the City of La Quinta is able to install permanent storm
drainage facilities to serve that area. Flooding will occur under some
circumstances, for example, when the water surface elevation in Oleander
Reservoir exceeds E1.49 the flap gates will prevent inflow to the reservoir
through the double 36 inch diameter conduits. Similarly when the water
surface in Oleander Reservoir approaches E1.52, the capacity of the 60 inch
RCP will be reduced significantly. However, the flooding that may occur with
the project facilities installed should be less than under pre -project
conditions.
4.4.10 Bear Creek Channel - Underdrains Drains were provided under
the Bear Creek Channel soil cement lining to prevent development of uplift
pressures on the lining that could occur as the result of temporary saturation
of the adjacent soils during storm events. The drains, consisting of 6 inch
diameter perforated plastic pipe within a gravel envelope wrapped in filter
fabric, were located at the base of each side of the channel lining at the
junction of the side slope and invert. Outlets into the channel were provided
at about 1000 foot intervals. Transverse finger drains at a 20 ft. spacing
were also provided under the side slopes of the soil cement channel lining
adjacent to the side drainage inlets to prevent uplift from seepage flows when
water is impounded in the basins. The finger drains connect to the
underdrains running along the channel at the SDI locations.
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4.5 Oleander Reservoir
4.5.1 General Description The existing Oleander Reservoir will
collect storm run-off from the Bear Creek System and from the drainage areas
north and west of the reservoir (sub -drainage area J - total drainage area
1.4 m12) and then discharge it to the CVSC via the LQEC. Figure 9 shows the
area/capacity curve of the reservoir. In developing this capacity curve, it
was assumed that, prior to an SPF event, the reservoir would be filled to the
outlet crest level of E1.35. It was also assumed that the minimum freeboard
for the reservoir embankment is one foot (i.e., a maximum allowable water
level of E1.54). The storage volume available between E1.35 and E1.54 equals
1926 AF.
With the previously constructed outlet section under the bridge at Eisenhower
Drive, during an SPF event the runoff is too large to be contained in Oleander
Reservoir without overtopping. It was found to be necessary to enlarge the
outlet, and also to provide flood detention upstream of Oleander Reservoir in
order to handle the SPF run-off. As mentioned in Section 2.2, a hydrograph
with the design storm centering over the entire drainage area (D.A,. = 15.85
m12) was used to route the SPF through the entire Bear Creek System and check
the adequacy of Oleander Reservoir, and determine the capacity required in the
Upper Bear Creek Detention Basin.
4.5.2 Oleander Reservoir Outlet Figure 10 depicts the
cross-section of the original channel constructed at the outlet of Oleander
Reservoir under the Eisenhower Drive bridge and the corresponding discharge
rating curve. As shown, for a maximum allowable reservoir water level of
E1.54, the maximum outflow to the LQEC channel was only about 6500 cfs, which
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is less than the channel capacity of about 7600 cfs. Calculations indicated
that, without widening the outlet, the reservoir could only safely contain the
runoff from a 150-year storm over the Bear Creek System. With the outlet
enlarged to allow the maximum outflow to reach the LQEC channel capacity of
7600 cfs, the reservoir could contain about the 200-year storm. This,.
however, is still less than the SPS. The Upper Bear Creek Detention Basin was
designed to attenuate design flow reaching Oleander Reservoir so that the SPS
could be handled.
This enlarged outlet section and the resulting discharge rating curve for
Oleander Reservoir to the LQEC is also shown on Figure 3. When the outflow is
smaller than about 2000 cfs, the backwater from the downstream LQEC channel
controls the water level in Oleander Reservoir. When the flow exceeds about
2000 cfs, the flow control shifts to the outlet structure, which acts as a
weir, i.e., discharge is at critical depth.
4.6 La Quinta Evacuation Channel Capacity Figure 11 depicts the layout
of the LQEC between Oleander Reservoir and the CVSC. The LQEC is about 3.5
miles long and consists of two distinct reaches. The lower 2.4-miles is a
trapezoidal earthen channel, 50-foot wide with 3.5:1 side slopes, and with the
top of embankment at EL.50. The upper 1.1 miles is an irregular shaped
grass -lined channel, containing golf course facilities, with a total storage
I volume of about 320 AF to water surface E1.49. The top of the embankment of
this reach varies from EL.50. to 51.5. Ave. 50 (Sta 56+95) separates these
two reaches. Outflow from Oleander Reservoir to the channel is controlled by
a constricted section under the Eisenhower Drive bridge as discussed In
Section 4.5.2.
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Since the runoff from the Bear Creek System will eventually discharge via the
existing Oleander Reservoir and the LQEC into the CVSC, the capacity of the
Bear Creek System detention and conveyance facilities depends on the capacity
of the LQEC and concurrent flow conditions in the CVSC- As,stated in Section
3.3, it was assumed that the SPF event will occur over the Project drainage
area simultaneously with a 100-year flood event in the adjacent Deep Canyon
drainage area. This results in a maximum CVSC water surface at E1.39.4.
However, since these two flood peaks are not coincidental, a water level of
EL.39.0 was assumed at the junction for backwater computations in the LQEC.
This is considered to be conservative. Figure 12 depicts the routed water
level histories at Oleander Reservoir and at the junction of the LQEC and
CVSC. As shown, about 5 hours after the start -of the SPF event, the water
level at the junction reaches E1.35, equal to the crest elevation of the
outlet from Oleander Reservoir to the LQEC. About 6.5 hours after the onset
of the SPS, Oleander Reservoir will reach its maximum water level of E1.54,
while the water level at the LQEC/CVSC junction will be about EL.39.
Using this downstream water surface control, a set of backwater curves from
the CVSC to Ave. 50 were computed and a channel capacity rating curve (Figure
13) was established. This rating curve was then used as an outflow rating
curve for a "reservoir" simulating the channel between Oleander Reservoir and
Ave. 50. As shown on Figure 13, when allowing a mini mum freeboard of one foot
(i.e., maximum channel water level of E1.49), the maximum channel capacity is
about 7600 cfs.
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1 1
5.0 EAST LA QUINTA SYSTEM
5.1 System Description The East La.Quinta System intercepts and
controls runoff originating from 2.5 m12 of drainage area in the foothills
east and southeast of Avenida Bermudas, from the area south of Calle Tecate to.
the Upper Bear Creek Training Dike, and from the presently developed area of
the City of La Quinta south of Calle Durango. The East La Quinta System, as
shown on Figure 1, consists of:
0 Upper Training Dike
0 Calle Tecate Detention Basin
o. East La Quinta Channel
0 Avenida Bermudas Detention Basin
0 Heritage Club Facilities
0 60-Inch Diameter Buried Stormwater Conduit
The system intercepts, detains, and conveys storm runoff past the presently
developed eastern limits of La Quinta to the LQEC, which discharges to the
CVSC and thence to the Salton Sea.
5.2 Upper Training Dike
5.2.1 General Description The Upper Training Dike diverts
stormwater flows from 0.37 m12 of drainage area east of the dike into the
Calle Tecate Detention Basin.
The dike, located to the west of a broad shallow natural drainageway at the
base of the foothills, was designed to contain the runoff from the SPF event
basically within the existing drainageway. The slope of the natural
drainageway varies from 3 to 4 percent. This is sufficient to develop high
-40-
velocities in runoff flows during major storm events. Riprap protection was
provided along the slope and toe of the dike for the lower 1000 feet of length
to provide scour protection. Riprap protection was not provided along the
remainder of the dike, as the principal flows, which emerge from the foothill
drainage channels, will not impinge directly on this reach of the dike.
The top of the dike will also serve as a District access road along an 18-inch
diameter water line buried on the west side of the dike, and to a District
water supply reservoir located south of the Project.
Drainage ditches are provided along the west side of the dike to intercept
runoff from the adjacent graded fill. These drainage ditches direct the
runoff to drain inlet facilities at Stations 208 + 60 (inlet to Calle Tecate
Detention Basin) and 214 + 45 (Lower Water Storage Reservoir Site).
5.2.2 Channel Locationand Geometry The Upper Training Dike was
designed to intercept the surface run-off from sub -drainage area P4. The dike
parallels an existing shallow drainage channel and is about 1750-foot long.
The slope of the existing ground along the toe of the dike is about 0.04. No
excavation was required along the dike. Based on a fluvial geomorphology
study by S. A. Schumm (References No. 11 and 12), the channel geometry along
the dike was developed from the mean annual flow and thesediment
characteristics. Using the sediment characteristics of this area, it was
estimated that over the course of time, prior to any major flood event, the
channel along the dike will be about 15 to 20 feet wide. This was the basis
used for computing the channel hydraulics and determining the required
embankment height.
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5.2.3 Channel Hydraulics and Protection Procedures similar to,
those used for the Upper Bear Creek Training Dike (Section 4.4.4) were applied
to determine the required dike height and to size the riprap for bank
protection. The factors considered are summarized below:
0 Normal depth (Yn): A Manning's n of 0.025 was used to compute the
water depth along the dike for a peak flow of 500 cfs (about 40% of
the P4 runoff will discharge directly into Calle Tecate Basin).
0 Roughness effect (Yr): The Manning's n may vary from 0.025 to 0.034
(Section 4.2.4).
0 Super elevation (Yb): 0.2 foot and 0.5 foot of superelevation
allowances were added to the upper 1200 feet and lower 500 feet of
the dike, respectively.
0 Side inflow effect (Ys): 0.5 foot of wave allowance was added
throughout the entire reach for the local side inflow effect.
0 Freeboard (Yf): one foot was provided for additional freeboard.
Table 9 shows the amount of each of these factors at various location along
the dike and the dike height provided.
For the anticipated velocities, it was computed that a 15-inch d50 light class
riprap (Reference 19) is large enough for bank protection. A 4.5-foot deep
cut-off was provided to protect against undercutting.
-42-
5.3 Calle Tecate Detention Basin
5.3.1 General Description As shown on Figure 14, the basin is
located south of the intersection of Calle Tecate and Avenida Bermudas. The
basin contains about 200 AF of storage to El-299, which is one foot below the
embankment crest. This provides temporary detention of storm runoff and
detention of debris from the 0.60 m12 of drainage area tributary to the
basin. (Sub -drainage areas P3 and P4). The basin is sized to detain the
entire SPF runoff volume.
Basin side slopes vary from 5 to 1 in soil to about 1.5 to 1 along the exposed
rock on the east side of the basin. Stormwater runoff will enter the basin
from the Upper Training Dike via a 5:1 sloped inlet protected with riprap, a
drainage ditch entering at the southwest corner of the basin and another
drainage ditch entering near the northwest corner of the basin.
The storm volume detained in the basin will drain to the East La Quinta
Channel via a low level outlet structure with a 36-inch diameter CSP drain
outlet located in the northeast corner of the basin. After a storm has
passed, detained stormwater will continue to drain from the reservoir for
about 5 days until the basin is empty. The bottom of the basin is sloped
between 1.6 to 2.5 percent toward the outlet structure to promote complete
draining.
A concrete lined emergency overflow spillway, excavated into rock at the
northeast corner of the basin, is provided to protect the embankment against
overtopping in the event water levels in the basin rise above the design water
surface for any reason. The 50-foot wide s pillway will discharge a maximum of
approximately 300 cfs without overtopping the basin embankment.
-43-
5.3.2 Layout and Studies The Calle Tecate Detention Basin,
because of its close proximity to the developed area -of La Quinta, has
potential value for use as a recreational facility. In addition, the size of
the area tributary drainage changed several times during the design as a
result of changes in the location of the Upper Bear Creek Training Dike
(Section 4.2). Accordingly, several alternative layouts were evaluated during
the course of the design. These evaluations, which primarily focused on the
shape of the basin, included:
0 basin layouts to minimize the length along Calle Tecate (generally
rectangular with longer axis north -south).
0 basin layouts to minimize excavation -costs (roughly square
configuration).
0 basin layouts which would be able to contain one to two Little
League baseball diamonds (generally rectangular with longer axis
east -west).
Basin capacities ranged from 320 AF with the Upper Bear Creek Training Dike at
its upper (El.480+) location, to 200 AF as finally designed (with the Upper
Bear Creek Training.Dike at El.410+).
The basin shape was ultimately determined on the basis of least cost with
capacity to contain the SPF runoff from the contributing drainage area as
defined by the final location of the Upper Bear Creek Training Dike.
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In general, the most cost effective basin layouts resulted from minimizing
basin depth relative to surface area, and in locating the basin away from the
steeper existing grades.
5.3.3 Flood and Debris Detention The Calle Tecate Detention Basin
was designed to fully detain the SPF ru n-off (176 A.F.) and debris production
(6.2 A.F.) from sub-dra inage areas P3 and P4. A 36-inch diameter CSP outlet
pipe was provided to drain the detained water over about a 5 day period. The
bottom of the basin is at EL.265. The design maximum water level is at EL.299
with one -foot of freeboard. The volume -capacity curve is shown,on Figure 14.
A reservoir routing was performed to determine the o utflow hydrograph. This
basin absorbs the peak inflow of 1460 cfs (100-year) and limits the release
thr ough the outlet works to about 100 cfs, thus minimizing the downstream,
channel facilities required.
5.3.4 Inlets Three inlets were designed to bring the local
run-off into the basin. As shown on Figure 1, part of surface run-off from
sub -drainage area P4 will be flowing along the Upper Training Dike (Section
5.2). It was estimated that the peak flow (100 yr) will be about 500 cfs at
the inlet to the basin. Based on Knauss' (Ref. No. 10), a 30-foot wide inlet
was provided to limit the maximum unit discharge to about 20 cfs per foot. A
5:1 slope was used for the inlet channel, with a required riprap size W50) of
about 15" (or light class, Reference 19).Two east -west interceptor ditches,
one basically along Calle Tecate and the other about 900 feet to the south
were al I so provided to collect the surface run-off from the graded compacted
f ill area (sub -drainage area P3) and drain it to the basin. It was estimated
that the maximum flow in these ditches would be about 300 cfs and 400 cfs
respectively. Riprap was provided at the channel inlets to the basin.
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5.3.5 Outlet Structure The low level outlet consists of a 15-foot
high 72-inch diameter RCP vertical riser with 1100 feet of 36-inch diameter
corrugated steel pipe (CSP) outlet laid at a slope of 0.0074, discharging to
the East La Quinta Channel. The concreteriser has three rows of four 15-inch
square openings, offset 45 degrees at each row. The openings have a clear
vertical spacing of 30 inches. The 36-inch CS P was grouted into the bottom
(El.265.0) of the riser. Discharge from the low level outlet will vary with
the detention basin water surface and will approach 100 cfs with the basin at
its maximum water surface. The computed outflow rating curve is shown on
Figure 15.
5.4 East La Quints. Channel
5.4.1 General Description The East La Quinta Channel intercepts
runoff from 0.14 m12 of drainage area in the foothills east of Avenida
Bermudas and conveys this runoff, together with the low level outlet releases
from the Calle Tecate Detention Basin, to the Avenida Bermudas Detention
Basin. The channel is also designed with capacity to convey runoff (See
Section 6.0) from sub-drainagq area LQ1 in the presently developed area of La
Quinta south of Calle Madrid when a storm drain system for the City La Quinta
is implemented.
The East La Quints. Channel follows the existing natural drainage channel at
the toe of the foothills, from the outlet of the emergency spillway at the
Calle Tecate Detention Basin to the Avenida Bermudas Detention Basin. The
channel, which follows the steep natural drainage slope (approximately 0.04),
will be exposed to high velocities during significant storm events and has
been lined with light class riprap (Reference 19) below the point of major
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inflow, Sta. 140 + 85. One quarter ton riprap (Reference 19) has also been
placed at the location where the 36-inch diameter Calle Tecate Detention Basin
low level outlet conduit discharges.into the channel to protect the channel
against high exit velocities. There is also a short reach of the channel
downstream of the Avenida Bermudas Detention Basin which connects to the
Project channel facilities in the Heritage Club development area, as described
in Section 5.6.
5.4.2 Channel Lining In the early stage of Project design, both
one -side riprap bank protection and fully lined riprap protection were
considered. However, as discussed in Section 4.4 for the Bear Creek Channel,
one -side riprap bank protection causes design uncertainties and maintenance
problems for the system. In addition, the East La Quinta Channel is
relatively narrow. When the cut-off depths for one -side protection were
consi dered, the costs for a fully -lined channel were, found to be comparable.
Since the full lining provides a more secure design, this was provided
starting at the outlet of the,36-inch diameter CSP drain pipe, and extending
downstream to the Avenida Bermudas Detention Basin.
5.4.3 Channel Geometry A trapezoidal channel with 2.5:1 side
slopes was selected, with full riprap lining as discussed above. The total
drainage area of the East La Quinta system is only about 2,.5 m12. therefore,
each point of local side inflow represents a large incremental increase in the
flow along the main channel. Also, as discussed in Section 3.1, due to the
relatively small drainage area, peak flows from a 100-year storm are larger
than those from an SPF event and therefore controlled the design. Within this
3000-foot long channel reach, the design flow varied from 420 cfs at the
47-
36-inch diameter CSP outlet, to 1020 cfs at the entrance to the Avenida
Bermudas Detention Basin. Due to this flow variation, channel bottom widths
ranging from 12 feet to 30 feet were designed so that the resulting required
embankment height was kept within 5 feet. Table 10 gives the designed channel
width and embankment heights.
5.4.4 Channel Hydraulics and Protection Due to the small drainage
area tributary to the reach 900 feet downstream from the Calle Tecate
Detention Basin (a part of sub -drainage area Ql), it was estimated that the
peak surface run-off (100-year storm) was only about 80 cfs. The existing
topography indicated that this runoff would enter the channel relatively
uniformly along this entire 900 feet length; therefore, only an earth training
dike was provided in this reach.
The fully lined riprap channel starts at the 36-inch diameter CSP outlet from
the Calle Tecate Detention Basin (Sta. 159+00). This is also the location of
the main surface run-off from sub -drainage area Ql.
The required bank heights were determined by taking into account all the
factors that could effect the channel water surface elevation. They are:
0 Normal Depth (Yn): The normal depths referred to here are the
computed maximum depth in each sub -reach using Manning's "n" = 0.030.
0 Superelevation (Yb): In curved channel reaches, Yb is the
additional cross wave height due to curvature. Since the
superelevation effect was found to be small, no bottom banking was
required.
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0 Roughness Effect (Yr): The estimated Manning's "n" for light class
riprap (d50 = 15") ranges from 0.030 to 0.035. An allowance, Yr, of
an additional 0.5 foot of water depth was provided to account for
possible roughness variation.
0 Side Inflow Effect (Ys): Side inflows may generate additional wave
heights. A 0.5 foot allowance was allocated to account for this
effect.
0 Freeboard (Yf): One foot of additional freeboard was included in
the design of the bank heights.
Table 10 summarizes the required bank heights and the amount of each of these
factors at various locations along the channel. As shown, the design Yt
values are equal to or greater than those required.
The maximum computed flow velocity was 14 fps, therefore, a light class riprap
W50 = 16 inches) (Reference 19) was used to protect the channel from
erosion. It should be noted that, at the'inlet to the Avenida Bermudas
Detention Basin, the channel width was expanded from 20-feet to 40-feet so
that the flow velocity could be limited to about 14 fps and light class riprap
(Reference 19) could be used for erosion protection at the inlet also.
5.5 Avenida Bermudas Detention Basin
5.5.1 General Description The Avenida Bermudas Detention Basin is
designed to handle runoff and retain debris from 0.42 m12 of drainage area in
the foothills to the south and from the presently developed area to the
southwest of the basin. Runoff to the basin will be conveyed by the East La
-49-
I Quinta Channel to a riprap protected inlet at the upper end of the basin. The
basin has been sized to contain the computed debris volume (3.8 AF) from the
SPF storm event. The basin outlets into a riprap lined channel at the north
end. There is also a low level outlet structure located at the northerly end
of the basin. Since the basin has not been sized to attenuate the design
storm peak inflow, the,capacity of the outlet is equal to that of the inlet.
Some significant attenuation will occur during smaller storms. The outlet
channel discharges to Project facilities constructed'in the proposed Heritage
Club development area to the north, as described in Section 5.6. Subsequent
to the original design of this facility, the District located a potable water
stor age tank site on the ridge southeast of the basin, which required the
addition of an access road t o the tank site through the basin. The tank
access road will also serve as access to the bottom of the basin for removal
of storm debris and other maintenance.
Early in the design effort, studies were conducted on other possible detention
basin locations along the East La Quints. Channel as alternates to the single
Calle Tecate Basin to provide flood flow attenuation. These studies concluded
that, due to topographic constraints and potentially large rock excavation
quantities, the economic size of basins along the channel route would be quite
limited and not adequate to contain the runoff from the tributary drainage.
The District agreed with this and directed Bechtel to proceed with design on
the basis of providing flood flow attenuation at the Calle Tecate Detention
Basin, with the Avenida Bermudas Detention Basin designed to provide debris
detention only.
-50-
5.5.2 Debris Production and Detention Sincethe East La Quinta
Channel was designed with fully lined riprap protection, no sediment erosion
should occur in the channel. The discharges from Calle Tecate basin and
sub -drainage area LQ1 were assumed to be essentially free of sediment.
Therefore, the Avenida Bermuda Detention Basin was designed to detain only a
debris volume of 3.8 AF from sub -drainage areas Q1 and Q2. As discussed,
previously, no additional storage was provided to attenuate the peak flow.
5.6 Heritage Club
5..6.1 General Description Heritage Club is a proposed golf
course/condominium development located east of -Avenida Bermudas. The proposed
development will integrate stormwater conveyance and detention basin
requirements of the East La Quinta System into the landscaping and golf course
grading for the development. See Figure 16 for the project- related
facilities which have been constructed and which would be part of the proposed
Heritage Club development.
5.6.2 Heritage Club Detention Basin The run-off from the East La
Quinta System, including the run-off from sub -drainage areas LQ1, LQ2, LQ3 &
LQ4A, will either discharge directly into the LQEC channel via the 60" RCP
buried conduit "Line A", or overspill into a large detention basin in the
Heritage Club development area. Allowing for a minimum one foot freeboard,
the large basin has a storage volume of about 520 A.F. below E1.59. An
additional 20 AF of detention storage is available in other Project facilities
upstream of the large basin. The SPF hydrographs for sub -drainage areas LQ1,
LQ2, LQ3, and LQ4.bave been truncated at a discharge equal to the 100-year
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flood peak (Section 3.1.3). This is based on the assumption that a future
storm drain system to be implemented by the City of La Quinta for these LQ
sub -drainage areas would be designed for a 100-year storm.
5.7 60-Inch Diameter Buried Stormwater Conduit
5.7.1 General Description The 60-inch diameter RCP buried
conduit, which is shown on Figure 1, will convey flows to the LQEC from the
East La Quinta System collection and detention facilities for the drainage
areas east and south of the presently developed area of La Quints, and from the
presently developed area south of Calle Sonor a. The inlet is located in the
Heritage Club development south of the large detention basin, at an elevation
sufficient to provi de gravity flow to the LQEC. A portion of the runoff from
sub -drainage areas LQ2, LQ3, and LQ4A in the presently developed area of La
Quinta, also will be conveyed directly to the conduit via storm drain "Line B"
of the Heritage Club facilities. The location of the buried stormwater
conduit was selected to minimize disturbance to existing developed property in
La Quinta. The outlet is located in the south bank of the LQEC at Station
20+50, adjacent to a landscaped depression in the golf course facilities
presently located within the LQEC channel. The flow line of the outlet is set
above the bottom of the depression but below the LQEC channel grade. This
arrangement was necessary to provide minimum cover of 2.5 feet on the conduit
north of Ave. 52. The conduit will intercept and directly divert smaller
storm flows, and a portion of larger storm flows, to the LQEC. Storm flow in
excess of the conduit capacity (about 150 cfs) will flow into the large
detention basin in the Heritage Club development. At that time, the flap gate
at the end of "Line B" will close and all run-off from subdrainage areas LQ2,
LQ3 and LQ4A will also spill over into the large basin via "Line C" and
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"Line D". After the storm has passed the stored water will be released into
the LQEC via an outlet structure in the basin connected to the buried
conduit. This arrangement provides the following functions:
0 Small storm flows are diverted directly to the LQEC and are kept off
the golf course, which reduces maintenance requirements and
out -of -play periods.
0 The volume of flow carried by the conduit during the design storm
reduces the required detention storage capacity of the basin by
about 100 AF.
0 The conduit serves as means of draining the basin after the storm
passes and flow in the LQEC recedes.
The conduit size was selected on the basis of an economic evaluation of
conduit cost versus basin cost.
The pipe will flow full and have a maximum internal pressure of about 20 feet
in the reach north of Ave. 52. A rubber gasketed bell and spigot joint was
selected to accommodate this internal pressure requirement.
The conduit has a drop inlet located near the outlet, to introduce local
runoff from a proposed small subdivision which would belocated along the
south bank of the LQEC in this area.
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6.0 PRESENTLY DEVELOPED AREA OF LA QUINTA
6.1 Introduction The La Quinta Stormwater Project protects the
presently developed areas of the City of La Quinta from runoff from the
adjacent foothills and from flows in Bear Creek. While the Project does not
intercept runoff from drainage areas within the developed areas of the city,
it does include capacity for storm drainage facilities to be provided in the
future by the City for the developed area south of Calle Sonora. Provisions
have also been made for temporary drainage of areas adjacent to Oleander
Reservoir and the LQEC. The provisions and assumptions made regarding such
future storm drainage facilities are described below.
6.2 Runoff from Areas Contributing to the East La Quinta System The
presently developed area of the City south of Calle Sonora generally slopes
north and east. The lowest point of this area is at the intersection of Calle
Sonora and Avenida Bermudas. The elevation at this intersection (El.62+) is
sufficient to allow gravity conveyance of runoff from the developed area to
the LQEC, or to the large detention basin in the Heritage Club development.
From discussions with the District, it was assumed that for design of the East
La Quinta System facilities, the future Citystorm drain facilities would
intercept and convey the .100-year storm runoff developed in subdrainage areas
LQ1, LQ2, LQ3, and LQ4A to the intersection of Callis Madrid, Colima, No I gales,
and Sonora r espectively with Avenida Bermudas. (See Figure 1) Accordingly,
the conveyance and detention features of the East La Quinta Channel, Avenida
Bermudas Detention Basin and Heritage Club flood control facilities were
designed to accommodate the 100-year peak flow rates and the truncated SPF
storm volumes (Section 3.0) originating from these subdrainage areas as
follows:
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0 Runoff from subdrainage area LQ1 will enter the East La Quinta
Channel east of Calle Madrid and be conveyed to detention basins in
the Heritage Club Development for temporary storage. -
0 Runoff from subdrainage areas LQ2, LQ3, and LQ4A will enter the
"Line B" storm drain (which has been installed as part of the
Heritage Club work) adjac ent to Avenida Bermudas and eitherflow to
the LQEC via Lines 1"B" and "A" or flow via Lines "C" and "D" to the
large detention basin in the Heritage Club development for temporary
detention.
6.3 Runoff from Areas Contributing to Bear Creek System Inlets have
been provided in the east embankment of the Bear Creek Channel for
intercepting the runoff that develops between the Channel embankment and the
original Bear Creek dike at Stas. 65+00 and 106+00.
A 60-inch diameter RCP conduit, with an inlet structure just west of the
intersection of Avenida Obregon and Avenida Montezuma, has been provided to
convey runoff from a 100-year event to Oleander Reservoir from the presently
developed area generally to the northwest of a line between the intersections
of Avenida Obregon and Calle Nogales with Avenida Montezuma (see Section 4.4.9
also). This facility replaces the inlet to the original Bear Creek channel
created by the Avenida Obregon grade crossing of the channel.
Two 36 inch diameter CSP flapgated conduits located at the west end of Calle
Tampico discharge through the Oleander Reservoir embankment into the reservoir I
area to provide localized drainage during events up to about a 100 year
-55-
I frequency storm. During larger flood events, the water levels in Oleander
Reservoir will close the flap gates, which have been provided to prevent
release of water from the reservoir. This may cause local runoff to flood the
area adjacent to th e inlet. Under pre -Project conditions flooding would have
occurred in this area when water levels in Oleander Reservoir and the original
Bear Creek channel outlet reached about E1.49. It was assum ed that permanent
facilities to correct this potential,flooding situation would be provided by
the Ci ty during implementation of its Master Drainage Plan.
Small flap gated drain inlets have also been constructed, or planned for
installation, in the 60-inch diameter RCP buried conduit in the East La Quinta
System discharging to the LQEC. Since the design water level in the LQEC is
higher than the existing ground levels to the south, the effectiveness of
these installations wiil be limited. It is assumed that these installations
are temporary and will be replaced during implementation of the La Quinta
Master Drainage Plan.
MT.=
7.0 INSPECTION AND MAINTENANCE CKITERIA
7.1 General An overall inspection of all Project facilities will be
performed at least once a year,and also following any storm activity which
produces significant runoff in the Project area, or following any significant
seismic event in the area. Video tape and photos will be taken and logged,
showing the general condition of Project facilities and any areas of special
interest. Maintenance will be performed to restore any eroded areas in
embankments or in riprap installations which are more than one foot below
design grade or which obstruct access. Perform ditching and berming above
areas of heavy erosion in earthen excavated surfaces, as feasible, to minimize
future erosion. References to drawings in the following sections are to the
as -built" Project drawings for the construction contract.
7.2 Channels and Training Dikes
7.2.1 Upper Bear Creek Training Dike (Drawings C-841, 8 42, 843)
Check saddle dike a nd access road at east end for erosion. Inspect training
dike top and upstream face for erosion or displacement of material. Check for
deposition of material along toe of dike. Remove deposited material greater
than two feet deep along toe of dike for a distance of 30 feet from toe.
Grade along toe of dike to maintain drainage to west.
7.2.2 Bear Creek Channel (Drawings C-807 through 812, 814, 815,
816, and 819)
Inspect soil cement lining for cracking, separation of the horizontal layers
or eroded areas. Check rock excavations along channel and at drop structure
for stability and extent of spalling. Check drop structure for accumulation
-57-
11 1
of large boulders or debris that might not wash out in heavy flows. Inspect
local drainage inlets for condition of soil cement aprons and riprap and for
any obstructions to drainage. Check uuderdrain and SDI low level outlets into
channel and remove any obstructions. Inspect earthen embankment and
excavation surfaces for erosion. Inspect maintenance roads and ramps. Grade
as necessary to maintain access. At channel outlet to Oleander Reservoir,
check condition of any exposed "buried slope protection" concrete, and repair
any damage. Inspect double 36-inch diameter CSP culverts, clear any
obstructions in culverts and at inlet and perform any necessary maintenance on.
flap gates at outlet. To the maximum practical depth, clean and grout any
cracks or separations in soil cement lining over two inches in width. Restore
any eroded areas in the soil cement lining that are more than 6 inches deep or
100 square feet in area, in accordance withan engineered plan for such work.
Remove any large volume of unstable rock from excavated surfaces and remove
large rocks and debris from channel and drop structure. Add fill material in
drop structure as required to maintain design grade for safety.
7.2.3 East La Quints. System - Upper Training Dike
(Drawings C-884 & 886)
Check dike top and banks for erosion. Check riprap for displacement of
material.
7.2.4 East La Quints. Channel and Training Dike
(Drawings C-856-857 & 876)
As for 7.2.3, also check outlets of 36-inch diameter CSP's, one below Calle
Tecate Detention Basin and one below Avenida Bermuda's Detention Basin, for
obstructions or displacement of riprap.
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7.2.6 Channels Through Heritage Club Development Inspect
condition of riprap and grassed surfaces. Arrange with Heritage Club for any
needed remedial work on the grassed areas.
7.3 Detention Basins and Side Drainage Inlets
7.3.1 Upper Bear Creek Detention Basin
(Drawings C-834 through 839)
Inspect embankment for erosion or settlement and spillway concrete for
c racking, spalling or displacement. Check condition of riprap installations
at basin. Determinelamount of debris in basin -and remove if it exceeds 35,000
c.y. (approximately 10% of design capacity). Check condition of fencing at
top of spillway, repair as needed to maintain security.
7.3.2 Calle Tecate Detention Basin
(Drawings C-881 & 885)
Inspect embankment for erosion or settlement and emergency spillway concrete
for damage. Inspect low level outlet, remove accumulated sediment and debris
and check outlet pipe and side openings and clear any obstructions. Inspect
condition of riprap installations, Determine amount of debris in basin and
remove if more than 1,000 c.y.
7.3.3 Avenida Bermudas Detention Basin
(Drawing C-878)
_59-
Inspect embankment for erosion or settlement. Check riprap installations.
Inspect low level outlet, remove accumulated sediment and debris,and check
outlet pipe and side openings and clear any obstructions. Determine amount of
debris in basin and remove if it exceeds 600+ c.y.
7.3.4 Side Drainage Inlets
(Drawings C-822, 824 through 828)
Inspect soil cement surfaces for cracks or separation, clean and grout, to the
maximum practical depth, any of these over two inches in width. Inspect
embankments for erosion and settlement, and check riprap installations.
Inspect low level outlets, remove accumulated sediment and debris and check
outlet pipes and side openings and clear any obstructions. Remove any
accumulated debris that exceeds the following volumes:
SDI
No.
1 -
2300+
c.y.
SDI
No.
2 -
4200+
c.y.
SDI
No.
3 -
200+
c.y.
SDI
No.
4 -
3500+
c.y.
7.3.5 Detention Basins in Heritage Club Development Inspect
embankments for erosion or settlement. Check riprap installations. Inspect
storm drain outlets and clear any obstructions inspect concrete structures for
damage. Check low level outlet structure, remove accumulated debris and clear
any obstructions from the pipe outlet and side inlets. Remove any accumulated
debris that exceeds 1900 c.y. in the detention basin located north of Lot No.
225.
7.4 Buried Conduits
7.4.1 60-Inch Diameter RCP to La Quinta Evacuation Channel
(Drawings C-850, 851, 859, 861 & 863 plus JFD drawings
for Heritage Club Development)
Inspect inlet structure concrete and trash rack for damage. Clear all debris
from rack and pipe inlet. Inspect interior of pipeline, remove any buildup of
deposited material along invert of pipe that is over one foot in depth. Check
condition of manhole structures and lids and check that flapgates are closed
and operable. Inspect outlet -into the LQEC. Check for scour or deposition at
outlet and restore any areas more than one foot below or above design grade.
Inspect condition of concrete� Remove any obstructions at outlet and in
emergency outlet along top of structure. Check condition of protection
barrier on emergency outlet riser.
7.4.2 60-Inch Diameter RCP to Bear Creek Channel at Avenida Obregon
(Drawings C-822 & 848)
Inspect inlet for erosion and condition of riprap. Inspect condition of
headwall and exposed pipe. Remove any obstructions at inlet. Inspect
interior of pipe and remove any buildup.of dep osited material more than a foot
in depth. Check outlet to Bear Creek Channel, remove any obstructions and
clean and grout, as deeply as practical, any openings between the concrete and
the adjoining soil cement.
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References
1. "DRAFT - La Quinta Stormwater Project, Basic Design Criteria" Letter from
J. Reynolds to W. Longenecker, dated August 10, 1984.
2. "CVCWD - Cove Country Club Storm Channel, Grass Channel Design Report"
dated.Nov*ember 1979.
3. "Pressure Fluctuations in Submerged Jump" by S. Narasimham & V.P.
Bhargara, J. of Hydraulics, ASCE, March 1976.
4. "Hydraulic Design Criteria" Chart HDC 623, by U.S. Corps Engineers, WES.
1-73.
5. "Hydraulic Design of Flood Control Channels" U.S. Corps of Engineers,
EM-1110-2-1601, July 1970.
6. "Development of a Methodology for Estimating Soil -Cement Embankment
Damage Due to Flood Overtapping" Draft Report, Simons & Li Associate,
September 1985.
7. "Hydraulic Model Study of Palm Valley Stormwater Channel" by Western
Canada Hydraulic Laboratory, Port Coquitlan, B.C. Canada October 1982.
8. "Hydraulic Resistance of Artificial Strip Roughness" by D.W. Knight &
J.A. MacDonald., J. of Hydraulics, ASCE, June 1979.
9. "Design of Small Dams" by U.S.B.R. 1973 Edition p. 393.
10. "Computation of Maximum Discharge at Overflow Rockfill Dams" by J.
Knauss, ICOLD - Congress, New Delhi, 1979.
11. "Fluvial Geomorphology" by S.A. Schumm, "River Mechanics", Edited by S.
W. Shen, Colorado Stage University, 1971.
12. "Erosion of Cohesion Sediment" by ASCE Task Committee, 1968.
13. "Whitewater River Basin, Feasibility Report for Flood Control," Palm
Desert and La Quinta, Riverside County, CA, Stage III Appendix A,
Hydrology, U.S. Army Engineer District, Los Angeles, CA, June 1983.
14. "Precipitation - Frequency Atlas of the Western United States, Volume XI
- California" by J. F. Miller, H. R. Frederick and J. R. Tracey; NOAA
Atlas 2, U.S. Dept. of Commerce, National Weather Service, Silver
Springs, Maryland 1973.
15. "HEC-1 Flood Hydrograph Package - User's Manual" U.S. Army
Corps of Engineers, HEC, Davis, CA, September 1981.
16. "Hydrology Manual" Riverside County Flood Control and Water Conservation
District, April 1978.
-62-
17. "A New Method of Estimating Debris - Storage Requirements for Debris
Basins" by F.E. Tatum, 2nd National Conference on Sedimentation,
Subcommittee on Sedimentation, ICWR, Jackson, Mississippi, January
18-February 1, 1963.
18. "Research and Development Bulletin, Dam Construction and Facing with
Soil -Cement", PCA, 1971.
19. "Standard Specificati ons, Section 72, Slope Protection" State of
California, Department of Transportation, July, 1984.
-63-
LA QUINTA STORMWATER
PROJECT
DESIGN REPORT
TABLES
Table 1. 100-year Rainfall Depth/Duration Data
P
Duration Rainfall Depth (in.)
5 min.
0.47
10-min.
0.72
15-min.
0.92
30-min.
1.27
1-hr.
1.61
2 hrs.
1.97
3-hrs.
2.24
6-hrs.
2.8
12-hrs.
3.8
24-hrs.
4.8
(Source: U.S. National Weather Service, Reference 2,
Latitude 330 40'00", Longitude 116* 18'30").
I t
Table 2. Summary of Sub -Drainage Area Characteristics.
Drainage
Sub -Drainage
Area
L
Lca
S
Basin Lag
System Area
(mi.2)
(mi)
(mi)
(ft/mi)
n
(Minutes)
Bear Creek Pi
0.30
0.91
0.39
239.
0.035
12.
P2
1.00
2.41
1.03
437.
0.035
22.
01
8.56
6.20
2.60
826.
0.035
40.
0.24
-
-
-
-
-
Ml
0.8
1.90
1.00
921.
0.035
17.
M2
1.1
1.90
1.00
521.
0.035
20.
Ll
0.25
0.78
0.27
724
0.035
8.
L2
0.95
1.90
0.80
800:
0.035
17.
.Kl
0.2
0.39
0.06
1720.
0.035
3.
K2
0.9
1.80
1.00
740.
0.035
18.
1
1.4
1.90
1.00
375.
0.035
21.
East La Quinta P3
0.29
0.63
0.23
266.
0.015
4.
P4
0.42
0.83
0.33
942.
0.035
8.
Ql
0.14
0.52
0.19
1140.
0.035
6.
LQ1
0.20
1.05
0.39
105.
0.015
6.
Q2
0.08
0.66
0.26
1240.
0.035
7.
LQ2
0.28
1.21
0.47
85.
0.015
8.
Q3
0.23
0.75
0.41
826.
0.035
9.
Q4
0.15
0.64
0.38
1130.
0.035
8.
Q5
0.12
0.53
0.19
1700.
0.035
5.
Q61
0.13
0.68
0.33
133.
0.015
5.
Q7
0.19
0.75
0.38
141.
0.015
5.
LQ3
0.28
1.19
0.42
84.
0.015
7.
LQ4
0.31
1.11
0.42
45.
0.015
8.
`9
"AfiqES
'IGN FLOOD PEAK DISCH
SUMMARY DE� I
SPF RUNOFF
VOLUMES
AND DEBRIS PRODUCTION
su��DRAINAGEJ
DESIGN PEAK RUNOF - F
SPF DEBRIS
PEAK DISCHARGE
SYSTEM
REA
AREA
DISCHARGE(I )ISPF
VOLUME
PI
RODUCTION
cfs)
(mi
(cf S)
(Ac-ft)
yd3 )
SPF
loo yr
EEAR
PI
0.35
725
100
2700
645
725
CREE K
P 2
1.10
1720
306
16600
1720
1420
01
8.56
10020
2180
290C-00
10020
7740
02
0.24
410
ISO
1600
410
400
Ml
O.EO
1320
222
35 000
1320
1240
M 2
1.10
1770
503
23000
1770
1560
L 1
0.25
540
71
3300
410
540
L2
6-95
1500
261
42000
1580
.1510
KI
600
56'
3000
340
600
K2
0.90
14EO
248
35000
1460
1370
1.40
2210
588
13000
2210
1880
SUB -DRAINAGE
DESIGN PEAK
SPF RUNOFF
VOLUME
SPF DE13RIS
PRODUCTION
PEAK DISCHARGE
SYSTEM
AREA
AREA
DISCHARGEO)
..
(cfs)
(mi2)
(cfs
(Ac - f t)
(yd3)
SPF
100 yr
EAST LA
P 3
0.23
660
72
5000
475
660
QUINTA
P 4
0.37
Boo
105 -
5000
690
800
ol
0.14
320
40
2106--
270
320
LQI
4,3 0
=3
-
390
-20
4-
Q 2
0.06
170
.23
4100
150
170,
LQ 2
0.28
620
88
-
540
620
0:5
0.23
4 a- 0
65
10000
425
4SO
C4
0.15
1 =5 3 0
4
E Soo
280
Q
0.12
2 SO
34
2 EOO
235
2SO
c E
0.13
330
41
1500
265
3-30
c 7
0.19
550
31
300
400
550
1_03
0.2S
E20
68
-
540
620
NECITEL
SAN FRANCISCO
LQ4A
0.19
420
59
390
420
COACRELLA VAL t OIS�RCT
COACO J_jEY WATEF
JA
CALIFORMA
LA QUINTA STORMWATER PROJECT
BESI@4 KPORT
NCT;-:': I-
DESIGN PEAK
DISCHARGE
IS EOUAL TO
THE GREAi ER GF THE
SFF (STANDARD
FROJECT
NN_ -1
A Q I 3
F'-CCr I OF,
ICC-Y��-PEAX
r_-ISC..,!RGES_
System
Bear Creek
TABLE 4
PEAK DISCHARGE DATA AT POINTS OF CONCENTRATION
Point of (1)
Concentration
A
B
C
D
E
Drainage Area Design Peak (2)
(m12)
Discharge (cfs)
1.69
1840
11.05
10029
13.35
11500
14.45
12460
15.8
7650
East La Quints. F 0.23 500
G 0. 94 850
H 1.02 1020
1, 1.75 .2500
2.59 175
(1) See Figure 1 for location of Points of Concentration.
(2) SPF event or 100-year event as applicable. See Section 3.0.
Table 5. Summary of Debris Production Parameters.
Total Cor-
Ultimate
Total
Drainage
Drainage
Hypso-
3 Hour
rection
Debris
Debris
Area
Slope
Density
metric
Rainfall
Factor
Production
Production
Sub-draina&e
(m12)
(ft/mi)
(mi/mi2)
Index
(in)
M
(yd3/mi2)
(yd3)
Pi
0.30
239
(30%)
0.(100%)
0.16(20%)
5.05(100%)
6
65,000
1,200
P2
1.00
437
(52%)
1.36(98%)
0.29(52%)
5.05(100%)
27
57,OOU
15,000
0
8.8
826
(82%)
1.77(97%)
0.45(97%)
5.05(100%)
77
44t000
3001,000
MI
0.8
921
(87%)
2.04(96%)
0.40(89%)
.5.05(100%)
74
580000
35,000
m2
1.1
521
(60%)
3.10(88%)
0.33(70%)
5.05(100%)
37
56,000
23,000
Ll
0.25
724
(76%)0
0.(100%)
0.22(26%)
5.05(100%)
20
66,000
3,300
L2
0.95
800
(81%)
1.50(98%)
0.45(97%)
-5.05(100%)
77
58,000
KI
0.2
1720
(100%)
0.(100%)
0.19(22%)
5.05(100%)
22
68,000
3,000
K2
0.9
740
(76%)
2.19(95%)
0.42(93Z)
5.05(100%)
67
58,000
35,000
1
1.4
375
(45%)
0.92(99%)
0.27(37%)
5.05(100%)
16
55,000
13,000
P3
0.29
270
(33%)
0.(100%)
0.51(99%)
5.05(1002)
33
65,000
6,200
P4
0.42
940
(88%)
0.(100%)
0.15(20%)
5.05(100%)
Id
63,000
4,7UU
Q1
0.14
1140
(94%)
OJI00%)
0.19(22%)
5.05(IUU%)
21
71,000
2,100
Q2
0.08
1240
(96%)
0.(100%)
0.33(70%)
5.05(100%)
67
76JOU0
4,100
Q3
0.23
830
(82%)
2.504%)
0.36(86%)
5.05(106%)
66
67,000
10,000
#44
0.15
1130
(94%)
0.(100%)
0.40(89%)
5.05(100%)
84
7U,000
80800
Q5
0.12
1700
(100%)
0.(100%)
0.2400%)
5.05(100%)
30
72,OOU
23-600
Q6
0.13
130
(17%)
0.(100%)
0.42(93%)
5.05(100%)
16
72,OOU
1,5UO
Q7
0.1%.
140
(17%)
0.(IUUZ)
0.20(23%)
5.05(100%)
4
69,000
500
Note Debris production for sub -drainages LQI, LQ2, L(43, and Lq4 (City of La Quinta) ware not estimated because
Otoduction from these areas will be small.
La Quinta Stormwater Project
Design Report
Table 6
Summary of Embankment Height Design for Upper Bear Creek Training Dike
From
To
Sta.
Sta.
0+00
1+40
1+40
9+00
9+00
13+00
13+00
19+50
19+50
26+00
Notes: 1 (1)
(2)
(3)
(4)
Max
Bottom Flow
Width Velocity
(ft) (fps)
12 15
30 16.0
30 14.0
30 12.0
30 10.5
Bank Height Factors (ft)
Yn Ysd Yr Ys Yf
12.9
0.5
-
-
1.0
12.4
0.75
, .1
.2
1.0
11.9
1.0
.1
.2
1.0
11.5
0.75
.2
.2
1.0
10.7
0.5
.2
.2
1.0
Embankment
Height Yt
ReqId
Design
(ft)
(ft)
14.4
14.5
14.45
14.5
14.20
14.5
13.65
14.0
12.6
li.0
The required embankment height, Yt, is the computed normal
depth Yn (using n=0.025) plus the depths due to: sediment.
deposition, Ysd; roughness effect, Yr; local side inflow,
Ys; and a minimum freeboard, Yf, of one foot.
Yn represents the maximum computed depth in each reach
(downstream control).
Manning's n range is 0.025 to 0.034.
The maximum flow velocity occurs at the greatest sediment
deposition which causes the maximum channel slopes.
La Quints, Stormwater Project
Design Report
Table 7
Summary of Embankment Height Design for Upper Bear Creek Channel
Max
Reach
Bottom
Flow
Bank
Height
Factors (ft)
Embankment Height Yt (Ft)
From
To
Width
Velocity
YU
Ysd
Yr Ys
Yf
Req'd
Design
Sta.
Sta.
(ft)
(fps)
(left/right)
(left/right)
33+73
38+03
100
30
15.6-7.9
-
1.0 -
1.0
17.6/9.9
19/10.5
38+03
42+50
40-100
27
7.9
1-7/0
1.0 -
1.0
11-6/9-9
12.0/11.0
42+50
45+00
40
32
7.8
1.7/0
1.0 3.-0
1.0
14.5/12.8
14.5/13.0
45+00
49+57
40
33
7.0
1.7/0
1.0 -
1.0
10.7/9.0
11 0/9.5
49+57
66+00
40
35
6.5
-
0.8 -
1.0
8.3
9:0
66+00
80+00
40
37
6.2
0/1-5
0.8 -
1.0
8.0/9-5
8.5/10.0
80+00
85+00
37
6.7
-
0.8 3.0
1.0
11.5
12.0
85+00
97+70
40
39
5.7
.1.9/0
0.8 -
1.0
9.4/7.5
9.5/8.0
97+70
104+50
40
35
5.5
0.8 -
1-0
7.3
8.0
104+50
110+00
40
33
6.0
0.8 3.0
1.0
10.8
11.0
110+00
116+00
40
35
5.4
0.5 -
1.0
6.9
8.5
116+00
122+90
40
35
5.4
0/1.2
0.5 -
1.0
6.9/8.1
7.5/8.5
122+90
128+00
40
34
5.6
-
0.5 -
1.0
7.1
8.5
128+00
128+50
40
34.
5.6
0.5 -
1.0
7.1
9.0
Notes: (1) The required embankment height, Yt, is the computed normal
depth Yn (using n=0.020) plus the depths due to:
superelevation/banking, Yb; roughness effect, Yr; local
side inflow, Ys; and a minimum freeboard, Yf, of one foot.
(2) Yn represents the maximum computed depth in each reach.
(3) Manning's n range is 0.020 to 0.025.
(4) Channel side slope is 2(h): 1 (Y).
La Quinta Stormwater Project
Design Report
Table. 8
Summary of Embankment Height Design for Lower Bear Creek Channel
Max
Reach
Bottom
Flow
Bank
Height
Factors
(ft)
Embankment Height Yt (Ft)
From
To
Width
Velocity
Yn
Ysd
Yr
Ys Yf
Req'd
Design
Sta.
Sta.
(ft)
(fps)
.(left/right)
(left/right)
12+36
14+52
70
15
9.5-10.9
-
0.5
- 1.0
12.4
9.0/14.0(5)
14+52
15+02
70
12.5
11.0
-
0.5
- 1.0
12.5
14.0/14.0
15+02,
16+40
70
12.5
11.5
0/1.4
0.5
- 1.0
13.0/14.3
14.0/15.5
16+40
16+95
Drop Structure
16+95
18+19
40
16
12.5
0/1.8
0.5
- 1.0
14.0/15.8
15.0/17.0
18+19
21+88
40
14
13.5
0/1.0
1.0
- 1.0
16.5/16.0
16.5/17.0
21+88
27+73
40
13
14.0
0.5/0
1.0
- 1.0
16.5/16.0.
17.0
27+73
32+23
40-100
13
16.0
-
0.6
1.0 1.0
18.6
19.0
32+23
33+73
100
6
15.9
-
0.6
0.5 1.0
18.0
19.0
Notes: (1) The required embankment height, Yt, is the computed normal
depth Yn (using n=0.020) plus the depths due to:
superelevation Yb; roughness effect, Yr; local side inflow,
Ys; and a minimum freeboard, Yf, of one foot.
(2) Yn represents the maximum computed depth in each reach.
(3) Manning's n range is 0.020 to 0.025.
(4) Channel side slope is 2(H): 1 (V) except for the 70 foot
bottom width reach where a side slope of 1.5:1 was used.
(5), The last 200 feet of the left (west) bank is a rocky area.
Therefore, in this short reach the soil cement bank height
shows as less than required, since the bank above that
height is in rock.
La Quinta Stormwater Project
Design Report
Table 9
Summary of Embankment Height Design for Upper East La Quints, Training Dike
Max
Bottom
Flow
Bank
Height
Factors
(ft)
From
To
Width
Velocity
Yn
Ysd
Yr
Ys
Yf
Sta.
Sta.
(ft)
(fps)
10+00
10+75
15-30
15.5
1.9
0.5
0.5
0.5
1.0
10+75
14+25
15
15.0
1.9
0.5
0.5
0.5
1.0
14+25
26+25
15
.14.0
1.8
-
0.5
0.5
1.0
Embankment Height Yt
Req'd Design
(ft) (ft)
4.4 4.5
4.4 4.5
3.8 4.5
Notes: (1) The required embankment height, Yt, is the computed
normal depth depth Yn (using n = 0.025) plus the
depths due to: superelevation, Yb; roughness effect,
Yr; local side inflow, Ys; and a minimum freeboard,
Yf, of one foot.
(2) Yn represents the maximum computed depth in each reach.
(3) Manning's n range is 0.025 to 0.034.
La Quints. Stormwater Project
Design Report
.Table 10
Summary of Embankment Height Design for East La Quints, Channel
Max
Bottom
Flow
Bank
Height
Factors
(ft)
Embankment
Height Yt
From
To
Width
Velocity
Yn
Ysd
Yr
YS
Yf
Req'd
Design
Sta.
Sta.
(ft)
(fps)
(ft)
(ft)
132+00
136+56
30
13
2.9
.6
.5
-
1.0
5.0
6.0
136+56
140+00
Avenida
Bermudas Debris Basin
140+00
140+85
40-55
13
1.6
.5
.5
1.0
3.6
5.0
140+85
141+70
20-40
13
2.5
.5
.5
1.0
4.5�
5.0
141+70
143+00
20
li
3.0
-
.5
.5
1.0
5.0
5.0
143+00
144+50
12-20
11
2.2
.3
.5
.5
1.0
4.0
5.0
144+50
155+00
12
11.5
2.0
.2
.5
.5
1.0
4.2
5.0
155+00
159+00
12
11.5
2.2
-
.5
.5
1.0
4.2
5.0
159+00
168+22
12
8.0
1.0
-
�'.5
.5
1.0
3.0
5.0
Notes: (1) The required embankment height, Yt, is the computed
normal depth Yn (using n = 0.030) plus the depths due
to: superelevation, Yb; roughness effect, Yr; local
side inflow, Ys; and a minimum freeboard, Yf, of one
foot.
(2) Yn represents the maximum computed depth in each reach.
(3) Manning's n range is 0.030 to 0.035.
LA QUINTA STORMWATER
PROJECT
DESIGN REPORT
FIGURES
40 LEGEND
CL
SUB —DRAINAGE AREA
(SEE TABLE 3)
(SEE TABLE 4)
411 PROPOSED
ki HERITAGE CLUB
DEVELOPMENT
o
HANNE
RONDO c
im
A TA
rDET
IF
HIED
IT
pii
+00
RESERVOIR i- Mitt?.:
OLEANDER
DETENTION
AGIN ',_UPPER SEA IKC
OR REr_
TRAINING E
L�j STRUC, RE DRA
DRAINAGE &TENTION BASIN 02
01
ITEL
COACHELLA VALLEY WATER DISTRICT
LA QUINTA STORIAWATER PROJECT
3: DESIGN REPORT
SUB —DRAINAGE AREAS AND
POINTS OF CONCENTRATION
man
|
AVI!,rZ� ro" o"
E 3+7 7
tl t A Nil < 1" P.
N
. WO
(zi
out &�J E i
w
_S:
N
e�
7
./7 53
N �p
N W71;014
A\
-68 3
ao
0. 0-�
r X;
J,
2-�
?Ji
-,!EiNzrk C�, Pj!
"X
V
v
CF'
iL V.
C\
�c
pit'.
-14r
r
7i
7-Z—
"I
IAN
;78 75
497 t� A-
4 . Z
0
3 Q
r
I 77op
oF E
WENT,
s(p
5z
48
44
40
ra
wA-rag
L,,Ooo�
C)E5R]s
-sTc Ac.E
zo
ic.
0 50 100 200 300
GRAPHIC SCALE
0 100 zoo -AW 400 G000
UPPER BEAK 9K'BdEkION W
STORAGE IN ACRE-FEET
UPPER BEAR CREEK DETENTION -BASIN PLM AND DATA
UPPER BEAR CREEK DETENTION BASIN
PLAN
1) L D. .-`0 U R E 2
W771 LE." R I S S '10 R A G E, C d R V E
LR QUINTR STORMWRTER PROJECT
UPPER BEAR CREEK DETENTION BASIN—SPILLWRY RATING CURVE
X5.0
36"
355.0
LA_
350.0
C=
345.0
L4J
340.0
85
faE 335
330.0
OUTLET RRTING CURVE
—TOP OF DIKE RT EL.358.0
320.o E
0. 2001 400a swo- BOOM loom
OUTLOWQ(CFS)
FIGURE 3
LLI
—i
E
=1
E.
RIVE
-
MEMO
rowe
,MEMO
Sm
in
NMI
MW
law
I t.j=
cm�
Bill
now
mo - —
110�mll
u-uu dL,-UU 4utuu bU+UU bu+uu luu+uu Izo+ui
BEAR CREEK CHANNEL PROFILE
HORIZ. 1"= 2000'
VERT. 1"= 80"
VARIES
>
c'j
2
SOIL CEMENT LINING
b
LIM
I —
BEAR CREEK CHANNEL
TYPICAL SECTION
NTS
14U.0u 160+UU
TOE OF DIKE
uj
-j
-440
-- -- 7/_ L X-1 � I I N b -- LiK
T T- 0 F --D I--K E-
7
P-4 0-0-1
O-E -(F---- T-
J
210+00 220+00 230+00 240+00
UPPER BEAR CREEK TRAINING DIKE
PROFILE
HORTZ 1"= 1000'
VERT. I"= 40'
30'
EXISTING GROUND
2.5 2.5
R"T
IPRAP EMBANKMENT
UPPER BEAR CREEK TRAINING DIKE,
TYPICAL SECTIM
NTS
BEGHTEL
SAN FRANCISCO
COACHELLA VALLEY WATER DISTRtCT
COACHMA. CAUFORNIA
LA OUINTA STORMWATEA PROJECT
DESIGN REPORT
BEAR CREEK SYSTEM
PRO�ILE& AND'SECTIONS
DRAW" N&
6r- �r- Tnr-
r 4
F
CREEK
CHAAIAIEL'
,-C)EBRI5
ST6RAGF- :eURFACE L
zo
A i
;-4CT;: I
I TH: ow I
wj
IR CRES
Ro
.. ....
1,cL
262.0
. ...
EL (�4
FlitvisHl (Z
EXIST. 6ROUAI
600 4uu
SECTION
NT5
L� L:A
%cc
Llt
NOT E:
1. DE5FIS Sl'ORAGE SLlRF=AcE-
LONGITUDIWAL SLCF-= 15
ASSUMED TO BE EQUAL TO
ONE-HALF: OFTH= NATUF:;AL
GROUND SLOPE ALOW6 IN-
FLOW DIR-CTION, C)EE3F�js
STORAGE REC�UIRED AT THIS�
SIVE INLET IS 2,5,000 cy,
0 50 100 200 300
GRAPHIC SCALE
BECITEL
SAN FRANCISCO
COACHELLA VALLEY WATER DISTRICT
COACHELLA, CALIFORNIA
LA QUINTA STORMWATER PROJECT,
STR`C-'
T
C
JJE
_ T'
DESIGN -REPORT
BEAR CREEK SYSTEM 1
SIDE DRAINAGE INLET NO. 1
lag ft
%�;DUIE 51
Rft
180
> 170
'R
Z�-,
tu
_L6_0
Is'o
a
IN
-X Z
N-11
7w �j z
V;
'PLAN
EX157- 6ROUAID BEAR
CREEK
WEIR CREST Ft, 17,f.50 CHAvAIEL
_PEE3F\'I5_ STORAGE LINE
(SEE NOTE. I
/80
Exist c7ROWD
170
FIN15H E50TTOM GR,6.0E A1079
16o
150
NOT E:
1. DEESFIS STORAGE SURPACE-
LONGITUDINAL SLOP.=— IS
ASSU MED TO BE EQUAL TO
ONE—HALF: OF.THEI NATUF?,AL
GROUND SL0P9 ALOWG IN—
FLOW DIRECTION, VEE3RIS
STORAGE RECkUlKED 4�7 THIS
BID= INLET IS 4'Z00*0 ZY,
0 50 100 200 300
GRAPHIC SCALE
ME
VA XMASM
jo
<
ol
125 .0
0,
PLAN
iqEQq akEv<
D=L- BR 15 STORA, . ...... CHANAIE1
SURFACS- _L Ili
�5.Ee___ NOTE- I
190
WEIR'OREsr Etc. B/ o
80
cx/sr, 6,eCUAID7
kjj
BorToM O�F D65US BA SIAI
-60
sEcTroiv
NTS
F-) F
E3RIS STORAGE E5UFF=ACE
LONGITUE)INAL SLOPE I
5
-D 10 -=C�UAL TO
ASSLJM=
ON�-=-HALF OFTHE NATUK.AL�l
GROUND BLOPE ALONG IN-
FLOW C)-BRIS
STORAGE FZEQUIR�-=DA7 THIS
SIDE INLET IS .3000
0 50 100 200 300
GRAPHIC SCALE
Mail
-9u
PLAN
71)V6, ce�Razfivo
WEIR
VEOFZIIE� 15TOF;�A—GE
_50 SURFACE LI'NS- 110 45,4,C
(SEE NOTE.
-80,
V A 51, e
-lWe-67,eZ. 79. a,9
70
EL G?_.0
FINISY So TOM
6RAD6
GO
50
NOTE:
1. DEBRIS STORAGE SURFACE
I-ONGITUIDINAL SLOPE 115
ASSUMED TO SE EaLIAL TO
OKIE-HALF OF THE NATURAL
_&ROUND SLOPE ALONG IN-
FLOW DIFECTION, DE-CRIS
IBTCRAG= FZEQLJIREID AT 71-115,
SIDE INLET 15 55000 CY,
0 50 100 200 300
GRAPHIC SCALE
AREA (ACR ES)
TOP OF EMBANKMENT 150 120 40 0
55-
50-
-45-
SURFACE AREA
V 0 L U M E
u-
z 40-
0
SPILL
ZWAY-CREST
ui 35--
30-
27
0 400 600 1200 1600 2000
VOLUME (ACRE FEET)
OLEANDER RESERVOIR AREA/CAPACITY CURVE
BECITEL
SAN FRANCISCO
COACHELLA VALLEY WATT-RDISTRICT
COACHELLA, CALIFORNIA
LA QUINTA STOR,MWATER PROJECT
DESIGN REPORT
O�EWER RESERVOIR DATA
k EXISTING FACILITY
m ft oftwmm
[10-ff4-008
FIGURE
F—
LAJ
_j
L&j
L4J
L&j
cc:
r;7.nl.
P�f7l-1
67ff_]rA,-
45.0
ETM;vl"l
LA QUINTA STORMHATER PROJECT
OLEANDER RESERVOIR - OUTLET RATING CURVE.
. ............................................................. ............
WIDENED X-SECTION
ORIG. X-SECTION
7
ir
ORIGINAL OUTLET RATING CURVE
-WIDENED OUTLET RATING CURVE
.......... TOP OF DIKE AT EL.55.0
L_ I
15 FT.-�
17.3 FT.�
EISENHOWER BR. X-SECTION
(OUTLET)
20M. 4000. 600M a".
OU.TLOW,Q(CFS)
FIGURE 10
YAL 77-11;� :-�li
COACHELLA VALLEY
STORMWATER CHANNEL
m 6
(EXISTING) .429,
I A*'*--ntl-fh;-rA C7X/Af-1lA-rin*p._'
0)
A
I
32
E-
60"o
BURIED CONDUIT
PL A Al
SCA / E f' =
2000
tj
,6
70
DETAIL 1
N TS
LA QUINT14
EVACUAT101V CqAAIAIC--I- DATA
CHANIVEL GEOMETPY
FPOM
TO
b
Pit-4-5
56+95
GRASS
pElsenhowef(ALIE50)CGOLFCOURS'E)'
1/�RECWLAP SAIApE
,Bridge)
56 t95
159*86
EA RT'-'7'
.501
3.�5
/59'-86
161 f- 66
CONCRETE
50,
3.5 TO 2
161 t,56
168+16
CONCRETE
'501
2
/68*/6
169 i-dr,
CONCRETE
150,
2 TO 3.5
1(59*86
172tOO
EART14
-50' TO 60'
- 3.5 TO 2.5
172f 00
1
183 1-00
1 1
EARTH
.
80'
,
2.5
I
—
IVOQT�4EPLY SIDE
18.3 00
EIVD
TIJ,
�zb -4-0'
2.5
S00 T14 ER L Y SIDE
163+00
185+00
-COAICRETE
kb=,40T0.59
z.5 ro 1-5-.'
BANK
185-tOO
END
COMCRE TE
�zb 56'
SANK
I
L.Lj
I
LA QUINTA STORMHATER PROJECT
W.L. TIME. HISTORIES AT, CVSC AND AT OLEANDER RESERVOIR
60.0 1 . . . v . v . . . . . . . .. . . . . . . . . . . . . I . . . . . . . . . I . - . . -
a",
FrIT,
Ki- ul
-COACHELLA VALLEY STORMWATER CKV4NEL (CVS0 W.L. AT CONFLUENCE
WITH LR QUINTR EVACUATION CFR14NEL (FROM A 100-YR FLOOD EVENT
OVER THE DEEP CANYON AREA)
I . .......... ROUTED OLEANDER RESERVOIR W.L.. (FROM AiN SPF EVENT)
OF
1.0 2.0 3.0 4.0 5.0 S.0 7.0 6.0
TIME T(HOURS)
M-11'
FIGURE 12
ff3
F—
�E
45.0
z s "I,
9:�!A
LR QUINTR_ STORMWRTER PROJECT
CVSC BRCKWRTER EFFECT-EVRC. CHRNNEL RRTING RT AVE.50
I LA QUDffA EVACUATION CHANNEL RATING CLRVE AT RVE.50
—TOP OF CHANNEL EMBR-MENT. EL.50.0
.......... DESIGN MRXUlL" WATER LEVEL AT EL.49.0
am 40M mm em
FLOW Q(CFS)
FIGURE 13
292 9
293.
W5392154
E t9 81 rrao.
J
-1 w�_/
A,
An
10
A
i5
V
CALLE TECATE DETENTION BASIN
PLAN
0
64 IST E
W �eo
'b
36)
EXI ACrC- S9 15
/111 — - 31
0 50 100 200 300
GRAPHIC SCALE
lu
ILI
LL
:z
0
LIj
_j
w Z7
'26
0 40 so ISO lcoo 200 220
51-ORAGE IN ACRE-FEET
CALLE TECATE DETENTION BASIN
WATER AND DEBR15 STORAGE CURVES
BECHTEL
SAN FRANCISCO
COACHELLA VALLEY WATER DISTRICT
COACHELLA, CALIFORNIA
LA QUINTA STORMWATER PROJECT
DESIGUREPORT.
CALLETECATE DETENTION BASIN
PLAN AND DATA
107K-ooal F I G U R E 14
305
295
L4_
290
C=
L4j 285.0
1
280A
LLi
E5
F— 275.0
27a.0
265.0
LR QUINTR STORMWATER PROJECT
CRLLE TECATE BASIN LOWLEVEL OUTLET RATING CURVE
OUTLET RRTING CURVE
—TOP OF EMBAWMENT RT EL.300.0
M 20. 40. SeL M loeL 120. 140.
FLOW Q(CFS)
FIGURE 15
IS
WAM