27984 La Quinta Village Shopping CenterF-
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ON SITE
HYDROLOGY REPORT
for the
LA QUINTA VILLAGE
PROJECT
SUBMITTED BY:
THE
KEITH
COMPANIES
COACHELLA VALLEY
y
THE KEITH COMPANIES
APRIL 14, 1994
Introduction & Summary
The proposed La Quinta Village (Ralphs Shopping Center) is located
at the Northwest corner of Calle Tampico and Washington Street,
across from the La Quinta Civic Center. The project site is
comprised of approximately 9.2 acres of relatively flat terrain
having less than one foot difference in relief.
Design criteria established from the City of La Quinta ordinances
require retention of the 100 year, 24 hour storm on site with an
emergency escape overflow following existing drainage patterns.
The storm drain facilities at the intersection of Washington and
Tampico will be utilized only for draining the retention basin
after the storm waters have subsided. The ponding water within
the site requires mechanical forces to help in its subsidences
due to the percolation at this site is relatively nil.
Ponding water will inundate a portion of the parking area to a
maximum depth of 811. Circulation patterns will be altered with
this scenario, but the building structures will be protected and
alternate access will still be available completely around the
parking areas. The storm drain facilities will have a dry well
system to accommodate the low flow nuisance water and the storm
pipe handling the 14 year storm. Excess water will pond over land
into the retention basin through a landscaped scale.
Retention basin capacity will be graded with maximum 3:1 side
slopes and 6 foot depth containing 1.15 Acwft and the parking area
containing the remainder 0.4 Ac-ft. All calculations assume type
C soil and 0" percolation within a commercial development, due to
the constraints of the site, to existing conditions, and
experience at this location.
Hydrology/Hydraulic Review
The hydrology was reviewed using the Riverside County Synthetic
Unit Hydrograph method for the 100 year/24 hour event to determine
the volume of storm water to retain. Peak run of rates were
derived for the storm drain design using the Rational Table
method. (Riverside County Flood Control and Water Conservation
District 1978 manual).
Attached charts, computer prints, exhibits and maps identify the
parameters and variables used to estimate the peak run-off and
total run-off to be retained within the project site.
Retention Basin Volumes:
Corner Landscape Area: 1.15 Ac-ft (3:1 max slopes
6'deep)
Parking Lot Area: 0.40 Ac-ft (34,800 SF x Ave 0.5 deep)
Storm Drain Pipe:
Q= (. 463/n) D%S""-'
Q=(.463/.013) (2)86(.01)"A`
_ (35.62) (6.35) (.1)
= 22.6 <22.8 OK
n=0.013 D=24" S=0.010
riverside County Rational Hydrology Program
Civi1CADD/Civi1DESIGN Engineering Software, (c) 1990 Version 2.7
Rational Hydrology Study Date: 04 14 94
--------------------..____- __ ____
LA QUINTA VILLAGE SHOPPING CENTER _
JN 40090.00
BY: MR CHECKED KRS
Q10
********* _ --
Hydrology Study Control Information
********** -
-- ------------------ -- - -- - - --
Rational Method Hydrology Program based on -- - -� r
Riverside County Flood Control & Water Conservation District
1978 hydrology manual
Storm event (year) = 10.00 Antecedent Moisture Condition = 2
Standard intensity -duration curves
data (Plate D-4.1)
For the
[ Cathedral City ] area used.
10 year
storm 10 minute intensity
= 2.770
(in./hr.)
10 year
storm 60 minute intensity =
0.980
(in./hr.)
100 year
storm 10 minute intensity
= 4.520
(in./hr.)
100 year
storm 60 minute intensity
= 1.600
(in./hr.)
Storm event year = 10.0
Calculated rainfall intensity data:
1 hour intensity = 0.980 (in./hr.)
Slope of intensity duration curve = 0.5800
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Process from Point/Station 100.000 to Point/Station 300.000
**** INITIAL AREA EVALUATION ****
Initial area flow distance = 700.000(Ft.)
Top (of initial area) elevation = 41.500(Ft.)
Bottom (of initial area) elevation = 37.200(Ft.)
Difference in elevation = 4.300(Ft.)
Slope = 0.00614 s(percent)= 0.61
TC = k(0.300)*[(lengthA3)/(elevation change)]^0.2
Initial area time of concentration = 11.415 min.
Rainfall intensity = 2.566(In/Hr) for a 10.0
COMMERCIAL subarea type
Runoff Coefficient = 0.883
Decimal fraction soil group A = 0.000
Decimal fraction soil group B = 0.000
Decimal fraction soil group C = 1.000
Decimal fraction soil group D = 0.000
RI index for soil(AMC 2) = 69.00
Initial subarea runoff = 10.897(CFS)
Total initial stream area = 4.810(Ac.)
Pervious area fraction = 0.100
year storm
+++++t+++++++++++t++++++++++..++f+++....++.++..+++++++++++++++++++++++
Process from Point/Station 200.000 to Point/Station 300.000
**** SUBAREA FLOW ADDITION ****
COMMERCIAL subarea type
Runoff Coefficient = 0.883
Decimal fraction soil group A = 0.000
Decimal fraction soil group B = 0.000
Decimal fraction soil group C = 1.000
Decimal fraction soil group D = 0.000
RI index for soil(AMC 2) = 69.00
Time of concentration = 11.42 min.
Rainfall intensity = 2'.566(In/Hr) for
Subarea runoff = 8.042(CFS) for
Total runoff = 18.939(CFS) Total area
End of computations, total study area =
The following figures may
be used for a unit hydrograph
a 10.0 year storm
3.550(Ac.)
8.360(Ac.)
8.36 (Ac.)
study of the same area.
Area averaged pervious area fraction(Ap) = 0.100
Area averaged RI index number = 69.0
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(b) Curb Type
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L required
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BUREAU OF PUBLIC ROADS
DIVISION TWO WASH., D. C.
NOMOGRAPH FOR CAPACITY OF CURB
OPENING INLETS AT LOW POINTS �- �-
LEGEND
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4.81 ARE
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CITY OF LA OUINTA
LA QW11 A \410 S ROPPING MM
RYDROLCGY MAP
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