HomeMy WebLinkAbout431 34th Street Drainage Calculations
15‐050 Rite Aid – Bakersfield
431 34th Street
Bakersfield, CA
Updated: 7/16/2018
Drainage
Calculations
Prepared By:
Civil Design Studio, Inc.
Robert Winslow, PE
P.O. Box 199
Cambria, Ca 93428
805.706.0401
15‐050 Rite Aid – Bakersfield
Drainage Calculations Page | 1
Attn: Alerik Hoeh
City of Bakersfield
Department of Public Works
1501 Truxton Avenue
Bakersfield, Ca 93301
Subject: Rite Aid – Bakersfield
Re: Drainage Calculations
Alerik:
Please find enclosed the Drainage Calculations for the above referenced project.
The study calculations were prepared using the Rational Method and Mannings Equation.
Please contact me for any clarifications or supporting information you need with reference to
this report.
Regards,
Robert Winslow, PE
15‐050 Rite Aid – Bakersfield
Drainage Calculations Page | 2
Contents
Introduction .................................................................................................................................................. 3
Project Location ........................................................................................................................................ 3
Existing Conditions .................................................................................................................................... 3
Proposed Project ....................................................................................................................................... 4
Drainage Calculations ................................................................................................................................... 5
Rational Method Inputs ............................................................................................................................ 5
Site Hydrology ........................................................................................................................................... 5
Proposed Site Runoff ................................................................................................................................ 5
Report Conclusion ..................................................................................................................................... 6
Supporting Documents ................................................................................................................................. 7
NOAA Atlas 14 Point Precipitation Frequency Rainfall Intensity .............................................................. 7
15‐050 Rite Aid – Bakersfield
Drainage Calculations Page | 3
Introduction
Project Location
The proposed project is located at 431 34th Street in the City of Bakersfield, County of Kern, State of
California. The site is bordered by 34th Street to the north, commercial development to the west,
commercial development to the south, and commercial parking lot to the east.
Figure 1: Project Location
Existing Conditions
The site previously housed a commercial building that was demolished between 2006 and 2008 and has
been vacant from then until now. The existing conditions of the property is 100% impervious because
the entire site is either paved or building. Stormwater that falls onto the site, sheet flows north and
enter the City of Bakersfield storm drain system via the 34th Street curb and gutter.
15‐050 Rite Aid – Bakersfield
Drainage Calculations Page | 4
Proposed Project
The proposed project consists of renovating the existing parking lot, adding a new Rite Aid building, and
constructing a new driveway.
Figure 2: Proposed Project
15‐050 Rite Aid – Bakersfield
Drainage Calculations Page | 5
Drainage Calculations
Rational Method Inputs
The Rational Method will be utilized to calculate the anticipated runoff for the proposed development.
Inputs for the rational method equation include the following:
A weighted “C” calculation will be utilized to determine the “C” value for pervious and impervious areas,
for post development.
The site area tributary to the existing storm drain system has been measured at 1.23 acres.
The rainfall intensity is determined from a figure (included) provided by the NOAA Hydrometeorological
Design Studies Center, Atlas 14 Point Precipitation Frequency Estimates: CA. The value used for this
calculation is for a 2 year 10 minute storm. This value is 0.834 inches per hour.
Site Hydrology
The following table shows how the weighted “C” value was calculated.
Table 1: Existing Conditions Weighted "C" Value
Weighted “C” Value – Existing Conditions
Area Description Area, ac
"C”
Value
Product of “C”
and Area
Impervious 1.23 0.9 1.11
Pervious 0.00 0.3 0.0
Totals 1.23 n/a 1.11
Weighted "C" 0.90
Table 2: Proposed Project Weighted "C" Value
Weighted “C” Value – Proposed Project
Area Description Area, ac
"C”
Value
Product of “C”
and Area
Impervious 1.09 0.9 0.98
Pervious 0.14 0.3 0.04
Totals 1.6 n/a 1.02
Weighted "C" 0.83
Proposed Site Runoff
The proposed site runoff is collected via concrete curb and gutter improvements on the north and west
side of the proposed building. Stormwater will flow into depressed planters via curb cuts at the low
point in each gutter. Water in the depressed planter will flow to the low point at the northwest corner
of the property and discharge into the private driveway through another curb cut. From here,
15‐050 Rite Aid – Bakersfield
Drainage Calculations Page | 6
stormwater will enter the City of Bakersfield’s storm drain system in the curb and gutter along 34th
Street.
Q (Site Peak Flow Rate) = C (Runoff Coefficient) * I (Rainfall intensity) * A (Site Area)
QArea Exist = 0.90 * (0.834 in) * 1.23 acres = 0.92 cfs
QArea Proposed = 0.83 * (0.834 in) * 1.23 acres = 0.85 cfs
Table 3: Stormwater Runoff Comparison
Stormwater Runoff Comparison
Description Stormwater Runoff (cfs)
Existing Conditions 0.92 cfs
Proposed Project 0.85 cfs
Difference ‐ 0.07 cfs (decrease)
Report Conclusion
The proposed project provides for a decrease in stormwater runoff by 0.07 cfs. This is due to an increase
in onsite landscaping (pervious area). Therefore, the existing storm drain infrastructure (34th Street curb
and gutter) can handle the runoff from the proposed development.
15‐050 Rite Aid – Bakersfield
Drainage Calculations Page | 7
Supporting Documents
NOAA Atlas 14 Point Precipitation Frequency Rainfall Intensity