HomeMy WebLinkAboutTract 6612 Drainage Study Addendum-Final
MEMO
L:\Projects\2013\130036\DOCS\DESIGN\DRAINAGE STUDY\Amendment to T6129\Report Memo.docx 5080 California Avenue, Suite 220 Bakersfield, California 93309-1697 Tel (661) 616-2600 Fax (661) 616-5970 www.quadknopf.com
Date: March 6, 2014 Project No.: 130036-05
To: Manpreet Behl From: Catherine Williams Subject: Amendment to Tract 6129 Drainage Study cc: file
Background
The purpose of this addendum to the Tract 6129 Drainage Study is to add an additional tributary
area from Tract 6612 along Allen Road in order to demonstrate that increase flow from Tract 6612 will not adversely affect the existing drainage facilities of Tract 6129. Tract 6612 is a proposed apartment complex by Summerland Falls Investors, LP, located at the southeast corner
of Allen Road and Rein Road in Bakersfield, CA (APN 527-01-029). The additional discharge
from Tract 6612 will be collected in the existing catch basin on Allen Road. See calculations in
Attachment 1
Methodology The additional peak flow was determined using the rational method (Table 1). The intensity was
determined to be 1.62-inches using NOAA data for the 10-year 24-hour storm at the site
(Attachment 2). A 10-year 24-hour storm event was selected for this analysis based on criteria from the City of Bakersfield Subdivision Standards which classify the watershed being analyzed as a local waterway. Section 2.4.1.5 of the Subdivision Standards requires local waterways to be
analyzed using the 10-year 24-hour storm event.
The run-off coefficient (C) was determined by dividing the impervious area for the watershed by
the total watershed area. The calculated peak flow for the tributary area is 0.19-cfs.
In order to determine if the existing storm drain conveyance system in Tract 6129 is adequate enough to accommodate the additional flow from Tract 6612 the calculated peak flow from Tract
6612 was added to existing peak flow for each of the pipes downstream of the catch basin
(Attachment 3). No confluence analysis was performed in order to provide a more conservative
peak flow value for each pipe. The pipe peak flow values for existing flow on Table 1 were taken from the Tract 6129 drainage study initially prepared by Porter-Robertson Engineering and approved by the City of Bakersfield (Attachment 4).
ATTACHMENT 1
DRAINAGE CALCULATIONS
Summerland Apartments Tract 6612
Additional tributary area added to inlet i7 of Tract 6129
0.2 acres
3538 sf
5358 sf
0.6
108 ft
0.0021 ft/ft
0.93 ft/sec
1.93 min
0 min
1.62 in Value from NOAA see attached chart
Additional Flow Q=CiA 0.19 cfs
Table 1 Pipe Capacity
Reach1
Pipe Size
(in)1
Pipe
Capacity
(cfs)2
Existing
Flow (cfs)1
Flow
Added
(cfs)
Combined
Flow (cfs)
Is Total Flow Less
than Pipe
Capacity?
11 18 6.12 0.95 0.19 1.14 TRUE
10 18 6.30 2.70 0.19 2.89 TRUE
9 18 6.30 3.94 0.19 4.13 TRUE
1 24 20.23 15.53 0.19 15.72 TRUE
1 Value obtained from approved drainage study for Tract 6129 prepared by Porter Robertson
2 Value obtained from Bently FlowMaster Vi8. See attached calculations
Additional volume added to existing retention basin
Additional volume Q=0.15CA 0.018 ac-ft
Table 2 Retention Basin Volume
Existing
Basin
Capacity
(ac-ft)1
Required
Basin
Volume
(ac-ft)1
Addition
Volume
Added (ac-
ft)
Combined
Volume (ac-
ft)
3.77 2.5 0.018 2.52
Is Existing Volume
Greater than
Combined Volume?
TRUE
Flow Length
Tributary Area
Impervious Area
Pervious Area
10yr/24hr Rainfall Intensity
Runoff Coefficient
Roof to Gutter Time
Travel Time
Average Velocity
Average Slope
ATTACHMENT 2
NOAA SITE RAINFALL TABLE
ATTACHMENT 3
EXISTING PIPES EFFECTED EXHIBIT
0 130 260 ft.
ADDED TRIBUTARY AREA TO TRACT 6129
Legend
This map is a user generated static output from an Internet mapping site and is for general
reference only. Data layers that appear on this map may or may not be accurate, current, or
otherwise reliable. THIS MAP IS NOT TO BE USED FOR NAVIGATION.
Scale: 1:2,299
Map center: 6220921, 2337032
ATTACHMENT 4
EXCERPT FROM TRACT 6129 DRAINAGE STUDY
PREPARED BY PORTER ROBERTSON
ATTACHMENT 5
PIPE CAPACITY CALCULATIONS