HomeMy WebLinkAbout016 Stormwater Retention CalculationThe Boötes
Allison Sub PH 4A - Lots 1 & 2 Block 1
Stormwater Retention Pond Calculations
Design Rainfall Freq. 10 year
IDF coefficient a 0.64
IDF coefficient b
IDF coefficient n 0.65
Pre-Site Development Conditions
Contributing drainage area Square feet Acres C
Impervious 158,122 3.63 0.50
Total area 158,122 3.63
Composite C 0.50
Retention Pond Calculations
Q = CIA
C = 0.50 (post-development)
I = 0.41 in/hr (10-yr, 2-hr storm)
A = 3.63 acres
Qpost = 0.74 cfs
Retention Storage Provided with Subdivision(ft3) =5,330 ft3 (10-yr, 2-hr storm)
Post-Site Development Conditions
Contributing drainage area Square feet Acres C
Impervious 122,314 2.81 0.90
Landscaped 35,808 0.82 0.20
Total area 158,122 3.63
Composite C 0.74
Retention Pond Calculations
Q = CIA
C = 0.74 (post-development)
I = 0.41 in/hr (10-yr, 2-hr storm)
A = 3.63 acres
Qpost = 1.10 cfs
Retention Storage Requried (ft3) =7,945 ft3 (10-yr, 2-hr storm)
Additonal On-Site Retention Storage Required (ft3) =2,616 ft3 (10-yr, 2-hr storm)
User Inputs
Chamber Model: SC-740
Outlet Control Structure: No
Project Name: The Bootes
Engineer: Chris Budeski
Project Location: Montana
Measurement Type: Imperial
Required Storage Volume: 2616 cubic ft.
Stone Porosity: 40%
Stone Foundation Depth: 6 in.
Stone Above Chambers: 6 in.
Average Cover Over Chambers: 18 in.
Design Constraint Dimensions:(30 ft. x 50 ft.)
Results
System Volume and Bed Size
Installed Storage Volume: 2176.24 cubic ft.
Storage Volume Per Chamber: 45.90 cubic ft.
Number Of Chambers Required: 25
Number Of End Caps Required: 10
Chamber Rows: 5
Maximum Length:43.11 ft.
Maximum Width: 25.25 ft.
Approx. Bed Size Required: 1062.67 square ft.
System Components
Amount Of Stone Required: 96 cubic yards
Volume Of Excavation (Not Including
Fill):
138 cubic yards
Total Non-woven Geotextile Required:348 square yards
Woven Geotextile Required (excluding
Isolator Row):
24 square yards
Woven Geotextile Required (Isolator
Row):
25 square yards
Total Woven Geotextile Required:49 square yards
Impervious Liner Required:0 square yards