HomeMy WebLinkAbout23O - 2 Storm Calcs - Existing CstoreProject:23O - Atwell Suites Hotel - Bozeman MT
Subject:Storm Drainage Calculations - Existing C-Store Retention Pond
Date:4/22/2025
Engineer:Kevin May, P.E.
C-Store Drainage Basin Information (Existing Conditions)
Item Area (sf)C-Factor
Ex. Imperv. Surfacing 91803.4 0.9
Ex. Landscaping Area 6676.6 0.1
Total Area 98480.0
Composite C Factor 0.846
Contributing Area (sf)98480.0
Contributing Area (ac)2.261
Existing Retention Pond Sizing Calculations
Given: Q=CiA & V = 7200Q
C-Factor 0.846
I (in/hr)0.41
A (ac)2.261
Q (cfs) =0.784
V (cf) =5644
C-Store Drainage Basin Information (New Conditions)
Item Area (sf)C-Factor
New Imperv. Surfacing 90992.5 0.9
New Landscaping Area 11304.9 0.1
Total Area 102297.4
Composite C Factor 0.812
Area (sf)102297.4
Area (ac)2.348
Revised Retention Pond Sizing Calculations
Given: Q=CiA & V = 7200Q
C-Factor 0.812
I (in/hr)0.41
A (ac)2.348
Q (cfs) =0.781
V (cf) =5626
As shown, the revised contributing basin now includes additional landscaping area
which effectively reduces the total runoff reaching the existing pond area and reducing
the pond's required size; therefore, the existing pond is acceptable.