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Home My WebLink About11a Stormwater Retention Basin Calculations 4-19-2020Town Pump 6 Lounge Stormwater Calculations Retention Basin Calculation of Required Volume for Storm Retention Pond (Reference: Bozeman Stormwater Master Plan - 1982) Design Rainfall Freq. 10 year (see page III - 5 of master plan) IDF coefficient a 0.64 IDF coefficient b IDF coefficient n 0.65 Post-development Calculations C Areas (ft2):Landscape 1,431 0.20 Impervious 29,934 0.90 Total: 31,365 Retention Pond Calculations: Q = CIA C = 0.87 (post-development) I = 0.41 in/hr (10-yr, 2-hr storm) A = 0.72 acres Q =0.25 cfs required retention storage (ft3) =1,835 ft3 Volume held between contours: Cumulative Contour Area (ft2) Delta V (ft3) Volume (ft3) 4697.75 20 4698.00 1,068 136 136 4698.50 1,328 599 735 4699.00 1,325 663 1,398 4699.50 1,960 821 2,220 Design storage at 1.5' depth (ft3) =2,220 Town Pump 6 Lounge Stormwater Retention Basin Calculations