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<br />Page 44 <br /> <br />APPENDIX C <br /> <br />DETENTION POND DESIGN <br /> <br />1, Determine Pond Geometry <br />2, Determine depth - volume relationships <br />3, Compute Depths at Q5 and Q100 <br /> <br />4, Size Discharge for Q5 @ Depth 5 <br /> <br />5, Compute Discharge for 5 yr, release at 100 year depth and subtract from <br /> <br />Q100 <br /> <br />6, Size 100 year outlet for Q100 less value obtained in 5 <br />Sample Calculation: <br /> <br />Provide detention pond for a basin of 3.5 Ac and % Impervious = 70% <br /> <br />Q5 = .2 x 3.5 = .70 cfs <br /> <br /> <br />Vol5 = (36 x 70) 3,5 = 8800 cf <br /> <br />Q = 1,0 x 3,5 = 3,5 <br />100 = 3,5 cfs <br />VoI100 = (66 x 70) x 3,5 <br />= 16,200 cf. <br /> <br />Determine Depth/Volume Curve for Pond: <br /> <br />Assume 3' Deep Pond, shown below <br /> <br />Say AT is roughly twice the volume/depth or <br />op <br />ATop 16200 x 2 = 10800 SF <br />3 <br /> <br />try a pond of: <br /> <br />200' <br />3:H <br /> <br />~O""" <br /> <br />Use the formula: <br />Vol = 1/3 (AI + A2 +I/A1 x A2 ) D <br /> <br />SO' pi <br /> <br />Compute Stage-Storage: <br /> <br />H=Depth <br />o <br /> <br />A <br /> <br /> V ~V <br />0 <br /> 2370 <br />7100 2370 <br /> 7790 <br />8500 10160 <br /> 9240 <br />10000 19400 <br /> <br />1 <br /> <br />38 x 188 = <br /> <br />2 <br /> <br />44 x 194 = <br /> <br />3 <br /> <br />50 x 200 = <br />