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~~'`~ y~~sl~s <br />' ~~°' REVISED <br />7/30/85 <br />' /" Table 2 <br />SEDIMENTATION POND E DESIGN CALCULATIONS <br />' WEIGHTED CURVE NUMBER: (AMC II) <br />Total Drainage area is 35 ac. / <br />24 ac. roads & parking area - CN 87 C/ <br />11 ac. contoured range land - CN 70 <br />Weighted CN = (87 x 24) + (70 x 11) = 82 <br />' 35 <br />' DESIGN CRITERIA: (./ <br />- 35 ac watershed area <br />- 24 ac disturbance <br />' - AMC II Curve No. 82 <br />- 10-yr, 24-hr design event of 1.8" rainfall <br />' SEDIMENT VOLUME: <br />('1 Total Runoff (Q): 10-yr, 24-hr precipitation event = 1.8 in. Ci' <br />' `~" v' <br />1.8 in. rainfall @ curve number (82) = 0.52 in. runoff <br />0.52 (in) / 12(in/ft) x 35 ac. = 1.53 ac-ft `~ <br />' Peak Flow (gp): Type II storm, western Colorado, moderate slope, curve <br />number (82) = 32 cfs/in. runoff; 32 cfs/in. runoff x 0.52 in. runoff <br />' = 16.6 cfs uncorrected <br />Basin Slope Factor (actual slope 6%) = 1.11 `~ <br />' Basin Shape Factor (hydraulic length = 1,750 ft., equivalent area - 36.5 <br />ac) 35/36.5 = 0.96 ~ <br />' Corrected Peak Flow = 16.6 cfs x 1.11 x 0.96 = 17.7 cfs ~ <br />Soil Erodibility Factor (K): Winnevada-splitro series = 0.2 (SCS) <br />Length-Slope Factor (LS): <br />' LS = (L/72.6) m(430x2 + 30 x + 0.43) / 6.613) <br />_ (1,750/72.6) 0'5((430(.06)2 + 30 (.06) + 0.43)/6.613) <br />' = 2.80 °~ <br />Crop Management Factor (c): 1.0 ~^ <br />' Support Practice Factor (P): 1.0 ~~- <br />J ~ -8- <br />