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Revised 7/8/82 <br />Calculation of Inflow to Sediment Control Structure <br />• Time Parameters <br />Time of Concentration <br />From Figure 2.34, p. 82 <br />s = 40% nearly bare, untilled and alluvial fans, western mountains <br />v=64fps <br />tc = L/V = (1990 ft) _ (64 ft/s) = 31.1 s = 0.52 min <br />or from Equation 2.58, p. 83 <br />tc = 0.0078L0.77 (L/H)0.385 = 0.0078 (I990)0.77 (1990/759)0.385 <br />tc = 3.92 minutes <br />Lag Time <br />Equation 2.59, p. 84 <br />tL = 0.6 tc = 0.60(3.92) = 2.35 min <br />• Equation 2.60, p. 84 SCS method <br />tL = [L0.8(S+1)0.7] ,. [1900 Y0.5] . <br />L = 1990 ft <br />Y = 40.4% <br />S = 1000/CN - 10 = 1000/79 - 10 = 2.66 <br />tL = [(1990)0'8(2.66+1)0'7] ~ [1900 (40.4)0'5] = 0.09 hrs = 5.37 min <br />Time to Peak <br />Equation 2.40, p. 73 <br />tp = tL + D/2 <br />assume D = 1/3 tp <br />tp = tL + 1/6 tp <br />• tp = 6/5 tL = 6/5 (5.37) = 6.44 min <br />