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• The input parameters are: <br />Tc: 0.47 Hrs. <br />Curve No: 85 <br />Pond Elevation at start of storm: 7,376 <br />Rainfall: 1.8" in 24 hours (type II storm) <br />The detention time is defined as the time between the centroids of the <br />inflow and outfall hydrographs and is shown on the chart. <br />DITCH SIZING <br />6 Ditches are considered: <br />1) Haul Road Collection Ditch - Along east side of main haul road <br /> south of HG-8 <br />2) Perimeter Ditch around top of HG-8 <br />3) Feeder Ditch into east end of HG-8 <br />4) Highwall Diversion Ditch built in 1979 <br />5) Highwall Diversion Ditch built in 1981 <br />6) Diversion Ditch draining off of property to the east <br />The ditching around the overburden waste dump has already been con- <br />s tructed . <br />Ditch Calculations <br />• 1) Haul Road Collection Ditch <br /> Drainage area 160 acres <br /> Longitudinal slope 8$ (0.08 ft./ft.) <br /> Avg. ground slope 10$ <br /> CN 85 <br /> 1.8" rainfall, 0.65" runoff <br /> Peak Flow 10-Year Storm 145 cfs/in. runoff @ 16$ slope (Table <br /> D-2 TR 55) <br /> 145 x 0.65 in. runoff = 94 cfs <br /> Correct to 10$ slope <br /> 94 x 0.86 = 81 cfs (Table E-1 TR 55) <br />Use ditch section described: <br /> 10' bottom <br /> 2:1 side slope <br /> n = 0.035 <br />Then <br />d = 0.8 ft. <br />q=81 cfs <br />v = 9.4 fps <br />Riprap will be required to control erosion. <br />Ditch will be 3 feet deep. <br />2) Perimeter Ditch Around Pond <br />Drainage Area <br />• North Side - 93.4 Acres <br /> <br />