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• <br />NORTH TOPSOIL STOCKPILE DITCH <br />(ADD TO ILLUSTRATION 7) <br />Contributing Drainage Area = 0.90 acres <br />To determine Q actual, compare to runoff from other sections of the same topsoil <br />stockpile. <br />West Topsoil Ditch: Q = 5.7 ft /sec, Area = 2.43 acres Q/A = 2.35 ft /sec /acre <br />is <br />East Topsoil Ditch: Q = 3.6 ft /sec, Area = 1.45 acres Q/A = 2.48 ft /sec /acre <br />Use Average Q/A for North Topsoil Ditch: <br />Q/A = 2.42 ft /sec /acre <br />A = Contributing Drainage Area = 0.90 acres <br />Q required = (2.42)(0.90) = 2.18 ft /sec <br />Lining Material = Riprap <br />therefore, n = 0.04 <br />therefore, Max V = 12 <br />For D = 0.6 <br />Q = 2.18 <br />A =2D =0.72 <br />Wp = 2 V 5D =2.68 <br />R =A /Wp =0.268 <br />S = 0.06 <br />V = 1.49 ARi /3 Sin <br />n <br />(37.25)(0.72)(0.42)(.245) <br />= 2.76 <br />Q = VA = (2.76)(0.72) = 1.98 NO <br />Therefore, total Ditch depth = 0.7 + 0.3 = 1.0' <br />For D = 0.7 <br />Q = 2.18 <br />A =2D =0.98 <br />Wp = 2V5D = 3.13 <br />R =A /Wp = 0.31 <br />S = 0.06 <br />V = 1.49 (0.98)(0.46)(0.245) <br />n <br />= 1.49 (0.98)(0.46)(0.245) <br />n <br />= 4.11 <br />Q = VA = (4.11) (.98) = 4.03 OR <br />