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REVISED <br />7/30/85 <br />Table 5 <br />FISH CREEK TIPPLE <br />DIVERSION DITCH DESIGN CALCULATIONS <br />Assumptions: <br />10 -year, 24-hour precipitation event: 1.8 inches <br />Antecedent moisture condition (AMC): II <br />Disturbed land Curve Number (dirt road, soil group C): 87 <br />Undisturbed/reclaimed land curve number (contoured rangeland, good <br />condition, soil group C); 70 <br />Manning open channel flow equation: Q = 1.49/n R0.67 S0.5 A <br />Mannings "n" for earth channel = 0.03 <br />Ditch E-1 <br />Tributary area = 19.5 ac. disturbed, 15.5 ac. undisturbed <br />Weighted CN = 19.5 (87) + 15.5'(70) = 80 <br />35.0 <br />Total runoff @ CN(80) = 0.44 (in)/12 (in/ft) x 35 (ac.) = 1.28 ac -ft <br />Peak flow @ CN(80), 35.0 ac, Type II storm, western Colorado, steep <br />slope = 43 (cfs/in. runoff) x 0.44 (in. runoff) = 18.9 cfs <br />uncorrected <br />Basin slope factor (actual slope 110ix) = 0.925 <br />Basin shape factor (hydraulic length 2,200 ft., equivalent area 52 ac) _ <br />35/52 = 0.673 <br />Corrected peak flow = 18.9 cfs x 0.925 x 0.673 = 11.8 cfs <br />Design: trapezoidal ditch, 2.5 ft. deep, bottom width = 1.0 ft., side <br />slopes 2:1, gradient = 0.01 ft/ft, n = 0.03 <br />Flow conditions: depth = 1.08 ft., velocity = 3.48 fps, area = <br />3.39 sq. ft. <br />Check calculation: Q = VA = 3.48 x 3.39 = 11.8 cfs <br />-13- <br />