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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 v <br />Disturbed land Curve Number (dirt road, soil group C): 87 v <br />Undisturbed/reclaimed land curve number (contoured rangeland, good <br />condition, soil group C); 70 J <br />' Manning open channel flow equation: Q = 1.49/n R0.67 50.5 A L' <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 J <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 117) = 0.925 <br />' Basin shape factor (hydraulic length 2,200 ft., equivalent area 52 ac) = Lr <br />35/52 = 0.673 <br />' Corrected peak flow = 18.9 cfs x 0.925 x 0.673 = 11.8 cfs L~ <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 />N~ G ~U~,y <br />'; / <br />-13- <br />