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~. <br />` ~~ <br />•= ±%• <br />F~•• <br />~. <br />CRDA !1 COLLECTION DITCH DESIGN <br />References: Procedures for Determining Peak Flow in Colorado, <br />SCS, March 1984 <br />Collection Ditch for North and (lest Side of Pile <br />Area: 12.3 Acres = Aa <br />CN: 88; Appendix X, Permit Application, Pond 6. <br />Precipitation Event: 100 Year - 24 hour. <br />Precipitation: 2.2 inches; Figure S-7, Peak Flows. <br />Direct Runoff: 1.13 inches; Page 68, Peak Flow. <br />Average Slope: S = 0.25 z (Lc 25 + Lc50 + Lc75)/DA <br />z = Elevation Difference, Ft. <br />Lc! = Contour Lengths, Ft. <br />Da = Drainage Area, Ft2 <br />S = 0.25(310)(570 + 1060 + 260)/(12.3)(43560) = 0.27 <br />Peak Flor Calculations <br />1 = Slope Length = 1300'; Exhibit 9C <br />Ae = Equivalent Area = (1/209) 1.667 <br />(1300/209) 1.667 = 21.0 acres <br />qe = Unadjusted Peak Discharge = 32.0 cfs/in runoff <br />(9.4 acres, 16% slope, Type II storm, CN 88) <br />Figure S-lA Page 18, Peak Flows <br />Slope Adjustment = 1.10; Table E-1, Peak Flows <br />Qe = (32 cfs/in runoff)(1.13 in runoff) I.10 = 39.8 <br />Qa = Actual Peak FTows = Qe (Aa/Ae) = 39.8 (12.3/21.0) _ <br />23.3 CF5 <br />1/4 LMR NEW 10-23-87 <br />CRDA'I - 10 <br />