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':;~,• CRDA N0. 3 SE COLLECTION DITCN DESIGN <br />References: Procedures for Determining Peak Flow in Colorado, <br />SCS, March 1984 <br />Note: Acreage includes an additional 1.6 acres during construction which rill <br />be drained to the NY Coiiection Ditch upon completion of the pile. <br />Area: 28.4 Acres = Aa <br />CN: 90 <br />Precipitation Event: 100 Year - 24 hour <br />Precipitation: 2.2 inches; Figure S-7, Peak Flows <br />Direct Runoff: 1.27 inches; Page 70, Peak Flow <br />Average Slopes: S = 0.25 z (Lc25 + Lc50 + Lc75)/DA <br />z = Elevation Difference, Ft. <br />Lc~ = Contour Lengths, Ft. <br />Da = Drainage Area. Ft2 <br />S = 0.25(170)(630 + 580 t 720)/(18.4)(43560) = 0.10 <br />...: '• <br />Peak Flow Calculations <br />1 = Slope Length = 1200'; Exhibit 52 <br />Ae = Equivalent Area = (1/209) 1.667 <br />(1200/209) 1.667 = 18.4 acres <br />qe = Unadjusted Peak Discharge = 30.0 cfs/in runoff <br />(18.4 acres, 16z slope, Type II storm, CN 90) <br />Figure S-lA Page 18, Peak Flows <br />Slope Ajustment = 0.92; Table E-1, Peak Flows <br />Qe = (30 cfs/in runoff)(1.27 in runoff) 0.92 = 35.1 <br />Qa = Actual Peak Flows = Qe (Aa/Ae) = 35.1 (18.4/18.4) = 35.1 cfs <br />• (New 10-31-90) <br />CRDA3-7 <br />