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CRDA N0. 3 NM COLLECTION DITCH DESIGN <br />.:~ • <br />References: Procedures for Determining Peak Flow in Colorado, <br />SCS. March 1984 <br />Note: Acreage includes an additional 1,6 acres that will be drained into this <br />ditch upon coo4letion of the pile. <br />Area: ?6.5 Acres = Aa <br />CN: 90 <br />Precipitation Event: 100 Year - 24 hour <br />Precipitat?on: 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 />Lcie = Contour Lengths, Ft. <br />Da = Drainage Area, Ft2 <br />S = 0.25(170)(600 + 670 + 880)/(16.5)(43560) = 0.13 <br />_,;• <br />Peak Flow Caiculations <br />1 = Slope Length = 1500'; Exhibit 52 <br />Ae = Equivalent Area = (1/209) 1.667 <br />_ (1500/209) 1.667 = 26.7 acres <br />qe = Unadjusted Peak Discharge = 40.0 cfs/in runoff <br />(26.7 acres, 16; slope, Type II storm. CN 90) <br />Figure S-lA Page 18. Peak Flows <br />Slope Ajustment = 0.97; Table E-1, Peak Flows <br />Qe = (40 cfs/in runoff)(1.27 in runoff) 0.97 = 49.3 <br />Qa = Actual Peak Flows = Qe (Aa/Ae) = 44.3 (16.5/26.7) = 30.4 cfs <br />;• (New 10-31-90) <br />CRDA3-8 <br />