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CRDA N0. 2 PEST COLLECTION DITCH DESIGN <br />_, .'• <br />References: Procedures for Determining Peak FTow in Colorado, <br />SCS, March 1984 <br />Note: Acreage includes an additional 2.5 acres that rill 6e drained into <br />this ditch upon coopletion of the pile. <br />Area: 15.0 Acres = Aa <br />CN: 90 <br />Precipitation Event: 100 Year - 24 hour <br />Precipitation: 2.2 inches; Figure 5-7. Peak Flows <br />Direct Runoff: 1.27 inches; Page 70, Peak Flow <br />Average Slopes: 5 = 0.25 z (Lc25 + Lc50 + Lc75)/DA <br />z = Elevation Difference, Ft. <br />Lc8 = Contour Lengths. Ft. <br />Da = Drainage Area, Ft2 <br />S = 0.25(190)(670 + 840 + 680)/(25)(43560) = 0.16 <br />~' , <br />Peak Flor Catcuiations <br />1 Slope Length = 1620'; Exhibit 51 <br />Ae = Equivalent Area = (1/209) 1.667 <br />(1620/209) 1.667 = 3G.4 acres <br />qe = Unadjusted Peak Discharge = 44.0 cfs/in runoff <br />(30.4 acres, 16x slope, Type II storm, CN 40) <br />Figure S-lA Page 18, Peak Flows <br />STope Ajustment = 1.00; Table E-1, Peak Flows <br />Qe = (44 cfs/in runoff)(1.27 in runoff) 1.00 = 55.9 <br />Qa = Actual Peak Flows = Qe (Aa/Ae) = 55.9 (15/30.4) = 27.6 cfs <br />(Revised 10-31-90) <br />~._, . <br />CRDA2 - 5 <br />