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TABLE 4.6-28 -Storm Design -Maximum Runoff (D max) -Year 4 -Check Design <br />• 10 year - 24 hour storm = 1.8" <br />AMC = II <br />Area = 1.502 mil = 960 Acres <br />From SCS--Technical Release No. 55--"Procedures for Determining Peak Flows <br />in Colorado." <br />First of all determine a weighted curve number for the area according to acres <br />in year four of the runoff volume. <br /> Year Acres Curve No. <br />Center Ridge (Aspen Woodland) 125.06 54 <br />Center Ridge (Reclaimed-Pasture) 53.12 79 <br />Center Ridge (Reclaimed-Pasture <br /> Contoured) 233.41 75 <br />West Ridge (Spoil-Soil Group B) 292.67 67 <br /> (Reclaimed-Pasture <br /> Contoured) 100.00 59 <br />West Ridge (5oii Group C) 56.75 70 <br /> (Reclaimed-Pasture 50.00 75 <br /> Contoured 50.00 81 <br /> TOTAL 961.01 <br />• Curve No. Weighted = ((I 25.06)(54)+(53.12)(79)+ <br />(233.41)(75)+(292.67)(67)+(100.00)(59)+(56.75)(70)+(50.00)(75)+(50.00)(81)) <br />961.01 <br />= 68.40. (Use 68 for Curve No.) <br />By using Figure D-2, "Peak Rates of Discharge for Small Watersheds" (24- <br />hour-type II storm distribution), Sheet 3 of 3, for steep slope (16%), we find the peak <br />discharge for CN of 68 and 960 acres is 375 cfs/inch of runoff. Next we determine <br />the watershed runoff for year four in terms of inches for 961.01 acres and a total <br />runoff of 14.34 ac-ft. <br />Inches of Runoff - 14 34 - ft. x 12 in. = 0.179 inches <br />- 961. I ac. I ft. <br />Peak Discharge Before Adj. = 375 cfs/in. x 0.179 in. = 67.1 cfs. <br />Slope Adjustment Factor <br />Since the area that we are concerned with has o maximum of 12% slope in the <br />area, a slope correction factor of 0.90 is applied from Appendix E, Tabte E-I. <br />• <br />Peak Discharge = 67.1 cfs x 0.90 = 60.4 cfs. <br />Revised 7-81 4.6-88 <br />