Laserfiche WebLink
TABLE 4.6-28 -Storm Design -Maximum Runoff (Q max) -Year 2 <br />• 10 year - 24 hour Storm = l.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 two of the worst conditions of runoff volume. <br />Year 2 Acres Curve No. <br />Center Ridge (Aspen Woodland) 125.06 54 <br />Center Ridge (Reclaimed-Pasture) 53.12 86 <br />Center Ridge (Reclaimed-Pasture <br />Contoured) 233.41 81 <br />West Ridge (Spoil-Soil Group B) 392.67 67 <br />(Reclaimed-Pasture <br />Contoured) 50.00 59 <br />West Ridge (Soil Group C) 56.75 70 <br />(Reclaimed-Pasture <br />Contoured 50.00 75 <br />TOTAL 961.01 <br />• Curve No. Weighted = <br />((125.06)(54)+(53.12)(86)+(233.41)181)+1392.67)(67)+(50.00)(59)+(56.75)(70)+(50.00)(75)) <br />61. <br />= 69.94. (Use 70 for Curve No.) <br />By using Figure D-2, "Peak Rates of Discharge for Small Watersheds" (24-hour- <br />type II storm distribution), Sheet 3 of 3, for steep slope (16%), we find the peak <br />discharge for CN of 70 and 960 acres is 390 cfs/inch of runoff. Next we determine <br />the water shed runoff for year two in terms of inches for 961.01 acres and a total <br />runoff of 18.24 ac-ft. <br />Inches of Runoff - 18.24 - ft. x 12 in. = 0.228 inches <br />- 961.01 ac. I f t. <br />Peak Discharge Before Adj. = 390 cfs/in. x 0.228 in. = 88.9 cfs. <br />Slope Adjustment Foclor <br />Since the area that we are concerned with has a maximum of 12% slope in The <br />area, a slope correction factor of 0.90 is applied from Appendix E, Table E-I. <br />C <br />Peak Discharge = 88.9 cfs x 0.90 = 80.0 cfs. <br />Revised 7-81 4.6-85 <br />