Laserfiche WebLink
Subject PROTECTION OF THE HYDROLOGIC <br />• ~ SYSTEM (Continued) <br />H.C. V. F. N2. Somerset Mine <br />~ Pond No. 1, Computations <br />~. <br />CALCUEATION NOTES <br />By M.G.A. <br />Checked <br />Acct <br />July 19, 19 81 <br />Sheet No. 4 of 4 Sheets <br />Pond Size Required: <br />From Sheet 2, 10 year 24 hour runoff volume = 4630.44 cu. ft. <br />From Sheet 3, Soil loss per year = 80,2 x 3 = 240.60 cu. ft. <br />Total 4871.04 cu. ft. <br />Capacity Required = 4900 Cu. Ft. <br />Peak discharge into pond for 2.106 Acres @ CN 32 <br />From Fig. D-2, Peak rates of discharge for small water sheds, <br />i (24 hr. Type II, storm distribution). <br />Peak discharge per inch of runoff - 2.70 cfs. <br />~ Q = 0.8079 inches of runoff for 25 yr. 24 hr. storm, AMC-II. <br />2.70 x 0.8079 = 2.1813 cfs. <br />Overflow pipe = 10" dia. = 2.246 cfs at 0.41" head overpipe. <br />~ Pond No. 1, Design Capacities <br />Crest = 6367.75 - 8,812 sq. ft. area <br />3:1 Basin = 6367.63 = 5,580 sq. ft. area <br />High water = 6366.25 = 3624 sq. ft. area = 1.5 ft. freeboard <br />' bottom = 6363.15 = 856 sq. ft. area = 2.5 ft. water depth. <br />Outward slope of crest = 2:1. <br />Water Capacities- 6363.75 to 6366.25 = 5600 cu. ft. <br />6363.75 to 6367.63 = 11,950 cu. ft. <br />6363.75 to 6367.75 = 12,814 cu. ft. <br />Note: Reversing the runoff computations show that the 12,814 cu. ft., <br />less a 3 year accumulation of silt, will contain a storm event of 3.30 inches <br />with no overflow, which is greater than a 100 year-24 hour storm of 2.7 inches. <br />f <br />i <br />i <br />i <br />E <br />• <br />