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<br />Sediment Pond Sisina Calculations <br />(After Upper Part of Diversion Ditch has been Removed) <br />Area below reclaimed diveraion ditch = 11.9 acrea~ CN=79 <br />Area above reclaimed diveraion ditch = 31.9 acres CN=77 <br />------------ ------ <br />43.8 acres CN=77.5 <br />The 10 year-24 hour storm precipitation is 1.90 inches. <br />Runoff (using CN 77.5) is 0.41 inches. <br />Volume required to contain the 10 year-24 hour runoff is <br />43.8 acres x .41 inches/ 12 inches per ft = 1.5 acre-feet. <br />around water has not infiltrated into the pond since its <br />construction and therefore is not included is the pond volume. <br />The Universal Soil Loaa Equation is used to estimate sediment <br />•. deliverp rates to the pond. <br />A= R x R x LS x C z P <br />R =Rainfall factor = 30 <br />R = Soil erodibility factor = .24 M <br />LS = 11.9 (from "Applied Hydrology and Sedimentoloyy of Disturbed <br />Areas") <br />C = .20 (from above listed source) <br />P = Practice factor or deliverp ratio = .9 <br />A = 30 a .24 x 11.9 x .20 : .9 <br />= 15.42 tons per acre per year <br />Three year volume = 1542 x 43.8 acres x 3 yra <br />= 2026 tons <br />= 1.09 acre-feet <br />Total volume required = 1.50 ac-ft. + 1.09 ac-ft = 2.59 ac-ft. <br />The pond has been designed and built for 4.5 ac-ft of total <br />volume which is more than adequate. Current sediment yields are <br />lox and the pond does not require cleaning as of April, 1989. <br />• * nee revised Exhibit C-7 enclosed. <br />** from SCS, Meeker office. Page 13-13c <br />~g9 <br />