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• ATTACHMENT 2 Continued <br />Drainage Ditches <br />East side of spoil pile - peak flow: drainage a <br />Channel length = 1600 ft <br />Elevation = 8340-8210 = 130 ft <br />Tc = .10 hours (Figure S-5, Page 22) <br />Peak discharge = 900 csm/inch (Figure S-1, Page <br />21 cfs/inch runoff (Figure S-lA, Page 16) <br />CN = 90 10 yr runoff = .76 <br />(21)(.76) = 16 cfs @ 10 yr event <br />6~ <br />ni=u <br />-N 111= <br />_ III <br />-I~~=~ <br />III= Ili=111 <br />a = 17 acres <br />1) <br />4 = (0.025) (.5)(.61).67(.03).5 <br />Q = (59.44) (4! 5) (.72) (.17) <br />Q = 32.7 cfs I OK (~16 cfs req.) <br />Other Ditches (in pit) <br />Assume maximum load of any ditch is 1/3 of 10 yr event <br />(1/3)(42.7) = 14 cfs <br />Diversion Ditch <br />Peak runoff estimate drainage area = 34 acres <br />Channel length = 1000 ft <br />Elev = 8460-8275 = 185 ft <br />Tc = 0.5 - Use .1 <br />Peak discharge = 1000 csm.inch <br />CN = 85 33 cfs/inch runoff <br />(44)(.48) = 21 cfs <br />Since diversion ditch can handle 32 cfs, OK <br />Other ditches should be capable of carrying 14 c~s - Typical <br />