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<br /> <br />Drainage Area A-1 is the major area and the only area analyzed <br />i.n detnil. The amount of runoff will not be appreciably changed by <br />the mining operation within the area (runoff may be reduced) therefore <br />the following nnalyeis is based on the existing conditions only, sad <br />done not consider any change in character of the area. <br />Area ~ 330 Acres <br />I ~ 0.3 intensity <br />AI = 99 <br />i slope ~ 150 feet in 5000 38 average <br />Length of Area A-1 - 5000 lie, ft. <br />Concentration time "t" ~ 20 min, for 1000 ft, length <br />(40 min, for 5000 ft, length) <br />R~ t..-~.lli ~ a 1. B 5 <br />Q ~ AYR ~ 99 x 1.9 5193 c.f.s. <br />The expected runoff quantity at concentration point C-Arl ie <br />computed to be 193 c.f.s, maximum under present conditions and also <br />under the conditions of the site after the mining has been completed. <br />'Phe runoff presently concentrating at point CA_1 is being carried <br />under the Hr antner Ditch through a 48 inch C.M.P. A low area at the <br />inlet of the C.M.j~. serves as a retention pond and also allows a 12 <br />foot head to be put on the C.11.P. inlet. The capacity of the C.M.P. <br />is computed to be 200 c.f.s. There is no evidence of recent overt <br />toping into the Brnntner Ditch due to inadequate culvert sine. The <br />retention poad~forned by the Brnntner Ditcli embankment retsina <br />approximately 8 acre feat of water which provides protection against <br />over-topping into the Brnntner Ditch. <br />It is not recommended that the 48 inch culvert be enlarged. If <br />- 3 - <br />