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<br />each soil and vegetation type was calculated using pre- and postal ning 1:400 scale maps. <br />~~ <br />Curve numbers of 8D,7 and 74.2 were calculated for pre- and poatmining eondi ttona, <br />' respects vely. <br />Time o} concentration was detarnl ned for the watershed under both conditions using the <br />relati onshlp: <br />1140 (Y).5 <br />mere: <br />tc ~ Lime of concantrati on (hrs) <br />L ~ hydraulSe length (ft) <br />5 = (1,000/curve number) -10 <br />and <br />Y =average watershed slope (percent) <br />The average watershed slope was calculated by measuring at least ten unbroken al opea on <br />both the Dre- aM yoatmf ning watershed maps (sea Eahi 67ts 17-1 and t7-2). Tha hytlraulic <br />• ~ length of the watershed was determined by aeasuring the longest flow path from the most <br />distant watershed point to the outlet. Time of concantrati ons sere calculated to be .73t <br />and .965 hours for both pro- and postmining eondi ti ons, respects vely, <br />Sedi mentol ogy input parameters include particle stu dtstri buttons, sediment routf ng <br />parameters (average epees} is gravity, wsffiei ant for di atri hating sediaront load and hulk <br />specific gravity), so11 erndi bility (K), slope (5), slope length (L), eroppf ng or cover <br />(C) and conaervatS on praMlce (P) }aceora. For both conditions, ell of the sedimentol ogy <br />t nput parameters wi ih the eacapti on of the K, L, end S factara ware sal acted from SEDIMOT <br />ll batch input files used for designing the sediment ponds located to both mS of ng areas <br />(see Tab 13, Facilities). <br />An average K factor was deternined in both the pre- and poaUsining watersheds by figuring <br />the areal distribution of the same soil and vegetation types previously di acussed. <br />K-factors have heen seas fined to the soil types mapped for basal ins studs es (see Tab 9, <br />Soil Resources Survey). K-factors of .372 and .308 were respects vely seas goad to the <br />posbai ning soil (end vegetation) types of Trri gated pasture (loam to sandy loam) and <br />rangeland (loan io sandy loam). Tha poatM ning K-factors were Daaed on fha premining <br />17-85 Ravl sad 04/tt /88 <br />11 <br />~~ <br />REVISED MARCH 2006 Attachment 2.05.6(3)-2-97 <br />