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Input includes precipitation amount (inches), watershed area (acres), <br />• time of concentration (hours), runoff curve number (CN), representative <br />particle-size distributions of soils in the area, sedimentology <br />information, and spillway information. The drainage area for this <br />sediment pond was measured on a 1" = 400' topographic map (see Exhibit <br />. 7-7). <br />In some instances, the mining will cause the drainage area to change <br />during the life of the sediment structure. When the pit moves into the <br />watershed, runoff is intercepted by the pit and diverted away from the <br />structure. In these cases, a conservative procedure was used; the <br />structure was analyzed for the largest anticipated drainage area that will <br />contribute runoff to the structure. This condition usually occurs at the <br />start of mining and again during the reclamation period. <br />Following is a summary of the SEDIMOT II input values used in the Design <br />Report and the As-Built Report (see the Design Report for the derivation <br />of the input values); <br />10-year, 24-hour = 1.60 inches <br />25-year, 24-hour = 2.09 inches <br />100-year, 24-hour = 2.40 inches <br />SCS Type II Storm <br />CtJ = 78 <br />k = 0.22 <br />Disturbed Hydrograph (No. 1) <br />tc = 0.43 hrs. <br />Sediment = 1.8 acre-feetlYear or 3,119 tons/year <br />Specific Gravity = 2.5 <br />Submerged Bulk S.G. = 1.25 <br />LS = 29.59 <br />CP = 0.11 <br />The particle size distribution is based on representative soil samples <br />taken in the area. <br />C~ <br />3 <br />