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In some instances, mi ning will cause the drainage area to change during the life of the <br />sedimentation structure. When the pit moves into the Watershed, runoff 15 intercepted by <br />[he pit. In these cases, a conserve tlve procedure Was used; the structure was analyzed <br />for the largest anticipated disturbed dra Snage area that W111 contribute runoff to the <br />structure. It was estimated that this condition W111 occur Sf all of the proposed minlnq <br />area is disturbed and the area Ls In dif fecent phases of mining and reclamation. In <br />addition, the structure was conservatively designed to include adequate capacity for <br />sediment storage and to treat the runoff from a 10-year, 24-hour precipitation event. <br />Flnall y, the design conservatively assumed the pond is 100 percent full to [he emergency <br />spillway during the 25-year, 24-hour and 100-year, 24-hour precip3tarlon events and <br />provides for maintenance of adequate freeboard to prevent overtoppl ng of the embankment. <br />SCS Curve Number and "k" Fa ctoc. The curve numbers area based on information presented In <br />Attachment 13-1. The "k" factors were determined with the aid of the USDA-ARS's revised <br />USLE software package and are shown Sn Attachment 13-1. The curve numbers and "k" factors <br />were then "weighted" for each subwatershed as shown on the summary table ~1 Table 13-3-2). <br />A complete listing is shown in Pddendum 13-3-E. <br />• TABLE 13-3-2 <br />Weighted CN, k-Factors and CP <br />Pond 010 <br /> Watershed CN k Factor CP Area <br /> 2 91.00 ~ 0.16 0.486 123.d9 <br /> 52.00 0.29 0.113 402.2 <br /> 3 80.66 0.233 0.365 83.93 <br /> 4 91.00 0.240 0.600 2.81 <br /> 5 76.98 0.226 0.254 24.19 <br /> 6 91.00 0.240 0.600 6.54 <br /> 7 91.00 0.240 0.600 4.83 <br /> B 59.57 0.226 0.126 79.72 <br /> 9 68.09 0.234 0.155 152.51 <br /> 10 79.21 0.234 0.373 44.19 <br /> 11 90.72 0.240 0.595 14.31 <br /> 12 85.42 0.240 0.454 9.78 <br /> 13-3-3 Revised 09/08/95 <br />