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1. Provide storage and treatment for the runoff from the 30-year, 24-hour storm event <br /> without experiencing any discharge through the emergency spillway; .• <br />2. Provide an emergency spillway capable of passing runoff from the 25-year, 24-hour <br /> storm event; <br />3. Provide adequate storage for sediment generated, as determined from the Sedcad+ <br /> computer program. <br />4. Provide a nonclogging dewatering device and principal spillway that will provide <br /> adequate tletentl on time for the 1D-year, 24-hour storm event and still allow a method <br /> to dewater the pond down to the 100 percent sediment storage level in a re asonable <br /> amount of time. <br />Hydrology. The hytl ro logy of the watershed was analyzed utilizing the SEDCAD+ computer <br />program. SEDCAD+ is an enhanced PC version of the SEDIMOT II computer program written by <br />CLvil Software Design of Lexington, Kentucky. Tab 13, Attachment 13-1, contains a listing <br />and description of the SEDCAD+ input variables. In performing this analysis, the <br />characteristics of [he minesite and reclamation procedures along with on-site sediment <br />control procedures were considered. Addendums A, B, and C contain a complete listing of <br />the SEDCAD+ Snputs antl outputs for the 10-year, 25-year, and the 100-year design storms. • <br />Table 13-3A-1 contains the design hydrology summary. <br />TABLE 13-3A-1 <br />DESIGN HYDROLOGY SUP44ARY <br />POND 010 <br />Desc rlptlon 10-Y r, 24-Hr 25-Yr, 24-Hr 100-Y r, 24-Hr <br /> <br />Precl pitatlon Depth 1.7 In. 2.1 In. 2.5 in. <br />Inflow Runoff Volume 18.3 ac-ft 28.1 ac-ft 40.1 ac-ft <br />Pond Volume at Peak Stage 19.3 ac-ft 27.2 ac-ft 29.2 ac-ft <br />Peak Stage Elevation 6787.5 6789.8 6790.4 <br />peak Inflow Rate 109.3 cfs 167.6 cfs 232.9 cfs <br />Peak Dl scha rge Rate 18.8 cfs 102.9 cfs 160.0 cfs <br /> <br />Input consists of precipitation amount (Snches 1, watershed area (acres), time of <br />concentration (hoursl, runoff curve number (CN1, re presentative particle-size <br />distributions of soils in the area, sedimentology information, spillway information, etc. <br />The drainage area for this sediment pond was measured on a 1"=400' topographic map (see . <br />Exhibit 13-21. <br />13-3A-2 Revised 08/30/96 <br />