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4. Provide a noncloggi ng dewatering device and principal spillway that will provide • <br />adequate detention time for the 10-year, 24-hour storm event and still allow a method <br />to dewa ter the pond down to the 100 percent sediment storage level in a reasonable <br />) <br />amount of time, i <br />Hydrology. The hydrology of the watershed was analyzed utilizing the SEDCAD computer <br />program. SEDCAD is an enhanced PC versli on of the SEDIMOT II computer program written by <br />Civil 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 the minesi to and reclamation procedures along with on-site sediment <br />control procedures were considered. Addendums A and B contain a complete listing of the <br />+ I <br />SEDCAD inputs and outputs for the 10-year and the 25-year design storms. Table 13-5-1 <br />contains the design hydrology summary. <br />TABLE 13-5-1 <br /> DESIGN HYDROLOGY <br /> POND 009 • <br />Description 10-Yr ,24-Hr 25-Yr, 24-Hr <br />Precipitation Depth 1,6 in. 2.1 in. <br />Inflow Runoff Volume 3.46 ac-ft 9.27 ac-ft <br />Pond Volume at Peak Stage 9.90 ac-ft 15,06 ac-ft <br />Peak Elevation 7087.0 7091.0 <br />Peak Inflow Rate 8.59 cfs 44.92 cfs <br />Peak Discharge Rate 5.03 cfs 33.36 cfs <br />Input consists of precipitation amount (inches), watershed area (acres), time of <br />concentration (hours), runoff curve number (CN), representative particle-size <br />distributions of soils in the area, sed imentology information, spillway information, etc. <br />The drainage area for this sediment pond was measured on a 1"=400' topographic map (see <br />Exhibit 13-2), <br />In some instances, mining will cause the drainage area to change during the life of the • <br />sedimentation structure. When the pit moves into the watershed, runoff is intercepted by <br />13-5-2 <br />