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• Hvdrologv. The hydrology of the eater shed uas analyzed utilizing the SEDCAD computer <br />program. SEDCAD is an enhanced PC version of the SED IMOT [I computer program written by <br />Civil Software Design of Lexington, Kentucky. Tab 13, Attachment 13-1, contains a listing <br />t <br />and description of the SEDCAD input variables. In performing this analysis, the <br />characteristics of the 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 inputs and outputs for the 10-year, 25-year, and the 100-year design storms. <br />Table 13-3C-1 contains [he design hydrology summary. <br />TABLE 13-3C-1 <br />DESIGN HYDROLOGY SUNNARY <br />POND 005 <br /> Description 10-Yr, 24-Hr 25-Yr, 24-Hr 100-Yr, 24-Hr <br /> <br /> Precipitation Depth 1.6 in. 2.1 in. 2.4 in. <br /> Inflow Runoff Volume 4.64 ac-ft 9.75 ec-ft 13.44 ac-ft <br /> Pond Volume et Peek Stage 9.7 ac•ft 11.5 ac-ft 11.9 ac-ft <br />• Peak Stage Elevation <br />Peek Inflow Rate 6873.0 <br />23 <br />61 <br />cfs 6875.4 <br />54 <br />77 <br />cfs 6875.7 <br />86 <br />49 <br />f <br /> . . . c <br />s <br /> Peek Discharge Rate 13.35 cfs 46.54 cfs 72.17 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, sedimentology information, spillway information, etc. <br />The drainage area for this sediment pond was measured on a 1"=400' topographic map (see <br />Exhibit 13-2). <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 />the pit. In these cases, a conservative procedure was used; the structure uas analyzed <br />for the largest anticipated disturbed drainage area that will contribute runoff to the <br />structure. It was estimated that this condition will occur if all of the proposed mining <br />area is disturbed end the area is in different phases of mining and reclamation. In <br />addition, the structure was conservatively designed to include adequate capacity for <br />sediment storage end [o treat the runoff from a 10-year, 24-hour precipitation even[. <br />13-3-3 Revised 08/11/92 <br />