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Hydrology. The hydrology of [he watershed was analyzed utilizing the SEDLAD computer <br />program. SEDLAD is an enhanced PL version of the SEDIMOT 11 computer program written by <br />• ; <br />Livil 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, 0, and C contain a complete listing of <br />4 <br />[he SEDCAD inputs and outputs for the 10-yea r, 25-year, and the 100-year design storms. <br />Tahle 13-3-1 contains the design hydrology summary. <br />TABLE 13-3-1 <br />DESIGN HYDROLOGY SUMMARY <br />POND 005 <br /> Description__ _____10_Yr~24_Hr_____ _____25_Y ry 24_Hr____ _____100_Yry24-Hr <br /> Precipitation Depth 1.6 in. 2.1 in. 2.4 in. <br /> Inflow Runoff Volume 4.64 ac-ft 9.75 ac-ft 13.44 ac-ft <br /> Pond Volume at Peak Stage 6.51 ac-ft 8.47 ac-ft 8.77 ac-ft <br /> Peak Stage Elevation 6873.0 6875.2 6875.6 <br />• Peak Inflow Rate 23.61 cfs 54.77 cfs 86.49 cfs <br /> Peak Discharge Rate 14.30 cfs 50.46 cfs 77.88 cfs <br />Input consists of precipitation amount (inches), watershed area (acres), time of <br />concentration (hours), runoff curve number (LN ), representative pa rt icle-size <br />distributions of soils in the area, sediment of ogy 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 [he drainage area to change during the life of the <br />sedimentation structure. when [he pit moves into the watershed, runoff is intercepted 6y <br />the pit and diverted away from the structure. In these cases, a conservative procedure <br />was used; the structure was analyzed for the largest anticipated disturbed drainage area <br />that will contribute runoff to the structure. It was estimated that this condition will <br />occur if all of the proposed mining area is disturbed and [he area is in different phases <br />of mining and reclamation. In addition, [he structure was conservatively designed to <br />. include adequate capacity for sediment storage and to treat the runoff from a 10-year, <br />13.3-3 Revised 03/13/92 <br />