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Hydraulics. The hydrology of the watershed was analyzed utilizing the SEDCAD computer <br />• <br />program. SEDCAD is an enhanced PC version of the SEDIMOT II computer program. Tab 7, <br />Appendix 7-6f, Addendum 7-6f-A contains a listing and description of the SEDCAD input <br />variables. In performing this analysis, the charac to risti cs of the minesite and <br />reclamation procedures along with on-site sediment control procedures were considered. A <br />i ~ <br />I complete listing of the SEDCAD inputs and outputs for the 10-year, and the 100-year <br />design storms are provided in Addendum 2. A design hydrology and sedimentology summary is <br />provided below. <br />• <br />Description 10-Yr, 24-Hr 100-Yr, 24-Hr <br />Precipitation Depth 1,6 in. 2.6 in. <br />Inflow Runoff Volume D.7D7 ac -ft 3.486 ac-ft <br />Pond Volume at Peak Stage 24,68 ac-ft 29.77 ac-ft <br />Peak Stage 6775.1 6777.4 <br />Peak Inflow Rate 1,567 cfs 18,398 cfs <br />Peak Discharge Rate 0.475 cfs 6.353 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 7-7). <br />Curve Number and "k" Factor. The curve numbers are based on information presented in <br />~ Table 7-6G-2. The "k" factors rve re determined information in Tab 9 and are shown on Table <br />' 7-6G-3. The curve numbers and "k" factors were then "weighted" for the watershed, as <br />shown on Tables 7-6G-4 and 7-6G-5, <br />Precipitation and Storm Tvpe. The preci pi to [ion amounts at the Seneca II Mine permit area <br />for Che 10-year, and 100-year storms were obtained from NUAA Precipitation Freeuency Atlas <br />of the Western States - Volume I I - Colorado, 1973. A standard SCS Type I I syo rm was <br />utilized for each analysis. <br />• Unit Hydrog ra ph and Surface Condition. the SEDCAD computer program provides :hr?e anit <br />hydrogra ph shapes to choose from in detcrmininy the runoff characteristics or a wa h+r5hed. <br />The medium hydrny ra ph was used to generate the hvd royra ph. <br />:-6g-9 <br />