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• <br />DESIGN ANALYSIS <br />GENERAL <br />Sedimentation Pond 002 was evaluated and redesigned to meet or exceed <br />the design and performance requirements of the CMLRD while utilizing as <br />much of the existing structure and topography as was possible. Pond 002 <br />was designed to adhere to the following minimum specifications: <br />1. Provide storage for the runoff from the 10-year, 24-hour <br />precipitation event without having any discharge through the <br />emergency spillway (0.26 ac-ft.). <br />2. Provide an emergency spillway capable of passing runoff from <br />the 25-year, 24-hour storm event (0.33 ac-ft.). <br />3. Provide adequate storage for the sediment generated from the <br />10-year, 24-hour (MUSLE) storm event (2.0, 10-year, 24-hour <br />MUSLE storm events or 0.049 ac-ft.). <br />4. Provide a nonclogging dewatering device and principal spillway <br />that will provide adequate detention time for the 10-year, <br />24-hour storm event and still aTTow a method to dewater the <br />• pond to the 100 percent sediment storage level in a reasonable' <br />amount of time. <br />HYDROLOGY <br />The hydrology of the watershed was analyzed by utilizing the SEDIMOT II <br />computer modeling program. In performing this analysis, the <br />characteristics of the minesite and reclamation procedures along with <br />onsite sediment control procedures were considered. Addendum A, B, and <br />C contain complete listings of the SEDIMOT II inputs and outputs for the <br />10-year, 25-year, and 100-year design storms, respectively. Table 1 is <br />a summary of these results. <br />Input consists of precipitation amount (inches), watershed area (acres), <br />time of concentration (hours), runoff curve number (CN), representative <br />particle-size distributions of soils in the area, sedimentology <br />information, spillway information, etc. The drainage area for Sediment <br />Pond 002 was determined from a 1" = 400' topographic map (see Exhibit <br />13-4). <br />• 2 <br />