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<br />1. Provide storage for the runoff from the 10-year, 24-hour storm <br />event without experiencing any discharge through the emergency <br />spillway (5.74 ac-f t.) <br />2. Provide an emergency spillway capable of safely passing runoff <br />from the 25-year, 24-hour storm event (11.05 ac-f t.) <br />3. Provide an embankment with sufficient freeboard to contain the <br />lOC-year, 24-hour storm event without overtopping the embankment <br />{14.93 ac-ft.) <br />4. Provide adequate storage for sediment generated from soil <br />erosion. The Universal Soil Loss Equation was used to estimate <br />soil loss on an annual basis (provides approximately 4.5 years <br />of sediment storage). <br />5. Provide a nonclogging dewatering device and principal spillway <br />that will provide adequate detention time for the ZO-year, <br />24-hour storm event and still allow a method to dewater the pond <br />down to the 100 percent sediment storage level in a reasonable <br />amount of time. <br />Hvdrology <br />The hydrology of the watershed was analyzed utilizing the SEGIMOT II <br />computer program. In performing this analysis, the characteristics of the <br />minesite and reclamation procedures along with on-site sediment control <br />procedures were considered. Addendum A, B, and C contain complete <br />listings of the SEDIMOT II inputs and outputs for the 10-year, 25-year, <br />and 100-year design storms. Table 1 is a summary of these results. <br />TABLE 1 <br /> <br />As-Built Hydrology and Sedimentology Summary <br />.Structure 008 <br />_'= <br />_s ai <br />DESCRIPTION lOyr-24hr 25yr-24hr 100.yr-24hr <br />Precipitation Depth <br />Inflow Runoff Volume <br />Pond Volume at Peak Stage <br />Peak Stage <br />Peak Inflow Rate <br />Peak Discharge Rate <br />Basin Trap Efficiency <br />Detention of Flow (sediment) <br />Detention of Hydrograph Centers <br />1,6 in. 2.09 in. 2.4 in. <br />5.74 ac-ft 11.05 ac-ft 14.S3 ac-ft <br />12.73 ac-ft 19.12 ac-ft 21.08 ac-ft <br />11.84 ft 14.66 ft 15.43 ft <br />39.79 cfs 87.50 cfs 123.27 cfs <br />1.42 cfs 18.76 cfs 23.06 cfs <br />100.00 ~ --- -- - <br />49,85 hr --- -- - <br />14.59 hr --- -- - <br />7-6f.1-4 <br />