PERMFILE49404 - Laserfiche WebLink

Home Browse Search

i Sediment Pond 008 was designed to adhere to the following specifications: 1. Provide storage for the runoff from the 10-year, 24-hour storm event without experiencing any discharge through the emergency spillway (5.74 ac-ft.) 2. Provide an emergency spillway capable of safely passing runoff from the 25-year, 24-hour storm event (11.05 ac-ft.) 3. Provide art embankment with sufficient freeboard to contain the 100-year, 24-hour storm event without overtopping the embankment (14,93 ac-ft.) 4. Provide adequate storage for sediment generated from soil erosion. The Universal Soil Loss Equation was used to estimate soil loss on an annual basis (provide three years sediment storage). 5. Provide a nonclogging dewatering device and principal spillway that will provide adequate detention time for the 10-year, 24-hour storm event and still allow a method to dewater the pond down to the 100 percent sediment storage level in a reasonable • amount of time. Hydrology The hydrology of the watershed was analyzed utilizing the SEDIMOT II computer program. In performing this analysis, the characteristics of the minesite and reclamation procedures along with on-site sediment control procedures were considered. Appendix A, B, and C contain complete listings of the SEDIMOT II inputs and outputs for the 10-year, 25-year, and 100-year design storms. Table 7-6e-1 is a summary of these results. TABLE 7-6e-1 Design Hydrology and Sedimentology Summary Structure 008 DESCRIPTION l0yr-24hr 25yr-24hr 100yr-24hr Precipitation Depth 1.6 in. 2.09 in. 2.4 in, Inflow Routed Volume 5.74 ac-ft 11.05 ac-ft 14.93 ac-ft Pond Volume at Peak Stage 9.61 ac-ft 16.42 ac-ft 18.39 ac-ft • Peak Stage Peak Inflow Rate 11.59 39.79 ft cfs 14.62 87.49 ft cfs 15.38 123.27 ft cfs Peak Discharge Rate 1.41 cfs 18.60 cfs 22.79 cfs Basin Trap Efficiency 100.00 % --- -- - Detention of Flow (sediment) 49.85 hr --- -- - Detention of Hydrograph Centers 14.60 hr --- -- - 7-6e-2