1988-04-18_PERMIT FILE - C1981008A (2)

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TABLE 7 Spillway Data Summary Sediment Pond 002 Principal Spillway: Type . . . . . . . Riser Inlet (CMP) Orifice Diameter . . . 0.5-inch Inlet Elevation. . 5697.0 10-year, 24-hour Peak Stage. . . . . . . . . 5699.44 Emergency Spillway: Type . . . . . . Drop Inlet (CMP) Barrel Diameter . . . 12.000-inch Riser Diameter . . . . 12.000-inch Length of Barrel . . . 75.000-ft Vertical Head Drop 5.5-ft. Entrance Loss Coef. 1.000 Bend Loss Coef. . 0.500 Wier Coef. . . . . . 3.100 Orifice Coef. . . . . 0.600 Manning Coef. 0.025 Inlet Elevation. . 5700. 10 25-year, 24-hour Peak Stage. . . . . . . . . 5700.03 The entrance to the emergency spillway is located more than three (3) feet above the principal spillway. There will be no flow through the emergency spillway inlet as a result of the runoff from a 10-year, 24-hour precipitation event or less. The peak stage of the 25-year, 24-hour storm event (Elev. 5700.03) is approximately at the inlet elevation (5700.10) of the emergency spillway. The emergency spillway is capable of passing the runoff from the 100-year, 24-hour storm event with adequate freeboard to ensure no overtopping of the embankment. Pond No. 002 - North Ditch In order to contain runoff from the existing reclaimed, a contour ditch is required along the reclaimed area north of Pond No. 002, flowing into Pond No. 002 (see Exhibit 13-4) . For the design of the contour ditch, the SEDIMOT II model was used to predict the runoff from the watershed. The peak inflow rate for the ditch was assumed to be the same as for Pond No. 002 for a conservative approach. The 10-year, 24-hour storm event was used in the design (see Addendum A) and the peak flow is 3.45 cfs. Based on this peak discharge, the Dodson and Associates, Inc. 's computer software was used to design the ditch sections based on the solution to Manning's equation. 11