PERMFILE56263

• Permit No: C1981008A
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: NH1 TAB 13 ATTACHMENT C SEDIMENTATION POND 002
• Media Type: D
• Archive: Yes

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-f t.
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.
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