2018-08-08_PERMIT FILE - C1982056 ‎(17)‎

• Permit No: C1982056
• IBM Index Class Name: Permit File
• Doc Date: 8/8/2018
• Section_Exhibit Name: EXHIBIT 08 TAB 1 SEDIMENT CONTROL PLAN
• Media Type: D
• Archive: No

REVISED
8/8/85
Table 4
SEDIMENTATION POND E
RISER PIPE DESIGN CALCULATIONS
Required sediment storage = 0.64 ac -ft.
From stage - storage table, 0.64 ac -ft = 51.8 ft.
- set bottom of dewatering hole @ elevation 51.8
Weighted Curve Number = 82 (AMC II)
10 -year, 24-hour runoff volume is 0.52 in/12 (in/ft) x 35 ac = 1.52
ac -ft.
Peak flow for 10 -year, 24-hour event, Type II storm, moderate slope,
CN = 82, drainage area = 35 acres is 17.7 cfs corrected
Inflow Hydrograph:
Triangular hydrograph w/peak flow of 17.7 cfs, volume of 1.52 ac -ft
Time base: 2.7 hours
Time of peak flow = 1.0 hours
L Centroid of inflow = 1.1 hours
Outflow Hydrograph:
Equation for 2 -inch orifice: Q = C'a (2 gH)`
C' = orifice coefficient = 0.6
a = area of orifice = r2 = 0.022 ft
g = gravitational constant = 32.2
Peak Outflow:
Runoff volume = 1.52 ac -ft
Sediment volume = 0.64 ac -ft
2.16 ac -ft total volume
From stage -storage table, 2.16 ac -ft = 55.4 ft.
- set top of riser pipe @ 55.0 ft.
Maximum head: 55.0-51.8 ft. = 3.2 ft
From orifice equation, peak outlflow is 0.19 cfs
Time required to drain 1.52 ac -ft at flow rate of 0.19 cfs is 96.E
hours
1► Centroid of outflow = 96.8 hours/2.85 = 34 hours
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