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

Table 2
SEDIMENTATION POND E DESIGN CALCULATIONS
WEIGHTED CURVE NUMBER: (AMC Ii)
Total Drainage area is 35.5 ac.
22.8 ac. roads & parking area - CN 87
12.7 ac. contoured range land - CN 70
Weighted CN = (87 x 22.8) + (70 x 12.7) = 81
35.5
DESIGN CRITERIA:
- 35.5 ac watershed area
- 22.8 ac disturbance
- AMC II Curve No. 81
- 10 -yr, 24 -hr design event of 1.8" rainfall
SEDIMENT VOLUME:
Total Runoff Q): 10 -yr, 24 -hr precipitation event = 1.8 in.
1.8 in. rainfall @ curve number 81 = 0.48 in. runoff
0.48 in / 12 (in/ft) x 35.5 ac. = 1.42 ac -ft.
Peak Flow (gp): Type II storm, western Colorado, moderate slope, curve
number 81 = 32 cfs/in. runoff; 32 cfs/in. runoff x 0.48 in. runoff
= 15.4 cfs uncorrected
Basin Slope Factor (actual slope 6%) = 1.11
Basin Shape Factor (hydraulic length = 1,750 ft., equivalent area - 36.5
ac) 35.5/36.5 = 0.97
Corrected Peak Flow = 15.4 cfs x 1.11 x 0.97 = 16.6 cfs
Soil Erodibility Factor (K): Winnevada-splitro series = 0.2 (SCS)
Length -Slope (LS);
2
LS = (L/72.6) m (430x + 30 x + 0.43) / 6.613)
= (1,750/72.6) 0.5 ((430(.06)2 + 30 (.06) + 0.43)/6.613)
2.80
Crop Management Factor (C): 1.0
Support Practice Factor (P): 1.0
- 8-8 - Revised 10/19/88