APPCOR10792

• Permit No: C1981026
• IBM Index Class Name: Application Correspondence
• Doc Date: 7/31/1980
• Doc Name: OSM COAL PRODUCTION & RECLAMATION FEE REPORT
• Media Type: D
• Archive: No

A1'1'ACHML~ 'I 2
~DIMENTATION POND #1 DESIG~
Pit #1 Pond #1
Total Drainage Area = 106 acres
Runoff
Area I (north drainage, east of
diversion ditch)
Sediment
.1 acre-ft x
acre
10.6 acre
06 acres =
Drainage area = 29 acres CN - 84
Channel length = 1600 ft (Avg) 5~ slope
Elev = 8275-8200 = 75 ft
Tc = .12 hours
Peak discharge = 960 csm/in
29 cfs/inch runoff (4~ slope mod)
29 (.48) = 13.9 cfs @ 10 yr event
29 (.75) = 21.8 cfs @ 25 yr event
Area II (south drainage area)
See Septem
correspond
Drainage area = 77 acres
Channel length = 2500 ft (Avg)\ 4$ (Mod slope)
Elev = 8300-8200 - 100 ft //
Tc = .18 hours
Peak discharge = 840 csm~inch
60 cfs/inch runoff
60 (.48) = 28.8 cfs @ 10 yr event
60 (.75) = 45.0 cfs @ 25 yr event
Total peak flow at dam Spillway is:
10 yr event: 13.9 + 28.8 = 42.7 cfs
25 yr event: 21.8 + 45.0 = 66.8 cfs
t
19, 1979 MLRB
in Appendix Q.
Reference: Pr cedures for Deter-
mining Peak F ows in Colorado,
Soil Conserva ion Service, USDA,
March, 1977.
Required Pond Capacity 106 acres x .48
Required runoff capacity = 12 = 4.2 acre ft
Rquired sediment capacity = 10.6 acre ft
Total = 14.6 acre ft
Pond will be designed for 15.0 acre ft.
Emergency Spillway
Peak flow for 25 yr event = 67 cfs
From Manning Q = 1n49 AR.67S.5
Using trapezoidal section, earth with vegetation)
j-~? ~ A = 10 f t 2
_ ~ ~ WP = 12.47
iT w Si ~ i ~ R = A = 10
e' WP 12.4
n = .03
= 0.80
Q = 1039 (10)(.80).67(.05).5
49.67 (10)(0.86)(0.22) = 94.2 cfs ~ 67 OK