PERMFILE111032

• Permit No: C1981046
• IBM Index Class Name: Permit File
• Doc Date: 9/20/1982
• Section_Exhibit Name: Permit Application to Page 105
• Media Type: D
• Archive: No

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Drainage Area 1 will be unaffected by mining. Current conditions are soil type C,
range in good condition. Preminin~ conditions in Drainage Area 2 include some range,
similar to Drainage Area 1, and some highly disturbed area with no vegetative cover
and very high infiltration rates. In the postmininR condition, these disturbed areas will
be reclaimed and the infiltration rates will decrease.
Drainage Area 1 flows into an unnamed tributary and enters Fourmile Creek
several miles downstream of the mine. Drainage direction is primarily east. Drainage
Area 2 includes the disturbed area (5.24 acres). Flow in Drainage Area 2 is primarily
south, directly into Fourmile Creek.
Curve numbers for Drainage Area 2 are calculated as follows:
Preminin 5.24(70) + 69.76(75) = 75
g ~ 75
Postmining 5.24(85) 7569.76(75) = 76
2) Calculate time of concentration,Tc (hours)
Average velocity,V, is found using Figure H.S.
According toSCS, Tc can be calculated using:
To V x 3600
Drainage Drainage
Area 1 Area 2
Average Slope 27% 63`/,
(H/L)
V 1.3 fps 2 fps
T~ .53 hr .17 hr
36