PERMFILE59604

• Permit No: C1981041A
• IBM Index Class Name: Permit File
• Doc Date: 7/3/2002
• Doc Name: A-2 Part 2
• Section_Exhibit Name: Tab 13 Appendix 13-2 pg CRDA1-1 to RSS-35
• Media Type: D
• Archive: Yes

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North Decline Final Reclamation
Powderhorn Coal Company
Riprap Size Aeguirements for North Decline Drainage Channel
BECTION 1
Riprap Size = 12"
Slope = 0.075
Discharge = 470 cfs
Manning's n = 0.0395 x ds tis = 0.0395 x 1t~6 = 0.0395
At n = 0.0395, V = 10.84 fps (from FIAMASTER program)
Drainage Criteria Manual rock size requirements:
VSO.tT = 5.8
dso . (Sg-1) .
where: V = velocity in feet/sec
S = channel slope in feet/foot
SS = specific gravity of rock
dso = riprap site
assume: SS = 2.5
dso = ( (10.84 x 0.075o.t~) / ( (2.5-1)0.~ x 5.8) )Z
dso = 0.85' = 10.2"
r 1
U
therefore, 12" rock is acceptable
SECTION 2
Riprap Size = 6"
Slope = 0.025
Discharge = 470 cfs
Manning's n = 0.0395 x dsotie = 0.0395 x O.St~b = 0.0352
At n = 0.0352, V = 8.26 fps (from FLOMASTER program)
dso = ( (8.26 x 0.025.77) / ( (2.5-1)0'~ x 5.8) )Z
dso = 0.34' = 4.1"
therefore, 6" rock is acceptable
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(New 2-26-92)
NDEC - 13