PERMFILE67446

• Permit No: C1980007
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Exhibit 51 Appendix L
• Media Type: D
• Archive: No

PEAK RUNOFF CALCULATIONS OF LRP, REVISED 1996
Ref. Peak Flows m Colorado SCS, March 1980
Slope Face East North West South
(sf) Plan Area ~ 204,620 224,500 151,350 53,800
(%) Grade 50 % 50 % 50 % 50
(acres) Plan Area 4.7 5.15 3.5 1.23
SCS Runoff Curve Number: Coal Refuse = 75
Reclaimed Surface = 88
Scope Adjust Factor: E - 1.17; N - 1.17; W - 1.17; S - 1.12
Tr-55, Table E-1
SCS CN 75 SCS CN 88
1.8-In., 10-Yr., 24-Hr. Type II 0.29 0.81
Runoff (In.) _
2.2 In., 25-Yr., 24-Hr. Type II 0.48 1.13
Runoff (In.) _
2.8-In., 100-Yr., 24-Hr., Type II 0.83 1.64
Runoff (In.) _
• Assume Worst Case -All Surface SCS CN = 88
Peak Runoff
E 100-Yr. (10 cfs/in Runoff) (1.64 in Runoff) (1.17) = 19.2 CFS
N 100-Yr. (10.8) (1.64) (1.17) = 20.7 CFS
W 100-Yr. (7.8) (1.64) (1.17) = 15.0 CFS
S 100-Yr. (3.5) (1.64) (1.12) = 6.4 CFS
E 25-Yr. (]0) (1.13) (1.17) = 13.2 CFS
N 25-Yr. (10.8) (1.13) (1.17) = 14.28 CFS
W 25-Yr. (7.8) (1.13) (1.17) = 10.3 CFS
S 25-Yr. (3.5) (1.13) (1.12) = 4.4 CFS
E ]0-Yr. (10) (0.81) (1.17) = 9.5 CFS
N 10-Yr. (10.8) (0.81) (1.17) = 10.23 CFS
W 10-Yr. (7.8) (0.81) (1.17) = 7.4 CFS
S 10-Yr. (3.5) (0.81) (1.12) = 3.2 CFS
Peak Flow for Runoff Control Ditches
East Ditch 100-Yr Event = 19.2 + 6.4 = 25.6 CFS
North Ditch 100-Yr Event = 19.2 + 20.7 + 6.4 = 46.3 CFS
West Ditch 100-Yr Event = 15 CFS
• Sou[h Ditch 100-Yr Event = 6.4 CFS