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• <br />APPENDIX 2.05.3-6A (Continued) <br />Sedimentation Pond Design - Prior to Post-Mine Topographic Grading <br />Discharge Calculations <br />See Map 11 for the boundaries of watershed areas referred to below. <br />Area A <br />Area - 47.9 acres <br />Change in elevation - 337 feet <br />Channel Length - 2200 feet <br />CN number * - 75 <br />Precipitation* <br />100-year/24-hour - 2.3 inches <br />25-year/24-hour - 2.0 inches <br />10-year/24-hour - 1.6 inches <br />Runoff <br />100-year/24-hour = 0.59 inches <br />25-year/24-hour = 0.38 inches <br />10-year/24-hour = 0.20 inches <br /> <br />Siope adjustment factor* <br />• <br />slope - <br />15.3X <br />slope adjustment = 0.99 <br />Equivalent drainage area* = 51 acres <br />Equivalent peak flow * = 54 cfs/in. for 51 acres <br />Calculations: <br />l J <br />Q 100 yr. _ (54 cfs/in) (0.59") = 31.9 cfs ~ (.99) = 24.7 cfs <br />Q 25 yr. _ (54 cfs/in) (0.38") = 20.5 cfs ~ (.99) = 19.1 cfs <br />Q 10 yr. _ (54 cfs/in) (0.20") = 10.8 cfs ~ (.99) = 10.1 cfs <br />* Source - USDA-SCS Technical Release No. 55 and Procedures for Determining Peak <br />Flows in Colorado, March 1980. <br />- 249 - (Rev. 5/86) <br />