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NORTH DECLINE RECLRMATION <br />POND N0. 7 <br />• <br />Sediment Pond No. 7 Runoff Calculations, 10-Year, 24-Hour Storm <br />Powderhorn Coal Company <br />BASIN CHARACTERISTICS <br />DRAINAGE AREA (SQ. MI.) = 0.015 <br />STREAM LENGTH (MI.) = 0.232 <br />ELEVATION DIFFERENCE (FT.). = 52.000 <br />RUNOFF CURVE NUMBER, CN = 82.000 <br />MINIMUM INFILTRATION LOSS (IN./HR.) = 0.000 <br />PRECIPITATION FOR SPECIFIED STORM <br />ADJUSTED PRECIPITATION FOR SELECTED STORM (IN.) = 1.40 <br />UNIT HYDROGRAPH PARAMETERS <br />• UNADJUSTED TIME OF CONCENTRATION (HR.). 0.10 <br />ADJUSTED TIME OF CONCENTRATION (HR.) 0.10 <br />' DURATION OF EXCESS RAINFALL, D (HR.) = 0.01 <br />TIME TO PEAK (HR. ) '. = 0.07 <br />BASE TIME (HR. ) = 0.19 <br />QPEAK (PEAK FLOW IN CFS FOR UNIT HYDROGRAPH) = 103.8 <br />RESULTANT HYDROGRAPH VALUES <br />PEAK DISCHARGE (CFS) <br />RUNOFF VOLUME (ACRE-FEET) . <br />TIME TO PEAK DISCHARGE (HR) . <br />= 3.81 <br />= 0.23 <br />= 12.02 <br />USED SCS TYPE II 24-HOUR GENERAL STORM <br />For She small additional acreage added during the reclamation phase sediment <br />volume calculations are assumed to be directly proportional to the acreage. <br />The sediment volume calculated in Appendix X, Volume 3 was 0.021 acre-feet <br />for 7.22 acres. For th 9.6 acres draining into the pond during the reclamation <br />phase the sediment volume is calculated to be 0.028 acre-feet. <br />CN Calculation: 50% sage grass, 20% cover, C Soil Group = 78 <br />50% roads (dirt), C Soil Group = 87 <br />Average CN 82 <br />• <br />(Revised 10-7-92) <br />NDEC - 1 <br />