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RUNOFF.WK1 <br />SEDIMENT POND 5 CAPACITY <br />Sediment pond 5 is located below and south of the reclaimed <br />bench along Hubbard Creek. The pond was constructed when <br />the mine site was being reclaimed in 1986. The pond's capacity <br />is in question because the lower collection ditch, Ditch D, was <br />regraded in 1988. The regraded ditch directs a larger drainage <br />area into pond 5 than sass anticipated by the 1986 design. <br />The run-off calculations presented below are calculated based <br />on the manual - Procedures for Determininfi Peak Flows in <br />Colorado - published by the Soil Conservation Service March <br />1984. <br />Assumptions: <br />Drainage areas are calculated with a planimeter from <br />Exhibit H-1. Only that portion of the areas that will <br />drain to pond 5 are included in the calculation. Therefore <br />only a portion of Areas C and E are included in this <br />calculation. <br />Areas Total Area Acres Draining to Pond 5 <br />A 5.5 5.5 <br />B 3.8 3.8 <br />• C 15.5 10.9 <br />D 3.9 3.9 <br />E 6.2 4.5 <br />10 Year 24 Hour Storm Event = 1.7" <br />CN 73 for undisturbed area - figure S-3 <br />- Soil group C, Absarokee, Dollard & Work <br />- 30% Cover Density <br />- Average of Oak-Aspen CN 67 and Juniper grass <br />cover CN 80. <br />CN 74 for reclaimed areas - figure S-4 <br />- Soil group C <br />- Similar to pasture of range in good condition <br />RUN-OFF VOLUME - - POND 5 <br /> PRECIP DIRECT RUN-OFF <br />AREA ACRES CURVE AMOUNT RUN-OFF VOLUME AF <br />A 5.5 74 1.7 0.22 0.10 <br />B 3.8 74 1.7 0.22 0.07 <br />C 10.9 73 1.7 0.20 0.18 <br />D 3.9 73 1.7 0.20 0.06 <br />• E 4.5 73 1.7 0.20 0.07 <br />TOTAL REQUIRED WATER VOLUME 0.49 <br />C-13 <br />3-29-91 <br />=9 <br />