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Parameter <br />Sub -Basin <br />N -F <br />Sub - Basins <br />N -B + N -C + N -D <br />T (sheet flow) (hr) <br />0.08 <br />0.15 <br />T (shallow concentrated) (hr) <br />0.0 <br />0.01 <br />Tch (channel) (hr) <br />0.05 <br />.08 <br />Tc (hr) <br />0.13 <br />0.24 <br />Q„ (cfs) <br />610 <br />445 <br />Qioo (cfs) <br />0.72 <br />2.4 <br />Parameter <br />Water Tank <br />Access Road <br />Ditch <br />Mine Access <br />Road <br />Culvert <br />Design Flow (cfs) <br />0.72 <br />0.72 <br />Side Slope <br />1:1 <br />Bottom Width (ft) <br />0.2 <br />Channel Depth / Culvert Diameter (ft) <br />1.0 <br />1.0 <br />Flow depth (ft) <br />0.5 <br />0.35 (exit) <br />Headwater depth (ft) <br />0.5 <br />Velocity (ft/s) <br />2.2 - 3.8 <br />3.0 (exit) <br />Slope (ft/ft) <br />0.06 - 0.01 <br />0.02 <br />JD -8 Mine - Drainage Design Plan 8 <br />NOTES: <br />Table 4. Non - Contributing Drainage Peak Discharge (Q100) <br />To pass the N -F Q loo flow rate, conveyance structures will need to meet the requirements shown in Table 5. <br />Table 5. Diversion Drainage Structure Parameters <br />(1) Although design capacity is met with a 12 -inch (1.0 ft) diameter culvert, all culverts installed by Cotter for storm water <br />conveyance will be minimum 18 -inch diameter. <br />(2) Varies with channel slope <br />Although the average channel slope for the water tank access road ditch is approximately 4.0 %, a <br />conservative estimate of channel slope of 1.0% has been used to establish the capacity requirements in the <br />lower /flatter portion of the ditch. If necessary due to site conditions, ditch capacity may be supplemented <br />with a second ditch/berm on the water tank access road shoulder. A continuous grade exists to the south <br />east along the water tank access road which was verified by site inspection. <br />Flows from the water tank access road ditch are passed through the existing culvert beneath the mine <br />entrance road and around the mine site. An analysis of the existing 12 -inch diameter culvert installed <br />beneath the mine access road (Table 5, Attachment 1a) indicates sufficient capacity to pass the design <br />discharge. However, this culvert will be replaced with a minimum 18 -inch diameter culvert to reduce the <br />potential of plugging with wind -blown debris and animal denning activities. The natural drainage directing <br />4122A.120702 Whetstone Associates • <br />