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JD-8 Mine—Drainage Design Plan 8_ <br /> Table 4. Non-Contributing Drainage Peak Discharge (Q1oo) <br /> Sub-Basin Sub-Basins <br /> Parameter <br /> N-F N-B+N-C+N-D <br /> Tsh(sheet flow)(hr) 0.08 0.15 <br /> Tso(shallow concentrated)(hr) 0.0 0.01 <br /> Teti(channel)(hr) 0.05 .08 <br /> Tc(hr) 0.13 0.24 <br /> Q„(cfs) 610 445 <br /> Qioo(cfs) 0.72 2.4 <br /> To pass the N-F Q100 flow rate, conveyance structures will need to meet the requirements shown in Table 5. <br /> Table 5. Diversion Drainage Structure Parameters <br /> Water Tank Mine Access <br /> Parameter Access Road Road <br /> Ditch Culvert <br /> Design Flow(cfs) 0.72 0.72 <br /> Side Slope 1:1 <br /> Bottom Width(ft) 0.2 <br /> Channel Depth/Culvert Diameter(ft) 1.0 1.0(1) <br /> Flow depth(ft) 0.5 0.35 (exit) <br /> Headwater depth(ft) 0.5 <br /> Velocity(ft/s) 2.2—3.8(2) 3.0(exit) <br /> Slope(ft/ft) 0.06—0.01 0.02 <br /> NOTES: <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 mininum 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 la) indicates sufficient capacity to pass the design <br /> 111 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 />