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<br />• <br />r1 <br />U <br />New Horizon 2 <br />Reclaimed San Miguel Power Drainage Channel Design <br />Introduction <br />The design of the reclaimed drainage channel in the New Horizon 2 permit area was based on <br />DMG regulations for conveyance of overland flow of watersheds less than one square mile. The <br />reclaimed channel is shown on Map 2.05.4-2 between points CC to CC'. The premine drainage <br />channel slope is 3.70 percent and the postmining drainage channel will be 3.70 percent. <br />Design <br />For the design of this reclaimed channel, the SEDCAD + model was used to predict runoff from <br />the watershed (see Attachment C). A 10-year, 24-hour precipitation event was used in the design. <br />The peak flow was determined at the downstream end of the drainage channel. Following is a fist <br />of main input factors. <br />Input Channel CC-CC' <br />Precipitation 2.0 in <br />Drainage Area 89.26 ac <br />CN 81 <br />L 2300 ft <br />Y 85 ft <br />Output <br />Q 32.55 cfs <br />Based on this discharge, SEDCAD+ was used to design the reclaimed drainage channel bottom <br />width based on Manning's equation calculation. The shape of the channel was assumed to be <br />trapezoidal with 10h:1 v side slopes. The channel bottom width was increased to insure that the <br />(Revised July 2006) ATTACHMENT 2.05.4(2)(C)- 3-1 <br />