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New Horizon 2 <br />Reclaimed Krill 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 AA to AA'. The premine drainage <br />channel slope is 3.0 percent and the post- mining drainage channel will be 3.18 percent. <br />Desion <br />For the design of this reclaimed channel, the SEDCAD + model was used to predict runoff from <br />the watershed (see Attachment A). A 10 -year, 24 -hour precipitation event was used in the design. <br />The peak flowwas determined at the downstream end of the drainage channel. Following is a list <br />of main input factors. <br />Input <br />Channel AA -AA' <br />Precipitation <br />2.0 in <br />Drainage Area <br />159.75 ac <br />CN <br />81 <br />L <br />4000 ft <br />Y <br />165 ft <br />Output <br />Q 31.38 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:1v side slopes. The channel bottom width was increased to ensure that the <br />(Revised June 2010) Attachment 2.05.4(2)(c) -1 -2 <br />