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• <br /> <br />n <br />U <br />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 DMG <br />regulations for conveyance of overland flow of watersheds less than one square mile. The reclaimed <br />channel is shown on Map 2.05.4-2 between points AA to AA'. The premine drainage channel slope is 3.0 <br />percent and the postmining drainage channel will be 3.18 percent. <br />Design <br />For the design of this reclaimed channel, the SEDCAD + model was used to predict runoff from the <br />watershed (see Attachment A). A 10-year, 24-hour precipitation event was used in the design. The peak <br />flow was determined at the downstream end of the drainage channel. Following is a list of main input <br />factors. <br />Ingut Channel AA-AA' <br />Precipitation 2.0 in <br />Drainage Area 159.75 ac <br />CN 81 <br />L 4000 ft <br />Y 165 ft <br />OutpU( <br />O 31.38 cfs <br />Based on this discharge, SEDCAD+ was used to design the reclaimed drainage channel bottom width <br />based on Manning's equation calculation. The shape of the channel was assumed to be trapezoidal with <br />10h:1 v side slopes. The channel bottom width was increased to insure that the peak velocity was below <br />the limiting velocity of 5.0 fps. Below is a summary of the input factors and the results determined by the <br />computer program. <br />ATTACHMENT 2.05.4(2)(c) - 1-1 <br />