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<br />L~ <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 DMG <br />regulationsfor 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 CC to CC'. The premine drainage channel slope <br />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 the <br />watershed (see Attachment C). A 10-year, 24-hour precipitation event was used in the design. The <br />peak flow was determined at the downstream end of the drainage channel. Following is a list of main <br />input factors. <br />InDUt 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 />Out ut <br />Q 32.55 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 <br />with 10h:1 v side slopes. The channel bottom width was increased to insure that the peak velocity was <br />below the limiting velocity of 5.0 fps. Below is a summary of the input factors and the results <br />determined by the computer program. <br />(Revises 2/00> ATTACHMENT 2.05.4(2)(C)-3-1 <br />