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• sections G-G' through J,1' show the ground as it currently exists. Additional mining was not <br />conducted in Area No. 3 as originally proposed. No Turther grading is proposed for Mining Areas <br />2or3. <br />Postmining drainage channels were designed, constructed, and maintained to the following <br />specifications: <br />1. Gentle sloping banks which shall be stabilized by vegetation; <br />2. Prevent additional conVibutions of suspended solids to streamflow and to runoff <br />outside the permit azea; <br />3. Blend with the undisturbed drainage above and below the area to be reclaimed; <br />4. Safely pass the runoff from a 10-year, 24-hour precipitation event. <br />The reclaimed drainages are designed to safely pass the 10-year, 24-hour precipitation event <br />and to be stable. The peak flow was determined by using the SEDIMOT II computer program. <br />Attachment A in Tab 13 contains a listing of the input parameters for obtaining the peak flows for <br />the reclaimed drainage channels. The peak flow determination assumed the total watershed of <br />• the reclaimed channel and was determined at the downstream end of the channel. Most of the <br />reclaimed channel reach will not have to handle that large a peak flow rate. This was done to <br />ensure chat the drainage channel capacity will be adequate and conservatively designed. <br />A limiting permissible velocity of 5.0 feet per second (fps) was used to insure that the postmining <br />drainage channels would be nonerodible and stable. The permissible velocity was obtained, <br />Table 3.4, from "Red Book' by Barfield et al., 1981 for a grass mixture vegetated channel. The <br />shape of the reclaimed channel was assumed to be Vapezoidal with 5h:1v side slopes as a worst <br />case condition. The side slopes will be no steeper than 5h:1v. <br />The channel bottom was calculated using Dodson and Associates TRAP computer program (see <br />Attachment J, Tab 13). The channel width was increased to insure that the peak velocity was <br />below the limiting velocity. The typical Vapezoidal channel section will be used for the entire <br />length of the reclaimed channel. <br />The design of the reclaimed channel at the Nucla Mine is shown in Tab 20, Attachment C. <br />The SEDCAD+ Version 3.0 computer program was used for the redesign of the Nucla postmine <br />channel. Peak flow and channel geometry were both gained from this program. Typical input <br />• <br />20-4 <br />