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• 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 and <br />to be stable. The peak flow was determined by using the SEDCAD+ Version 3.0 computer <br />program. A listing of the input parameters for obtaining the peak flows for the reclaimed drainage <br />channels are attached. The peak flow determination assumed the total watershed of the reclaimed <br />channel and was determined at the downstream end of the charinel. Most of the reclaimed channel <br />reach will not have to handle that large a peak flow rate. This was done to ensure that the drainage <br />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 velocitywas obtained, Table <br />3.4, from "Red Book" by Barfield et al., 1981 for a grass mixture vegetated channel. The shape of <br />the reclaimed channel was assumed for design purposes to be trapezoidal with 10h:1 v side slopes <br />as a worst case condition. The side slopes will be no sleeper than 10h:1v. <br />The channel bottom was calculated using the SEDCAD+ Version 3.0 computer program. The channel <br />width was increased to insure that the peak velocity was below the limiting velocity. The typical <br />trapezoidal channel section was selected for design purposes only for the entire length of the <br />reclaimed channel. "Reclaimed Drainage Channel Design" on the following pages contains the <br />specific design information of the reclaimed drainage channel in the eastern portion of the New <br />Horizon 2 permit area (San Miguel Draw). <br />The reclaimed drainage channels will be topsoiled and revegetated according to Sections 2.05.4(2)(d) <br />and (e) respectively. <br />Slides and Other Damage <br />WFC does not anticipate any problems with slides at New Horizon 2 Mine during the term of mining <br />and reclamation activities. <br />. (REVISED 15 Nov 02) 2.05.4(2)(c) - 5 <br />