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<br />4.6 Bench Drainage <br />As shown on Drawing No. MG-R-C-001, the benches will be <br />sloped 27 back towards the pile and 27 towards the perimeter <br />drainage channels. This will allow surface runoff from con- <br />structed slopes to drain properly. The benches will drain in <br />east and west directions. <br />A peak discharge of 6.6 cfs was computed for 100 year-24 hour <br />precipitation event for the bench at elevation 6760 ft. The <br />bench slope of 27 will accomodate this discharge with a nor- <br />mal depth of approximately 0.3 ft. and a velocity is 3 fps. <br />Therefore, the grassed benches will provide adequate erosion <br />protection. <br />4.7 Temporary Collection Channels on Refuse <br />Due to the pile development configuration, two ditches, one <br />along the southeast side and the other along the southwest <br />side will be constructed to carry surface runoff from the <br />pile area. Although these channels will not be constructed <br />until future stages of pile construction, the design provi- <br />sions are provided herein as a part of the overall plan. The <br />east side channel will have a slope of about 14.39 and the <br />west side will have a slope of 13.3%. A triangular channel <br />with 2H:1V side slopes and one foot deep will carry 25 cfs at <br />13.32 slope with a velocity of 12.5 fps. Therefore, these <br /> <br /> <br />•. ; <br /> <br />i <br />-' <br />~• <br />16 <br />