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99 61109 18:39 ~ 3 363 985 9947 SftK DENVEP~ 66 <br />BATTLE MOUNTAIN RESOURCES, SAN LUIS PROJECT <br />CMLRD ADEQUAGY LETTER RESPONSES <br />Page 24 of 28 <br />Velocities resulting from the 100-yr, 24-hr storm range from 2.6 to <br />3.7 fps, depending upon the location within the impoundment and based <br />on a "Y" sloped channel with 2H:lV side slopes. A minimum riprap D <br />of 0.8 inches is required to stabilize channel bottoms. A channe~ <br />depth of three ft is sufficient to carry storm runoff at all <br />locations. The channel design is shown on Figure E.1. Runoff <br />calculations and riprap sizing data are contained in Attachment 14. <br />43. The spillway design calculations are provided in Appendix L. A <br />velocity of ]0.5 fps results in the channei below the concrete <br />control section for the PMf flow event. A smaller channel for the <br />100-yr, 24-hr event is aiso proposed and shown on Figure f-3. The <br />100-yr chanrtei is proposed to be riprapped whi)e the PMF channel is <br />proposed to be revegetated. No stability calculations or construction <br />specifications were provided. Please provide the foilowing: <br />a. A cross-section of the final spillway channel; <br />b. Riprap size based on stability calculations; <br />c. Riprap end bedding specifications; <br />d. Ve)ocity in the revegetated section of Channel; end <br />e. Revegetation specifications if different from general <br />specifications. <br />The final 100-yr spillway channel will have a bottom width of <br />10 ft with 2H:1V side slopes. The 100-yr event is expected to <br />produce a peak discharge of 615 cfs which will result in a flow <br />depth of 1.6 ft at a velocity of 21 fps. The cross section of <br />this channel has been added as Figure E-1. <br />Grouted riprap will be used to stabilize the channel. A grout <br />thickness of one ft 1s required, with a riprap size of 1.33 <br />to 1.5 times the grout thickness, or a diameter of :1.33 to 1.5 <br />ft. <br />Riprap sizing is as stated above. A Type I bedding gradation <br />as recommended in the Urban Storm Drainage Criteria Manual is <br />sfiown below: <br />U.S._ Standard Sieve Percent Pass1~„q by Wieight <br />3/8" 100 <br />N4 95-100 <br />N16 45-80 <br />N50 10-30 <br />N100 2-10 <br />N200 0-2 <br />This bedding gradation is adequate for most riprap and grouted <br />riprap applications. <br />