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<br />1 BATTLE MOUNTAIN RESOURCES, SAN LUIS PROJECT <br />CMLRD ADEQUACY 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 "V" sloped channel with 2H:1V side slopes. A minimum riprap D <br />of O.S cch~es 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 10.5 fps results in the channel below the concrete <br />control section for the PMf flow event. A smaller channel for the <br />100-yr, 24-hr event is also proposed and shown on Figure F-3. The <br />100-yr channel is proposed to be riprapped while the PMf channel is <br />proposed to be revegetated. No stability calculations or construction <br />specifications were provided. Please provide the following: <br />a. A cross-section of the final spillway channel; <br />b. Riprap size based on stability calculations; <br />c. Riprap and bedding specifications; <br />' d. Velocity in the revegetated section of channel; and <br />e. Revegetation specifications if different from general <br />specifications. <br />a. 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 27 fps. The cross-section of <br />this channel has been added as Figure E-1. <br />' b. Grouted riprap will be used to stabilize the channel. A grout <br />thickness of one ft is 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 />c. Riprap sizing is as stated above. A Type I bedding gradation <br />as recommended in the Urban Storm Drainage Criteria Manual is <br />shown below: <br />U.S. Standard Sieve Percent Passing bv,Neiaht <br />3f 8" 100 <br />#4 95-100 <br />' #16 45-80 <br />#50 10-30 <br />#100 2-10 <br />#200 0-2 <br />j This bedding gradation is adequate for nwst riprap and grouted <br />riprap applications. <br />1 <br />