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Response to DRMS Adequacy Review (5) — Cotter SR -13A Mine Reclamation Plan Amendment <br />Drawings: <br />11. Sheet 2. The response to this comment is adequate. <br />12. Sheet 3 and hydraulic analysis. The analysis and design for the spillway are adequate. <br />However, no design or analysis is provided for the spillway chute (between the weir and the <br />toe of the embankment). The spillway chute in the revised Drawing 3 appears to beat a 3H: <br />IV slope. <br />a. Please provide an analysis addressing the spillway chute hydraulics and riprap <br />sizing. The riprap sizing methodology should be consistent with the steep slope. <br />b. Please provide a design that reflects the material necessitated by the analysis and <br />dissipates the energy at the toe of the embankment. <br />The spillway chute for the working pond has been regraded and flattened to a <br />maximum slope of 10% to provide a more reasonable discharge velocity for the 100 - <br />year event. The worksheet for Trapezoidal Channel 2 (the spillway chute) is <br />included in Attachment 1 and gives a calculated velocity of 5.73 ft/sec and a normal <br />depth of 0.26 feet. These values were converted to meters and a similar analysis was <br />performed using the HEC -11 methodology. Results of this analysis show that a <br />minimum D5o of 5.3 inches is required. The D59 = 8 inch rock specified is therefore <br />adequate. <br />13. Sheet 5. The response to this comment is adequate. <br />General Comments: <br />14. Page ESWMP -S, second paragraph. The response to this comment is adequate. <br />3 <br />