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investigation together with output tables and graphs for peak flow conditions for the 100 -year <br />and PMF analysis; a summary of the results can be found in Appendix B. <br />Flip Bucket and Plunee Basin Calculations <br />Hydraulic calculations were completed for these components of the facility because none could <br />be found in the original design documentation. Calculations are included in Appendix B. <br />A discharge flow of 210 cfs was utilized, which is the greatest discharge calculated for the drop <br />pipe by the HEC -RAS modeling when the Flip Bucket was not submerged. For these conditions <br />and the anticipated duration of flow within the Drop Structure, calculations support that the <br />dimensions for the Flip Bucket and Plunge Basin identified on the Construction Drawings are <br />reasonable. <br />Results and Conclusions from HEC -RAS Model <br />The following results and conclusions were reached based on modeling of the South Diversion <br />Ditch and Drop Structure: <br />During the 100 -year Flood: <br />1. For existing conditions, nearly all, 96 %, of the 100 -year peak flow from Areas A, B, and <br />C will be carried downstream in the South Diversion Ditch system, bypassing the tailing <br />impoundment, with only a peak flow of 12 cfs entering the impoundment at the upstream <br />end of the ditch. This minor flow into the impoundment can be eliminated by <br />constructing a 12 -inch raise of the embankment near Station 38 +43 (raise to a top <br />elevation of approximately 8626 feet). <br />2. At the peak of the 100 -year flow, an estimated 180 cfs would discharge through the Drop <br />Structure conduit, and approximately 112 cfs would flow over the embankment at the <br />Drop Structure assuming a raise is placed as described in the preceding paragraph 1. <br />3. Unless blockage occurs, the culvert should carry all flows up to approximately 170 cfs; <br />flows in excess of that rate would start to overflow at the Drop Structure. <br />During the PMF: <br />1. The peak inflow into the South Diversion Ditch system is about 4315 cfs at about <br />4.30 hours into the flood hydrograph. <br />2. Significant overflow occurs at the Drop Structure, estimated to be a peak of between <br />1336 and 1412 cfs at time 4.20 hours, depending on the analysis approach used. Refer to <br />Figure 17. <br />3. Significant overflow occurs into the tailing impoundment through the embankment <br />saddle at Station 30 +34 estimated at a peak discharge of 1930 cfs at time 4.40 hours, and <br />at the upstream end of the ditch, Station 38 +43 with a peak discharge estimate of 646 cfs <br />San Luis Project Miller Geotechnical Consultants <br />Tailing Dam Data Report 32 February 2014 <br />