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intensity curve and a SCS number 70 runoff curve. The 100 year <br />• 24 hour precipitation remains unchanged from the approved <br />permit value of 2.90 inches of rainfall. The peak discharge <br />has been calculated to be 292 cfs in the south diversion ditch <br />and 80 cfs in the north ditch (Drainage D). <br />The diversion ditches are located on Figures C-3 and C- <br />4. Diversion ditch designs are shown on Figure C-10. Figure <br />C-10 also includes designs for the drop structure inlet, the <br />drop structure and the drop structure outlet including the <br />stilling basin. Design calculations are contained in Appendix <br />H. <br />In the event that the PMF occurs, perimeter diversion <br />ditches will be breached and the PMF inflows could occur into <br />the tailings disposal area. The disposal area has been designed <br />to store the probable maximum flood (PMF) from all upgradient <br />catchments and the tailings disposal area itself. For design <br />• purposes, an eight hour Probable Maximum Precipitation (PMP) <br />event producing 14.0 inches of rainfall over the 1.29 miz <br />catchment area has been used. The catchment area includes <br />drainages A through D, the tailings disposal area, and areas <br />peripheral to the disposal area. Peak discharge from this event <br />is predicted to be 9220 cfs. <br />During Phase I of the operation of the Facility, PMF <br />inflows will be contained by the main and upper splitter. <br />During Phase II of the operation of the facility, storm inflows <br />will be contained by the main embankment. Figure D.6-2 shows <br />the freeboard required to contain PMF inflows as a function <br />of the elevation of the tailings. Appendix I contains the PMP <br />inflow calculations. <br />C~ <br />D-42 <br />