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RESULTS OF FLOOD MODELING DURING THE PMF <br />The total area of all basins contributing to the tailing pond is about 11.52 square <br />miles, which is 7,373 acres. The total volume of the 5.6 -inch storm over this area would be <br />about 3,441 acre-feet. According to the HEC-1 model, about 359 acre-feet would be lost to <br />infiltration and other abstractions. A copy of the HEC-1 output file is included in Appendix C. <br />The remaining 3,082 acre -feet would accrue to storage in the tailing pond. The volume of <br />baseflow, which is estimated to be 3.61 cfs per square mile, would be 82 acre -feet during the <br />24 -hour period after the onset of the storm. <br />The flood routing model indicates that Ute Creek Reservoir would be overtopped <br />during the PMF. It is thus a reasonable assumption that Ute Creek Reservoir would fail <br />during this storm and the 130 acre -feet normally stored would be emptied into the tailing <br />pond. However, it is our opinion that the flood wave and additional volume of water from <br />failure of Ute Creek Reservoir would not cause a domino effect and would not damage the <br />tailing pond embankment. East Branch Reservoir would not be overtopped and thus it is not <br />likely that it would fail during the PMF. With the additional volume from the Ute Creek <br />Reservoir failure and baseflow during the 24 -hour period after the onset of the storm, the total <br />inflow to the tailing pond during the PMF would be 3,294 acre - feet. <br />Based on the pond configuration at the time of the fall -2003 survey, we can conclude <br />that the PMF, in conjunction with failure of Ute Creek Reservoir, would not overtop the tailing <br />pond and that there would be about 2.9 feet of residual freeboard to the dam crest. The <br />water level in the pond would be expected to rise about 5.1 feet during the storm. <br />Due to the constantly changing configuration of the tailing impoundment, the critical <br />characteristic of the PMF is the total pond inflow volume. As long as the amount of surcharge <br />storage capacity in the pond exceeds this amount with an allowance for inflows to the pond <br />after the PMF, this analysis indicates that the tailing pond would be capable of containing the <br />runoff resulting from the PMF event. It is important to note that any excess capacity in East <br />Branch Reservoir below the level of the emergency spillway would reduce the flood volume <br />that would flow into the tailing pond up to a maximum of 676 acre -feet, which is the total flood <br />12 <br />