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1 should increase to 800 feet or less from the dam crest. The spillway has ~~ capacity of 135 CFS. The decant water recycle system could also be utilized as an erergency spillway in an extreme flood event, thereby doubling emergency releases. Since tailing deposition changes the impoundment configuration continuously, the impoundment is surveyed annually, and a revised dam volume versus elevation fill curve is developed. HYDROLOGY W. W. Wheeler and Associates, Inc. have performed several flood studies i`or the areas tributary to the Henderson process water system, including both snowflooci and rainflood events. The snowflood hydrology was reviewed by Wheeler in a 1982 report: "Rainflood and Snowmelt Studies for the Henderson Mill Site". The results indicate a Prob<~ble Maximum snowflood event would result in a peak flow of 90 CFS tributary to the Upper bypass ditch, and a peak flow of 115 CFS tributary to the Lower bypass ditch. These ditches will bypass all but 500 acre-feet of the flood. An additional :!,500 acre- feet of flood water would enter the system from that area that is below the interceptor ditches and cannot be bypassed. If the PM snowflood occurred when Ea:;t Branch Reservoir is full and the tailings water pool was already at the 1000 foot beach limit, the resulting 3,000 acre-feet flood intake would be delivered to the tailing pool. Under this scenario and utilizing the tailing dam #1 fill curve revised by survey in .July of 1993, the water pool would increase from 3056 acre-feet at a water surfacer elevation of 8770.50 feet to a volume of 6056 acre-feet at a water surface elevation of 8776.13. The tailing dam would then have a remaining free board of 4.86 feet and dry beach of at least 700 feet. The beach slope was measured 0.7% in a November 1994 survey. Rainflood hydrology was reviewed by Wheeler in 1982 and again in 1994. The 1994 study: "Henderson Tailing Complex Probable Maximum Flood Hydrology" reviewed both the probable maximum local storm flood and the probable maximum ~3eneral storm flood events. Besides being based on the probable maximum precipitation, these studies also include other "worse case" conditions such as the storalae reservoirs being full at the beginning of the event, total failure of the bypas!~ ditches, and overtopping Ute Creek Reservoir embankment resulting in dam failure. The Ute Creek reservoir storage volume is therefore routed as additional flow into tfie tailings pool. The local storm probable maximum event predicted results in a tailings pool volume of 7310 acre-feet at an elevation of 8778.0 feet, with a remaining freeboard of 2.99 feet and a dry beach of at least 400 feet. The general storm probable maximum event predicted results in a tailings fool volume of 8140 acre-feet at an elevation of 8779.3 feet, with a remaining freeboard of 1.69 feet and a dry beach of at least 250 feet.