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<br />", q '\ {" Q 8 <br />UU1UO <br /> <br />Revised Supplemental Draft Environmental Assessment-Chapter 3-Affected <br />Environment and Environmental Consequences <br /> <br />Ute Water Conservancy District Pump Plant-Spring Flooding <br /> <br />Issue: Effects of each alternative on spring flooding of Ute Water pumping plant. <br /> <br />Existing Conditions: The Ute Water pump plant historically flooded when river <br />flows were high and the Colorado River exceeded elevation 4,732 feet. Ute Water <br />constructed a concrete retaining wall to an approximate elevation of 4,738 feet to protect <br />the pump plant from flooding. The estimated 100-year to 500-year flood events at the <br />dam are 44,500 cfs and 52,800 cfs, respectively (Norval, ,1998). The highest recorded <br />flow in this stretch of the Colorado River was 36,000 cfs in'1983. According to Ute <br />Water, the river elevation at that flow was just below the top of their retaining wall <br />(elevation 4,738 feet). Ute Water placed sand bags on top ofthe wall as a precautionary <br />measure, and subsequently has raised the wall to' elevation 4739.8 feet. <br /> <br />Impacts <br /> <br />No Action: The No Action Alternative would allow Ute Water to operate their <br />pump plant as they have historically. <br /> <br />Conventional Fish Ladder: The fish ladder would be designed so it would have <br />no effect on flood flows in the Colorado River. <br /> <br />Downstream Rock Fish Passage: The fish passage would also be designed so it <br />would have no effect on flood flows in the Colorado River. <br /> <br />Downstream Rock Fish Passage with Whitewater Recreation Features: Same <br />as the Downstream Rock Fish Passage Alternative. <br /> <br />Dam Removal: With dam removal, the Colorado River elevations at the Ute <br />Water pump plant would be lower at all flow conditions. Flood flow elevations at the <br />pump plant would be reduced by about 1.5 feet by removing the dam. Dam removal <br />would, therefore provide some additional protection from flooding. As discussed <br />. previously, Ute Water would not be able to pump water when river flows drop below <br />elevation 4,722 feet and dam removal would negatively affect Ute Water's ability to <br />pump at other times of the year without implemented mitigation measures (see pages 18 <br />and 19). Option 3, which involves construction of a low head. dam immediately <br />downstream from the pump plant, would change existing river elevations and would not <br />provide any protection from flooding. <br /> <br />Recreation Resources <br /> <br />Issue: Effects on Colorado River boating in the Grand Valley vicinity. <br /> <br />29 <br />