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<br />001275 <br />Draft Task 7 Technical Memorandum <br /> <br />. <br /> <br />. <br /> <br />comparative information between alternative projects. A greater amount of information on <br />physical characteristics was available for the Stagecoach and Ellchead sites than the Williams <br />Fork site. To allow comparison of projects on an equal basis, several simplifying assumptions <br />were applied to normalize cost estimating parameters. All estimated costs reference the <br />Engineering News Record Cost Construction Index No. 4777 (January, 1991). These figures <br />were not intended to represent discrete, absolute numbers. <br /> <br />Elkhead Enlargement <br /> <br />The cost estimate for the Enlargement at Ellchead Reservoir was based on a new <br />reservoir with a total active capacity 52,000 af. This configuration requires a new dam crest <br />elevation of 6,418 feet. The new spillway elevation would be 6,406 feet, or an increase from <br />existing conditions of 39 feet. The existing Ellchead Dam was an earthfill structure which will <br />be raised by a downstream earthfill addition. The dam will have a new structural concrete <br />spillway as an integral part of the embankment or through a saddle in the existing topography <br />off the west end of the dam. The conceptual total costs of this dam raise and associated work <br />would be in the range of $15 - $20 million. <br /> <br />Stagecoach Enlargement <br /> <br />The maximum reasonable dam size at the existing Stagecoach Reservoir is controlled by <br />the right abutment topography, rock quality and preservation of the existing dam features to the <br />maximum extent possible. Elevation 7,231.5 reflects the new top of dam and elevation <br />7,221.5 reflects the new spillway crest elevation. This represents an increase in the spillway. <br />elevation of 21.5 feet. The volume of storage below the spillway crest is 52,000 af. The <br />existing Stagecoach Dam is a recently constructed (1989) roller compacted concrete (RCC) <br />dam which would be raised by a downstream RCC addition. 1)J.e dam would have a spillway <br />integral with the RCC embankment. The conceptual total costs of this dam raise and <br />associated work is in the range of $6 - $10 million. <br /> <br />Williams Fork Reservoir <br /> <br />The maximum reasonable dam size on the Williams Fork River near Hamilton is 85,000 <br />af (crest elevation at 6,397 feet). This produces a reservoir with 70,000 af of storage below <br />the spillway elevation of 6,385 feet. The Williams Fork dam is configured as a rockf"tll <br />structure with a structural spillway as an integral part of the embankment. The conceptual <br />total project cost of this dam and reservoir is approximately $30 - $45 million. <br /> <br />CONCLUSIONS AND RECOMMENDATIONS <br /> <br />Conclusions <br /> <br />In Task 7 of the Feasibility Study, five alternatives were evaluated using a basin water <br />rights and hydrologic model. The evaluation studied the performance of alternatives of three <br />demand levels. Modeled water delivery strategies included the development of one new <br />storage projects, enlargements of two existing storage projects and conversion of a portion of <br />the Juniper Reservoir water rights to an instream flow on the Yampa River. Evaluation criteria <br />of the alternatives included shortages to basin demands, reservoir contents and environmental <br />aspects. <br /> <br />20 <br /> <br />.r> <br />