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<br />iv <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />,I <br />I <br />I <br />I <br />I <br />I <br /> <br />ANALYSIS OF ALTERNATIVE USES <br /> <br />The purpose of the Hardin Dam Project would be to increase the availabil- <br /> <br /> <br />ity of water supplies in the lower South Platte Basin by storage and regula- <br /> <br /> <br />tion of presently unregulated streamflows. Water could then be made available <br /> <br /> <br />at the desired time and place.for various uses. As noted above, quantifica- <br /> <br /> <br />tion of the demand for new water supplies was not attempted in this study. <br /> <br />Project flood control benefits associated with reduction of downstream <br /> <br /> <br />flood damages by storage in the reservoir were evaluated for the 100-year and <br /> <br /> <br />25-year flood events. It was found that providing flood protection for the <br /> <br /> <br />lOO-year flood was not economically feasible. At a 25-year level of protec- <br /> <br /> <br />tion, which corresponds to about 200,000 ac-ft of flood storage, providing <br /> <br /> <br />flood protection appears to be economically feasible. Therefore, it was <br /> <br /> <br />decided to complete the evaluation considering a proj ect with and without <br /> <br /> <br />200,000 ac-ft of flood control storage, as previously described. <br /> <br />The proj ect' s hydroelectric power gemerating potential was also evalu- <br /> <br /> <br />ated. It was found that hydropower generation would not be economically <br /> <br /> <br />feasible, if present values of capacity and energy were used. This was partly <br /> <br /> <br />due to the current surplus of electric generating capacity in the region. The <br /> <br /> <br />potential for future feasibility is enhanced should energy values continue to <br /> <br /> <br />escalate. A re-evaluation and optimization study of hydroelectric power <br /> <br /> <br />generation should be conducted if the proj ect investigations proceed to the <br /> <br /> <br />feasibility level. <br /> <br />PRELIMINARY DAM AND SPILLWAY DESIGN <br />Hardin Dam would consist of a three zone earthfill structure with a <br />maximum height of 136.5 ft at an elevatlon of 4614.5 for the project with <br />flood control and 130.5 ft with an elevation of 4608.5 for the project <br />without flood control. Positive foundation cutoff would be provided by a <br />slurry trench 3 to 5 ft wide and up to 150 ft deep. Internal embankment <br />drainage would be provided by a chimney drain. Upstream erosion protection <br />would be provided by a soil cement facing on a 3.0 h:l.0 v slope. Downstream <br />a 2.5 h:l.0 v slope would be faced with vegetation. <br />