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<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 />4.0 DESIGN ALTERNATIVES <br /> <br />The El khead Lake dam si te is physi cally suited to accommodate a dam up to <br />about 130 feet high, or 40 feet higher than the existing darn. A dam of this <br />hei ght would produce a reservoi r wi th a total storage capacity of <br />approximately 35,000 acre-feet. There is no need for such a large reservoir <br />at thi s time, but if the energy industry were to accelerate in the future, <br />further enlargement of Elkhead Lake Dam might be the most economical storage <br />alternative in the region. <br /> <br />For this study, three alternative designs were made and appraisal-level cost <br />estimates prepared. The alternatives are described in the following paragraphs <br />and the cost estimates '!re expressed graphically as a function of increase in <br />dam height and reservoir capacity in Figure V.3. The cost estimates represent <br />the cost of constructi on i ncl udi ng a 15 percent conti ngency, and engi neeri ng <br />and constructi on management fees. No all owances were made for esca 1 ati on, <br />interest during construction, or other financing costs. <br /> <br />Alternative 1 <br />The minimum modification to the existing structure required to meet the SEa <br />requirement to pass the PMF involves excavating an auxiliary spillway channel <br />11 0 feet wi de through the 1 eft abutment, and ra i si ng the dam crest five feet <br />with roller compacted concrete. This design was prepared for the CDO\~ and <br />submitted to the SEO for approval prior to this study. The estimated cost for <br />this alternative is $425,000. <br /> <br />Alternative 2 <br />The dam could be raised up to 15 feet and the maximum normal reservoir level <br />10 feet, providing about 4,800 acre-feet of additional storage without <br />completely replacing the existing service spillway. Any enlargement greater <br />than this would require relocating the spillway further up the left abutment <br />and would result in a significant increase in construction cost. The <br />alternative would consist of excavating an auxiliary spillway channel 220 feet <br />wide through the left abutment and utilizing the excavated material to raise <br />the dam 15 feet. The concrete ogee structure of the existing spillway would <br /> <br />- 41 - <br />