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<br />. <br /> <br />The total estimated excavation volume would be about 70,000 cubic <br />yards. Most of the excavation in the south abutment would require <br />blasting. Investigation by Chen and Associates, as described in <br />Appendix 0, indicates that the abutment can be benched on an overall <br />one to one slope. For the feasibility cost estimates, it was esti- <br />mated that three-fourths of the excavation would be in rock requiring <br />blasting and one-fourth would be common excavation. <br />The spillway floor would have a concrete thickness of about 12 <br />inches. The north spillway wall would be of variable thickness, <br />depending on the required height. At the maximum section the wall <br />would be about 40 feet high with a base thickness of roughly 36 inches. <br />Counterforts would be required along much of the north wall. The <br />south wall of the spillway would be lined only to the extent necessary <br />to prevent erosion during normal operational spillway releases. <br />With the enlarged spillway, the probable maximum flood could be <br />passed if the dam crest is raised 10 feet to elevation 9473. About <br />0.3 foot of freeboard would be available above the maximum water sur- <br />face, assuming the outlet works would not be operating. The freeboard <br />would be about 1.6 feet if the outlet works is used to help pass the <br />flood. <br />As discussed in the geotechnical report, Appendix 0, the down- <br />stream slope of the dam embankment would be stabilized if the dam is <br />enlarged at a two horizontal to one vertical slope. Approximately <br />55,000 cubic yards of material would be required to raise the dam <br />crest to elevation 9473. It is anticipated that earth and rock exca- <br />vated during the spillway enlargement would be used for the dam embank- <br />ment. <br /> <br />. <br /> <br />As shown on Figure 12, the new dam toe would be extended about 80 <br />feet downstream. Therefore, the outlet works tunnel would have to be <br />extended about 60 feet so that reservoir releases would not affect the <br />embankment. The new tunnel would be constructed to match the existing <br />concrete tunnel cross section. A preliminary cross section for the <br />proposed tunnel extension is shown in Figure 13. The tunnel would be <br /> <br />. <br /> <br />-47- <br />