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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 />-23- <br /> <br />was selected for additional, more detailed evaluation and scheme 3 was elimi- <br />nated from further consideration. <br /> <br />A preliminary review meeting was held on November 19, 1986 with Mr. Nick <br />loannides and Mr. Keith Eberhart of the CWCB to discuss the results of our <br />evaluations. At that time, Mr. Ioannides inquired as to the possibility of <br />increasing the crest height of the dam in order to reduce the spillway width <br />and associated concrete costs. Because of the existing crest configuration, <br />we believe that a crest raise of over 2 to 3 feet would only be possible if <br />retaining walls were constructed on both the upstream and downstream edges of <br />the crest, or if a downstream dam raise were constructed. Precast retaining <br />wall systems are available up to 5 feet in height. Cast-in-place walls or <br />reinforced earth walls would be required for heights above 5 feet. In addi- <br />tion, walls in excess of 4 to 5 feet in height present increased safety risks <br />to recreational users of the area and may also affect the overall stability of <br />the dam. We evaluated scheme 3 including a 5-foot crest raise using precast <br />concrete retaining walls. Our evaluations indicated that an approximate <br />20 percent reduction in the spillway width would be possible under these con- <br />ditions; however, overall costs were not significantly lower to offset con- <br />cerns related to the level of protection provided by the response time of an <br />early warning system as well as operation and maintenance considerations. <br /> <br />A similar comparison of schemes 2 and 4 indicated that the cable-tied <br />modular-block mattress system would be approximately 30 percent higher in cost <br />than a soil-cement overtopping protection system. The mattress system has not <br />been used in the U.S. for overtopping protection and some uncertaintie~ exist <br />concerning the effectiveness of such a system for a dam as high as Sheriff <br />Reservoir Dam. Based on these considerations, scheme No. 2 was selected for <br />additional, more detailed evaluation, and scheme No.4 was eliminated from <br />further consideration. <br /> <br />Scheme Nos. 1 and 2, are hereafter referred to Options 1 and 2, respec- <br />tively. Results of our conceptual designs and cost estimates for these two <br />options are described in more detail in the next section. <br /> <br />IV.6 Plan of Development <br /> <br />Introduction - Feasibility level design concepts of Option 1 are <br />illustrated in Figures 6 through 8. Figure 6 shows the general plan including <br />the location of the new spillway overflow section, stilling basin, spillway <br />channel enlargement, modification of the embankment crest, construction <br />staging area, and waste excavation disposal area. Typical sections of the <br />crest raising, and widened spillway channel are given in Figure 7. A typical <br />section through the spillway crest structure and stilling basin is given in <br />Figure 8~ <br /> <br />Feasibility level design concepts of Option 2 are illustrated in Figures <br />g and 10. Figure g shows the general plan including the location of the <br />overflow section, flow-training berms, crest-raising berm, construction <br />staging area, and waste excavation disposal area. Typical sections and <br />details of the overtopping protection, flow-training berm, and crest-raising <br />berm are shown in Figure 10. <br />