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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 />similar to the emergency spillway cross-section. <br /> <br />Based on the geotechnical investigation (see attached Appendix D), the existing <br />dam embankment does not meet stabil ity design standards for static and seismic <br />loadings. Therefore, additional fill is required on the downstream slope to <br />increase the embankment stability. Before any fill is placed, the top 5-feet of <br />the existing embankment will be removed due to the poor compaction of this <br />material. In addition, the upper I-foot of the downstream slope will be stripped <br />to remove vegetation and other debris. The new fill placed will be compacted to <br />design standards and constructed at a slope of 2.25H:1V. The existing riprap on <br />the upstream face of the dam will be replaced in the areas that are disturbed by <br />construction. <br /> <br />Alternative #2 - Alternative #2 is presented in Figure 5.4 and evaluates the <br />potential of raising the dam embankment approximately 5.5 feet to an elevation of <br />10,404 feet and enlarging the existing emergency spillway to pass the PMF. The <br />proposed emergency spillway crest will be set at elevation 10,392 feet to meet <br />the City's water storage allocation. By raising the dam crest 5.5 feet the <br />bottom width 0 f the proposed emergency spi 11 way will be 115 feet. The proposed <br />emergency spillway will have 2H:1V sideslopes and a top width of 163 feet. <br />Riprap protection will be placed along the slope adjacent to the dam embankment. <br />A concrete grade beam will be required to provide a permanent crest elevation and <br />to prevent erosion during operation of the emergency spillway. <br /> <br />As in Alternative #1 before the additional fill is placed the upper 5-feet of the <br />existing dam will be removed and replaced with compacted fill. Therefore, a <br />total of about 10.5 feet of embankment will actually be constructed. The down- <br />stream slope will be placed at a slope of 2:25H:1V to increase stability. The <br />existing 20-inch outlet decant pipe will be extended to meet the toe of the <br />downstream embankment. Riprap will be required along the upstream face of the <br />dam to protect against wave action of the reservoir. <br /> <br />Alternative #3 - Alternative #3 considers widening the existing emergency spillway <br />to safely pass 1/2 of the PMF. Figure 5.5 presents a sketch of this alternative. <br />The proposed emergency spillway will have a crest elevation of 10,392 feet and a <br /> <br />35 <br />