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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 /> <br /> <br />approximately 250 feet in length, is at elevation 9300 (gage height 24.1). <br />Reservoir routings were performed for the existing conditions and three <br />rehabilitation design alternatives considered. All routings began with the <br />reservoir water surface at the spillway elevation. The outlet works capacity <br />was not included in the routings. Revised area-capacity curves were used; <br />based on new topographic maps produced from an aerial survey performed during <br />the summer of 1986. These curves are shown in Figure V.5. <br /> <br />The PMF routed through Twi n Lakes Reservoi r, for the exi sti ng conditi ons, <br />resulted in a peak outflow discharge of 5,660 cfs, with a maximum water <br />surface elevation of 9301.1. Thus, the PMF overtops the dam by 1:1 feet. The <br />PMF was routed for each of the rehabil i tati on alternati ves di scussed in <br />Section 4 of this Chapter. Alternative No.1 calls for the replacement of the <br />earth dam wi th an RCC structure. The dam woul d have a 25-foot overflow <br />section at elevation 9303 for nuisance flows. The dam crest, approximately <br />450 feet in length, would be at elevation 9306. Finally, an earth dike would <br />be constructed at the existing spillway section. Discharges exceeding the <br />nuisance flow would overtop the RCC dam crest without causing failure: <br />Routing of the PMF for Alternative No.1 resulted in a maximum water surface <br />elevation of 9308.4. Therefore, the earth dike crest elevation would be set <br />at 9309.4 to provide one foot of freeboard. <br /> <br />Alternative No.2 includes an RCC overflow dike 360 feet in length, placed at <br />the existing spillway location. The RCC dike would raise the crest elevation <br />of the spillway by 8 feet, to elevation 9303. The existing earth dam would be <br />raised 8 feet to elevation 9308. Routing of the PMF for Alternative No; 2 <br />resulted in a maximum water surface of 9307.0 feet, thus providing one foot of <br />freeboard. <br /> <br />Alternative No.3 also includes an RCC dike constructed to elevation 9303 at <br />the existing spillway location. Similarly, the dam would be raised to <br />elevation 9308. These represent identical hydraulic conditions, as <br />Alternative No.2, where the computed maximum water surface for the PMF was <br />9307.0 feet. <br /> <br />-59- <br />