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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 /> <br /> <br />=~=====================:======================================================= <br /> <br />Table V;2. Twin Lakes Dam <br />Rehabilitation Alternative No.2 <br /> <br />o Excavate portion of dam and replace outlet works. <br /> <br />o <br /> <br />Raise dam crest from elevation <br />capacity of approximately 460 <br />flooding. <br /> <br />9300 to 9308 to provide storage <br />acre-feet and freeboard duri ng <br /> <br />o Construct RCC overflow dike spillway across existing spillway channel <br />with a crest elevation of 9303. <br /> <br />o Pl ace fi lter bl anket on downstream face and foundati on surface to <br />control and collect seepage. <br /> <br />o Install toe drain system to collect and discharge seepage. <br /> <br />o Flatten downstream slope to 2.5:1 with sand and gravel pit run <br />materi al . <br /> <br />o Grout dam foundation rock; <br /> <br />o Remove existing riprap and place soil cement for slope protection and <br />seepage reduction. <br /> <br />Seepage Reduction Options <br /> <br />1. Slurry wall through embankment. <br />2. Impervious upstream facing zone and blanket. <br /> <br />Spi 11 way Opti on <br /> <br />Construct earth dike across existing spillway channel and provide a <br />rock cut spillway on the right abutment of the dam. <br /> <br />=============================================================================== <br /> <br />In terms of embankment stability, the technical degree of confidence for this <br />alternative is high. Proper control, collection, measurement, and discharge <br />of seepage would significantly reduce its threat to the dam's safety. <br />Reducing seepage flow through the dam and foundation appears to be feasible <br />and will also enhance stability. <br /> <br />Replacing the outlet works structure entirely provides a high degree of <br />technical confidence. <br /> <br />-65- <br />