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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 />Oa!lns <br /> <br />Appraisal-level designs and cost estimates were prepared at each dam site. In <br />order to determine storage volume and properly size the outlet works and <br />spillways associated with each structure, area capacity tables were <br />calculated, hydrographs were developed, and floods were routed through the <br />reservoirs. For the mainstem sites, dams were designed to store 50,000 ac-ft, <br />150,000 ac-ft, and 300,000 ac-ft. Either embankment dams or roller-compacted <br />concrete dams, or both, were designed at each site, depending on the <br />foundation conditions and material availability. Because lake Avery Oam is an <br />off-channel structure with reduced storage, potential dams were designed to <br />store 20,000 ac-ft, 40,000 ac-ft, and 60,000 ac-ft. <br /> <br />The following is a site-by-site sunmary of the conclusions regarding each dam <br />site studied. <br /> <br />lake Avery Dam <br />The subsurface investigation on the left abutment confirmed the existence of a <br />cap of relatively impervious transported material overlying the terrace <br />gravel s i dentifi ed by previ ous i nvesti gati ons. The thi ckness of the <br />impervious mantle ranged from two feet at the west end of the abutment near <br />the exi sting dam, to twenty-fi ve feet at the eastern end of the abutment. The <br />material in the western half of the abutment is a brown clay of low <br />plasticity. In the eastern half of the area studied, the clay is underlain <br />and inter-tongued with a light brown mottled silty clay. <br /> <br />It is not recommended that the silty clay be left in place as a foundation <br />materi al, because of its porous and coll apsabl e nature. The cl ay, on the <br />other hand, appears to have suffi ci ent strength to ti e into an impervi ous <br />embankment. In the case of a zoned embankment, however, the shell zone should <br />be founded on top of the underlying gravel. <br /> <br />The quality and thickness of the impervious cap should be sufficient to <br />provide an effective impervious barrier, if left in place. It is recommended, <br />however, that in areas where the natural blanket is thinner, it should be <br />augmented by an additional thickness of the same material borrowed from an <br />adjacent location. <br /> <br />E-5 <br />