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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 />storage by 2400 acre-feet. The auxiliary spillway channel would be 150 feet <br />wide, the dam would be raised 10 feet, and the service spillway ogee five <br />feet. The estimated cost was $1,284,000. <br /> <br />The alternative designs were reviewed with the City in conjunction with the <br />results of the water analysis and it was decided to proceed with a <br />feasibility-level design for an enlarged Elkhead Lake Dam with the capability <br />of providing 2400 acre-feet of additional storage and the capacity to safely <br />pass the PMF without overtopping the dam, <br /> <br />The feasibility design consists of excavating an auxiliary spillway channel <br />and using the excavated material to raise the embankment dam 10 feet to <br />elevation 6385. The raised upstream slope and downstream slope would be 2.5H <br />to 1 V, The upstream slope woul d be protected wi th rip rap. The chimney <br />fil ter in the exi sti ng dam woul d be extended upward, and the fi nger drai ns <br />along the foundati on woul d be 1 engthened to the downstream toe to transmit <br />seepage. The outlet gate controls and housing would be raised, but no other <br />modifications to the outlet works would be required. <br /> <br />The concrete horseshoe-shaped ogee spillway crest would be raised five feet to <br />elevation 6370. The upstream portion of the spillway containment walls would <br />have to be raised, as would the bridge across the chute. The auxiliary <br />spillway would be an unlined channel 150 feet wide at the control section, <br />whi ch is a projecti on of the center1 i ne of the dam. The upstream end of the <br />spillway would be at elevation 6375 and would be flared. Downstream of the <br />contro 1 secti on, the chute woul d slope three percent and mai nta in a constant <br />width of 150 feet. <br /> <br />Raising the dam and excavating the auxiliary spillway would necessitate <br />interru~tion of traffic on the county road that passes over the dam. <br />Following conclusion of the modifications, the road would be realigned. After <br />passing over the new crest of the dam, the road would cross the upstream end <br />of the auxiliary spillway channel and rejoin the existing county road at the <br />top of the left abutment, <br /> <br />E-5 <br />