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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 />classification allows for a lesser design flood. If the opposite were to occur, a flood <br />much larger than the 1 DO-year flood, the water would overtop the dam and likely <br />cause dam failure. The proposed spillway width would be 30 feet. The proposed <br />spillway would pass twice the 1 DO-year flood discharge with no freeboard, and the <br />1 DO-year flood with a minimum of 4 feet of freeboard between the maximum water <br />surface elevation and the dam crest. Figure 5 presents a typical cross section of <br />the spillway channel at the dam centerline. <br /> <br />A majority of the spillway would be excavated from native soils. It is <br />estimated that a significant quantity of sandstone and shale bedrock would also <br />require excavation. Sand and gravel deposited in the upper end of the existing <br />reservoir would be mechanically removed to stabilize the upper portion of the <br />lakebed and limit its washing into the reduced reservoir pool. The upper end of the <br />existing reservoir would be graded to direct sand, gravel and flood flows to be <br />carried over the spillway. Excavated soils would be disposed of on the bench south <br />of the reservoir. <br /> <br />Armoring of the channel is not expected to be necessary because the <br />spillway control and a significant portion of the outlet channel are founded on <br />bedrock. The detailed geotechnical investigation determined that the bedrock is not <br />easily erodable, so the control section of the spillway is not expected to require <br />concrete armoring. The spillway discharges directly back into the existing channel <br />at the south side of the valley below the dam, eliminating the need for a berm to <br />redirect flow to the natural channel. This project avoids the major cost of channel <br />stabilization by maintaining the channel in the existing location, which eliminates <br />the project design review by EI Paso County, and by utilizing excavated bedrock as <br />armor for the channel. Some future channel degradation may be expected. This <br />project does not address the issue of the access road erosion. The existing dam <br />and outlet work facilities would not be removed, thereby eliminating the costs <br />associated with dam removal and channel stabilization/restoration inherent with the <br />other alternatives. <br /> <br />32 <br />