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to conditions where pool regulation, upstream and downstream, is not • <br />possible. <br />2. Entrances for the Redlands site should be located downstream <br />from the spillway apron. Preliminary computations indicate that the <br />apron area will be flow depth and/or velocity barriers to fish passage <br />during low flow periods. Also, flows from the sluice gates may be a <br />velocity barrier depending on tailwater conditions. Therefore, location <br />of entrances with respect to the sluice gates should be carefully con- <br />sidered. <br />3. Trash and debris passing down the Gunnison River should be <br />diverted away from new structures to prevent damage. A trash shear boom <br />or trashrack/louver should prevent or reduce damage to fishway structures. <br />If a louver system is used, fish would be prevented from entering the <br />power canal or other undesirable areas. <br />4. The construction of structures in the river will change <br />existing flow patterns, so sedimentation impacts should be considered. <br />Some alternates may permanently block portions of the existing spillway <br />and cause sediment deposition upstream from the dam in the "still" water <br />areas. Also, the downstream side of a structure is usually where a gra- <br />vel bar (deposition) forms. Sedimentation problems should be reduced <br />through design or at least considered as periodic maintenance impacts. <br />5. A ladder structure that blocks a portion of the spillway <br />will reduce the flow capacity of the existing spillway. A preliminary <br />analysis of a shortened spillway should determine the effect of various <br />floods on the upstream water elevations and the dam itself. The fish <br />ladder operation will also be affected by the resulting increased <br />upstream water surface level. <br />IV. PRELIMINARY ALTERNATIVES. <br />A. Background Information. <br />In the early stages of this feasibility study, many varied <br />alternatives were considered. Nine alternates were reviewed at a scoping <br />meeting attended by representatives of the FWS and the U.S. Army Corps of <br />Engineers, Walla Walla District. The alternates were judged on the basis <br />of biological advantages and disadvantages, technical advantages and <br />disadvantages, effect of fishway operation on RWPC, and cost. <br />• <br />6 <br />