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Chapter II Description of Alternatives 18 similar to proposal No. 2A, but over two times more expensive. It was not considered for more detailed study due to its relatively high cost. This concept relies on withdrawing water through the top of the trashrack structure and through ports or windows provided in the top 54 feet of the trashrack structure. Proposal No. 2B is very similar to proposal No. 2A except that additional openings are provided in the sides of the trashrack structure to increase the operating range compared to proposal No. 2A. Using underwater construction methods, the top of the trashrack structure, elevation 3,652, would be removed providing a semicircular opening having an area of 318 square feet and a radius of 14.25 feet. Also, 15 ports,S per level with 3 levels, that are 13 feet high by 7 feet wide would be cut in the concrete walls of the trashrack structure. The elevation at the bottom of the lower ports would he at elevation 3,598. To force the flow through the top opening and through the ports, the top 37.5 feet of the existing trashrack opening would be closed and the lower 50 feet blocked by a relief gate. To close the upper portion of the opening, plates would be installed over the existing trashracks. The relief gate, which would be 50 feet high and semicircular in shape, would be installed in the existing stoplog guides. The relief gate would be designed with relief panels to protect the system and trashrack structure from excessive differential head. Unlike Proposal No. 2A, the relief gate would be suspended from wire ropes and operated by a hoist. To accommodate all of the equipment and to provide trashrack slots up to the surface, a hoist deck would be provided at elevation 3,715 and supported by columns down to the top of the existing trashrack structure. Port gates, 8 feet wide and 54 feet high, which would operate up and down in the existing trashrack slots, would be provided to block off the ports when they are not needed. Trashrack panels, 8 feet wide by 60 feet high would be attached to the top of the port gates. Like the relief gates, the port gates would also he operated by hoists. With the bottom of the existing trashrack structure blocked and the ports closed by the port gates, the warm surface water would be pulled from the top of the reservoir and into the semicircular opening similar to proposal No. 2A. These flows are protected by the raised trashrack panels attached to the port gates. As the reservoir drops and there is not sufficient submergence, the port gates are lowered to provide sufficient intake area. Eventually as the reservoir drops, the level would be below the top of the trashrack structure, elevation 3,652, at which time the total flow would go through the ports. If 40 feet of submergence is necessary, the system would be fully effective down to reservoir elevation 3,638 providing an effective operating range of 62 feet. During periods when selective withdrawal is not needed, the relief gate would be brought up and stored near the surface to conserve the warm water in the lake and minimize head loss. Proposal No.3 - Controlled overdraw through existing trashrack structure, The benefit of this proposal was an operating range of80 feet. The disadvantage of this alternative over proposal2A was its higher cost and complexity. This proposal was brought forward for more detailed cost analysis. The feasibility level cost estimate for this proposal is $44,500,000. The proposal is functionally similar to proposal 2A, but nearly three times more expensive. It was not considered further because of its relatively high cost.