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(b) Bar screen may be installed across all four power canal headgates. The head loss through the screens is approximately 0.2 foot with all gates fully open. This bar screen will not be installed until it is determined that the ladder successfully passes fish into the forebay. (c) The ladder structure blocks a portion of the spillway that would normally pass riverflows. Therefore, sediment may accumulate behind the diversion dam in the ladder and trashrack area. RWPC may be asked to open the sluice gates for the purpose of flushing accumulated sediment from behind the dam. (d) Construction of the fish ladder will only have minor impacts on RWPC. The bar screen installation, if necessary, would be scheduled to coincide with the dewatering of the potiver canal for maintenance. Also, the upstream cofferdam can be constructed around the ladder structure only and not interfere with the power generation and irrigation flows into the power canal. (e) The trash shear boom will reduce the. amount of trash and debris that RWPC must handle at the dam, in the power canal, and at the powerhouse. However, if the bar screen is added, a greater portion of the debris will be handled at the dam. Because of this overall reduction of debris, RWPC will still be responsible for debris removal. (2) Impacts Affecting FWS. (a) FWS will operate and maintain the fishraay facility. This alternate will require that fish be released from the trap periodically (check trap every day during migration season), weir boards be installed or removed, the auxiliary flow valve and entrance slide gates be adjusted, and debris be removed from the fish ladder trashrack. (b) Also, some maintenance of mechanical equipment (valve, slide gates, fish hoist) is required intermittently to keep these items in proper working order. 5. Estimate of Costs. a. Table 3, Estimate, Alternate No. lA, presents the materials and installation costs of the fish ladder, bar screen, and trash shear boom. At the feasibility study level, a contingency factor • of 25 percent is added to the materials and installation costs to account 21