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screens that can be installed in a submerged location without mechanical cleaning were rated as the best potential device for this project. The two objectives for this project require two different screen alternatives, one that prevents escapement of all life stages and the second that protects to the current industry standard. In this project, impingement was deemed an acceptable consequence of in-reservoir protection. This allowed the evaluation of higher (2 ft./sec.) velocity fixed screens in this project for both objectives. In addition, for the protection to current industry practice option, a secondary protection mechanism was evaluated in each reservoir in addition to the fixed screens to protect at high flow events. Control structures are feasible at both reservoirs. The best location for the structures is on the primary outlet to the reservoir. To meet the criteria for full exclusion set in this study, the primary outlets for each reservoir would be reconstructed and. enlarged to safely discharge flows up to the 100 year event. The best screen type for these reservoirs is a fixed plate screen that functions while submerged. This is a cylindrical screen type with a pneumatic backwash system for cleaning. In addition, the reservoir level would be reduced by 1-3 feet below the spillway crest to prevent spills and escapement. There would be no additional screening protection on the spillway for this alternative. A The control type that meets the criteria for current industry practice is a cylindrical screen on the primary outlet in combination with a barrier net placed in front of the spillway. The primary outlet would require enlargement but would not pass all flows up to the 100 year event. High flows would be released through the service spillway of the reservoir. The escapement protection for these spills would be the barrier net, 1/4 inch mesh and suspended from the surface to the bottom of the reservoir. The net bottom is anchored to the reservoir bottom and weighted for its entire length to insure a complete seal at the interface between the net material and reservoir bottom. The cost for each of the options varied substantially. For full exclusion at Elkhead Reservoir, costs were estimated at approximately $33 million to exclude all life stages egg size and larger and pass the 100 year event. Capital costs for controlling at Elkhead Reservoir to the current industry practice were approximately $900,000.00. The main difference in cost being the small screen opening, larger screen area and physical dam modifications needed to control all flows through a screening facility for the full exclusion option. Control options at Highline Reservoir ranged from approximately $8 million for the full control option to approximately $300,000.00 for controlling to the current industry practice. The selection of an alternative control option at either reservoir should consider collecting additional data that was not available for this analysis. The main data needed includes escapement information of the species present in the reservoirs. Currently there is no escapement data collected at either reservoir or in the receiving streams below to determine the size classes, timing and the population size of the fish leaving the reservoir and resident in the streams downstream of the facilities. Further, there is little information to determine which of these species that leave the reservoir are successful in surviving and recruiting to adult stages and successfully reproducing in the rivers downstream. Annual escapement rates should be monitored to determine which control option would be most cost effective. The size class of fish leaving can greatly impact the cost of the selected facility. If only juvenile and adult sizes are leaving, larger mesh sizes can be used in the screens thereby reducing the cost substantially over the protection option for smaller, egg and larval life stages. Control Structure Feasibility Evaluation III Miller Ecological Consultants, Inc., February 18, 1997