7845 - Laserfiche WebLink

Home Browse Search

i?. usual downstream passage facilities. Most screening facilities have some sort of safe passage feature for the fish to move safely around the dam or diversion structure and back to the receiving stream downstream of that structure. + This project has several features which make the selection of feasible control options unique. The current technology includes both physical and behavioral techniques to control fish passage. In this case,-the behavioral techniques will not stop the passive life stages that may be present and are only marginally effective on controlling active life stages. For these reasons, behavioral techniques were not considered feasible control options at either Elkhead or Highline reservoirs. hi s study Physical control devices include several types of screening devices. Since the objective of t is to control escapement, the best location for controlling the fish is within the reservoir. Any device placed downstream of the reservoir would require construction of a stream channel and physical screening facility large enough to protect to the maximum flow event. Further, the facility would need to be designed to function at the current industry standard for the full range of flows. The wide range of flows from flood flows to near zero would be very difficult to protect with one facility. This may require one facility designed to work at high flows and another to work at the low flows. Further, any fish that get to the downstream facility are already moving toward habitat occupied by the endangered fish species. Any facility downstream of the reservoirs also would require a fish bypass or collection facility and some type of fish handling or disposal. All of these factors eliminate the downstream location as a feasible option. Physical facilities designed for in-reservoir control include both high velocity and low velocity screens. Both the high and low velocity screens constructed in the reservoir would have to be designed to operate for the full range of flow conditions. High velocity screens include Eicher and Modular Inclined Screens. Both of these screen types are intended for use within a reservoir outlet or penstock and both require fish bypass. To meet the criteria set for this study, the reservoir outlets would have to be reconstructed to a size that would pass all flow up to the 100 year event and include the screen. The fish bypass would require a fish collection facility that could retain any bypassed fish for either disposal or transport back to the reservoir. This would require additional operation and maintenance funds for the life of the project. This additional cost in excess of the capitol cost for reconstruction of the outlet works and requirement for fish handling makes these screen types lower priority for selection than types that have no fish bypass or fish handling . Low velocity screens include traveling and fixed screen types. The traveling screens all require considerable operation and maintenance costs. In addition, there is a possibility that escapement can occur as screen seals wear. The gap between the screen and the seal could exceed the 3/32 inch opening for the criteria for this project. This would not meet the exclusion criteria for the project. The traveling low velocity screens would require a large screen face relative to the flow rate ratio and do not work in a submerged location. The large size would require considerable capitol cost for construction of the civil works associated with these types of screen and high annual operation and maintenance costs. Therefore, traveling screens were not selected for further evaluation in this project. Fixed screens are generally designed for low approach velocities to eliminate fish impingement. Most fixed low velocity screens have a traveling brush to clean the srceen face of debris. Any such mechanical device requires additional maintenance over an non-mechanical system. Therefore, fixed Control Structure Feasibility Evaluation II Miller Ecological Consultants, Inc., February 18, 1997