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Rotating Fish De-watering Screen, Lower Granite Dam

The Rotating Fish De-watering Screen Prototype is located at McNary Dam in Eastern Washington. The purpose of the prototype is to test the reliability, effectiveness and effects on fish of this concept for concentrating juvenile salmon for transport downstream by barge. Existing fish screening methods in place utilize flat panels to divert juvenile salmon from the turbine intake flows and direct them to a fish collection facility. From this point they are barged and moved downstream past the remaining dams on the Columbia River System. These flat panel screens are currently cleaned with an automated brush system which has proven ineffective and has led to excessive debris loads and damage to the screens. The prototype seeks to eliminate this problem by utilizing a rotating screen that is cleaned by overhead high pressure water jets.

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The screen itself is comprised of wedge wire screen panels supported on a cylindrical framework. This framework is then supported by four wheels which are each driven by variable frequency motors. The motors are synchronized via torque balancing to obtain smooth rotation of the screen. The prototype screen is 4 feet in diameter and 24 feet long. The rotating screen is cleaned by high pressure water and its position in the water stream can by controlled through the actuation of two pairs of screw jacks. The prototype includes inlet and drain plumbing, valves and structures for inserting and removing test debris and fish to the stream. Stream flows are on the order of 60 cubic feet per second.

Lund Engineering, Inc was responsible for the design and engineering of the screen, screen supports, the screen drive system and controls, the high pressure cleaning and debris removal system, and the screen positioning jacks and controls.