Studies to Establish Design Criteria for Fish Passage Facilities:
Prototype Testing of a Cylindrical Dewatering Screen at McNary Dam 2001-2002

Video Files

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Video 1 This evaluation of a prototype cylindrical dewatering screen was conducted by National Marine Fisheries personnel and funded by the Walla Walla District of the U.S. Army Corps of Engineers. Overhead views of the test area are shown, with individual views of the following components: 1) the approach flume, where the test fish and debris are introduced; 2) the entrance transition section; 3) the cylindrical dewatering screen; 4) an exit transition section; 5) a secondary dewatering area; 6) the fish collection area. Video 2 Small schools and individual fish are shown exiting the cylindrical dewatering screen. These test fish are juvenile Pacific salmonids (Oncorhynchus spp.) collected from gatewells at McNary Dam. The fish drift downstream with the flow, typically in positive rheo-taxis orientation. A few fish actively swim against the flow and move upstream. Video 3 Water at the surface inside of the cylindrical dewatering screen is shown, and fish and debris are seen moving downstream. No fish impingement occurs, and most vegetation is carried along with the flow. Debris builds up in about the last 20 cm of the screen, but it eventually reaches a point of accumulation that enables the flow to sweep it downstream. Fish do not appear to be adversely effected by the debris buildup. Video 4 An overhead view of the variety of debris being swept downstream with the flow. Types of debris include aquatic vegetation, pieces of thistle, and leaves. Very little debris impinges on the walls, except at the exit point of the cylindrical dewatering screen. Video 5 Debris passes downstream through the screen and accumulates at the exit point. This debris is a mixture of aquatic vegetation and pieces of thistle. As the screen rotates, a small amount of debris is removed from the flow and deposited in a debris trough running along the top of the cylinder. Approximately five gallons of debris is removed for every 200 gallons tested. Video 6 Debris passes downstream through the screen and accumulates at the exit point. This debris is a mixture of aquatic vegetation and leaves. The screen rotates and removes small amounts of debris. Video 7 Debris passes downstream through the cylindrical screen and accumulates at the exit point. This debris is a mixture of woodchips and aquatic vegetation. The screen continues to rotate, but it removes only a small amount of this debris. Video 8 Wood chips pass through the cylindrical screen and accumulate at the exit point. The screen is not rotating during this part of the evaluation. Woodchips are semi-buoyant and impinge readily on the bottom of the screen. The pile of chips increases quickly. Most other types of debris quickly accumulates to a point where sufficient surface area exists for the flow to sweep the debris pile downstream, even when the screen is not rotating. The stiffness and irregularity of the woodchips allow sufficient flow through the pile to continue accretion. The last two screen sections were completely covered to a depth of nearly 15 cm. Video 9 Overhead view of woodchips passing through the cylindrical screen and accumulating at the exit point. The screen is not rotating during this part of the evaluation. Water depth is about 0.4 m, and a small school of subyearling chinook salmon (fork length around 110 mm) move downstream through the screen. The fish appear to be swimming well under control with no sign of impingement as they approach and pass the accumulation of wood chips.

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last modified 10/06/2006