U.S. awards $1.8 million weir contract for 980-MW McNary

The Corps of Engineers has awarded a $1.8 million contract to Tri-State Metal Fab Inc. to build a temporary spillway weir as a prototype fish bypass structure for the 980-MW McNary project on the Columbia River in Washington.

The Corps said the temporary spillway weir at McNary Lock and Dam would help it develop information for improving downstream passage conditions for juvenile salmon and steelhead in the Columbia. (HNN 10/23/06) Tri-State, of Spokane, Wash., is scheduled to complete the work in March, followed by biological testing in spring and summer 2007, the Corps said.

�The prototype weir will allow flexibility in testing to help determine the best location and flow to attract juvenile fish to the bypass entrance,� Ken Hansen, the project’s hydraulic engineer, said. �The information we gather in testing the weir will help us make informed decisions as we design permanent surface bypass systems for McNary.�

The new weir is different from past weirs the Corps has built, including removable spillway weirs already installed at its 810-MW Lower Granite and 603-MW Ice Harbor dams. A third removable weir, for 810-MW Lower Monumental, is scheduled for delivery and installation in February. (HNN 9/5/06) That weir is �removable� by controlled descent to the bottom of the dam forebay.

At McNary, the temporary spillway weir is a component of a two-year testing program for acquiring information prior to installation of a more permanent system, the Corps said. The 35-foot-tall, 50-foot-wide steel structure will weigh about 250,000 pounds, and can be fitted into any one of McNary’s 22 spill bays to create surface spill.

Juvenile salmon and steelhead using the surface bypass route will pass the dam near the water’s surface, under lower accelerations and lower pressures than otherwise would be possible, providing a more efficient and less stressful route while reducing migration delays at the dam.

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