U.S. Army Corps Hires
by Samantha Bates
WALLA WALLA - The U.S. Army Corps of Engineers has announced a $1.8 million contract with a Spokane company to build a temporary fish bypass system for McNary Dam.
Tri-State Metal Fab Inc. will build a temporary spillway weir that will be used to find the best route for juvenile fish through the dam.
The temporary system will be cheaper in the long run because it will allow a permanent one to be more efficient, said Gina Baltrusch, public affairs specialist for the Corps of Engineers.
"We'll be able to make some determinations on where fish like to pass," she said.
The weir will be about 35 feet tall, 50 feet wide and will weigh about 250,000 pounds, the Corps said. It is different from other spillway weirs in that it will fit into any of McNary's 22 spillways. It is expected to be completed in March.
But during its test period of two years it will be slotted into just a few of the 22 spillways. Baltrusch said tests already have been completed that show the general area where fish prefer to pass the dam. The weir will determine which of those spillways is the most efficient. That way, when the Corps installs a permanent weir, it will be in the best location. The more permanent structure is called a Removable Spillway Weir. Such a structure was installed at the Lower Granite Lock and Dam on the Lower Snake River in Washington in 2001.
That weir installs into a spillway and is removable during flooding events. The weir allows for juvenile fish to pass through the dam by surface flow. On its Web site, the Corps said juvenile fish prefer surface flow passages over "existing pressurized 50-foot-deep flow under current spillgates."
By having a system that is easier for the fish to use, it will reduce migration delays at the dam and allow more fish to pass.
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