Steel Curtain Designed To Preserve Young Salmon Huge Device Will Extend 80 Feet From Face Of Lower Granite Dam
The U.S. Army Corps of Engineers is assembling a steel curtain that will stretch 1,100 feet upstream and reach as deep as 80 feet from the face of Lower Granite Dam along the Snake River in an effort to revive the river’s imperiled salmon and steelhead runs.
The $11.2 million steel curtain will weigh 4 million pounds.
Corps officials and others hope the curtain, known as the “behavioral guidance structure,” will steer young salmon and steelhead migrating downstream into the floating surface collector at the dam west of Pullman.
The collector, which weighs 2,500 tons, functions like a steel chute to sweep the young fish over a spillway and around the dam’s turbines.
Brayton Willis Jr., the corps’ project manager at Walla Walla, said the curtain will be in place by April 1. That is usually when the small fish begin reaching Lower Granite, the first dam they encounter on their seaward migration.
The corps has spent about $42 million on the experimental surface collector, which is also anchored to the upstream face of the dam. Another project has added a 25-foot-deep scoop of steel to its bottom to help collect more of the fish that otherwise would pass through the dam’s turbines.
The floating surface collector is an attempt to duplicate the design of Wells Dam on the Columbia River. That dam, which has its spillways directly above the hydroelectric turbine intakes, is among the best at safely passing young fish.
It uses a relatively small volume of water to collect and divert the young fish around the dam’s turbines.
But there is a hitch. The new, improved surface collector and its steel curtain will have to outperform the old one to convince state and tribal fisheries managers.
“If there isn’t a radical improvement, we don’t see justifying spending any more money studying it,” said Stephen Pettit, the Idaho Fish and Game Department’s staff fisheries biologist at Lewiston, who monitors the conditions affecting salmon smolts.
If the curtain and collector can collect 80 percent of the young salmon and send them safely over the dam’s spillway, Pettit said, it would be encouraging.
So far, the device has not come close. The surface collector study ends this year, although there is talk of extending the work.
xxxx HOW IT WORKS The curtain is designed to steer steelhead and salmon into a collector, which functions like a steel chute to sweep fish over a spillway and around the dam’s turbines.