#4. Rocky Reach juvenile fish bypass installation — forebay pile | |
Project address: |
Every year, up to 6 percent of the salmon and steelhead runs perish in the turbines in their seasonal migration to the sea. To deal with this conservation challenge, the district was faced with a choice: Either spill 40 to 50 percent of the water by the dam, at a cost of reducing power generation by $25 million a year; or construct a pipe around the turbines through which fish could pass through unharmed. The fish bypass was determined to be the most cost-effective solution to this environmental problem. The project has two parts. First, the fish are collected in the forebay, or upstream side of the dam. The second part involves transporting fish through a 4,600-foot bypass conduit to a discharge point in the tailrace, or downstream side of the dam. Traylor Pacific is constructing the forebay fish collection system. This work involves many technical challenges, since much of the work is under water. Existing surface collectors and intake screens were demolished, and several thousand tons of steel and concrete structures are being placed below the river. Pilings were drilled into the bedrock below the Columbia River, and a gigantic steel lattice with a concrete base weighing more than 5 million pounds was lowered into place last November. Very large pumps will create water flows of up to 7,000 cubic feet per second, attracting the fish into the conduit.
The juvenile fish run is anticipated to begin next spring, and the entire project will be in place by then to accommodate migrating fish.
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