Lower Granite Offers Salmon New Routeby Mike Lee, Herald staff writer
Tri-City Herald, April 14, 2002
LOWER GRANITE DAM -- If the behemoth structure under Kevin Crum's feet was stood on end almost anywhere in the Mid-Columbia, it would rank as one of the region's tallest buildings.
The "removable spillway weir" -- known as the RSW to the acronym-prone Corps of Engineers -- would reach three-fourths of the way up the 150-foot water tower on Road 68 in Pasco. And it takes up more space than 200 parked transit buses.
As is, the weir is mostly submerged in the lower Snake River canyon on the reservoir side of the first dam that millions of juvenile fish encounter on their journey from Idaho to the ocean.
And Crum hopes the new multimillion-dollar structure makes that trip a little easier.
It's the kind of contraption that environmentalists are apt to criticize as "gold-plating" dams that they think should be removed to create a free-flowing river.
But the weir has high-level supporters, including the regional administrator of the National Marine Fisheries Service, who singled it out on a recent trip through the Tri-Cities as a potential bright spot in efforts to balance the needs of salmon and against the demands of power production.
If the weir helps salmon and steelhead, it could be adopted all the way down the federal system of eight dams on the Snake and Columbia rivers.
And if that happens, the region could produce power with a substantial amount of water that currently is spilled instead of turning turbines.
Preliminary testing started last week on the 2-million-pound apparatus, which cost $11.5 million to build, barge and install at Lower Granite. It's designed with ballast tanks to submerge in the Snake if extraordinary floods are expected.
For the next several weeks, U.S. Geological Survey technicians will insert radio transmitters in tiny migrating fish, cart them back upstream and track their journeys past the dam using equipment stored on three boats that float near the rush of water crashing down the face of Lower Granite.
After perhaps just two years of testing, the region will know if it has a winner in the spillway weir.
In 2000, the National Marine Fisheries Service decided against tearing out Lower Granite and its three sister projects on the lower Snake in favor of pursuing a vast array of habitat improvements and technological upgrades.
The weir is a possible solution to slowed fish passage at dams and to the kind of stress endured when finger-length salmon dive through standard spillways. The concept proved attractive during a five-year test at Lower Granite with another prototype device, the "surface bypass collector."
Now near the end of its useful life, the rusting bypass collector confirmed for regional fish experts an important facet of fish behavior in the late 1990s.
"It became apparent that the surface flow conditions were the most effective," said Crum, manager of the weir project for the Corps. "If we hadn't done all that testing, we wouldn't be standing on this weir."
That is to say, young fish appear to prefer to travel near the top of the river and when possible they will stay there.
The bypass collector showed that 30 percent to 40 percent of the fish approaching the dam would follow just 3 percent or 4 percent of the flow over the dam. "It more mimics natural fish behavior," said Nola Conway, Corps spokeswoman.
Such efficiency was alluring to scientists and prompted development of the weir, which allows fish to slide down the face of the dam in a rush of frigid water.
Otherwise, fish have three options: They can go through the turbines, a route generally deemed the least healthy; they can be diverted into the juvenile bypass facility and loaded into barges, a controversial measure; or they can use standard spillways, a route favored by many and previously the closest thing to natural conditions.
The trouble with existing spillways -- designed initially to pass flood waters -- is that their openings are about 50 feet below the reservoir surface.
"The spillways were obviously never designed with fish passage in mind," said Tim Wik, Corps fish biologist.
Fish diving to use the spillways are subjected to much higher water pressure and water velocities than they are used to. That can leave them disoriented and easier prey for birds that gather at the face of the dam.
There's also been substantial concern about atmospheric gases that are dissolved in river water by the spill, something the Corps has addressed with a spillway attachment called a flow deflector.
The weir offers another route, essentially a man-made waterfall that cascades from the top of the reservoir to the tailrace below.
No big pressure changes. And no deep-river searches for an opening.
"This is really the first attempt to alter the original spillway design," Crum said.
The weir was barged upriver from Vancouver last summer, and a short test was performed in November to make sure it didn't cause unanticipated fish deaths.
Wik said early results show weir-passed fish have roughly the same mortality -- about 2 percent -- as they do in the standard spillway. What isn't known yet is how much more quickly salmon will get past dams if they take a more natural surface route.
Preliminary biological tests were run last week and the full-scale effort starts this week as the annual salmon migration starts to pick up steam. "This is probably as comprehensive of a test as you will find anywhere," said Wik.
Corps officials shy away from talking about power benefits of the new spillway system, in part because they want to keep the focus on salmon.
"We didn't go out to try to develop something that would use less water for power production," Conway said. "One of the benefits just happens to be for power."
Besides, there's relatively few specifics about large-scale power advantages, given all the possible configurations of the hydrosystem.
"It's a little harder to figure out some of the big-picture questions," Wik said. "We haven't really looked that far."
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