Salmon get Gift from Corpsby Thomas P. Skeen
Walla Walla Union-Bulletin, March 7, 2005
A $20 million device being installed at the Ice Harbor Dam
will help ease smolts' trip to the Pacific Ocean.
BURBANK -- To appreciate what a new modified spillway at Ice Harbor Dam holds for young salmon, think like one.
Imagine yourself as a 4- to 6-inch smolt with no choice but to obey a primal urge to migrate down the Snake and Columbia rivers toward a destiny with the Pacific Ocean.
You're going with the flow with other smolts, swimming at your normal depth of 10 to 15 feet. Then the current you've homed in on leads to something nature never programmed your species to negotiate.
In this case, that something is a concrete edifice built by the U.S. Army Corps of Engineers that spans the Snake River upstream from Burbank in Walla Walla County.
Suddenly, what was a gentle current in the Lake Sacajewa reservoir now feels like a powerful hydraulic vacuum pulling on you as you near the spillway. Overcoming your swimming ability, the faster current rapidly sucks you down 50 feet below the reservoir surface into the entry of the enclosed chute.
Tumbling in the turbulence as you plunge through the guts of the structure, the passage through the dam ends when you're flushed into a downstream pond.
If you're among the 98 percent of smolts that enter the spillway system and survive, according to government fish monitoring counts, you get to do it all over again four more times through different dam configurations on the Columbia River as you continue to the ocean.
But you may not be in as good a shape as you were when you started out.
The effect of clashing currents and pressure changes on smolt depends a lot on reservoir levels, water temperatures, flow volume and at what point they enter the spillway, says Ice Harbor biologist Mark Plummer. He says he's seen smolt come through in good condition, while others might have their eyes bulging out after being unable to adjust to varying pressures.
"It's kind of like having the bends for a diver," Plummer says.
The spillway turbulence also causes greater mixing of water and air, heightening levels of dissolved atmospheric gases in the river that can disorient fish and make them easier targets for predators downstream.
It's a trip that 3.5 million salmon and steelhead smolt faced last year as they made their way through some or all of the Corps' four lower Snake River dams, according to the Northwest Power and Conservation Council's Fish Passage Center in Portland. The center provides fish data to state, federal and tribal organizations that monitor salmon runs.
Another 19 million were spared the perils, having been captured at collection sites above Lower Granite Dam, the most upstream of the Snake River dams. Those yearlings were transported by truck and barges to be released below Bonneville Dam on the Columbia River.
David Hurson, the Corps' Walla Walla District fisheries biologist, says that of the smolt that pass through the Snake River dams, about two-thirds go through spillways. Others find their way through surface water bypasses or hydroelectric production intakes, where screens route them away from turbine blades.
Although spillway survival is high, smolt passing through Ice Harbor should have a less stressful journey this year. That's the aim of the $20 million device the Corps is currently installing at the 44-year-old dam.
It's called a "removable spillway weir," and it changes the existing spillway configuration to make it more like a water slide for smolt than a plunge down Niagara Falls.
Seventy-feet wide, tall as a 10-story building and weighing 850 tons, the steel behemoth has been two years in the making. It was assembled in Vancouver, Wash., and barged upriver through Ice Harbor's navigation lock in late February.
Plummer says it will be sunk into position and attached to the dam in time for biological testing when the annual smolt migration starts in April.
Its removable feature - the weir remains attached but can be lowered out of position - will come into play should river flows reach levels requiring greater spillage to prevent breaching of the dam's earthen section.
Plummer says a key feature of the weir is that it allows smolt to enter the dam at their typical 10- to 15-foot swimming depth, eliminating the rapid pressure change they endure while being drawn into the deeper entrance of the original spillway.
The higher entry level also means less water is needed for fish passage - 12,000 cubic feet per second compared to 280,000 cfs through the original spillway. And with less water there comes less turbulence and lower levels of dissolved gases, Plummer adds.
Another benefit the Corps touts is that the water the weir will save can be put to other uses for which Ice Harbor and its companion dams on the Snake River were designed.
The dams were built in the early 1950s through the mid-1970s with locks to extend commercial navigation inland from the Pacific Ocean to Lewiston. Though to a far lesser extent than their Columbia River cousins, they also generate hydroelectric power and provide crop irrigation.
However, with increasing environmental and political pressure in the 1990s to protect and restore salmon runs or risk removal of the dams, the Corps has put fish-saving innovations on the front burner.
Installing diversion screens over water intakes for hydroelectric generators to channel smolt away from turbine blades was among early efforts. Last year the Corps built a collection and bypass system at Bonneville Dam to route smolt down a chute and deposit them more than a half-mile downstream in faster-moving water, away from predators that feed in pools below the dam.
The result of those and other improvements in the river system have been four consecutive years of the highest returns of adult wild and hatchery spawners since the late 1930s. But Corps and federal fisheries experts are quick to say the larger runs also have much to do with improved conditions in the ocean for Pacific salmon and stricter harvest regulations.
"There are more fish in the Snake River system today than there were before these dams were built," says Walla Walla District Corps spokeswoman Nola Conway, who recalls times as a girl growing up in the region when the river sometimes was not much wider than a big creek.
But some groups with a stake in protecting Pacific Northwest salmon runs have yet to fully embrace Ice Harbor's new spillway weir, similar to a prototype installed in 2001 at Lower Granite Dam near the Idaho border.
"It looks like it could have some promise for spring migrants," says Bob Heinith, hydraulic program coordinator for the Columbia River Inter-tribal Fish Commission. "But we don't really see any survival or passage advantages over what is there now."
While smolt will no longer have to undergo the stress of being pulled down to the original, deeper spillway entrance, he says, they will be passing through the dam from a greater height.
"It's described as a fish slide, but the fish are sliding a much longer distance," Heinith says. "We're not sure what that could mean."
And with only two years of data collected at Lower Granite's prototype weir - salmon spend one to five years at sea before returning upstream - he says it's too early to say how successful the innovation might be.
"There should be full testing at Lower Granite before we go forward with any more of these," Heinith says.
In the meantime, he adds, the Corps could better use the $20 million spent on the Ice Harbor weir for backlogged fish-passage maintenance and proven enhancements elsewhere on the river system.
Conway, however, says construction is already under way for another spillway weir to be installed in 2007 at Lower Monumental, the dam upstream from Ice Harbor. Federal funding for a weir also is being sought for the next upstream dam, Little Goose.
For Columbia River dams, she adds, the Corps is already developing plans for weirs and other surface bypass systems.
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