Running The Dam Gauntlet

In the name of science, a rubber fish serves as stunt double

Every year in pageants that are as ancient as they are majestic, recently spawned salmon, steel-head trout and other fish make their way down the Columbia River, on the Oregon-Washington state border. As they do, they attempt to run a sometimes lethal gauntlet of six to eight hydroelectric dams.

The massive structures, including the legendary Bonneville Dam outside Portland, Ore., have elaborate and labyrinthine fish bypass systems to help the creatures past the turbines. Nevertheless, at Bonneville as many as 45 percent of the fish go through the turbines in the summer. The enormous, propellerlike blades, which can reach 75 revolutions per minute, are too large and slow to purée the fish. Rather they subject them to turbulence, rapid changes in hydrostatic pressure and strong shear forces. Of the creatures that go through Bon-neville, up to 12 percent perish as a result of their injuries—or, more likely, because they are no match for predators in their weakened state.

Now, in an effort to better understand the forces that affect the fish, engineers at Pacific Northwest National Laboratories (PNNL) are testing a six-inch-long, sensor-packed rubber fish that will act as their eyes and ears inside the turbine. They hope that data from the sensors will allow developers to make turbines that are more fish-friendly as well as more efficient.

The rubber-fish experiment is part of a U.S. Army Corps of Engineers study in which scientists are releasing live salmon smolts to make their way through modified and unmodified turbines. Equipped with radio transmitters, the fish are located and recaptured downstream and inspected for injuries. With these live fish, researchers see the results of the turbulent encounters but learn nothing of the forces that injure the creatures.

Out on the upper deck of Bonneville Dam on an early December afternoon, Thomas J. Carlson, manager of PNNL's sensor-fish project, strolled in a chilly rain, a rubber fish in his jacket pocket. "We're hangers-on to the biological testing program," he explains, waiting for a pause in the corps' live-fish experiment. Finally, he enters the plywood shed where test fish are released into tubes that guide them down into the turbine. A few tense moments pass as the fish at first refuses to power up. At last it's a go, and Carlson drops it down the tube.

Each sensor fish—at $5,000 apiece— does not swim; it just goes with the flow, measuring and storing information as it passes through the turbines. Inside are a pressure transducer and accelerometers that account for directional acceleration from gravity. Microprocessors inside the fish send digitized data from the sensors to onboard memory. Researchers download the data by plugging lead wires in the rubber fish's tail into the serial port on a desktop computer.

Fifteen seconds after Carlson releases the fish, its journey through the turbine is over. Moments later the radio crackles as technicians in patrol boats down at the base of the dam call in with good news. "We have the signal," a worker reports, much to Carlson's relief. Six chemically activated balloons attached to the fish have inflated to golf-ball size, bringing the sensor fish to the surface. "Sensor fish is in the boat," the radio chatters.

A successful release and catch is no small feat. The previous week, nylon lines connecting the balloons to the first two test fish sawed through one another, sending $10,000 down to the bottom of the Columbia. The project team, working feverishly over Thanksgiving weekend, used metal rings to attach the balloons more securely to the remaining fish.

Keeping the sensor fish's delicate instruments dry is another challenge. In fact, on this run the fish leaks, and the data are lost. "It's about as messy of a sensor job that you might want to do, outside of something in space," Carlson notes. The next day's run is more successful, generating good data.

The timing is perfect. The old federal hydropower system, an economic mainstay of the Pacific Northwest, where electricity rates are among the lowest in the U.S., "has been patched together over the years, and now it's time to replace the turbines and generators," Carlson explains. "This opportunity for rehabilitation comes around only once every 50 to 60 years."

Happily enough, it turns out that a more streamlined turbine blade design that creates less turbulence and more laminar flow is not only better for energy production but also better for the fish. As a result, Carlson says hopefully, modified turbine design may be "one of the few fish survival enhancements that can end up paying for itself."

—Pat Janowski at Bonneville Dam

PAT JANOWSKI is a freelance writer in Portland, Ore.

GOING WITH THE FLOW: A rubber fish records the forces that affect live fish when they swim through the turbines of the Bonneville Dam on the Columbia River.
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