RICHLAND, Wash. – When salmon swim through dam turbines, the changes in pressure can be catastrophic to their bodies. Researchers are trying to figure out how improve fish survival rates. And the U.S. Army Corps of Engineers is paying attention.
The science starts at the Pacific Northwest National Laboratory’s Mobile Aquatic Barotrauma Laboratory, a small trailer outside the lab’s new aquatic research center. Fish swim inside four oval tanks, each about as wide as a basketball hoop.
Research scientist Richard Brown can create different amounts of pressure in each of these tanks to simulate the pressure fish experience when swimming through a hydroelectric dam turbine.
“This is very unique because this is the only system that can preform really rapid decompressions across the whole broad range of pressure changes,” said Brown.
As fish swim toward the dam, pressure increases. But as soon as they pass through the turbine blade, pressure drops dramatically in seconds.
Fish experience something akin to the bends in divers.
“Salmonids, and a lot of fish we have, have a swim bladder inside them. That’s what causes the damage inside them when that expands and can rupture,” said researcher Brett Pflugrath.
The fish’s swim bladder is an organ that controls its buoyancy. Pflugrath points out a balloon in one of the pressure chambers. It represents a fish’s swim bladder. He begins to raise and lower the pressure.
“If we increase the pressure, that balloon will actually get much smaller,” Plugrath said.
He then decreases the pressure, and the balloon gets much larger. “Right now, it’s at about 1/3 the pressure we feel right now,” Plugrath says of the chamber.
Pressure changes vary between turbines. They also change depending on the depth fish are at when they approach dams.
Researchers can connect injuries they see in fish with different types of pressure changes, Brown said.
“So that when they build a new turbine, the pressure changes will be mild enough so that you won’t see injuries or mortality,” Brown said.
Dam turbines are built to last 50 years, said Shawn Nelson, a project manager with the U.S. Army Corps of Engineers. The Corps will replace turbines at Ice Harbor Dam, on the lower Snake River outside Pasco, Wash., in 2015. Engineers are using research from Pacific Northwest National Laboratory to design the turbines.
“50 years ago, the design tools they had then, versus what we have now, are quite a bit different,” Nelson said.
Engineers can run through multiple iterations until they create a model that has the most energy efficient and fish friendly turbines. Building and installing a turbine costs $20 to $25 million, Nelson said.
“We are seeing efficiency improvements. We are seeing fish survival improvements,” Nelson said. “From an environmental perspective, it’s a sustainable option. And from a power perspective, we’re gaining power.”