Sensors the size of fish have been developed to measure the stresses placed on fish as they pass through the blades of hydropower turbines. Data from the sensors will be downloaded to help engineers design safer fish passages through hydropower dams. Courtesy of Daniel Deng/PNNL
Researchers send ‘sensor fish’ through hydroelectric dams to better understand the forces they encounter and to develop modifications to improve survival rates.
April 29, 2014—An international team of researchers is developing and testing a school of high tech “sensor fish” to more precisely record the significant forces that migrating fish encounter when passing through the turbines of hydroelectric dams. The team’s work will lead to engineering interventions that will make hydroelectric dams safer for fish.
Countries in Asia and South America are aggressively developing new hydropower facilities, capitalizing on abundant river resources. Hydropower is a highly cost-effective renewable energy source that is especially appealing to developing countries and is prized for its consistent power-generating ability. But the facilities can conflict with the migration patterns of such species as salmon, sturgeon, and catfish, many of which are either endangered or serve vital roles in local economies.
“Around the world, many big dams are being planned—the Mekong River, the Amazon River, the Yangtze River,” says Zhiqun (Daniel) Deng, Ph.D., the chief scientist of the hydrology group at Pacific Northwest National Laboratory (PNNL), in Richland, Washington. “Our goal is always sustainable hydropower. The ultimate goal is to maximize power generation while minimizing the ecological impact. I think every civil engineer wants to do that.”
Deng is part of an international team researching this issue. The team includes Richard S. Brown, Ph.D., a senior research scientist for PNNL, which is supported by the U.S. Department of Energy. Brown and Deng have traveled extensively to work with researchers from Australia and Laos, along the vast Mekong River, where 1,200 species of fish are found. The fish are vital, providing nearly 50 percent of the protein in most local diets and serving as an important cash crop as well.
Deng notes that although the survival rate of a species that migrates through a dam regularly is often documented, the mechanism of the injuries or deaths are more complex and sometimes not well understood. A better understanding of those mechanisms would enable the development of more effective strategies to enable fish to pass through the dams without harm.
“When a fish passes through the turbine environment, there are three main injury mechanisms,” Deng says. The first is pressure. The fish undergoes an increase in pressure in the intake followed by a sudden decrease around the runner blade. This rapid decrease in pressure could create barotrauma in which some species of fish suffer profound injuries to eyes, bladders, and internal organs. The second source of injury is the system of rotating turbine blades; the blades can strike a fish, creating severe injuries. Finally, fish can be disoriented or killed by the turbulence around the turbine.
“We developed this sensor fish to understand the physical conditions fish experience when they pass through the dams,” Deng explains. “We build the sensor fish so its weight and size are similar to a migrating young salmon. We have a lot of sensors so we can measure the pressure, the 3-D acceleration for the impact, and the 3-D rotational velocity.” The sensor fish are released into the water, pass through the turbines, and are collected on the other side. The data from the sensors is then downloaded and analyzed.
Deng says that the research has shown that different turbine types create different environments and risks for migrating fish. Prevalent in the Pacific Northwest, large Kaplan turbines—which are a propeller-type with adjustable blades—create fewer strike injuries because of their limited number of blades, for example. Francis turbines, conversely, are inward-flow reaction turbines—used widely around the world—that tend to create more strike injuries.
The picture becomes more complex because some species are more prone to barotrauma than others, and smaller fish slip more easily between the blades of a turbine than larger fish. Thus, a solution that works in one river and with one dam type might not directly address the problems of another.
“It’s a complex issue, but we are trying to have some framework to address this. One thing cannot address this alone. We require a marriage between biology and engineering,” Deng says. He notes that the research is aimed at finding the most economical, cost-effective solutions to the problem.
“When you have a chance to replace an old turbine, you can have a new design so that you can improve those areas accordingly,” Deng says. “If the pressure change is too large we can change the [lowest pressure] point. You can increase that point so the pressure change is not as severe. They can change the blade shape so the turbulence is smaller and the blade strikes could occur less often.”
Deng says bypass systems and diversions are also effective in sparing fish in some cases. Screens can keep fish away from the turbines while spillway weirs allow them a passage near the top of the dam,
The team recently published a paper on its findings, Understanding Barotrauma in Fish Passing Hydro Structures: A Global Strategy for Sustainable Development of Water Resources in the journal Fisheries, and a paper in the Journal of Renewable and Sustainable Energy, focusing broadly on creating sustainable hydro in the Lower Mekong River Basin.