Measuring water flows to help fish at hydropower plants

Researchers from Luleå University of Technology recently visited Karlstad University to measure water flows in specially constructed channels. The purpose is to understand how fish, such as trout, respond to changes in currents and how fish passages can be improved to facilitate fish migration around hydropower plants.

This autumn, Sofia Larsson, Associate Professor in Fluid Mechanics at Luleå University of Technology, has collaborated with researchers in ecology and biology at Karlstad University to study water flows and fish behavior. In Karlstad, researchers have built channels that simulate natural fish habitats, studying, among other things, how trout react to different flow conditions. Through these studies, the researchers hope to gain a better understanding of how fish passages, specially designed structures that help fish bypass hydropower plants, can be improved. Sofia Larsson conducted her measurements using an advanced optical method called Particle Tracking Velocimetry (PTV), which allows for precise capture of water movement in three dimensions, gathering large amounts of detailed information.

A Lot of Information at Once

"PTV provides us with all three velocity components in a volume, meaning we get a lot of information at once," explains Sofia Larsson. The PTV system is funded by the Kempe Foundations and Luleå University of Technology's lab fund.

In the specially constructed channels, researchers measure how different water flows impact trout behavior. The research aims to find connections between fish behavior and different flow conditions, such as how they choose to swim at different speeds and how they utilize energy.
"We hope to observe how fish respond to different flow conditions and draw conclusions that can help us improve fish passages," says Sofia Larsson.

Sofia Larsson, Assistant Professor at Luleå University of Technology.

Combining expertise in ecology, biology and technology

The project "Fauna Passages – Hydraulic Functionality for Good Ecological Status" is funded by the Swedish Energy Agency through the innovation program Sustainable Hydropower (HÅVA) and is a collaboration between Luleå University of Technology, Karlstad University, and the Swedish University of Agricultural Sciences in Umeå. The long-term goal of the research is to improve the design of fish passages so that fish can more easily bypass hydropower plants both upstream and downstream. These passages are crucial for preserving fish populations in waterways where hydropower plants often hinder fish migration.
"We combine our expertise in fluid mechanics with the biologists' and ecologists' knowledge to truly understand how we can create technical solutions that benefit both the fish and the environment," says Sofia Larsson.

The next step in the project is to process the collected flow data and compare it with the results from observations of fish behavior. The aim is to contribute concrete recommendations on how fish passages can be improved. The project will continue through the end of the year and is expected to provide important insights into how best to design environmental measures at Swedish hydropower plants to protect fish populations.

While Sofia Larsson conducted her measurements in the channels, Gunnar Hellström and Anders Andersson, both Associate Professors in Fluid Mechanics, and Senior Lecturer Robin Andersson were also on-site in Värmland, inspecting fishways in another work package within the same project.

• Fluid mechanics