Using turbulence to guide salmon and eels away from turbines
Hydropower is an important source of renewable energy, yet dams and other facilities can represent a real threat to migrating fish like salmon and eels, with millions killed in turbines every year. Researchers in the FishPath project aim to exploit the innate response of fish to turbulence to develop an innovative system to guide fish away from turbines, as Dr Ana T. Silva and Dr Torbjørn Forseth explain.
A large number of dams and other hydropower facilities have been built on European rivers, and while they are a valuable source of renewable energy, they also represent a significant threat to migrating fish like salmon and eels. Bar-racks have been installed at smaller hydropower stations to prevent fish from entering turbines, however it has proved more difficult to find effective solutions for larger facilities, now researchers in the FishPath project are investigating a new option. “We are looking to exploit the innate behaviour of fish, their response to turbulent Eddies, to keep them away from turbines,” explain Dr. Ana T. Silva and Dr Torbjørn Forseth, the project’s leaders, and Senior Research Scientists at the Norwegian Institute for Nature Research (NINA). Turbulence itself is a very complex phenomenon, and researchers are looking to understand how fish respond to it. “Fish have several sensory organs that are able to track things like water velocity,direction of the flow and turbulence,” continues Dr Forseth. “Our expertise lies in looking at how fish respond to these very different properties of the velocity and turbulence.”
Understanding turbulence
A fish might look to exploit a turbulent Eddy in some circumstances, while in others they might avoid it, a topic that researchers are investigating in the project. The goal is to identify the specifications of turbulence that will either repel or attract fish and use that information to developed a new guidance system for fish, with a focus on European eel ( Anguilla anguilla), and Atlantic salmon (Salmo salar). In particular researchers are looking at salmon smolts, the stage in their lives when they prepare to head out to sea. “It’s very interesting to try and find out how fish respond to turbulence. Changes in one parameter lead to different behavioural response,” Dr. Silva outlines. A number of campaigns and experiments have been conducted with fish
under laboratory conditions at the Hydraulic Engineering and Water Resources Management at ETH Zurich, helping the project team build a fuller picture. “We follow a very detailed approach in the lab, where we test the fish for different structures that we know go into producing certain types of Eddies, and explore how the fish respond to them,” says Dr. Silva
-ADV) and an optical technology, (Particle image velocimeter - PIV), generating a lot of information about the hydraulic characteristics of these Eddies. The next step is then to understand how turbulence influences the path of fish, from which researchers can then look to develop structures which create the right kinds of Eddies to guide them away from the turbines. “Most of the water flowing in a river close to a hydropower dam goes into the turbines, and you need to establish a bypass outside that. The main challenge is to guide the fish across that flow to the safe channel,” explains Dr Forseth. The structure is likely to be placed quite a large distance away from the main intake to a hydropower station ( where the velocities are very high). “The typical water velocity in an intake channel is more than a metre per second, which is too strong for most of the species so we need to work at slightly lower velocities,” continues Dr Forseth.
“We are looking to exploit the innate behaviour of fish, their response to turbulent eddies, to keep them away from turbines.”
“We ran some experiments with salmon smolts, and eels, looking at different types of Eddies. We characterised the hydraulics and analysed data on the response of the fish.”
The project team has also conducted computational fluid dynamics (CFD) modelling and physical measurements using an acoustic technology (Acoustic doppler velocimeters
This structure will be rigorously tested under laboratorial conditions, at different scales, from small scale at the Hydraulic Engineering and Water Resources Management at ETH Zurich in Switzerland, to medium scale in the Laxelerator, flume at R&D Vattenfall, in Sweden, with the goal of conducting a full-scale test in the Mandal river in southern Norway in 2026. The Mandal
River did not attract salmon for a long time due to acidification, but the population has since recovered, now the aim is to provide safe passage past the intake to the Laudal power plant. “This is an example of the type of large hydropower station for which we need alternative solutions. We are targeting these larger facilities,” says Dr Forseth. The major focus of attention in the project is salmon and eels, but other migratory fish are also at risk, and Dr Silva is keen to look at whether this turbulence-based approach could prevent other species from entering turbines. “Hopefully we will have the opportunity to test this structure later on some cyprinids, a large family of carp-like fish that are common in Europe,” she says. “It is certainly possible that such structures could be used with other species. It will require certain adjustments and a deeper understanding of how these fish react to turbulence, but it’s something that we would like to look at in future.”
Protecting fish
The main target species at this stage is salmon however, with researchers working to achieve a high bypass rate. The initial results are very promising, and Dr Silva believes this structure holds a lot of potential in terms of reducing the numbers of salmon smolts killed in hydropower stations before they get out to sea. “Our findings so far suggest that this structure can lead to a very high rate of passage for salmon smolts past hydropower facilities,” she stresses. Eels
are proving more challenging, partly because less is known about them. “The general level of knowledge on the behaviour of eels is much poorer than it is for the Atlantic salmon, which is among the most well-studied fish species in the world,” says Dr Forseth. “We are still at a stage where we are trying to understand the fundamental response of the fish to the different turbulent Eddies. We know that specific types of turbulent Eddy influence fish, but the nature of that influence varies across different species, depending on their morphometrics.”
Other related projects are also ongoing, that will contribute to the wider goal of reducing the numbers of fish killed in hydropower facilities.“
For example we are working on using Artificial Intelligence (AI) to predict the paths of eels, which will then help us design more effective structures,” says Dr Silva. Researchers are also considering the characteristics of the fish at different life stages, with another project focused on kelts, large salmon. “A few salmon are able to return after spawning and prepare to spawn for a second or even third time. During this period of their lives salmon are called kelt,” explains Dr Forseth. “We are taking a similar approach to that followed in FishPath to understand how kelts react to hydraulics and how they can be guided away from the intake to a hydropower station. We are working on several projects in parallel, that we hope will open up some fresh insights.” says Dr Silva.
Observation of Vortices in Fluid Motion
Eddies in water were observed and first reported close to 500 years ago by none other than Leonardo Da Vinci. By describing the swirling water motion behind a bluff body, da Vinci provided the earliest known reference of the importance of vortices in fluid motion:
“Observe the motion of the surface of the water, which resembles that of hair, which has two motions, of which one is caused by the weight of the hair, the other by the direction of the curls; thus the water has eddying motions, one part of which is due to the principal current, the other to the random and reverse motion.”
“So moving water strives to maintain the course pursuant to the power which occasions it and, if it finds an obstacle in its path, completes the span of the course it has commenced by a circular and revolving movement.”
“... The small eddies are almost numberless, and large things are rotated
only by large eddies and not by small ones, and small things are turned by both small eddies and large” presage Richardson’s cascade, coherent structures, and largeeddy simulations, at least…”
Leonardo da Vinci was the first to sketch the water vortices that are now being used in the FishPath project. He was a pioneer in flow study and visualization with his sketches and observations.
FishPath
Turbulent eddies to create paths for safe downstream migration for salmonids and eel past hydropower intakes
Project Objectives
FishPath develops innovative eddy-based guidance structure to aid migration challenges, focusing on eddy-fish interactions. Using live-fish experiments and computational fluid dynamics models, we analyze eddies generated by specific structures to create guiding systems for salmon and eel. Flume experiments and live-fish trials refine designs, leading to full- scale tests in rivers.
Project Funding
This project was funded by the Norwegian Research Council (programme/activity ENERGIX; Project No.: 320700), with support from hydropower industry and the Norwegian Environment Agency.
Project Partners
Main Partners: • NINA • ETH Zürich • NTNU • NORCE • SINTEF Energy International Partners: • University of Michigan • Technical University of Denmark, DTU • Karlstad University Industry Partners: • Eviny, Fornybar Norge, Hafslund Eco, Sira-Kvina, Skagerak Energi, TrønderEnergi/ANEO, Å Energi, Vattenfall R&D, FishConsulting GmbH, Miljødirektoratet, Norges Vassdrags- og Energidirektorat (NVE)
Contact Details
Project Coordinator, Ana T. Silva Norwegian Institute for Nature Research – NINA Høgskoleringen 9, 7034 Trondheim, Norway T: +47 455 03 711
E: ana.silva@nina.no
W: https://www.nina.no/FishPath
Ana T. Silva is a senior researcher at the Norwegian Institute for Nature Research (NINA). With nearly two decades of experience, she has dedicated her work to developing innovative solutions aimed at ensuring the safe migration of fish within regulated river systems. Her efforts are geared towards minimizing the adverse effects of human-induced alterations on aquatic biodiversity.
Torbjørn Forseth is also a senior researcher at NINA with more than 30 years of research on salmonid fish ecology and management. He has been working extensively with solutions to environmental challenges in hydropower regulated rivers and during the last 15 years with innovative solutions for two way fish migration.
