Turbulent eddies to create paths for safe downstream migration for salmonids and eel past hydropower intakes

Fish on their downstream migration in rivers often encounter hydropower dams and intakes and tend to follow the main flow into the turbines where they may be injured or killed. While fine-meshed racks and bypass constructions can prevent fish from entering, they are costly and challenging to construct and operate in larger systems. Thus, many hydropower facilities have no or poor protection systems for downstream migration fish. There is a need to develop alternative guiding systems that are cost-effective and easier to operate. Via their sensory systems, fish can detect turbulent movements (eddies) in the water and respond by avoiding them or by exploiting the eddies for swimming. In FishPath we are using these abilities to develop turbulent eddies based guiding structures for salmon, trout and eel. As a start we have developed and successfully validated a computer model system to study the eddies created by a reference cylinder. We proceeded to model the eddies created by a hydrofoil with different appendices (mounted on the hydrofoil) to check which configurations that provides the type of eddies that may guide the fish. Next the behavior of the eddies will tested in a small flume. In 2022 we will study how fish respond to such eddies in live-fish experiments. Next, we need to align the objects that produce the desired eddies to create a fish path that the fish will follow, also explored by modelling and experiments. Once the candidate guiding systems have been developed their ability to guide fish will be tested, first in a relatively small laboratory flume, next in a large flume and finally the most promising in a full-scale prototype test in a river with a relatively large hydropower intake. Results will be compiled in a practical guideline for eddy based guiding system, where we will also explore how the knowledge on turbulence and fish can be used in mitigation of other migration challenges (e.g., upstream migration).

Fish on their downstream migration in rivers often encounter hydropower dams and intakes and tend to follow the main flow into the turbines where they may be injured or killed. While fine-meshed racks with a bypass can prevent fish from entering, they are costly and challenging to install and operate, particularly in larger systems. Thus, many hydropower sites have no or poor protection systems for downstream migration. Despite recent promising results on fish guidance racks, there is a need to develop next generation systems that are cost-effective, easier to operate and provide high guidance efficiency at low power production losses. Via their sensory systems, fish can detect turbulent circular currents (eddies) in the water, and respond to them either by avoiding or by exploiting them for swimming. In FishPath we will utilize these abilities to develop turbulent eddies based guiding system for salmon, trout and eel. To do so we first need to explore the behavior of eddies created by different objects (e.g. cylinders and hydrofoils) in the flow and how the fish species respond to different types of eddies. The behavior of the eddies will be studied by computational modelling and experiments in small flumes. The responses of fish to different eddies will be explored in a series of fish flume experiments. Next, we align the objects that produce the desired eddies to generate fish paths for the fish to follow, also explored by modelling and experiments. Once the candidate guiding systems have been developed, their efficiencies to guide fish will be investigated first in a medium laboratory flume and then in a large flume. Finally, the most promising system will be tested in the field at a relatively large hydropower intake. Results will be compiled in a practical guideline for design of eddy based guiding system, where we will also explore how the knowledge on turbulence and fish can be used in mitigation of other migration challenges (e.g. upstream migration).