Attraction channel as entrance to fishways

Abstract: The utilization of rivers for hydropower production leads to problems for fish migration. Migratory fish that swim upstream for reproduction need to overcome obstructions to reach their spawning grounds. On their way upstream they follow high water velocities. Since most of the water in regulated rivers flow through the power plants the fish is often attracted to the turbine outlets. To guide the fish past the power plants, fishways are often used. However the efficiency is often low due to inefficient attraction water. An attraction channel that uses a small fraction of the tailwater, or any free stream, is studied. The channel is open and U-shaped. A local acceleration of the water is created by changing the cross sectional area in the downstream end of the channel. The flow in the channel is measured with LDV in a lab setup to examine the acceleration of the water, and in full-scale to investigate the fish tendency to use the channel. The results show that the velocity out of the channel can be as much as 38 % higher than the approaching flow. The acceleration is detectable downstream the channel up to 18 times the exit water depth of the channel. The results from the field work shows that fish do use the channel and it is important that it is painted dark.