Whole field flow measurements of attraction channel as entrance to fishways

Sammanfattning: Migrating fish that swim upstream rivers for reproduction need to overcome obstructions like hydropower plants in their path to the spawning grounds. To guide the fish pass the obstruction fishways are often used. Since most of the water in regulated rivers flow through the power plant fish are often attracted to the turbine tailrace instead of the fishways. The efficiency of the fishways is often low due to inefficient attraction water. In this report an attraction channel which uses a small fraction of the tailwater, or any free stream, to create the attraction water is studied. The channel is open and Ushaped. A local acceleration of the water is created by changing the cross sectional area in the downstream end of the channel. The flow through the channel is subcritical and the bump which accelerates the water also blocks the water flowing into the channel. To study how the water flows are affected of the blockage as the geometry is altered, a model of the channel is studied in lab scale using Particle Image Velocimetry (PIV). With PIV instant flow field can be studied in a plane of the flow. The results show the water flow in and around the channel and how the flow pattern in the channel changes with water depth. Increased depth over the bump increases the downstream traceability of the acceleration. It is also shown that it is possible to obtain accelerations up to 50% downstream the attraction channel compared to the pure flow upstream.