Most hydro-electric schemes use the maximum available amount of water for generation, typically only allowing 2-5% of the base flow to bypass the turbines for environmental compensation. As a result the vast majority of fish encountering a hydro-electric station will potentially pass through the turbines. This can impact not only the resident fish in the vicinity of the station, but also upward and downward migrating fish, such as eels and salmon.
It has been estimated that up to 10% of fish that enter a turbine will be killed as a result of direct impact with the runner blades and high pressure changes as the fish pass the turbine. For pelagic species the death rate can be as high as 50%. The impact on a fish population can therefore be significant when migrating fish encounter a series of hydro-electric stations, or a tidal barrage is installed.
The traditional solution has been to install physical screens to prevent the fish entering the intake, but these have a high capital cost and need regular cleaning to prevent blockages occurring, especially during the ‘smolt season’, when screens with a smaller clearance are used.
The patented BioAcoustic Fish Fence (BAFF) was specifically developed for this application, as it enables downward migrating fish to be guided out of the main flow and into the bypass channel. Typical deflection efficiencies for salmon smolt of 80%+ have been measured.
When eels also need to be deflected High Intensity Lights can be installed, either on their own or in conjunction with a BAFF system to enhance the performance of the overall system. Upstream passage can also be enhanced with the installation of suitable eel bypasses or pumped systems.
For further information on the systems available please contact FGS.