Hydraulic modelling at Finsjö Övre hydropower plant : Study for evaluation of a fishway's attractiveness

Abstract: In connection with the government’s approval on the proposed national plan (NAP) in 2019, it has become highly topical to find solutions problems regarding fish migration in Swedish watercourses. At Finsjö Övre hydropower plant in Emån, a new type of fishway is planned to be installed and evaluated starting at the end of 2022. The fishway is a double Archimedes screw turbine that has never been assessed in a Nordic country. The energy company Fortum is operating the power plant. Fortum’s main purpose with the installation is to evaluate the double-screw turbine to gain knowledge about how it performs in Nordic conditions and with Swedish fish species. The evaluation of the fishway will focus on why fish choose to use it or not. It will then be advantageous to have knowledge of velocities in the area below the fishway since fish´s choice of route is affected by that.   The goal of this project was to investigate flow velocities below the intended fishway through hydraulic simulations. Then by the results produce a basis that can be helpful in future evaluations of the fishway’s function for upstream fish migration. In addition to this, to also link the results to previous studies on upstream fish migration to be able to detect shortcomings. In that case to give suggestions for improvement measures.   Field measurements were conducted to collect data on the environment at the hydropower plant. The environment was then recreated in the simulation software HEC-RAS and the planned fishway was added to the model. Three different flow scenarios were assessed and information on flow velocities was obtained.   The simulations showed that the velocity distribution below the fishway probably is suitable for most fish species due to both fast and calm water near the fishway’s opening. No obvious shortcomings emerged. However, the volume flow rate from the fishway is low and is below the recommended guide values. Upstream fish migration will probably work best at low volume flow rates in the river since the velocity of the attraction flow then is relatively high compared to the currents from the hydropower plant. The higher flows from the hydropower plant and the spillway, the less attractive the flow from the fishway becomes.