Functionality of Depth Restricted Inclined Fish Screens (DRIFS) for downstream passage of brown trout

This project will test how well the partial alpha screens work at the Väsa power plant in Österdalälven by giving young trout tiny trackers to trace their movements over two years. This will show how easily the fish can get past the screens, how they behave before and after trying to pass, and how water flow affects this. The results of the project will be important for developing the concept of partial alpha screens and how they can be improved and used in other locations.

In the past decade, a number of innovative solutions for downstream passage have been presented. One solution that has shown positive results is the use of low-sloped screens with small gaps that guide downstream-migrating fish towards a bypass channel when they approach the turbine intake at a power plant, known as alpha screens.

Partial alpha screens only extend 3-4 meters below the water surface, which poses economic and practical benefits compared to screens that reach down to the bottom in front of a power plant’s turbine intake, since studies of salmonid behavior during downstream migration have found that they mainly use the upper part of the water column during their migration. However, the functionality of these screens has never been evaluated. Partial alpha screens have therefore been installed in the upper parts of the Dalälven River (Österdalälven) to be examined.