Where: Aurland municipality – Vangen power station by Lake Vassbygdvatnet in the Aurland river system.

Challenge

The Aurland river system has a vulnerable sea trout population and a small salmon population, and every fish counts. Vangen power plant draws its water from Lake Vassbygdvatnet, where the fish live. During the inspection of the waterway, 80 fish were found prior to the intervention.

The solution had to keep fish out of the tunnel, preventing them from following the water into the intake and on through the power plant. At the same time, up to 90 m³ (90,000 litres) of water per second had to flow through freely, allowing power generation to continue as before. The screens also had to stay clean, as a fine-mesh screen quickly becomes clogged with moss, twigs and leaves.

Measures

To keep fish out of the tunnel, we have developed and installed a fish screen at a depth of 10 metres, specially designed for the intake at Vangen. Work began in 2019, and the screens were installed in early 2021.

Key features of the solution:

• Eight intake screens at a depth of ten metres: The intake has two openings, each with four screens. Each screen measures 5 x 2.6 metres, and together they cover 104 m². Each screen weighs 400 kilograms.
  
• Designed for high water flows: The intake screens are engineered to withstand a flow of 90 m³ of water per second, the maximum operating flow at Vangen power plant. Several types of steel were tested before the final design was selected.
  
• Positioned at depth: Because the grates are positioned deep underwater, moss, twigs and leaves floating on the surface are kept away.
  
• Developed by in-house experts: The idea came from Hafslund’s own employees, and the grates were manufactured by a workshop in Sogndal.

Results of the measures

The fish screen keeps fish in the river system while Vangen power plant continues to operate as before. What began as a trial screen has become a solution that works in practice, year after year.

The results include:

• No fish in the tunnel: Before the measures were implemented, 80 fish were found in the tunnel. Since the screens were installed, that number has dropped to zero.
  
• Gentle on the fish: Camera monitoring shows that fish turn away from the screens, and no fish have been recorded as trapped. A tagging study has also confirmed that fish find their way back to Vassbygdvatnet.
  
• A durable solution: The screens have been in operation since 2021 without clogging and are maintained by Hafslund’s own staff.

The experience at Vangen shows that power generation and nature conservation can go hand in hand when solutions are tailored to local conditions. We will apply this knowledge to our work on fish and waterways at Hafslund’s other power plants.