The Cantonal Council of Solothurn in Switzerland has granted a building permit for the restoration of the Winznau weir, clearing the way for construction to begin in late summer 2025. The weir, part of Alpiq’s Gösgen hydropower plant, is over 100 years old and will now be preserved and modernised rather than demolished.
Alpiq Hydro Aare AG, owner and operator of the plant, had a valid permit to demolish the structure but opted instead for sustainable restoration. In recognition of this decision, the company received the Solothurn Heritage Prize in 2024.
The project aims to maintain the historic structure’s original appearance while upgrading it to meet modern safety and environmental standards. Work will include improvements to flood protection, the addition of a new fish migration facility, and the construction of a quieter small-scale hydropower plant.
Preparatory work on site will begin in the coming months, starting with the removal of the weir staircase on the Olten side. Major construction is expected to run until 2027. A new bicycle and pedestrian bridge will open by the end of 2026, allowing for continued crossing during the works and enabling the restoration of the existing footbridge.
Thomas Fürst, Managing Director of Alpiq Hydro Aare AG, described the permit as a key step forward: “We are so pleased that the decision to sustainably restore the weir has been so well received and that we can improve the weir by adding a wide bridge over the Aare that fits the historical character of the Winznau weir.”
The restoration is part of a broader upgrade linked to the Gösgen hydropower plant’s new concession, which has been in effect since 2020. The project includes structural upgrades for earthquake resilience and flood management, ecological improvements, and enhanced infrastructure to support continued renewable energy generation. Total investment for the upgrade is approximately CHF 63 million.
