The Winznau weir on the Aare near Olten will be renovated over the next few years to comply with guidelines and regulations on flood protection and earthquake safety. Alpiq Hydro Aare AG will sustainably renovate the facility between 2025 and 2031.
The new licence for the operation of the Gösgen hydroelectric power plant has been in force since 1 January 2020. It also includes the renovation of the Winznau weir. The conversion and modifications are in line with the new Swiss federal regulations and take into account future requirements for flood and earthquake safety. To meet these requirements, Alpiq is refurbishing the weir, which is over 100 years old. The project envisages a sustainable renovation. The historically valuable weir superstructure will remain in its current form, so that the structure retains its typical character.
Construction work will begin in late summer 2025. The main renovation work is expected to be completed in 2027. It will affect the hydroelectric power plant, the fish migration facilities, the new slow traffic bridge, the dam beam storage facility and the scour protection in the Aare below the weir. Each of the five weir openings will then be renovated in annual stages.
The new cycle bridge is scheduled to open towards the end of 2026, which will then enable the renovation of the old footbridge. The project has been specially adapted to ensure that cyclists and pedestrians can cross the Aare with as little disruption as possible during the construction work.
Progress and schedule
Progress and schedule
We currently anticipate construction to take place in several stages until 2031. Construction is scheduled to begin in late summer 2025.
2023
- Further in-depth planning and verification of the new variant
- Preparation of the post-approval dossier for the project amendment for preliminary review by the authorities
- Completion of gravel fills along the side dams of the Obergösgen canal
2024
- Tendering and start of execution planning
- Re-authorisation procedure
- Parallel further implementation of compensation and replacement measures
2025
- Expected building permit
- Start of construction of doping power plant and fish migration plant
- Construction of low-speed bridge
- Renovation of scour protection
- Start of refurbishment of defence shooters every 1 year approx. one defence field per year until 2031
2026
- Completion and commissioning of doping power plant and fish migration plant
- Completion of new low-speed bridge
- Completion of scour protection refurbishment
- Renewal of dam beam bearings
- Continuation of refurbishment Wehrschützen
Questions and answers
Questions and answers
Why – in contrast to earlier plans – the characteristic weir bridge may now be retained?
- According to detailed analyses that were added to the SIA standards relating to structural retention in 2017, retaining the weir in its current form is actually now a realistic option. The detailed analyses, which better depict the actual behaviour of structures in the event of an earthquake, enable buildings to be renovated in a sustainable way and, according to the experts, provide undeniable, clear, scientific evidence of the Winznau weir’s ability to withstand earthquakes.
Where can I cross the river during the construction period?
- There will be a temporary passageway that will remain open during the entire construction period.
Will there be a swimming area with a sandbank below the weir?
- No. The area surrounding the weir is hazardous and swimming there is dangerous. After all, a large volume of water could be discharged via the weir at any time – even on a sunny summer’s day – for example, in the event of a machine breakdown at the power plant in Niedergösgen.
History
Who is Alpiq Hydro Aare AG?
Alpiq Hydro Aare AG is a wholly owned subsidiary of Alpiq. The company owns and operates the three run-of-river power plants on the River Aare in the canton of Solothurn.