Gösgen hydropower plant, modernisation of the Winznau weir

The Winznau weir requires refurbishment in order to comply with guidelines and regulations relating to discharge capacity and seismic safety. Between 2025 and 2031, Alpiq Hydro Aare AG will implement the renovation of the structure and won the Solothurner Heritage prize 2024.

The new concession for the operation of the Gösgen hydropower plant has been in force since 1 January 2020. It also includes the renovation of the Winznau dam. The conversion and adjustments are based on the new federal legal provisions and take into account future requirements regarding safety in the event of flooding and earthquakes. In order to fulfil these requirements, Alpiq is renovating the over 100-year-old weir system and is pleased to have found an option that preserves the historic structure. The work will take around six years.

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.

Winznau explanation

Renovation of Winznau weir

1. Renovation of existing weir and existing gates

2. New doping power plant and improved fish migration facilities

3. New low-speed bridge

4. New dam beam bearing

5. Renovation of scour protection

Progress and schedule

We anticipate an approximately five-year construction period. Because the project is being adapted with regard to the new option, the detailed planning has to be updated again.

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

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.