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Investing in the future of hydropower – Gigerwald reservoir drained completely for construction works


Over the coming months, Kraftwerke Sarganserland AG (KSL) will be renovating the Gigerwald dam facility (SG) in the Tamina valley. These works have been made necessary by progressive sedimentation*. This investment by Axpo and KSL secures the long-term reliability of the facility and affirms their commitment to strengthening renewable energies in Switzerland.

At the Gigerwald dam run by KSL, sedimentation has now risen up to the level of the bottom outlet intake*. The facility is currently able to operate as normal – but operation may become limited should nothing be undertaken soon. Construction measures must be taken in order to ensure safe operation of the facility over the coming decades. Hence why KSL will be carrying out the necessary work on the dam facility over the coming months. This will involve raising the intake structure for the bottom outlet and works water* by around 20 metres. The cost of the construction project is around 25 million Swiss francs. All necessary approvals were already granted in late 2020 by the authorities concerned.

Major construction site in winter

The Mapragg hydropower plant will not continue operating while construction is ongoing, since the Gigerwald reservoir will need to be fully drained. Construction works will take place in winter, when there is less water flowing that would need to be channelled through the construction site and also because production losses would be greater in summer. Initial arrangements have already been ongoing since autumn 2021 to ensure that work can be carried out efficiently over the winter. These include diverting traffic, assembling cranes, installing a concrete plant, delivering building materials and setting up a camp for staff. Around 50 people will work on the construction site while building works are carried out over the winter.

The Gigerwald reservoir will be drained completely at the beginning of October and the Mapragg power plant shut down. Work on the dam facility is likely to continue until end of April 2023. This should allow the facility to come back into operation in early summer 2023.

The building works will lead to road closures and traffic diversions in the local area. Runoff from the Tamina and Seez rivers will also be slightly higher over the winter as a result of the Mapragg power plant being shut down.

Information event for local residents

KSL will be holding an information event for local residents on Tuesday 26 April 2022. The event will take place at 7 pm in Vättis sports hall. There is no need to register for the event.

*Bottom outlet

The bottom outlet is the lowest closable opening in a dam facility. One of its functions is to allow a dam facility to be fully drained. A functioning bottom outlet is central to the safe operation of a dam facility. The operator will need to take action if the sedimentation rises up to the level of the bottom outlet.

*Works water

The water that runs through and powers the turbine in a hydropower plant. 


Most hydropower plants have to deal with sedimentation issues. Rivers carry sediments (sand, gravel), which are then deposited in the dam facility. There are different methods of tackling sedimentation. One possible way is to dredge the sediments or sluice out the reservoir. A more expedient method for the Gigerwald dam facility, however, is to raise the bottom outlet. 

Axpo Holding AG

Corporate Communications


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