25.06.2024 In September 2022, Axpo and Kraftwerke Sarganserland AG (KSL) interrupted the comprehensive refurbishment work on the Gigerwald dam facility in Calfeisen Valley and postponed it for two years. The reason behind this decision was the scarcity of electricity during the winter months of 2022/23. The refurbishment work is now back on track. This work is essential for the safe, long-term operation of the facility and the reservoir must be entirely emptied.
Faced with the limited supply situation in winter 2022/23, Axpo and KSL decided to postpone the refurbishment of the Gigerwald dam facility for two years. This made it possible to provide up to 160 GWh of winter electricity from the water in the reservoir and from circulation operations. Construction measures can no longer be delayed if safe operation of the facility over the coming decades is to be ensured.
The refurbishment of the Gigerwald dam facility was made necessary by progressive sedimentation*. It 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. KSL has therefore restarted the refurbishment following a two-year interruption.
This will involve raising the intake structure for the bottom outlet and works water* by around 20 metres. Axpo and KSL are investing around 25 million Swiss francs in the refurbishment, thereby affirming their commitment to strengthening renewable energies in Switzerland.
The Mapragg hydropower plant will not continue operating while construction is ongoing as the Gigerwald reservoir needs to be fully drained. The majority of the construction work 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. When the refurbishment work resumes, KSL will be able to draw on the preparations made in 2022. For example, two cranes have already been installed and the personnel camp and concrete plant were erected back in 2022. Around 50 people will work on the construction site while building works are carried out over the winter.
The Gigerwald reservoir will be completely drained in late September and the Mapragg power plant will be shut down. Work on the dam facility is likely to continue until the end of April 2025. This will allow the facility to come back into operation in early summer 2025.
Kraftwerke Sarganserland AG (KSL) is a partner company of Axpo Power AG and the canton of St. Gallen. Axpo holds 98.5% of the shares and the canton of St. Gallen has the remaining 1.5%.
*Sedimentation
Most hydropower plants have to deal with sedimentation issues. Rivers carry sediment (sand, gravel) that is then deposited in the reservoirs. There are different methods of tackling sedimentation. One possible way is to dredge the sediment or sluice out the reservoir. A more expedient method for the Gigerwald dam facility, however, is to raise the bottom outlet.
*Bottom outlet
The bottom outlet is the lowest closable opening in a dam facility. One of its functions is to allow a reservoir to be fully drained. A functioning bottom outlet is central to the safe operation of a dam facility. If the sedimentation rises up to the level of the bottom outlet, the operator needs to take action.
*Works water
The water that runs through and powers the turbine in a hydropower plant.
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