20.12.2024 | Work on the Gigerwald dam is going according to plan, even in the middle of winter
Special construction site - extraordinary insights
An empty reservoir, an exposed bottom outlet, two cranes on the top of the wall, a large installation site at the foot of the 150 metre high dam - and all this in the snow, at sub-zero temperatures and at an altitude of around 1300 metres. The pictures of this unusual construction site are correspondingly spectacular.
One thing is certain: the 50 or so construction workers currently working on the Gigerwald dam have to be able to withstand the cold. The dam wall lies deep in the shadow of the mountains, an icy wind blows through the narrow Calfeisental valley and there is already quite a lot of snow in mid-December. But the workers don't seem to mind, and the work is running at full speed in two shifts.
The challenging partial renovation of the Gigerwald dam has a long history. Sophisticated planning and a great deal of engineering expertise were required to establish the key points of the major project. The increasing silting up of the lake bed presented Axpo and Kraftwerke Sarganserland AG (KSL) with a problem: the bottom outlet, i.e. the plug of the reservoir so to speak, was in danger of silting up. This meant that the reservoir could no longer be emptied and operations would be restricted. The bottom outlet should therefore have been raised by around 20 metres as early as 2022. Due to the impending power shortage at the time, Axpo/ KSL decided to postpone the project by two years.
Now, in the winter of 2024/25, work is in full swing (see here the TV report from SRF). Extensive preparatory work began in the summer. The Gigerwald reservoir was then completely drained to expose the bottom outlet. Numerous other work steps are necessary to ensure that this can be raised at all (see photos in the picture gallery above):
The residual emptying of the reservoir was brought forward as the headwater had a high sediment content, which could have damaged the turbines in the Mapragg power station further downstream. The high sediment deposits upstream of the intake posed a further challenge, but this was overcome. The time-critical work began on 30 September. This included the installation of a so-called dewatering system so that the water from the Tamina could be drained away. The demolition of the ceiling of the existing bottom outlet then began using rope cuts, which went well and on time. The lower bend of the headrace was also constructed in November and the first prefabricated concrete parts will soon be installed.
The weather has co-operated for the most part so far. Snow has already fallen, but not in quantities that would cause problems. Work only had to be stopped on one day because a storm swept over the construction site at over 100 kilometres per hour. We can only hope that the weather will continue to be favourable in the new year and that work can continue without interruption.
Before that, however, the Calfeisental will be quiet for a few days when the construction workers go home for the holidays. But then it's full steam ahead again in January. The schedule is demanding, with construction work due to be completed by the end of April 2025 and the plant scheduled to reopen in May 2025.
Investment in long-term security of supply
In view of the tense supply situation in the winter of 2022/23, Axpo and KSL postponed the partial renovation of the Gigerwald dam by two years. The necessary structural measures could no longer be postponed to ensure that the plant can be operated safely for the coming decades.
The work has become necessary due to progressive siltation. This had already reached the height of the bottom outlet inlet. The intake structure to the bottom outlet and the headrace will therefore be moved upwards by around 20 metres. Axpo and KSL are investing around CHF 25 million in the partial refurbishment and are reaffirming their commitment in favour of renewable energies in Switzerland.
