Islas balancing reservoir to undergo extensive renovation

13.05.2025 – Investment in supply security: Albula-Landwasser Kraftwerke AG (ALK) will renovate the Islas balancing reservoir from July 2025, investing around CHF 5 million in the project. The reason for this is progressive damage to the reservoir seals. 

During periodic condition assessments, employees noticed that the sealing of the Islas balancing reservoir near Bergün, built in 1966, was deteriorating. The embankment sealing above the elevation of 1,413 metres above sea level is particularly affected, where damage to the sealing and binding layers and to the building connections has been identified. The basin floor itself is in good condition but requires selective adjustments to the inlet and outlet structures and the drainage shafts.

To ensure long-term operational safety and prevent energy losses, the basin must be comprehensively renovated. The work includes the replacement of the embankment sealing over an area of around 4,600 m², the renewal of the connection joints, and local concrete repairs and drainage work.

In order to maintain power plant operations during the construction period and avoid energy losses, a new relief structure and a temporary water diversion of the Tischbach stream will be implemented in advance. This will ensure that energy production at the Filisur level remains unaffected during the construction period.

The repairs will take place between July 2025 and October 2026. The costs amount to around 5 million Swiss francs. This investment will renew a key component of the region's sustainable and secure energy supply.