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Skanska to upgrade Gråsjø and Trollheim hydropower dams in Norway

Skanska, the Sweden-based multinational construction group, has been contracted by Norway's state-owned renewable power producer Statkraft Energi to refurbish and upgrade four dams and one flood gate.

The NOK 508 million (US$ 54.2 million) contract, will entail the modernization of the structures, which impound reservoirs serving the Gråsjø and Trollheim hydropower plants in Surnadal municipality in Norway’s southwestern county of Møre og Romsdal, Skanska announced on 9 October.

The construction work is expected to start in Q1 2021 and to be completed by September 2025. Both powerplants are wholly owned and operated by Statkraft Energi AS.

The dams at Gråsjø impound reservoirs for the powerplant with the same name, while the dam at Follsjø provides water for the Trollheim plant. The 15 MW Gråsjø station, which was commissioned in 1970, has a single unit that generates average annual output of 78 GWh under a head of 61 m utilising water from the Lake Gråsjø. The plant regulates the Folla river, with water discharged after production into Lake Follsjøen. The Follsjøen is also the regulation reservoir for the 130 MW Trollheim plant, which was commissioned in 1968. Its single Francis turbine generates average annual output of 851 GWh under a head of 402 m utilizing water from the Follsjøen reservoir. Inflow from the tributaries of the Surna river, Bulu, Folla, Rinna and Vindøla, is collected in the Folldalen Valley in the Gråsjøen (el. 483–430 m) and Follsjøen (el. 420–375 m) reservoirs. Water is discharged back into the Surna river after passing through the Trollheim powerplant.

Skanska is also currently carrying out civil works on behalf of SFE Produksjon, the generation arm of the Norwegian utility Sogn og Fjordane Energi AS (SFE), for the 47 MW Østerbø hydropower plant, located on the Sognefjord in the municipality of Høyanger in western Norway. The contract, worth NOK 350 million (US$  41.7 million), includes the construction of a 7.1 km-long headrace tunnel as well as the drilling of shafts, and blasting and concrete work in the powerhouse. Construction of the plant began in May 2017 and is scheduled to be commissioned in autumn 2022.