Norway

Implenia and Risa to build Tunnel for Hydropower Plant in Vest-Agder

Implenia, in partnership with Norwegian infrastructure construction company Risa AS, has won a contract from energy company Agder Energi. The consortium will build a dam and a new transfer tunnel for an existing hydroelectric power plant at the Langevatn reservoir in the county of Vest-Agder in southern Norway. The contract for this complex infrastructure project is worth approximately 600 million Norwegian kroner (62 million euros).

 

7 km of new Tunnel to be built

At a length of 210 m and a height of 40 m at its highest point, the new dam will double the reservoir’s capacity to 46 million m3. The old dam will be demolished. The transfer tunnel that takes water from Lake Langevatn to Lake Nåvatn is vulnerable to rock collapses. Implenia and its partner are therefore rebuilding a 7 km section in parallel with the existing tunnel, which is 13 km long in total. The four current tunnel inflows will be redirected to the new tunnel or rebuilt. Apart from during certain clearly defined times, the reservoir and the existing tunnel will continue to operate throughout the entire construction period of around three years. The project is scheduled for completion at the end of 2020.

The job presents various technical challenges. Despite the reduced water level in the Langevatn, there is likely to be water throughout the construction site. The new inflows for the transfer tunnel will also have to be built in flowing water, so the team will have to cope with constantly changing water levels.

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