Skagerak upgraded the rock-fill dam at Sønstevatn from summer 2012 to autumn 2014.
After this modification, the dam at Sønstevatn was 1.9 metres higher than the previous dam. This makes it safer and better able to withstand increased precipitation levels in the future. The highest regulated water level (HRV) and lowest regulated water level (LRV) were not changed in connection with the modification.
The appearance of the dam was improved. It was lined, meaning that every stone is stacked on both the upstream and downstream slopes. When the existing dam was built in the 1960s, tipped rockfill was a common method to use on the downstream slope. A new boat ramp is now available on the north side of Sønstevatn lake (by the road that goes along Imingdalen valley towards Vikvatnet).
The upgrading work at Sønstevatn dam took place in a way that caused as little disturbance to neighbours and users of the area as possible. The work was successful and had no noticeable impact on the surroundings. The dialogue with the municipal authorities, land owners and users of the area was positive both before and during the work. Skagerak Kraft, and Skanska as the main contractor, have received much positive feedback on the information, handling and not least the appearance of the dam after the upgrading work.
Dam crest 2015
Skagerak Kraft was awarded the Norwegian National Committee on Large Dams' award ‘Damkrona 2015’ for outstanding architecture and good landscape design. Among other things, the dam was used as a background for a TV advertisement for Suzuki.