Power producer Skagerak Kraft is to upgrade two of its seven dams in the Siljan watercourse, while also building new floodways to increase flood diversion capacity at Sporevann and Vanebu. The work is being done to meet new regulatory requirements from NVE. It also takes into account climate change with more severe weather fluctuations.

Dam Vanebu 
Location: Siljan kommune, Telemark
Highest regulated water level: 254,41 metres above sea level
Lowest regulated water level: 247,41 metres above sea level 

Dam Sporevann 
Location: Siljan kommune, Telemark
Highest regulated water level:  346,75 metres above sea level 
Lowest regulated water level: 339,75 metres above sea level  

– The flood diversion capacity is not satisfactory today. In addition, we are upgrading the dams and have included a climate adjustment in flood calculations so that we can be prepared for a wilder and wetter climate, says Åsmund Hasaas of Skagerak Kraft.

Skagerak Kraft has chosen to build labyrinth spillways at these two dams.

– Labyrinth spillways will give the dams a distinctive character: the dams will zigzag like several Ws, in and out of the reservoir to achieve sufficient spillway length. This provides greater spillway length and thus greater capacity to divert floodwaters, says Hasaas.

Construction period

Work will begin at the end of May 2023 and is expected to be completed by October of the same year. During this period, there will be construction traffic to and from the dams, and some noise can be expected.

The area around the dams will be used as a rigging area for offices, equipment, materials, and cars. Unfortunately, this will result in less available space around the dams than normal during the period. At Sporevann, the access road to the reservoir will be used, and the recreational area will be affected by this traffic.

Low water level The water level in Vanebu and Sporevann will be low this summer, but not below the lowest regulated water level. The water level in Mykle may also be affected. Mykle will be used as a buffer reservoir to reduce the risk of having to interrupt work in a flood situation.

In 2022, there was also a low water level throughout the summer, but without final approval from NVE, the work could not be carried out last year.

– We understand that this may cause inconvenience for outdoor activities, but the work is necessary to maintain our facilities in a safe manner, says Hasaas.