News item | 2011-08-17 | 10:25 AM

Dams made safer for increased water flows

The great expansion of hydro power in Sweden began 100 years ago, and reached its peak in the 1950's. The dams that were erected to store and regulate water were built to handle a flow so great that it occurs only once every 100 years.

The amount of water passing through the system has increased signifi cantly since then. Vattenfall is therefore workingto renovate all the dams so that they can cope with a flow of water that occurs roughly once in 10,000 years. In total, some 30 dams have been reinforced or, in some cases, supplemented with additional dams, so that we can feel confi dent that they can cope with the increasing volume of water. New spillway gates have been built in some dams to allow more water through. (These are used to discharge any water that does not pass through the hydro power turbines.)

“In some places, we have widened the spillways to allow more water through,” says Claes-Olof Brandesten, Head of Dam Security at Vattenfall. “Elsewhere,we have reinforced the dams to temporarily store and slow down water fl ows. These projects also mean that we have greater margins in the event of extreme or unexpected weather conditions.”

Vattenfall invested about SEK 2 billion between 2001 and 2011 in dam-safety improvement work.

Some ongoing projects

  • The largest project is underway in Bergeforsen in the Indal river where a new spillway will be constructed over the next few years. Work is expected to begin in the summer of 2011.
  • Many of the dams in the Lule river have been reinforced to allow them to store water and slow down its flow.
  • In Stenkullafors in the Ångerman river, one of the existing spillway gates has been widened to allow more water through: about 400 cubic metres more per second.