Avalanche risk along a 420 kV transmission line in Iceland

Abstract

Two transmission lines between Flj6tsdalur and Reyöarfjöröur in northeast Iceland have been investigated conceming snow avalanche hazard. As a basis for the calculations of the return periods of the avalanches, weather and snowanalyses are perfonned for the surrounding weather observational stations. A model analysis is perfonned for some weather situations with a high avalanche risk in order to calculate the snow drift in the mountainous areas around the transmission lines. Run out distances for avalanche profiles passing the masts are perfonned using GIS systems and different avalanche runout programs. Level of probability of simultaneous failure for both the lines is specified less than approximately 6.5xl0-4 per year. For each mast, the risk level must be considerable lower than for the transmission lines as a whole, and this question has been treated statistically in this paper. To attain the specified safety goal a total sum of 82 masts have to be designed to withstand loads from avalanches. In addition, some other masts might be influenced by avalanches passing under the lines between masts. For the 82 exposed masts, the avalanche impact forces are calculated due to the accepted risk level for the transmission lines and the forces are also calculated for the cables exposed to avalanches. A discussion of possible different types of avalanche masts and other means of protective measures are discussed related to protective solutions in Iceland and Norway.