The effect of dam constructions as mitigative measures: 14 years of experience from a full-scale project

Abstract

The Ryggfonn project is a full-scale project for determination of avalanche behavior. Measurements of velocities, impact pressures and observations of flow patterns around a 15 m high and 75 m long earthfill dam, have been carried out for the last fourteen years. The studies demonstrate that dam constructions in the runout zones of avalanches have limited effect on stopping dry snow avalanches. Concerning wet snow avalanches, a retaining dam can reduce the velocity efficiently and also stop the avalanches, if the speed is below certain values. Our full-scale experiments show that a 15 m high dam is needed to stop wet snow avalanches with a frontal speed of 20 m/s. Protection of buildings by using retaining dams should be used with caution where specific safety requirements exists. Their use should be restricted to areas where the avalanche runout and velocity is well defined and the designed reduction of the run out distance is limited. However, where the goal is to lower the frequency of wet snow avalanches, as for increasing regularity and safety on roads, dam constructions have an important mission. Air blast generated by avalanches can cause serious damage to vehicles, buildings and other constructions. Our experiences demonstrate that dams can work as protection for road-traffic and other facilities if they can be located close to the dam at the leward side.