Paravalanches et barrières à neige

Two different types of long term avalanche control structures are distinguished: structures in the starting zone, which prevent avalanches from triggering and structures in the track and runout zones which reduce the damaging effect of descending avalanches. In the starting zone permanent supporting structures like snow bridges or snow nets are used. They support the snowpack in such a way that the release of avalanches is prevented. The arrangement and design is made according to the "Swiss guidelines on avalanche control structures in the starting zone". Supporting structures are designed for snow pressure forces, which depend mainly on the snow depth and on, snow gliding. In loose ground the foundations consist of drilled anchors (typical length 3-6 m), steel bed plates (excavation >0.5 m) or concrete socles (size>0.5*0.5*0.5 m). Slopes from 30° to 50° are considered to be within the range, which justifies structures. The continuous arrangement of structures is preferred. The structure height is decisive for the avalanche safety in extreme situations. The structure height has to be bigger than the extreme snow depth with a return period of 100 years expected at the structure location. The slope distance between two lines of structures ranges typically between 20 and 35 m. On a 45° slope for the protection of one hectare about 650 m of structures are necessary. The maintenance costs are approximately 0.5% of the initial construction costs. Finally the effect of snow drift fences and deflector snow fences are shown and illustrated.