Vallee de la Sionne

The official homepage for the Vallee de la Sionne test site can be found at:
The site is maintained and operated by the Swiss Federal Institute for Snow and Avalanche Research.
The Vallee de la Sionne test site is located close to the ski resort of Anzere in the Valais region of Switzerland. The path has ~1300 m of vertical extent from the summit to the river. The views below show the path from the reinforced observation bunker and a view from the lower part of the path looking towards the observation bunker.
               
The frequent avalanches down the path keep it free from trees. Indeed, the trimline for the large avalanche in 1999 can be picked out due to the presence of new growth trees (see below). Subsequent avalanches have struck and bent the new growth trees.
 
           
 
The main instrument bunker is only safely accessible by helicopter during the winter season and it is here that our radar instrument is installed. The bunker is built on two levels. The upper level contains the instruments, which are protected from the avalanche by steel shutters. The lower level is often under the snow in winter and is where the scientists are based during the experiments.
           

The height difference between the river and the bunker means that in the majority of cases, it is only the powder component of the avalanche that reaches the bunker. However, larger events, such as that in 1999, can bury the bunker, which requires a bit of snow tunnelling!

In addition to the instruments in the bunker, a variety of pieces of equipment are deployed in the path to measure various properties of the flow. A cluster of these instruments is found at an elevation of 1650 m, including a tall mast that houses pressure sensors for measuring the powder cloud, as well as other instrumentation for obtaining the local velocity and depth for the dense component of the flow, and a large pressure sensor, which can be seen to the right of the tower on the right-hand figure of the two images below.
 
  
Data from these path-based instruments is fed into an underground control station before being relayed down to the bunker. In the left-hand figure below, Martin Hillier is checking the data acquisition for the upward looking radar buried in the path that monitor local mass balance changes.
  
 
 
The most visible instrument in the path is the 21 m high tower that Martin Kern and Kevin Chetty are inspecting in the right-hand figure, above. Pressure and velocity sensors are used to elucidate the vertical profile of flow properties as well as the depth of the different layers of the avalanche.


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