Ryggfonn experimental site
EU Contract no. EVG1-CT2002-00059

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  PLEASE FOLLOW THIS LINK FOR IMAGES OF OUR 2005 AVALANCHE RELEASE


Site description
  • The Ryggfonn avalanche test site in Norway is an instrumented avalanche path in western Norway that has been in use since 1983.
  • The path has a vertical drop of 900m, a total path length of 2000m and an average inclination of 30 from the dam to the starting zone.


  • xxxxxxThe Ryggfonn Avalanche Path

    xxxxxxThe Ryggfonn Avalanche Path.

  • The volumes of the released avalanches range from 5,000 to 500,000m3 and the maximum observed velocity of an event is 60ms-1.


  • xxxxxxAn avalanche at Ryggfonn observed from the opposite mountainside

    xxxxxxAn avalanche at Ryggfonn observed from the opposite mountainside.

  • Avalanches at Ryggfonn occur naturally, but can also be triggered by explosives that are installed before the winter season begins.


  • xxxxxxAn avalanche at Ryggfonn triggered by explosives

    xxxxxxThe triggering of an avalanche by explosives.

Catching dam
  • At the start of the runout zone towards the bottom of the path a 100m long and 16m high catching dam has been installed. An instrument tower on top of this dam is equipped with strain gauges.


  • xxxxxxAerial view (a) of the catching dam at Ryggfonn
    xxxxxxAerial view (b) of the catching dam at Ryggfonn

    xxxxxxAerial views of the catching dam at Ryggfonn.

Monitoring equipment
  • Some 230m upslope of the dam a 4.5m high concrete structure has been installed that is equipped with load plates and load cells. Each load plate has an area of 0.60 x 1.20m and a load capacity of 833 kPa.
  • Another 90m upslope, a steel mast is equipped with load plates. However, due to the high avalanche velocities and impact pressures at these locations, these installations have suffered occasional damage at the hands of particular avalanches.

  • For images of how the load plates were installed, please click [ here ].


  • xxxxxxSteel mast with load plates in the Ryggfonn path

    xxxxxxSteel mast with load plates in the Ryggfonn path.

Data types
  • However, even with this damage, it has been possible to collect valuable data from these instruments, such as the way in which avalanche impact pressures vary with height in the flow and through time.


  • xxxxxxLoad cell results from the upper cell (blue), middle cell (orange) and lower cell (purple) for an avalanche occurring on the 17th February 2002

    xxxxxxLoad cell results from the upper cell (blue), middle cell (orange) and lower cell (purple)
    xxxxxxfor an avalanche occurring on the 17th February 2002.

  • The instruments on the avalanche dam also provide information on the manner in which avalanches interact with such structures. This is important for improving dam design criteria.


  • xxxxxxAvalanche striking the dam at Ryggfonn.

    xxxxxxAvalanche striking the dam at Ryggfonn.

Deposit mapping SATSIE Improvements
  • As part of the SATSIE project we will be improving the instrumentation at Ryggfonn. This will help us to understand exactly how avalanches behave. The dynamics of snow avalanches are not well understood and are also difficult to determine. Our investments at Ryggfonn should greatly increase our knowledge in this area.
  • We will be installing:


  • - (1) Pulsed Doppler radar for velocity measurements,
    - (2) Pairs of frequency stepping (FMCW) radar in the ground at the dam site and some 100m
    xxxxxxupslope,
    - (3) Load plates in the ground in front of the dam and on the dam side for measurements of
    xxxxxxshear and normal forces,
    - (4) Sensors for monitoring the snow cloud at the uppermost mast,
    - (5) Seismic analysis equipment (e.g. Geophones) to compute avalanche behaviour from the
    xxxxxxseismic signal.
 

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