Debris-flow monitoring Spreitgraben

Situation

Thawing permafrost was held responsible for several rock fall events that initiated in the north face of the Ritzlihorn (3263 m asl) in the Bernese Oberland in 2009. Up until 2011, large debris flows followed every summer after those events, depositing several 100’000 m³ of debris in the Aare River, causing significant aggradation. The debris flows have eroded a deep channel into the landscape and repeatedly threaten the road acting as only access to the local village as well as a major mountain pass named Grimsel. The main transit gas pipeline connecting Northern Europe and Italy was even relocated to the opposite side of the valley due to the debris flow hazard.

Solution

Geopraevent installed a comprehensive monitoring system for road security including automatic road closure and local authority alert. Additionally, all data is continuously recorded in order to improve the understanding of the physical processes causing the debris flows. The monitoring system consists of the following components:

  • Several trigger lines spanned across the channel
  • Two radar gauges to estimate flow height and debris flow magnitude
  • Two laser profile scanners that permanently examine the channel profile
  • A Doppler radar for detection of movements in the starting zone of the debris flows
  • Four webcams with live-access and infrared floodlights that allow day and night alarm verification
  • The online data portal combines all components and illustrates their data with around the clock access for authorized users.

The different measurement devices converge into one system that is itself linked to the a set of alert equipment. In case a critical threshold is exceeded, the system detects an event and triggers an alarm. The alarm sets off different alert mechanisms, such as automatic road closure by means of traffic lights, alarm lights and horns as well as text messages to local authorities. A detailed illustration of the system is provided in this article by NZZ am Sonntag (description in German).

The monitoring system is very user friendly. It is a perfect tool to increase the road safety as well as to analyse and document events easily.

Ricarda Bender-Gàl

Hydraulic Engineer, Civil Engineering Office Canton Bern

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