Advanced Debris-Flow Monitoring and Alarm System at Spreitgraben

Abstract

After a rock avalanche in 2009, the Spreitgraben avalanche course in the Bernese Oberland, Switzerland, has experienced extremely erosive debris flows that pose an increasing threat to infrastructure and residents. Following first events, an extensive alarm and research system was installed that is designed to alert residents and automatically close off the endangered cantonal road. The alarm system is composed of several vertical trigger lines and gauge radars mounted above the channel. Geophones provide a backup detection system in case of trigger line disruption. Early warning data stems from a weather station and several webcams monitoring extended parts of the channel. Repeated terrestrial InSAR measurements provide information about rock instabilities in the starting zone on the northeast face of the Ritzlihorn. To better understand the process chain of the Spreitgraben debris flows, a third subsystem consists of several research components. Two profile scanners constantly sample the channel cross section in order to investigate debris-flow dynamics. Additionally, two different models of Doppler radar systems are being tested at the Spreitgraben site. These are aimed at an early detection of debris flows in order to prolong the warning time provided by the conventional warning system. The entire system is connected to an extensive data transmission and information dissemination system that allows for continuous system monitoring and provides around-the-clock data access to local authorities and decision makers. Though 2012 and 2013 remained uneventful, the alarm system provided successful alerting throughout the debris-flow seasons of 2009 through 2011 and provides valuable insight to debris-flow process understanding.