Journal cover Journal topic
Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/nhess-2016-321
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
13 Oct 2016
Review status
A revision of this discussion paper was accepted for the journal Natural Hazards and Earth System Sciences (NHESS) and is expected to appear here in due course.
Rapid Detection and Location of Debris Flow Initiation at Illgraben, Switzerland
Fabian Walter1,2, Arnaud Burtin3,4, Brian McArdell2, Niels Hovius3, Bianca Weder1, and Jens M. Turowski3 1Laboratory of Hyrdaulics, Hydrology and Glaciology, ETH Zurich, 8093, Switzerland
2Swiss Federal Institute for Forest, Snow and Landscape Research WSL, 8903, Switzerland
3GFZ German Research Centre for Geosciences, 14473, Germany
4Institut de Physique Du Globe de Paris, 75238, France
Abstract. Heavy precipitation can suddenly mobilize tens to hundreds of thousands of cubic meters of sediments in steep Alpine torrents. The resulting debris flows (mixtures of water, sediments and boulders) move downstream with velocities of several meters per second and have a high destructive potential. Warning schemes for affected communities rely on raising awareness to the debris flow threat, precipitation monitoring and rapid detection methods. The latter, in particular, remain an ongoing challenge, because debris-flow-prone torrents have their catchments in steep and inaccessible terrain, where installing and maintaining instrumentation is difficult. Here, we propose a simple processing scheme for seismic network data. We use debris flow and noise seismograms from Illgraben, Switzerland, a torrent, which produces several debris flow events per year. Automatic in-situ detection is currently based on geophones mounted on concrete check dams and radar stage sensors hung above the channel. The proposed approach has the advantage that it uses seismometers, which can be installed at more accessible locations, and where a stable connection to portable phone networks is available for data communication. Our data processing uses time-averaged ground vibration amplitudes to estimate the location of the debris flow front. Applied to continuous data streams, inversion of the seismic amplitude decay eliminates the need for single-station-based detection and knowledge of the local seismic velocity model. This makes the approach suitable for automation, as seismic phase identification is unnecessary and the amplitude averaging significantly reduces data volume. We apply our approach to a small debris flow event on 19 July 2011, which was captured with a temporary monitoring network. The processing rapidly detects the debris flow event half an hour before its front arrives at the torrent mouth and 8 minutes before detection by the current alarm system. An analysis of continuous seismic records furthermore indicates that detectability of Illgraben debris flows of this size are unaffected by changing environmental and cultural seismic noise. We therefore propose that our method reliably detects initiation of the Illgraben debris flows and can thus form an important ingredient in the next generation of early warning schemes.

Citation: Walter, F., Burtin, A., McArdell, B., Hovius, N., Weder, B., and Turowski, J. M.: Rapid Detection and Location of Debris Flow Initiation at Illgraben, Switzerland, Nat. Hazards Earth Syst. Sci. Discuss., doi:10.5194/nhess-2016-321, in review, 2016.
Fabian Walter et al.
Interactive discussionStatus: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version      Supplement - Supplement
 
RC1: 'Review', Anonymous Referee #1, 16 Nov 2016 Printer-friendly Version 
AC2: 'Response to Review', Fabian Walter, 20 Dec 2016 Printer-friendly Version 
 
RC2: 'Review', Anonymous Referee #2, 22 Nov 2016 Printer-friendly Version Supplement 
AC3: 'Response to Review', Fabian Walter, 20 Dec 2016 Printer-friendly Version 
 
AC1: '"To Editor"', Fabian Walter, 20 Dec 2016 Printer-friendly Version 
Fabian Walter et al.

Video supplement

Debris Flow Front Location with Seismology
Fabian Walter
doi:10.5446/20232
Fabian Walter et al.

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Short summary
Debris flows are naturally occuring mass motion events, which mobilize loose material in steep Alpine torrents. The destructive potential of debris flows is well known and demands early warning systems. Here we propose seismic detection of ground vibrations induced by a debris flow event in Switzerland. Our method efficiently detects the initation of the event and traces its front propagation within the torrent channel.
Debris flows are naturally occuring mass motion events, which mobilize loose material in steep...
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