A debris-flow alarm system for the Alpine Illgraben catchment: design and performance |
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Authors: | Alexandre Badoux Christoph Graf Jakob Rhyner Richard Kuntner Brian W McArdell |
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Institution: | (1) Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland;(2) WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland;(3) Teysseire & Candolfi AG, Visp, Switzerland |
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Abstract: | We describe the development, implementation, and first analyses of the performance of a debris-flow warning system for the
Illgraben catchment and debris fan area. The Illgraben catchment (9.5 km2), located in the Canton of Valais, Switzerland, in the Rhone River valley, is characterized by frequent and voluminous sediment
transport and debris-flow activity, and is one of the most active debris-flow catchments in the Alps. It is the site of an
instrumented debris-flow observation station in operation since the year 2000. The residents in Susten (municipality Leuk),
tourists, and other land users, are exposed to a significant hazard. The warning system consists of four modules: community
organizational planning (hazard awareness and preparedness), event detection and alerting, geomorphic catchment observation,
and applied research to facilitate the development of an early warning system based on weather forecasting. The system presently
provides automated alert signals near the active channel prior to (5–15 min) the arrival of a debris flow or flash flood at
the uppermost frequently used channel crossing. It is intended to provide data to support decision-making for warning and
evacuation, especially when unusually large debris flows are expected to leave the channel near populated areas. First-year
results of the detection and alert module in comparison with the data from the independent debris-flow observation station
are generally favorable. Twenty automated alerts (alarms) were issued, which triggered flashing lights and sirens at all major
footpaths crossing the channel bed, for three debris flows and 16 flood flows. Only one false alarm was issued. The major
difficulty we encountered is related to the variability and complexity of the events (e.g., events consisting of multiple
surges) and can be largely solved by increasing the duration of the alarm. All of the alarms for hazardous events were produced
by storms with a rainfall duration and intensity larger than the threshold for debris-flow activity that was defined in an
earlier study, supporting our intention to investigate the use of rainfall forecasts to increase the time available for warning
and implementation of active countermeasures. |
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Keywords: | Alarm system Debris-flow detection Debris-flow observation Rainfall intensity– duration threshold Hazard awareness Swiss Alps |
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