Abstract
Debris flows are a type of mass movement that occurs in mountain torrents. They consist of a high concentration of solid material in water that flows as a wave with a steep front. Debris flows can be considered a phenomenon intermediate between landslides and water floods. They are amongst the most hazardous natural processes in mountainous regions and may occur under different climatic conditions. Their destructiveness is due to different factors: their capability of transporting and depositing huge amounts of solid materials, which may also reach large sizes (boulders of several cubic meters are commonly transported by debris flows), their steep fronts, which may reach several meters of height and also their high velocities. The implementation of both structural and nonstructural control measures is often required when debris flows endanger routes, urban areas and other infrastructures. Sensor networks for debris-flow monitoring and warning play an important role amongst non-structural measures intended to reduce debris-flow risk. In particular, debris flow warning systems can be subdivided into two main classes: advance warning and event warning systems. These two classes employ different types of sensors. Advance warning systems are based on monitoring causative hydrometeorological processes (typically rainfall) and aim to issue a warning before a possible debris flow is triggered. Event warning systems are based on detecting debris flows when these processes are in progress. They have a much smaller lead time than advance warning ones but are also less prone to false alarms. Advance warning for debris flows employs sensors and techniques typical of meteorology and hydrology, including measuring rainfall by means of rain gauges and weather radar and monitoring water discharge in headwater streams. Event warning systems use different types of sensors, encompassing ultrasonic or radar gauges, ground vibration sensors, videocameras, avalanche pendulums, photocells, trip wires etc. Event warning systems for debris flows have a strong linkage with debris-flow monitoring that is carried out for research purposes: the same sensors are often used for both monitoring and warning, although warning systems have higher requirements of robustness than monitoring systems. The paper presents a description of the sensors employed for debris-flow monitoring and event warning systems, with attention given to advantages and drawbacks of different types of sensors.
Highlights
Debris flows are a type of mass movement that consist of highly concentrated dispersions of poorly sorted sediment in water that may move at very high speeds and have great destructive power [1,2,3,4,5,6,7]
This paper provides a review of sensors and systems for debris-flow monitoring and warning, with focus on the equipment to measure parameters of moving debris flows
This paper has presented an overview of the sensors and systems most commonly employed for debris-flow monitoring and warning
Summary
Debris flows are a type of mass movement that consist of highly concentrated dispersions of poorly sorted sediment (from clay- to boulder-sized particles) in water that may move at very high speeds and have great destructive power [1,2,3,4,5,6,7]. The stage height and number of boulders gradually decrease, and the surge is charged with pebble-sized fragments and becomes more and more dilute until it appears as muddy water [1, 8] Some of these features are reflected in the graphs of stage versus time (Figure 1). Conditions required for debris-flow occurrence include the availability of relevant amounts of loose debris, high slopes and sudden water inflows that may come from intense rainstorms, collapse of channel obstructions, rapid snowmelt, glacial lakes outburst floods, etc. Debris flows can discharge large quantities of debris (with volumes up to millions of cubic meters) with high velocities (velocities of about 5 m/s are quite common, and values greater than 10 m/s have been measured) This causes them to be highly hazardous phenomena; debris-flow hazards result in high risk when they encroach urban areas or transportation routes. Geotechnical monitoring of debris-flow initiation, which essentially deals with slope instability processes, is not considered in this paper
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