Debris Flow Sensors

1) Wire sensors

Wire sensors detect a debris flow when the wires laid out inside of river channels get cut by a debris flow. Consequently, every time a wire gets cut by a debris flow, it requires repair work. Prior to installing a wire sensor, it is extremely important to determine the appropriate height at which to install the wire sensor according to the scale of debris flow potentially anticipated in the area. It is also crucial to carefully determine the appropriate positioning of the wires in order to prevent accidental or unintentional activation of the sensor by animals, driftwood, and/or fallen trees.

2) Vibration sensors

Vibration sensors detect the vibration of the ground soil in case of a debris flow. Prior to installing a vibration sensor, it is extremely important to determine what level of vibration is appropriate to activate the sensor in case of a debris flow. It is also important to keep in mind the risk of unintentional activation caused by earthquakes, as well as areas in which there is construction traffic and other vibration causes that may activate the sensor.

3) Light sensors

Light sensors detect a debris flow when they intercepts the light axis installed through a river channel. Prior to installing a light sensor, it is important to determine the appropriate positioning. The risk of unintentional activation caused by animals, driftwood, snow, fog, and other conditions, also needs to be taken into consideration.

4) Acoustic sensors

Acoustic sensors detect the sound propagating underground in case of a debris flow. Prior to installing an acoustic sensor, it is important to determine the appropriate acoustic level at which the sensor is activated. It is necessary to take into consideration the risk of unintentional activation caused by traffic in the area, including construction as well as ordinary traffic.

Needless to say, it is crucial to make sure that all of the workers will have enough time to evacuate far enough from the site once any one of the sensors above is activated and before the debris flow reaches the construction site.

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Translated from Journal of Japan Sabo Association, Sabou to Chisui, Vol.124, pp.45-47, 1998