Illgraben

In 2015 the system has been installed at the Illgraben, near Leuk in the canton Vallis in Switzerland. The catchment area of 9.5 km² extends from the summit of the Illhorn at 2716 m a.s.l. down to the Rhône valley at 610 m a.s.l.. This is one of the most active debris flow catchments in the Alps, where up to seven debris flow or debris flood events with an annual sediment discharge of several hundred thousand tonnes occur in this catchment every year, with a great variability of flow properties. The test site is well equipped with ultrasonic and radar level sensors, geophones, force plates and video cameras along the whole channel. Since 2015 two of the infrasound/seismic detection systems have been installed at the Illgraben catchment (Figure 1). One of them is placed in the upper catchment area directly at the canyon rim (Station 1 in the overview at Figure 1a). This station, which was only installed in the season 2015 and 2016, was equipped with a Chaparral infrasound sensor and a SG-5 geophone. From 2018 to 2020 another station, consisting of an Electret-microphone and a SM-6 geophone, was installed at the canyon rim at the upper catchment. The other station (Station 2) located down in the valley close to the channel mouth at check dam 27 has been replaced by a new MAMODIS station in 2021.

Fig. 1: (a) Overview of the test site Illgraben (red line: catchment area); (b) Closer view of the monitoring Station 2 and sensor setup (Source: Google Maps).