E3S Web of Conferences 415, 03002 (2023)
DFHM8

https://doi.org/10.1051/e3sconf/202341503002

Performance of the debris flow alarm system ALMOND-F on theRochefort Torrent (Val d’Aosta) on August 5, 2022
Massimo Arattano1*, Marta Chiarle1, Velio Coviello2 and Guido Nigrelli1
1 CNR IRPI, Strada delle Cacce 73, 10135 Torino, Italy
2 CNR IRPI, Corso Stati Uniti 4, 35127 Padova, Italy

Abstract. On August 5, 2022 in the Rochefort torrent (Val Ferret, Mont Blanc), a debris flow occurred that
invaded the road connecting the valley with the village of Courmayeur. The debris flow interrupted the car
traffic and damaged the bridge that crosses the torrent and the aqueduct that serves the municipality ofCourmayeur. Due to the recurrence of similar events, in 2017 the Valle d’Aosta Region had decided toinstall a monitoring and warning system for debris flows, close to the bridge on the Rochefort torrent, tointerrupt the traffic in both directions through a pair of traffic lights in case of debris flow. The system,
named ALMOND-F (ALarm and MONitoring system for Debris-Flow), has been installed along the torrent,
few tens of meters upstream of the bridge. ALMOND-F adopts a warning algorithm that is based on thevariation of the seismic signal intensity produced by debris flows and that had been thoroughly tested inprevious years in the instrumented area of the Gadria basin. On August 5, 2022 the warning system activated
the traffic lights and stopped the traffic about three minutes before the debris flow invaded the road. It is thefirst time that the ALMOND-F system is utilized in a real risk situation to protect the population, after someyears of controlled tests carried out in an instrumented area. Even though this represents an undoubted
technological success, the installation of ALMOND-F requires several issues to be addressed to grant thehighest level of safety. For instance, the presence of other active debris-flow channels and/or natural risks
in the same valley may represent a limitation to the installation of a site-specific alarm system. The
installation of the Rochefort torrent, opportunely optimized also on the basis of the feedbacks of the August5, 2022 debris flow event, could become a useful case study and so provide indications and suggestions on
the mitigation of the debris flow risk through the use of warning systems.

1 Introduction
In recent years, a growing number of monitoringsites are adopting seismic sensors for the debris-flow
detection [1]. Low-cost and easy-to-install sensors suchas geophones are attractive because they can provide
monitoring data with high spatial and temporal
resolution, at a safe distance from the channel. However,their use in operational alarm systems is still scarce
given that instrument maintenance and data analysis
require efforts and skills in signal processing [2,3].
Several debris flow events have occurred in the pastin the Rochefort torrent [4,5], located close to the villageof La Palud, in the municipality of Courmayeur (AO,(Fig.1a)). The Rochefort torrent drains a basin of about
2.8 km2 and extends between 4014 m a.s.l. (Dente delGigante) and 1400 m a.s.l. (confluence with the Dora diFerret); the upper part of the basin hosts the Rochefort
Glacier (0.5 km2). Some debris flow events were of
considerable magnitude and the Valle d’Aosta Region,
at first, and the municipality of Courmayeur, in a secondtime, have thus decided, in 2017, to install and maintaina debris flow warning system on the torrent. The system
can stop the traffic on the road that crosses the torrent,
through a pair of traffic lights, and alert the authorities

in case of debris flow, also providing a series of photos,
shot in real time by the videocamera connected to thesystem.
The alarm system that has been installed wasdesigned, realized and tested through a collaboration
between the Research Institute for Geo-HydrologicalProtection (Istituto di Ricerca per la Protezione
Idrogeologica – IRPI) of the Italian National ResearchCouncil (CNR) and the private company Siap + Micros
S.p.A.
The debris flow warning system, named ALMONDF (ALarm and MONitoring system for Debris-Flow), isthe result of an experimental research on the seismic
detection of debris flows that CNR–IRPI began in the90s. The initial researches were carried out in theinstrumented area of the Moscardo torrent (Paluzza,Udine), which is still active nowadays [6] and were thencontinued in the experimental installation of the Gadriatorrent (Lasa, BZ), managed by the Civil Protection
Agency of the Autonomous Province of Bolzano [7].
The analysis of the first seismic signals recorded in theMoscardo torrent has evidenced the possibility ofdeveloping an algorithm that could recognize the debris
flows on the basis of the vibrations that they induce inthe ground [8].

* Corresponding author: massimo.arattano@irpi.cnr.it© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0(https://creativecommons.org/licenses/by/4.0/).

E3S Web of Conferences 415, 03002 (2023)
DFHM8

https://doi.org/10.1051/e3sconf/202341503002

installed even in the harsh conditions typical of Alpineenvironments.
In order to be able to test both the hardware anddifferent types of algorithms, a special test area was set
up in the Gadria torrent [7]. These tests provided theexperimental data for the development of an automatic
recognition algorithm based on the analysis of thesignal-to-noise ratio detected by a linear array of seismic
sensors [10].

2 Characteristics of the ALMOND-F
alarm system at the Rochefort Torrent
The ALMOND-F alarm system installed on theRochefort torrent consists of the hardware produced by
the company Siap + Micros S.p.A on which is
implemented a site-specific version of the algorithm
developed by the CNR-IRPI in 2019 [10].
The algorithm operating on the Rochefort torrent
processes in real time the seismic signal detected bythree different geophonic sensors positioned a few tensof meters away from each other, parallel to the course ofthe torrent, on the left bank, a few tens of meters
upstream of the bridge to be protected (Fig 1b).
The original algorithm [10] was modified andcalibrated at the site of the Rochefort torrent, to avoid
maintenance interventions on the sensors in case ofvariation of the background noise, and also to filter thenumerous local low-magnitude earthquakes. This
modified version of the algorithm has been named
EAGLE-DFO (EArly Ground-vibrations to LEad traffic
at Debris-Flow Occurrence).

3 Performance of ALMOND-F during
the eventOn the occasion of the debris flow event of 5 August
2022, the ALMOND-F system demonstrated excellent
reliability, recognizing the arrival of the debris flow
about 2,5 minutes before its arrival near the first
upstream sensor (18:52:28 CEST). The first detection
was produced by a precursory surge that propagatedabout two minutes before the arrival of the main debrisflow front (Fig. 2). The recognition of the debris flow by
the algorithm produced the lighting of two traffic lights
placed at both ends of the bridge (18:50:00 CEST), thus
blocking traffic in both directions about 4 minutes
before the arrival of the main front at the road crosssection (18:54:00 CEST).
At the same time, the system sent an e-mail to alert
the local authorities of the imminent occurrence of thedebris flow, also reporting the occurrence of the event,always by e-mail, to the offices of the CNR-IRPI in
Turin and of the system manufacturer Siap + Micros
S.p.A.
The videocamera located in correspondence with thecontrol unit (point number 4 in Fig. 1b) also allowed tocollect a sequence of images of the arrival of the debris
flow and of the invasion of the road as shown in Fig. 3,informing the authorities of the conditions of the road sothey could better plan the interventions to beimplemented.

Fig. 1. a) The Rochefort torrent (Courmayeur, AO). The blacksquare indicates the location of the monitoring system(Basemap Geoportale Valle d’Aosta); b) 1,2,3: location of thethree geophones, 4: location of the ALMOND-F central unit,
5: location of the bridge

Starting from 2012, research activities were thus
concentrated on the individuation of the most efficientmethod to process the seismic signal for theidentification of such an algorithm [9] and,
contemporarily on its development [10].
The research activities were carried out incollaboration with a private company that provided thehardware equipment, on which the algorithm could beimplemented. The idea was to develop an alarm system,
based on the detection of the seismic signal, that could
represent a significant advance compared to the systems
available at the time and to provide, from the beginning,
the conditions for practical application of the algorithm
in the field. To this aim, a robust and energeticallyautonomous equipment was needed that could be

2

E3S Web of Conferences 415, 03002 (2023)
DFHM8

https://doi.org/10.1051/e3sconf/202341503002

located in correspondence with the ALMOND-F alarmsystem.

4 Maximizing the effectiveness of adebris flow alert system
The good performance of the alarm system of theRochefort torrent during the debris flow event of August
5, 2022 undoubtedly constitutes an important scientificand technological success, both in terms of thealgorithm performance and hardware reliability.
The EAGLE DFO algorithm did not send any false
alarm through e-mail in the five years of operation thatpreceded the debris flow of August 5, filtering the other
different sources of vibration present in Val Ferret(passage of vehicles on the road, earthquakes, torrentialfloods, passage of animals, etc.). At the same time, thealgorithm was able to recognize the occurrence of thedebris flow at the first occasion, stopping traffic earlyenough, and reporting the event to the local authorities.
The possibility of installing the sensors in a safe
position, sufficiently far from the torrent bed, also
ensured that the system was not damaged by the debris
flow, thus making it still functional in the event of asubsequent debris flow wave or event. This is somethingthat can sometimes happen in the following hours ordays, as occurred in Valpelline (located about 30 km
west of the Rochefort Torrent) during the same
meteorological event, when the same two torrents
experienced two debris flow events 18 hours apart fromeach other.
The simple installation of an alarm system in atorrent, however, is not in itself sufficient to guarantee acomplete safety with respect to debris flow phenomenaof the entire valley that hosts it. In fact, there are issues
that must be addressed with extreme care in order toachieve the highest possible level of safety for thevalley. One of these is certainly the location of the traffic
lights intended to stop the traffic, which must be chosencarefully, taking into account the geo-morphology of thesite, the areas affected by any previous debris flows andthe advance with which the traffic lights can be turned
on before the arrival of the debris flow. Positioning thetraffic lights too close to the bridge to be protected couldin fact expose drivers to the possibility that some of theflow will reach them anyway. On the other hand, if thetraffic lights are too far from the bridge, some drivers
may have already passed them when they turn on.
Furthermore, if in the same valley there are othertorrents subject to debris flows, scenarios that foresee
the occurrence of several debris flows during the same
meteorological event must be considered. In fact,drivers stopped by traffic lights could find themselves
blocked in a queue or they could choose to make a uturn, thus being exposed to threats coming from othertorrents.
Finally, to be as effective as possible, the installationof a monitoring system must always be accompanied byadequate communication to the general public, so thatanyone passing through the area can correctly andunambiguously interpret the indications of danger andexactly what to do.

Fig. 2. Envelope of the seismic signal recorded by the threegeophones installed along the Rochefort torrent (labeled with
1, 2, 3 in Fig. 1a). The dashed line in the figure represents thedetection time.

Fig. 3. Sequence of images of the arrival of the debris flow andof the invasion of the road, shot by the videocamera that is3

E3S Web of Conferences 415, 03002 (2023)
DFHM8

https://doi.org/10.1051/e3sconf/202341503002

9.

M. Arattano, C. Abancó, V. Coviello, M.
Hürlimann, Comput. & Geosc., 73, 17-27 (2014)
10. V. Coviello, M. Arattano, F. Comiti, P. Macconi, L.
Marchi, Journ. of Geoph. Res. Earth Surf., 124 (6),1440-1463 (2019)
11. G. Nigrelli, M. Chiarle, J. of Mount. Sci., 18 (11),2842-2853 (2021)
12. M. Chiarle, M. Geertsema, G. Mortara, J.J. Clague,.
Glob. and Plan. Ch., 202, 103499 (2021)

As already mentioned, it is the first time that theALMOND-F system has been used in a situation of realrisk to protect the population. The alarm installation at
the Rochefort torrent could therefore constitute animportant case study, also to test people's behaviour inpresence of signs of danger. Authorities in charge of risk
management and mitigation could draw useful insightsfrom this case study, to provide local administratorswith guidelines and an ideal toolbox to deal with debris
flow risk mitigation.
Despite the long experimentation conducted over theyears in the Moscardo and Gadria torrents [7, 8, 10] todevelop the ALMOND-F system, and despite the goodfunctioning of this latter on the occasion of the debris
flow of August 5, 2022 in the Rochefort torrent, further
tests will be required to verify the full reliability of boththe algorithm and the replicability of the system in other
Alpine torrents.
The availability of reliable alarm systems is
becoming increasingly crucial in a context of climatechange [11], associated with growing slope instability,
especially in mountain areas [12]. Thus, the possibility
to further test the ALMOND-F system and improve its
performances will be of great help to increase thenumber of available and reliable alarm systems andbetter face the challenges posed by climate change.

References
1.

2.
3.

4.
5.

6.

7.

8.

M. Hürlimann, V. Coviello, C. Bel, X. Guo, M.
Berti, C. Graf, J. Hübl, S. Miyata, J.B. Smith, H.Y.
Yin, Earth-Sci. Rev., 199, 102981 (2019)
A. Badoux, C. Graf, J. Rhyner, R. Kuntner, B.W.
McArdell, Nat. Haz. 49 (3), 517–539 (2009)
M. Jacquemart, D. Tobler, C. Graf, L. Meier,Advanced debris‐flow monitoring and alarm system
at Spreitgraben, in Engineering Geology forSociety and Territory ‐ Vol. 3, 59–62 (2015)
M. Chiarle, S. Iannotti, G. Mortara, P. Deline,
Glob. and Plan. Ch., 56 (1-2), 123-136 (2007)
R. Paranunzio, M. Chiarle, F. Laio, G. Nigrelli L.
Turconi, F. Luino, Slope failures in high-mountainareas in the Alpine Region. PANGAEA, https://doi.org/10.1594/PANGAEA.903761(2019)
L. Marchi, F. Cazorzi, M. Arattano, S. Cucchiaro,
M. Cavalli, S. Crema, Nat. Haz. Earth Syst. Sci., 21(1), 87-97 (2021)
M. Arattano, V. Coviello, M. Cavalli, F. Comiti, P.
Macconi, J. Theule, S. Crema, Nat. Haz. Earth Syst.
Sci., 15 (7), 1545-1549 (2015)
M. Arattano, Monitoring the presence of the debris
flow front and its velocity through ground vibration
detectors, in Proceedings, Third Int. Conf. on
Debris-flow Hazards Mitigation: Mechanics,Prediction,andAssessment,editedby:
Rickenmann, D. and Chen, CL, Millpress,
Rotterdam (2003)

4