Brienz, a success story in slope movement monitoring

In a world where natural disasters can strike at any time, geohazard monitoring becomes an imperative to protect lives, property and communities.

Brienz today represents a success story of this type of action. A clear example of how science, technology and early warning systems save lives.

But let’s find out a little more about what’s going on in this corner of Switzerland.

Brienz, a village on the move in the shadow of a looming hillside

Brienz/Brinzauls is a small rural commune in the district of Albula, Switzerland (not to be confused with the village of the same name near Interlaken).

https://map.geo.admin.ch/?lang=en&topic=ech&bgLayer=ch.swisstopo.pixelkarte-farbe&layers=ch.swisstopo.zeitreihen,ch.bfs.gebaeude_wohnungs_register,ch.bav.haltestellen-oev,ch.swisstopo.swisstlm3d-wanderwege,ch.astra.wanderland-sperrungen_umleitungen&layers_opacity=1,1,1,0.8,0.8&layers_visibility=false,false,false,false,false&layers_timestamp=18641231,,,,&E=2764760.21&N=1171306.92&zoom=7

Built on a deformation of the hillside that stretches from the top of the Piz Linard to the Albula river, the village has not stopped moving. Or rather, tearing itself apart. In fact, surveillance of this area began around 1930, once the geological risks to which the urban centre was exposed became apparent.

Thus, the constant displacement of the ground is clearly perceptible, with several constructions cracked. Without going any further, the church tower itself shows a clear vertical deflection of half a metre.

The biggest threat to Brienz, however, is he hillside to the north of the village. And especially the compartment known as “The Island” (Insel in German), an area with a volume of about 2 million m³.

An early warning system designed to monitor geological hazards

As you can see, geological hazards are a constant in this part of Switzerland.

So, given the potential for a major rock and landslide, a comprehensive early warning system was installed in 2011 to facilitate geological monitoring.

As of today, this solution consists of:

• a georadar;
• a Doppler radar;
• one robotic total station;
• two time-lapse cameras (TLC) with automated image processing (DIC);
• several webcams (one of which is accessible from this link);
• two seismic stations;
• several weather stations (with similarities to the weather stations we offer at Arantec);
• fourteen permanent GNSS stations; and
• periodic LiDAR generation, drone and helicopter flights and GNSS measurements.

A detailed final protocol for the interpretation of early warning data and alarm threshold values was established in March 2023.

Chronology of a foretold landslide

The Insel compartment has been gradually increasing its activity in recent years. Rockfall, for example, has been quite common, although without posing severe geological hazards.

Similarly, some actions have been taken to reduce slope movements, such as the opening of a drainage tunnel in 2021. However, this solution does not seem to have had any effect.

However, October 2022 marks a turning point, with a perceptible acceleration of the Insel’s displacement, which increased until it exceeded 100 mm per day in May 2023.

It was at this point that the decision was taken to evacuate Brienz.

The approximately 85 permanent residents received a notice urging them to leave their homes between 9 and 12 May.

Night of 15-16 June: part of the mountain collapses

When a preventive evacuation of this nature is ordered, it is because there is a very high degree of certainty that something is going to happen. But, obviously, you don’t know when.

During the month that elapsed between the departure of the Brienz inhabitants and the collapse, rockfall was constant.

But the biggest landslide did not occur until mid-June, on the night of the 15th to the 16th.

The mass of earth and rocks that rushed down the mountain (approximately 1.2 million m³) was left near the village school, destroying a small shed in its path.

It is estimated that between two-thirds and three-quarters of the compartment has collapsed. Although detailed surveys are still being carried out, it is expected that the Brienz residents will be able to return to their homes in the coming months.

“At this stage, I’m not sure we will be able to return before next spring. However, it could have been a lot worse.

Renato Liesch, resident en Brienz

What lessons can we learn from this event?

This landslide, transmitted in near real time, has four key lessons to teach us:

• The importance of constant monitoring to mitigate geological risks: through advanced technologies, such as seismic sensors, inclinometers (similar to those we have installed in Castellfolit) and radars, it is possible to detect subtle changes in slope movements and other geological phenomena. These early warning systems allow preventive and evacuation measures to be taken before disasters occur.
• The relevance of geohazard planning and management: identifying high-risk areas, assessing the vulnerability of infrastructure and planning evacuation routes are some of the measures that should not be left to chance.
• The importance of collaboration between different actors (local communities, research teams, companies, etc.): joint research, knowledge sharing and active community participation are essential to develop sound and sustainable strategies.
• Awareness raising and education: it is essential that communities understand the geohazards to which they are exposed and know how to respond to them.

It must be recognised that this degree of monitoring and surveillance is unusual.

However, the changes that mountains are undergoing, in some cases aggravated by climate change (e.g. thawing permafrost), make it necessary to reinforce surveillance in areas subject to increased geological risks.

Brienz teaches us that investing in geohazard mitigation not only saves lives. It also preserves our future and enables us to build safer and more resilient societies.