On 15 June, 2023, more than 1.3 million cubic metres of rock and earth sped towards the Swiss alpine village of Brienz. Instead of tumbling towards sleeping residents, however, the landslide neared only empty beds and buildings. The village had been evacuated when precise and comprehensive monitoring data signalled the slide was imminent.
Monitored for several decades, various Hexagon technologies enabled hybrid approaches to measure the moving mountainside with high detail and frequency. This information, delivered to and interpreted by geological experts, allowed local authorities to issue warnings, road closures, and eventually evacuations, keeping Brienz’s 84 residents safe.
THE MOVING MOUNTAINSIDE BORDERING BRIENZ
The Alps were born from movement as the African and European tectonic plates slowly collided over millions of years, and movement continues to reshape these famed mountains today. Some of these changes stem from the climate, like precipitation and snowmelt, others have geological reasons, including steep terrain, erosion, rock and soil composition, and seismic activity.
Brienz, a picturesque alpine village in the Swiss canton Graubuenden, sits 1,150 metres high between the Piz Linard Mountain peak and the Albula river. Classic Swiss architecture is set against myriad green, broken only by the island of rock poised above the town.
According to Andreas Huwiler, the Head of Natural Hazards and Protective Structures for Graubuenden, “the area is of great geological interest because it has many rock combinations that interact or react in very special and complex ways, making it hard to predict how these rock piles will behave.”
The Brienz community has long traced the changes to the rocky slope above them, watching the evidence of mountainside movements infiltrate in the form of large cracks running along roads and building façades. However, accelerated movements in the 2000s meant resident observations and occasional manual measurements by experts had become insufficient to understand the situation, necessitating more precise and dense data collection.
EXPANDING MONITORING TECHNIQUES FOR DECISIVE DATA
From taking measurements manually to installing several automated systems that provide comprehensive data in concert, the monitoring concept in Brienz evolved over time according to need. Hexagon technologies and services provided data relevant to each stage of acceleration and risk.
“The instability has been getting faster over the past ten years, and alongside this acceleration, the monitoring concept has also been continuously expanded,” says Huwiler. “It started with fissure measurements carried out by hand. We then quickly switched to a total station measuring reflectors or fixed points for distance measurements.”
This early phase required campaign monitoring, in which measurements were taken periodically by an expert on site with a robotic total station from Leica Geosystems, part of Hexagon, to determine movements through deviations from baseline measurements.
A long-time sentinel watching over the mountain from a protective miniature cabin, the total station was installed and has been operational in Brienz since 2009.
“The total station, which has been here the longest, is of course very accurate and the results are very clear. It was built in 1998, so it is celebrating 25 years of service this year and we’ve never had a reason to replace it because it’s very reliable,” reflects Christian Vetch, Managing Director of HMQ Geomatik AG and part of the surveying team on the project.
However, as movements increased, more frequent data collection with an automated system became necessary. By adding a communication device and connecting the total station to Leica GeoMoS monitoring software, measurements were automatically collected, transferred, and analysed. With this information, experts could determine how fast and in what direction the rock face was moving.
REAL-TIME MONITORING WITH RADAR AND IMAGERY SYSTEMS
In 2019 when data from the total station indicated the movements were again accelerating, radar and imaging monitoring systems were added for comprehensive, real-time data. Alpine monitoring experts from Geoprevent, part of Hexagon, joined the project to develop, install and operate a monitoring concept using radar and imaging sensors to supplement the total station measurements.
For Geoprevent’s Andreia Farrér, a Monitoring Solutions Consultant who worked on the project, it was not only an interesting case, but a personal one: “From my bedroom window, I was able to watch the slope movements throughout my entire childhood,” he says. “That’s why it is pretty special for me to work on this project.”
Geoprevent installed an interferometric radar warning system, a rockfall Doppler radar alarm system, and a deformation camera to survey the area more extensively and continuously. Ground-based interferometric radar from IDS GeoRadar, part of Hexagon, together with Geoprevent's proprietary algorithms, delivered sub-millimetre displacements. Taking spatial measurements remotely, the radar observes the phase changes of reflected microwaves, comparing the measurements to calculate and detect deformations.
“Compared to other methods, we have a major advantage with the radars because we can take measurements at any time of day and, most importantly, in any weather, such as fog, snow, or rain,” explains Farrér. “This ensures that the most up-to-date information is available at all times.”
Additionally, the deformation camera takes high-resolution images of the rock face, tracking groups of pixels across images and measuring deformation based on the displacements of tracked pixel groups.
“We then provide this measurement data to the specialists in the community, specifically the early warning service, which includes various geologists and other specialists who look at the data and then interpret it,” says Farrér.
Geoprevent makes this data accessible to the experts through their online portal where the measurements are uploaded, processed and visualised for a clear overview of the real-time data, anytime.
“Real-time data is generally extremely important” continues Farrér, “because we want to record the development or possible changes on the mountain as early and as quickly as possible so that the authorities can implement safety measures, such as roadblocks or, as in this case, an evacuation.”
SOLIDARITY AMIDST UNCERTAINTY: BRIENZ’S EVACUATION AND RETURN
In late March, experts determined a collapse was imminent, making it necessary to prepare Brienz residents for evacuation.
“We saw before Easter that the acceleration of the island had increased significantly, and we could no longer rule out the possibility that it could collapse within a few weeks and then become a danger to everyone in the village,” reflects Christian Gartmann, media representative for the community.
With increasingly dramatic warnings from authorities, the residents packed their belongings and farmers relocated their animals. “On the evening of 8 May, the village was empty of people and animals. An eerie scene,” says Gartmann. “We didn’t know what was going to happen. Brienz could have been damaged or destroyed. We also didn’t know how long the evacuation would last. This uncertainty was very stressful for those affected.”
However, amidst this turmoil was a silver lining of Swiss-wide financial and housing support for the displaced residents.
“The solidarity was immense,” continues Gartmann. “As soon as we had to talk realistically about an evacuation, we immediately received offers of help from the neighbouring municipalities, but also from all over the canton and Switzerland. There were 84 people evacuated from this village and we were offered over 130 homes for them.”
When the collapse came, the rockslide debris overflowed onto a road bordering Brienz, stopping just short of the village — Brienz emerged unscathed. Afterwards, slope monitoring continued, now to determine when stability levels would indicate it was safe for residents to return. At the end of June, movements had slowed, and a phased return of relieved residents commenced.
As partners in this endeavour, Hexagon solutions helped ensure the Brienz monitoring team had the real-time information they needed to issue timely measures, including evacuation and the all-clear to return. While environmental monitoring cannot thwart a moving mountainside from collapse, it enables data-based decisions that keep those in danger’s path safe.
The monitoring story for Brienz continues as slope instabilities remain a risk. However, the community can rest assured that reliable data in the hands of experts will continue to create timely guidance and guide action.
