The experts say that water is the lubricant of Brienz. A clayey layer allows the village of Brienz/Brinzauls and the slope above it to slide down the valley. What if you could drain the water from the landslide? Would that slow down or even stop the slide? The geologist Reto Thöny and his team have searched for similar examples all over the world.
How many other landslides have you found that were affected or “remediated” with technical measures?
Enough to be optimistic about Brienz.
And how many of them were successful, how many were not?
Almost all of the restructuring measures described in the literature were successful. However, this may also be due to the fact that people prefer to report on successes rather than failures. That's a shame because you can learn from partial successes and failures in the same way.
Where did you look for these projects? How many studies or books have you read for this? How many pages was that?
(Laughs) It was probably many hundreds of pages that we read and studied. But only a small part of it was really comparable and transferable to Brienz slip. Because what worked elsewhere doesn't necessarily have to be successful in Brienz as well.
“There are examples of successfully implemented restructuring measures all over the world.”
Every landslide is different: different rocks, different steepness, different water conditions in the soil. Isn't a comparison difficult?
Comparability is in fact the biggest challenge in such literature studies. To do this, you have to study the individual landslides and the rehabilitation projects very carefully and then weigh up what is important. That's why we weren't looking for the perfect image of the Brienz landslide. Instead, we wanted to find out which remediation measures worked well or did not work well in the event of similarly large landslides or under similar geological and hydrogeological conditions.
How can you judge which of the other landslides could work for us and which would not?
In order to assess this, you have to know exactly and compare landslides. That is why our extensive research with numerous drilling and field tests lasting several years was so important. The evaluations of the last four holes on the Berg landslide have only recently been completed.
The most famous example of a functioning drainage system is less than 100 kilometers from Brienzer Rutsch in the Maggia Valley in Ticino. Can you describe the landslide in Campo Vallemaggia?
The Campo Vallemaggia landslide in Val di Campo is around twice as large as that of Brienz in terms of area and around four times as large in terms of volume. The slip speeds before the renovation were well below those currently measured in Brienz, but the two villages of Campo and Cimalmotto lying on the landslide nevertheless suffered considerable damage.
“The sliding movements were almost completely stopped within a short period of time.”
What has been done there to renovate it?
The experts disagreed as to whether subsoil water pressures or severe erosion caused by the Rovana River at the foot of the landslide were the main cause of the sliding movements. For this reason, a drainage tunnel under the landslide and a flood diversion tunnel were built for the Rovana.
And did it work?
Yes, the drainage tunnel worked. The sliding movements were almost completely stopped within a short period of time. Both parts of the village on the landslide have been habitable again since then.
However, the effectiveness of the diversion tunnel could no longer be proven.
Are there any other landslides that could be technically repaired?
Yes, there are examples of successfully implemented restructuring measures in literature all over the world. If you study them, you notice that when renovating large slopes, you rely almost exclusively on deep drainage measures.
With the two landslides La Frasse and Arveyes in the canton of Vaud and the Montagnon landslide in Valais, there are also three practical examples in Switzerland where drainage measures were successful.
Drainage stollen, as it could one day be built under Brienz slip, is one of the possible measures that you describe in your report. What other measures are there that have succeeded in other landslides?
Vertical and horizontal wells also showed good results in landslides in western Switzerland. Here in the canton of Grisons, large landslides such as those in Schuders or Heinzenberg could be fully or partially stabilized by raising rivers by means of barriers.
And why are they out of the question here?
The sliding speeds in Brienz are currently too high for drainage wells. The wells would shear off along the slide base even before they could have a sufficient effect. An effective elevation of Albula is only possible to a very limited extent because Surava is too low for that. And artificial raising of the entire valley floor and moving the Albula into a tunnel would be conceivable, but it would be a very big impact on the environment.
In your report, you describe in particular remediation measures for landslides in Switzerland. Are there no such projects abroad at all?
Yes, they do exist. Unfortunately, there are only a few well-documented examples of restructuring from abroad in the literature. In our study, however, we also included case studies from Canada and Italy. The effects there were similar to the examples from Switzerland.
Work has now begun on the exploratory tunnel below Brienz/Brinzauls. What is your forecast: Will it work?
It is extremely difficult to make a forecast in the event of the Brienz slide. The ongoing detailed geological investigations have not yet been completed. However, the exploratory tunnel will show whether the variant of deep drainage using drainage stollen at the Brienz site achieves the desired effectiveness.
“I'm optimistic”
Until when do we know if it works?
If we make progress on schedule with the exploratory tunnel, we should know more in spring to summer next year. However, the response of landslides to the exploratory tunnel will continue to be metrologically monitored and assessed until the end of 2023.
Settlements of the site have also been identified in Campo Vallemaggia. Do land and house owners in Brienz/Brinzauls now have to be prepared that the construction of the tunnel will change their properties?
Settlements on the surface of every tunnel structure must be expected, including when probing. The terrain is likely to be the largest directly above the tunnel. That is why the exploratory tunnel does not lead down to the village. The entire area is closely monitored using high-precision GPS measurements before, during and after construction of the exploratory tunnel.
At the moment, of course, we all hope that the renovation of the Brienz slide will be successful. What can you do if the tunnel is not successful? Have you found any other ideas in the many other landslides?
In landslides, which we have studied, deep drainage has always been the central element of the renovation. If the exploratory tunnel under Brienz slip shows that deep drainage is not having the desired effectiveness here, you would have to check whether you are achieving anything by combining various measures.
In the end, nature will tell us what is technically feasible. But we should leave no stone unturned. And as I said at the very beginning: I'm optimistic.
About the person
Reto Thöny, engineering geologist/hydrogeologist ETH, has been working intensively on Brienz slip since 2018. Together with his team from BTG Büro für Technische Geologie AG, he has searched all over the world for examples of how landslides can be stabilized through technical measures.
What inspires him about his work is the complex interplay of geological and hydrogeological processes during the Brienz landslide and the opportunity to contribute with expertise to understand the causes of the landslide and to find a solution so that the inhabitants of Brienz/Brinzauls can continue to remain in their village.
Reto Thöny is 39 years old. He lives in Igis with his wife and two children.
This interview was conducted on August 6, 2021 in the monthly Information bulletin from the municipality of Albula/Alvra on Brienzer Rutsch published. Christian Gartmann has been Communications and Media Officer at Municipality of Albula/Alvra to Brienz slip.