The Grisons village of Brienz between Lenzerheide and Davos has been sliding down the valley for years. Now a drainage tunnel should stabilize the mountain.
Brienz/Brinzauls, located on a sun terrace on the connecting road from Lenzerheide to Davos high above the Albula Valley, has probably been sliding down the valley since the last ice age. In the past 100 years, it was mostly a few centimeters per year. In the past 15 years, however, the situation has become unstable. Boulders seven times as thick as those at Bondo Rockfall are moving at an ever faster pace. The village, which has around 80 inhabitants, is currently moving around 150 centimeters downhill every year. The slide area in this mountain village at around 1150 meters is 2.4 square kilometers.
Buildings become uninhabitable
The church tower has been crooked for years, numerous houses have cracks. Now, however, the damage to buildings and infrastructure has increased significantly. As the Graubünden government announced on Thursday, it is to be expected in the medium term that the buildings will become uninhabitable and facilities will have to be abandoned.
Experts have been looking for possible solutions for several years. Although the investigations have not been completed, the canton wants to act now. According to the statement, initial findings have shown that reducing the water pressure can actually slow down the movements.
The government is therefore applying to the Great Council for a commitment loan of CHF 40 million to implement a definitive drainage tunnel. This should help to avoid even greater damage and costs for the village and the public sector.
“Try everything humanly possible”
With a drainage tunnel, water can be permanently drained from the slipping and solid mass under the village. “You have to try everything humanly possible to save the village,” said Mario Cavigelli, head of the Graubünden Department for Infrastructure, Energy and Mobility, on Thursday. The requested credit commitment is expected to be dealt with in the December session of the Grand Council.
For the time being, however, further follow-up investigations are necessary in order to be able to better plan and predict remedial measures and risk scenarios. The government has now approved a contribution of CHF 1.35 million for this work.
First hopeful results
A 635 meter long exploratory tunnel has been under construction below the village since May 2021. He brought the first insights into hydrogeological and geotechnical questions. It has been shown that the landslide in the area of the exploratory tunnel has actually slowed down, they say.
However, it is still unclear whether this exploratory tunnel can be expanded into the actual drainage tunnel in the future. Because, according to the geologists, it is not yet known how the optimal alignment of a drainage tunnel should run and how many and how long drainages have to be drilled into the rock around the tunnel in order to drain the water.
Depending on the variant (expansion of the existing exploratory tunnel into a drainage tunnel in stable rock, new construction of a second drainage tunnel in the slip mass or even a combination of both variants), costs of CHF 20 to 80 million can be expected, according to the government message .
The CHF 40 million now requested will probably cover the costs for variants based on expanding the exploratory tunnel into a drainage tunnel. These variants are expected to be feasible in the short term and with reasonable uncertainties.
Ultimately, however, it remains to be seen whether the structural measures can really slow down the landslide sufficiently to save Brienz. For this you have to wait for the further test results from the existing exploratory tunnel, says government councilor Cavigelli. The landslide has been monitored around the clock for years.