The Brienz slide in the Graubünden municipality of Albula/Alvra is still moving very fast, but the landslide has calmed down somewhat in recent months. However, the municipality continues to prepare for a possible worsening of the situation. At the same time, the construction of an exploratory tunnel is being prepared, which could drain the landslide and thus slow it down.
For the seventh time on Thursday evening, the municipality of Brienz/Brinzauls informed the population about the current situation in Brienz Rutsch and ongoing work to protect those affected and to repair the landslide. After sharp increases in speed in 2018 and 2019, the Brienz slide has calmed down somewhat overall since last winter. However, the village of Brienz/Brinzauls and the mountainside above are still moving very fast.
The village slides 1.10 m downhill per year, the mountain 2 to 6 meters per year. In the first half of June, the landslide on the mountain showed a sudden, sharp increase in speed and many rockfall events. The cause was heavy rainfall on June 7. The situation quickly calmed down again.
New holes to study the subsoil
On July 23, the first of four new exploratory drillings began, which will help investigate the subsoil above the village of Brienz/Brinzauls. Since the drilling is carried out on very rough terrain, a specially lightweight drilling rig had to be purchased. Their parts were flown to the drilling site by heavy-duty helicopter.
Another focus of ongoing work is clarifying the construction of an exploratory tunnel under the landslide and the village of Brienz/Brinzauls. Such a tunnel can help to drain and thus slow down the entire landslide.
The planned exploratory tunnel is to be drilled from above Tiefencastel in a right turn towards Brienz/Brinzauls. It is around 500 meters long and has a diameter of just over three meters. From this tunnel, which is built in solid rock under the sliding mass, smaller holes can be drilled to drain the landslide. It is possible to start construction of the exploratory tunnel from April 2021. If the results of the probing are good, the sounding tunnel can be converted into a drainage tunnel.
Effects of a rock slide on the Albula River
In the event of a major landslide, rock masses could reach the Albula riverbed and dam up the river there. In the worst case scenario, the water could reach the lower-lying districts of Surava below the railway line. How quickly a lake would form after a rock slide depends on the amount of water that the Albula then carries. The lowest houses in Surava would be reached after half a day or even after several days from rising water.
The maximum water level, around 10 meters below the train station, could be reached after days or even months. If landslide mass were deposited in Albula, the river would remove large amounts of debris. These would probably be deposited again in the area of the industrial zone above Tiefencastel and in the plain to Tiefencastel. However, the experts emphasized that the probability of a rock slide, which is so great that the Albula would jam up, is very low.
The renovation of drainage systems above Brienz has begun. By late autumn, several kilometers of open canals will be laid, which drain the area's surface water so that it cannot seep into the landslide.
Christian Gartmann is the media and communication officer for the municipality of Albula/Alvra for the Brienz slide.