Following the landslide at Piz Cengalo in 2017, the new protective structures in Bergell in the Swiss Alps are being built according to a pioneering concept

Before the landslide of August 2017: in front on the right, the Bondasca creek enters the picture and, in the center of the picture, flows into the Mera river, which flows down the valley to the left.The same view after the landslide: the Bondasca creek transported a huge mass of mud into the valley and destroyed some houses in the adjacent villages.

A gentle design is to integrate the dams and walls into the localities and the landscape

An innovative concept is being followed by the new protective structures that will, in future, protect villages in Bergell in the Swiss Alps from landslides and mudslides: in their design, they draw on traditional changes to the landscape caused by man, and thus aim to preserve or improve the quality of life for the inhabitants in addition to providing disaster protection.

We remember: on August 23, 2017, a mass of 3 Millionen m³ of rock broke off the mountain at Piz Cengalo above the large municipality of Bergell (Italian: Bregaglia) on the border with Italy and went down into the valley as an avalanche of mud and stone. It was the unimaginable amount of 500,000 m³, it mowed down everything in the valley of the Bondasca creek and caused severe destruction there and in the valley of the Mera river. 8 hikers died.

That was only the beginning of the threat: experts say that there are still about 5 million m³ hanging at the top of the mountain massif, which have become unsafe.

One reason is climate change, and it’s happening elsewhere, too: warming is disrupting permafrost in mountains, causing the ice at high elevations to thaw temporarily. This means that the rock, with its many cracks and fissures, lacks the glue, so to speak, that used to hold it together, and under certain conditions large amounts of material then go down into the depths.

In the case of the catastrophe in August 2017, the mudslide, known as a mudflow, started in dry weather of all times: the mass of rock falling from the mountain had crashed onto a glacier and with its weight had forced the water into the ground under the ice to the surface, so that all the ingredients for the slide were thus in place.

In September 2021, construction work began on improved protective dams in the valley with the villages of Bondo, Sottoponte, Spino and Promontogno.

An innovative objective had already been set in the tender: First, the protective walls and dams were not only to provide safety from the disaster of mudslide plus flood. Secondly, it was also a question of taking into account the concerns of the residents: The protective structures were to blend into the culturally and historically valuable landscape as much as possible.

For this reason, the competition explicitly invited interdisciplinary working groups to submit their ideas: engineers for water, road and bridge construction were to work together with experts for landscape design to come up with solutions.

The list of the members of the team that won 1st place is correspondingly long: Conzett Bronzini Partner (Chur), Caprez Ingenieure (Promontogno), Eichenberger Revital (Chur), mavo (Zurich) in collaboration with Müller Illien Landschaftsarchitekten (Zurich), and Conradin Clavuot (Chur).

Their recommendations focused initially, of course, on the usual structures against mudslides:
* a raised dam on the Bondasca creek where it comes down from the mountain,
* an enlarged catch basin for it,
* a protective wall also along the Mera river, into which the Bondasca creek flows,
* and some other things.

But what was ground-breaking was HOW the winning team placed these measures in the landscape.

The new valley of the Bondasca creek with the terraces instead of steep slopes on the sides.The new valley of the Bondasca creek.

Thus, the new valley of the Bondesca creek, which is now 12 m deep, is by no means bordered by steep concrete embankments. Rather, instead of steep slopes, there are staggered terraces.

They echo the image of the surrounding area, where residents have farmed since time immemorial.

“The surrounding topography was virtually projected into the project,“ says Ueli Weber, vice president of the municipality of Bregaglia, outlining the idea.

The gentle design also included the new embankment along the stream. On the village side, the embankment is designed as a dry stone wall, i.e., a wall made of small stones in loose layering entirely without mortar.

On the new dam itself runs a walking path for locals and tourists.

In the valley of the creek, the deeper, the thicker the massive stone chunks set in concrete. Above, they have dimensions suitable for humans, so to speak.

Beyond the dam walls, this has created new areas in the villages that can be used by the inhabitants. One report says that the residents are already busy planning to hold festivities there.

The new bridge Punt with more camber than usual.

The design of the new bridges was also based on the design familiar from the area: they are arched higher than is usual today – this also creates a greater flow under the arch.

Mostly boulders that came down into the valley with the rockfall were used in the construction. It is about 200,000 tons. Geologically, the rock is Bondasca granite. Studies showed, contrary to expectations, that it is of very good quality. In order to split it to the desired size, a special splitting machine was designed.

The very large boulders at the base of the dams are Soglio quartzite.

The very large boulders at the base of the dams are Soglio quartzite.

The careful design of the facilities was also intended to allay the fears of the residents that the protective measures would eventually grow over their heads, so to speak. In the future, some residents will have a wall 3 m high practically on their doorstep.

One description sums up: “Since our settlement areas have expanded considerably, natural hazards are moving ever closer. Protective structures in the future must be interwoven with the context of a place.“

The project was nominated for the Council of Europe Landscape Award.

Civil Engineering Office Graubünden

Bergell / Bregaglia: Piz Cengalo (Italian) (Italian)

Photos: Bergell municipality / Civil Engineering Office Graubünden

The new hiking trail.The walls also pick up the old design.The walls also pick up the old design.

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(19.06.2023, USA: 06.19.2023)