Debris flow in Chamoson

A debris flow in 2019 in Chamoson, Switzerland, a result of a violent storm, caused a flash flood and debris flow on the Losentz River, which passes directly through the village. The event was big enough to carry two vehicles in its path. Debris flow is relatively common natural hazard which occurs when unusual quantifies of rainfall transport sand, rocks, gravel or wood in a flash-flood-like event and can reach speeds up to 50 km/h.

The village of Chamoson is built on land which is made of thick layers of accumulated sediments. Although the village was built at its current location in the 19th century specifically to avoid exposure to the flooding of the Rhone River, Chamoson is nonetheless still exposed to hazards. It sits at the junction of two rivers, the Losentz and the Saint-André which can, during big rain events, like the one in 2019, and remains exposed to dangerous debris flows.

The Commune of Chamoson continues to work on protective measures for the village. Since 2011, they invested 7 million francs, and have again invested 10 million more as a result of the event of 2019. The investment has allowed the commune to reduce exposure specifically to debris flows, and now only the land directly next to the river remains in a high hazard zone, as the above map demontrates.

The commune has further plans to expand their public outreach and education by creating new hazard maps, which will explain current and future protection projects.

Additionally, the commune has set up an SMS alert system, which can activate barriers to reduce road access near the river during times of heightened hazard. As well, they have installed numerous panels which provide warning along local walking paths.

Flashing lights and sirens will be installed, in addition to the panels, to warn and inform pedestrians. As well, the commune plans to re-route the walking paths which cross the river. Having taken the lesson from the 2019 incident, the local authorities are now more clearly focusing on communicating about natural hazards to the public, and educating them about how to avoid the risk.

After the first debris flow in 2018, the Commune had already taken action to reduce public exposure to debris flow hazards, but have since learned that communicating their efforts to the public is also a necessary component of the management plan.

Reference

[1] Flyer of the Commune de Chamoson, available on www.chamoson.net/dangersnaturels