From rapid assessment to real-time warning: short-term rockfall monitoring along the Route d’Anniviers (Valais, Switzerland)

From rapid assessment to real-time warning: short-term rockfall monitoring along the Route d’Anniviers (Valais, Switzerland)

 

The Val d’Anniviers is one of the major valleys of the canton of Valais in Switzerland. Well known for its winter sports opportunities and for the villages of Grimentz and Zinal, the valley is accessible by a vertiginous road exposed to a wide range of gravitational hazards. Though the Route d’Anniviers is protected by multiple galleries, severe events can still impact the road.In March 2024, a series of rockfalls led to heavy accumulation of debris atop a road gallery at the entrance of the valley. A week later, on 29 March, bigger blocks hit the road and perforated the gallery. To avoid complete isolation, an alternative route estimated to be less safe was used from the other side of the valley. In this context, real-time monitoring became essential to support decision-making and rapid response during emergency operations and gallery rehabilitation. A first emergency phase focused on rapid assessment: Geoprevent was mandated by the local authorities to deploy an interferometric radar to monitor and accurately assess the area above the Croisettes sector (near Vissoie) and check whether significant movement was ongoing. Early observations suggested only limited changes. This initial phase helped establish shared situational awareness and informed the next steps toward an operational warning setup. An alarm system was then needed to be installed to increase the safety of workers during the gallery renovation, as well as to contribute to a longer-term mitigation plan. Geoprevent was mandated on 10 April by the local authorities and installed a rockfall Doppler radar on 22 April. This technology enables real-time detection of rockfall activity. The radar was coupled with traffic lights and alarm horns, allowing rapid road closure and immediate on-site warning in case of events. SMS and email alerts complement local signaling, and both radar data and live footage from a pan-tilt-zoom remotely controllable camera are available through Geoprevent’s online data portal for remote supervision and event review. This contribution  presents the phased monitoring and warning approach implemented at Vissoie—from rapid assessment to operational warning system —and discusses lessons learned for short-term monitoring, emergency installation, data interpretation, and reliable alerting to insure road and people safety in a complex environment.