Using geomatics and airborne laser scanning for rockfall risk zoning: a case study in the French Alps

In mountainous areas, rockfalls represent a major threat to human safety, public infrastructures and economic assets. Accurate mapping and qualification of risk areas are required so that public authorities can make secure and efficient decisions regarding town planning schemes. In France, Risk Prevention Plans (PPR) are standard documents that determine risk areas and building authorisations for ten-year periods. During the PPR revision of the town of Veyrier-du-Lac (France), we implemented a new methodology based on geomatics for rockfall risk assessment. Analysis of airborne laser scanning data, field data and 3D rockfall simulations was performed with geographic information system (GIS) to accurately map hazard areas and their associated intensity and frequency. Decision makers could then interactively discuss the implications of different hazard thresholds before the final risk maps were edited. The coordination of information in a GIS improved the interactions between experts and decision makers. The use of high resolution data and algorithms allowed a fine zoning of risk maps with quantification of forest protection effect in a complex environment.