An approach for evaluating the role of protection measures in rockfall hazard zoning based on the Swiss experience

Rockfall hazard zoning is essential for ensuring the safety of communities settled at the toe of potentially unstable slopes. Rockfall hazard zoning can be performed to include the effect of protection measures when land use restrictions might not be enough to mitigate hazards. The real effectiveness of the measures must be assessed to make sure they can play their role, especially in those cases when measures might have been installed at a given site for years. This article focuses on how to evaluate the effectiveness of rockfall protection measures and how hazard zoning can be influenced by their correct operation. The approach presented is divided into four main stages, which include a two-step procedure to evaluate the effectiveness of both existing and new protections. It is based on quite a comprehensive rockfall protection database built for the canton of Vaud in Switzerland, and on the Swiss Federal Guidelines for hazard zoning; however, all the methodological framework proposed and related considerations could be in principle extended to any other regional or national context in which a combination of intensity and frequency is used to assess rockfall hazards.