Regional rockfall hazard assessment in the Benasque Valley (Central Pyrenees) using a 3D numerical approach

Rockfall hazard assessment is a fundamental land planning tool in high mountain area. In this paper, a new rockfall hazard methodology is applied, based on the results of a 3D rockfall numerical model performed through an original simulation code. This is based on a lumped mass algorithm and allows to simulate rockfall motions in a spatially distributed way on a 3D topography described by a DTM. Model results can be combined in a GIS in order to produce physically based rockfall hazard maps according to a 3D matrix approach providing both a positional “hazard index” and a “hazard vector”. The method has been tested at a regional scale in the Benasque basin, a 290 km2 mountain area in the Huesca Province (Central Pyrenees, Spain). A DEM with cell size of 25*25 m has been used to describe topography. Information concerning lithology, geomorphology and vegetation of the area have been combined in a unique condition map to characterise the different slope materials and to identify outcropping areas and rockfall source areas. The model has been run with a stochastic approach and calibrated by geomorphological observations. Results have been combined in a 3D hazard rating matrix to obtain positional and vector hazard indexes. Different hazard maps has been produced in order to outline the exposed areas and to evaluate possible land planning solutions