Rockfall Hazard Analysis at Small Scale: A Numerical Study for the Estimation of Representative Slope Parameters

The identification of rockfall-affected areas depends on a large number of stochastic variables influencing both triggering and propagation phases. Therefore, rockfall hazard assessment presents huge uncertainties linked to the various scales of analysis. At the small scale (e.g. valley scale), a quick evaluation of rockfall hazard zones is generally required in order to highlight the most critical situations where more detailed analyses should be carried out. The Cone Method (Jaboyedoff and Labiouse 2011), recently implemented in the QPROTO plugin for QGIS, allows to reach this goal with simplified geometrical considerations. In a 3D analysis, the energy line angle and the lateral spreading angle α define a cone of propagation whose apex is located in the rockfall source point. The most significant issue in using the plugin is the evaluation of these angles, which must be defined by the users to consider all the rockfall dissipative processes included in the energy line method (Evans and Hungr 1993). In this paper a study concerning the influence of slope properties (forest coverage and slope inclination) and block characteristics (shape and volume) is proposed, in order to provide to the users of the plugin a preliminary dataset of calibrated angles.