Technical note: Preliminary estimation of rockfall runout zones

Rockfall propagation areas can be determined using a simple geometric rule known as shadow angle or energy line method based on a simple Coulomb frictional model implemented in the CONEFALL computer program. Runout zones are estimated from a digital terrain model (DTM) and a grid file containing the cells representing rockfall potential source areas. The cells of the DTM that are lowest in altitude and located within a cone centered on a rockfall source cell belong to the potential propagation area associated with that grid cell. In addition CONEFALL allows to estimate mean and maximum velocities and energies of blocks in the rockfalls propagation areas. Previous studies (Onofri and Candian, 1979; Toppe, 1987; Wieczoreck et al., 1999; Lied, 1977; Evans and Hungr, 1993; Corominas, 1996) indicate the slope angle cone ranges from 27° to 37° depending on the assumptions made, i.e. slope morphology, probability of reaching a point, maximum run-out, field observations, etc. Different solutions based on previous work and an example of an actual rockfall event are presented. In addition CONEFALL allows to estimate mean and maximum velocities and energies of blocks in the rockfalls propagation areas.