Assessment of Risk due to Debris Flow Events

The traditional approach to hydraulic engineering problems, such as the designing of dams or embankments or, specifically in the case of consideration, the designing of a settling basin for debris flows, is deterministic and uncertainties are not explicitly considered in the evaluation of the designed structure. Nowadays some effort is made to consider phenomena in a probabilistic rather than deterministic framework, in order to respond clearly to the demand for reliability. In this paper, failure, damage, and risk are exemplified for a debris-flow prone basin and considerations on the acceptable amount of risk are presented. The evaluation of debris flow hazard is carried out for a specific site (Acquabona, Italy). The standard methodology used to perform a risk assessment analysis is applied. All relevant failure modes are represented by failure functions and each of the function's variables is described by a statistical distribution; all relevant uncertainties are included in a Level II probabilistic calculation and failure probability is evaluated with a first order reliability method. Finally, the probability of failure is compared with the acceptable amount of risk.