Innovative Probabilistic Methodology for Evaluating the Reliability of Discrete Levee Reaches Owing to Piping

Traditionally, levees are a popular measure widely adopted for flood control, accepted and trusted by populations living in floodplain areas. The presence of levees sometimes might even induce a false sense of safety in the population, influencing their decision to develop further in floodplains, because they feel safer. Thus, failures of levee systems are potentially devastating, as they might induce loss of human lives, damages to properties, and economic loss. This study proposes an innovative methodology to estimate the reliability of levee systems, accounting for different sources of uncertainty, and to divide and classify discrete levee reaches, according to different fragility classes. The reliability analysis is performed by evaluating the probability of failure, as a function of a certain failure mechanism, conditioned by a given hydraulic load. Fragility curves are determined using two different methods: Monte Carlo data generation and the so-called approximate, first-order reliability method. Thus, once having assessed fragility curves for each discrete levee reach, different fragility indexes are introduced to assess the reliability of the levee system. As a test case, this methodology is applied to determine the probability of failure due to piping along a branch of the Po River (Italy), where the probability of failure in case of a synthetic 100-year return period flood event is additionally estimated. The computed fragility curves are in agreement with historical observations of levee breaches along the River