Reliability of flood embankments: a new methodology

Predicting the structural performance of embankments in extreme hydraulic conditions is essential to flood risk assessment. It is, however, a difficult task, owing to the general lack of information about the characteristics and conditions of earth structures in geographically extended and heterogeneous flood defence networks. The approach to flood embankment reliability currently adopted in the UK has some problematic aspects. In particular, the modelling of piping through the embankment is not completely satisfactory. Moreover, the use of condition grades, which lump together factors affecting different failure modes, may be misleading. The methodology presented in this paper, developed to overcome these limitations, is based on the estimate of the probability of breaching associated with a limited range of water levels. In this work, while other failure modes are treated with the traditional methods of structural reliability, through-piping is addressed with a rigorous elicitation of subjective probabilities. The methodology explicitly links the lack of knowledge to the uncertainty about the performance prediction. The final users are provided with tabulated solutions for a quick reliability assessment, the evaluation of uncertainty and the identification of the information needed to produce a better prediction.