Failure probability of regional flood defences

Polders in the Netherlands are protected from flooding by primary and regional flood defence systems. During the last decade, scientific research in flood risk focused on the development of a probabilistic approach to quantify the probability of flooding of the primary flood defence system. This paper proposed a methodology to quantify the probability of flooding of regional flood defence systems, which required several additions to the methodology used for the primary flood defence system. These additions focused on a method to account for regulation of regional water levels, the possibility of (reduced) intrusion resistance due to maintenance dredging in regional water, the probability of traffic loads and the influence of dependence between regional water levels and the phreatic surface of a regional flood defence. In addition, reliability updating is used to demonstrate the potential for updating the probability of failure of regional flood defences with performance observations. The results demonstrated that the proposed methodology can be used to determine the probability of flooding of a regional flood defence system. In doing so, the methodology contributes to improving flood risk management in these systems.