Improving the Representation of the Fragility of Coastal Structures: Brunel Seawall (Dawlish, UK)

The fragility of a flood defence is defined as the probability of it structurally failing when subjected to a particular loading. Until recently, the representations of a defence’s fragility adopted in UK flood risk analysis have been restricted to those that express the likelihood of failure conditionally on a single loading variable. Due to limitations relating to the modelling of the dependence structure between the hydraulic loading variables. In the coastal setting multiple loadings simultaneously act on a flood defence, each influencing the prevalence of different failure mechanisms to differing extents. Describing the probability of failure conditionally upon a single loading variable therefore has the potential to introduce inaccuracies into the analysis. By way of a case study, the changes that may be expected in the estimated fragility of a defence when its probability of failure is expressed explicitly conditional on multiple variables are examined. The inclusion of more detailed information about an asset and the effects of storm clustering are also shown to influence the estimated fragility.