Representing fragility of flood and coastal defences: Getting into the detail

Investment planning and decision-making for performance-based management of flood and coastal defence assets requires representation of their fragility. Generalised defence fragility representations by major asset types may be used for broad-scale systems analysis, but when making local asset management decisions more structure-specific representations become important. The FLOODsite and UK FRMRC projects have developed a Reliability Tool to generate structure-specific fragility curves, based on a reliability analysis of multiple potential failure modes linked by fault trees. To assist practicing engineers to understand, accept and start using fragility curves, work has been carried out under the UK PAMS (Performance-based Asset Management System) project to clarify the connection between deterministic and probabilistic approaches, and to demonstrate ways (including use of the Reliability Tool) of estimating or calculating defence fragility starting from conventional engineering practice. The paper will present conclusions from this work, giving some example comparisons between deterministic design and full reliability analysis.