Application of Fragility Curves in Operational Flood Risk Assessment

The aim of this article is to present and discuss fragility curves that were derived for numerous dikes in the Netherlands within the Dike Data Service Centre (DDSC) initiative. A fragility curve of a dike is a mapping from the set of loads, acting on the dike, to the set of conditional dike failure probabilities. The DDSC is a platform around a database for measurements related to water defences in the Netherlands. The measurements include real-time and historical data such as height measurements, pore water pressures, temperature etc. Besides the database functionality, the DDSC can be applied to interpret the information and issue warnings. The fragility curves were derived for failure mechanisms overtopping, piping and macro-stability as well as for combination of these mechanisms. Also, application of the fragility curves is addressed. The application includes: (i) insight into the effect of reducing uncertainties in subsoil-related parameters on the dike's reliability, (ii) derivation of the actual flooding probability and the actual local mortality risk, and (iii) prioritization of emergency flood measures. The derived fragility curves are conform findings of past studies: for water levels lower than the dike height, piping and macro-stability play an important role. Furthermore, the fragility curves prove to have an added value in operational flood risk assessment.