Fragility curves in operational dike reliability assessment

Operational flood prediction and flood risk assessment have become important components of flood management. One main aspect is the reliability assessment of the flood defence line during a flood event. This is generally performed by a comparison of the water level in the river to the crest height of the dikes whilst taking only hydraulic and geometric aspects into account. Additional information about material zones and material parameters are often available. However, these data are not in an appropriate shape when deriving the reliability of the flood defence line. This paper outlines how the fragility curve of a dike section is used to appropriately integrate geostatic and geohydraulic dike characteristics into operational flood management systems. Fragility curves are the result of a model-based reliability analysis and they summarise the dike performance depending on the water level. Failure modes such as piping or slope failure are included. In a case study, fragility curves for dike sections along the River Emscher (Germany) are determined. Their practical implementation in an operational flood management system shows an improvement in the operational reliability assessment due to the additional information taken into account. The use of fragility curves also supports the decision-making processes when emergency flood protection measures are required.