Influence of load interdependencies of flood defences on probabilities and risks at the Bovenrijn/IJssel area, The Netherlands

Abstract

In the Netherlands, flood risk analysis is usually carried out for a location, without considering potential flood defence failures in upstream areas. This may result in significant over- or underestimation of flood risks. The effect of upstream failures on failure probabilities and flood risks in other areas is called load interdependence of flood defences. This effect can be both positive and negative: loads on a certain defence can increase and decrease due to failures upstream. In this research a framework was developed which enables the consideration of these interdependencies in a probabilistic framework. This was done by using Monte Carlo with Importance Sampling and a fast inundation model, which enables considering many scenarios with many different breaches. The case considered was the Bovenrijn/IJssel area in the Netherlands, a lowland river area where dike breaches can have both positive and negative effects on the loads on other flood defence elements. The risk estimates and changes in water level probabilities in the considered area show a clear interrelation between loads on different elements of the flood defence system and demonstrate that the effects of dike breaches on loads and risks on other locations cannot be ignored in flood risk analysis.