Enhancing flood risk system robustness in practice: insights from two river valleys

Abstract

ABSTRACTDecisions about flood risk management are usually based on the reduction in flood risk compared to the cost of the strategy. It is common practice to express this flood risk (the combination of flood probabilities and potential flood damages) in a single number. The downside of this approach is that explicit information about how the system responds to the whole range of possible water levels or river discharges is lacking. This type of information is relevant when a robust system is desired. We consider robust (fluvial) flood risk systems to have the ability to remain functioning under a range of possible river discharges. This paper analyses system robustness for different system configurations of two embanked river valleys in the Netherlands: the IJssel River valley and the Meuse River valley. Comparing the results of these cases provides us with clues about how to enhance a flood risk system's robustness. The IJssel case shows that a system with embankments that will not breach when overflown scores best on overall system robustness. The Meuse case shows that systems with differentiation in protection levels along the river score best on overall robustness. Furthermore, we found that in systems with high protection standards, the most effective way to increase system robustness is by increasing the system's response proportionality. This means that the consequences of flooding increase proportionally to an increase in river discharge. These findings confirm that a system robustness perspective may help to develop strategies that reduce the flood risks without increasing the vulnerability to beyond-design floods.