How natural foreshores offer flood protection during dike breaches: An explorative flume study

Abstract

In this paper we describe one aspect of nature-based flood protection by foreshores in hybrid flood defences and discuss how foreshore ecosystem restoration can contribute to flood protection. Flood protection consists of flood prevention, by grey, green or hybrid defences, and flood impact reduction, by spatial planning to limit damage and crisis management to limit exposure. Reduction of flood impact is increasingly important because no flood defence system can provide 100% safety, especially with climate change and sea level rise. In this study we aim to understand and visualize the effect of foreshore characteristics (i.e., width, elevation and erodibility) on flooding impact in the hinterland of hybrid flood defences. As it is difficult to research real dike breaches, we do an explorative flume study to analyse the impact of a mimicked dike breach in the hinterland. Our physical scale model showed the presence of a non-erodible foreshore reduces flood damage in the hinterland. With regards to foreshore characteristics, mainly foreshore elevation and erodibility are important, while differing foreshore width has little additional influence. Already a narrow foreshore reduced flood impact in the flume hinterland. Our findings strengthen the appeal to integrate Nature-based flood protection by foreshores in hybrid flood defences. Grey flood defences can be turned into hybrid flood defences even if there is limited space for foreshore ecosystem restoration, for instance by managed realignment.