Flood risk reduction by parallel flood defences – Case-study of a coastal multifunctional flood protection zone

A coastal double-dike system, featuring parallel flood defenses with a culvert for tidal exchange, offers negligible improvement in flood protection compared to a single dike when the seaward dike is tall. The study, focusing on the Double Dike between Eemshaven and Delfzijl (Netherlands), quantifies hydraulic loads like overtopping, overflow, erosion, and discharge through the culvert during storms. While such systems aim to enable multifunctional land-uses in the inter-dike zone—such as aquaculture or salt marsh restoration—their primary benefit lies in supporting these activities rather than enhancing flood risk reduction. The research provides a framework for assessing double-dike safety, emphasizing that the landward dike must be sufficiently high to retain water during culvert non-closure events to achieve any meaningful flood protection.

Marijnissen, R. J. C., Kok, M., Kroeze, C., & van Loon-Steensma, J. M. (2021). Flood risk reduction by parallel flood defences – Case-study of a coastal multifunctional flood protection zone. Coastal Engineering, 167, 103903. https://doi.org/10.1016/j.coastaleng.2021.103903