Ecohydraulics of Surrogate Salt Marshes for Coastal Protection: Wave–Vegetation Interaction and Related Hydrodynamics on Vegetated Foreshores at Sea Dikes

Abstract

Vegetation on foreshores in close vicinity to sea dikes may prove beneficial as regulating ecosystem service in the context of coastal defense, dike safety, and flood protection by reducing loads on these defense structures. Predominantly, a decrease in wave heights and bottom shear stresses is hypothesized, which calls for an inclusion in design procedures of coastal defense structures. In contrast to heterogeneous and variable salt marsh vegetation, this study uses surrogate vegetation models for systematic hydraulic experiments in a wave flume, without modeling specific plant species a priori. Froude-scale experiments are performed in order to investigate the effect of salt marsh vegetation on the wave transformation processes on the foreshore and wave run-up at sea dikes. The effect of plant and wave properties on wave transmission, energy dissipation, and wave run-up at a 1:6 sloped smooth dike are presented and discussed, focusing on the wave–vegetation–structure interaction. Vegetated foreshores can contribute to wave attenuation, where an increasing relative vegetation height hv/h results in decreased wave run-up on the dike by up to 16.5% at hv/h = 1.0.