Modelled Impact of Vegetation Heterogeneity and Salt-Marsh Zonation on Wave Damping

This paper analyses the effect of observed vegetation characteristics on modelled wave heights. Detailed information on species composition, as well as on height, number of stems, and diameter of the plant species of a restored salt marsh on the Wadden barrier island of Terschelling was used to parameterize and apply the Simulating Waves Nearshore Vegetation wave model to a schematized restored salt-marsh zone in front of the dike. The results indicate that wave damping by vegetated forelands is strongly related to vegetation heterogeneity and salt-marsh zonation. The modelling works suggest that at the study site under storm conditions with a frequency of 5-10 times/y, a vegetated foreland of some 90 m in width will dampen the wave height more than 80%, whereas under extreme conditions (1/2000 y) a foreland covered with dense vegetation will dampen the wave height up to 50%. These results imply that at the study site a vegetated foreland in front of the dike leads to reduced wave attack on the dike, which may result in changed requirements for both height and revetment of the dike while maintaining the required safety level. Although there are still many questions concerning dimensions, management, and performance, developing a vegetated foreland seems an interesting strategy to adapt existing flood protection works to the effects of climate change.