Wave attenuation over combined salt marsh vegetation

The tidal flats often distribute different kinds of vegetation that jointly attenuate the waves. Understanding wave attenuation over combined salt marsh vegetation is crucial to the safety of coastal defences. This study conducted laboratory experiments to examine wave attenuation over vegetation combinations of Scirpus Mariqueter (SM), Spartina Alterniflora (SA) and Mudflat. Results show that the impact of vegetation combinations on wave attenuation lies between that of SM and SA, and this impact becomes limited when a wave breaks in the vegetation zone. A linear relationship exists between the wave transmission coefficient, k_t, and a new parameter, ζ, containing the Iribarren number, relative water depth, relative vegetation width, relative submergence, and vegetation density. It was found that each vegetation's contribution to overall attenuation is nonlinear with its cover percentage. This study proposed an empirical formula for calculating k_t over differently combined vegetation based on the individual contribution, as it was derived by considering multiple vegetation characteristics. Findings in this study will enable engineers to estimate wave transmission coefficient over differently combined vegetation on tidal flats, which will help understand wave attenuation processes and promote the development of ecosystem-based coastal engineering.