Modeling wave attenuation through vegetation patches: The overlooked role of spatial heterogeneity

Coastal wetlands serve as vital buffers against extreme hazards due to the wave-dissipating capacity of vegetation. While most studies assume a spatial-uniform vegetation cover when modeling wave attenuation through wetlands, they are far from homogeneous in reality due to life-stage dependent growths, die-offs, and zonation of different vegetation species. In the present study, the XBeach model was applied to explore the role of vegetation spatial heterogeneity on wave attenuations. Random distributed vegetation maps with the same coverage but diverse patch sizes are generated to replicate the complex patterns of real wetland vegetations. We focus on the attenuation of solitary waves and wave groups, representing tsunami and storm waves, respectively. Different wave heights, vegetation densities, and land slopes are considered. For solitary wave cases, it is found that smaller patch sizes lead to higher wave attenuation rates, lower run-up, and less inundation extents. For wave group cases, it is found that the attenuation rates are dependent not only on patch sizes but also wave frequencies; while the higher frequency wave components are attenuated at similar magnitudes by different patch sizes, the infragravity waves are much less attenuated by larger patch sizes due to the penetrating effects through the major gaps between patches. Both cases revealed that under the same vegetation coverage, smaller patch sizes outperform their larger counterparts in terms of wave attenuation capacity. Out study highlights the importance of vegetation spatial heterogeneity, which are seldom considered in evaluating the wetlands' capacity of attenuating extreme waves.