Physical and numerical modelling of wave transformation through a coastal canopy

Coastal canopies formed by aquatic vegetation (e.g. seagrass, mangroves) or corals can be found along many coastlines worldwide and often have a significant effect on the local wave dynamics. Over the past several decades, many studies have greatly increased our understanding on the physical interaction between coastal canopies and waves in the coastal ocean. However, whereas most studies have investigated (bulk) wave dissipation by coastal canopies through empirical formulations, relatively little attention has been paid to the specific instantaneous wave dynamics inside the canopy and how this mechanistically controls wave transformation over canopies. In this study, we extended a state-of-the-art numerical wave model with a canopy flow model to develop a more accurate formulation of the canopy drag force that controls rates of wave dissipation. To validate the model, experiments were carried in a large wave flume with a rigid, high-density model canopy. Model-data comparison using the in-canopy flow velocity and the wave height distribution over the canopy shows that the model is able to capture the essential physics. The results suggest that the canopy flow model increases the accuracy of the estimation of wave dissipation due to canopy drag. Wave attenuation by coastal canopies may be overestimated by wave models without a canopy flow model due to the lack of physics describing canopy flow attenuation