A Numerical Study on Wave Evolution in Interaction with Flexible Vegetation

Coastal wetlands are among the natural features with capability to reduce storm damage. Previous numerical studies on wave dissipation effects of aquatic vegetation typically apply some simplifications to vegetation behavior and mostly ignore spectral wave evolution. For instance, vegetation elements are usually assumed rigid or semi-flexible. Similarly, despite laboratory experiments that confirm the evolution of wave spectra over vegetation fields, nonlinear wave-wave interactions are generally ignored and a bulk dissipative measure such as reduction in root-mean-square waveheight is examined. Inadequate representation of wave and vegetation characteristics in numerical models reduce their capability in accurate prediction of coastal processes. To address these shortcomings, a time-domain nonlinear numerical model based on the Boussinesq formulation is developed and coupled with an enhanced vegetation representation that accounts for arbitrary rigidity. The model is validated with laboratory experiments and a frequency-dependent vegetative drag coefficient is obtained. The coefficient is then incorporated in a frequency-domain model to investigate the combined effect of vegetative wave dissipation and nonlinear wave-wave interactions in modulating the surface wave spectra. The effect of vegetation parameters such as rigidity, stem density, and state of submergence on wave characteristics is examined and implications in vegetation benefits in wave energy dissipation are discussed.