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Effects of Spatially Variable Drag Coefficient of Submerged Aquatic Vegetation on Surface Wave Dissipation
  • Ramin Familkhalili,
  • Navid Tahvildari
Ramin Familkhalili
Old Dominion University Research Foundation

Corresponding Author:[email protected]

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Navid Tahvildari
Old Dominion University
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Submerged aquatic vegetation in estuaries and coastal areas can alter the hydrodynamics of coastal waves by attenuating the energy of waves generated by storm surges and cyclones. Generally, wave attenuation by seagrass meadows is studied by considering a constant vegetation drag coefficient across the meadow which is an oversimplification. This study provides a better understanding of how submerged vegetation alters surface wave amplitude and velocity by developing a coupled flow-vegetation interaction model, which consists of a nonhydrostatic wave model and a numerical model for vegetation blade dynamics. The model captures wave attenuation rate and quantifies the effect of vegetation flexibility on wave attenuation. The vegetation model divides up each blade into an arbitrary number of segments that allows us to simulate strong deflection of blades under combined wave and current conditions. The two models are dynamically coupled which means that at each time step, the hydrodynamic model solves the free surface elevation and depth-varying velocity which is then used as input for the vegetation model. Then, the vegetation model calculates the effective drag coefficient of each segment of a stem in the canopy that is dependent on the forces applied over the blade and orientation of the blade. The computed vertically variable vegetation drag coefficient of each stem is then used in the hydrodynamic model for the next time step. Model results suggest that considering a rigid vegetation with simplified drag coefficient would result in larger vegetation-induced damping compared to flexible vegetation condition. The model results also confirm that there is a strong dependency between the vegetation-induced wave dissipation and vegetation parameters (e.g., canopy length and vegetation blade height).