Wave-driven flows over canopies of aquatic vegetation (such as seagrass) are characterized by the generation of a strong, shoreward mean current near the top of the canopy. This shoreward drift, which is observed to be up to 75% of the RMS above-canopy orbital velocity, can have a significant impact on residence times within coastal canopies. There have been limited observations of this current and an accurate formulation of its magnitude is still lacking. Accordingly, this study aims to develop a practical relationship to describe the strength of this current as a function of both wave and canopy characteristics. A simple model for the Lagrangian drift velocity to establish whether the magnitude of the wave-driven current increases with the above-canopy oscillatory velocity, the vertical orbital excursion at the top of the canopy, and the canopy density. An extensive laboratory study, using both rigid and (dynamically scaled) flexible model vegetation, will be carried out to evaluate the proposed model. Experimental results hope to reveal a strong agreement between predicted and measured current velocities over a wide and realistic range of canopy and wave conditions. Additionally, investigations will assess whether characterization of this wave-induced mean current will allow an enhanced capacity for predicting residence time, and thus key ecological processes, in coastal canopies.
Australian Department of Innovation, Industry, Science and Research's Collaborative Research Network Scheme
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