Reconfiguration of and drag on seagrass blades under orthogonal wave-current conditions

This work provides fundamental advances in flow-vegetation interaction. It improves our ability to model a key process in water environments, namely the role of aquatic vegetation in protecting shorelines from wave energy. Although wave damping by aquatic vegetation has long been noted, most researchers have only considered pure-wave conditions, and a handful of previous studies have considered co-directional waves and currents. To date, a predictor of wave damping under orthogonal wave-current conditions (i.e., the current is perpendicular to the direction of wave propagation), which usually corresponds to wave-induced longshore currents near the coast, has yet to emerge. We developed a theoretical model for predicting the reconfiguration of and drag on model seagrass blades in orthogonal wave-current conditions. The model is based on the scaling analysis of Luhar and Nepf (2011) and Lei and Nepf (2019), who described the bending of a flexible blade under steady flows, waves, and co-directional wave-current conditions. We extended these scaling laws first by investigating the dynamics of individual model seagrass blades in orthogonal wave-current conditions. Second, load cells were used to investigate the reduction in drag force on the blades. Finally, the model was extended to shoots within a meadow and then applied to predict wave attenuation over meadows of different heights, widths, and plant densities.