Exploring submerged vegetation controls on hydrodynamics and sediment resuspension in a back-barrier coastal bay

Qingguang Zhu, University of Virginia, Environmental Sciences, Charlottesville, VA, United States and Patricia Wiberg, Univ Virginia, Charlottesville, VA, United States
Abstract:
Aquatic vegetation can significantly alter flow structure and sediment transport processes in shallow coastal environments. Previous studies show that the vegetation interaction with flow and waves is non-linear and characterized by many thresholds. However, most of these studies either focused on small scale laboratory experiments or did not fully resolve the synergistic effects of flow-wave-vegetation-sediment interaction at a meadow scale. We focus our study on a shallow coastal bay in Virginia Coast Reserve (South Bay), which has been the site of a successful large-scale seagrass restoration effort. We apply a relatively high-resolution (~70 m) hydrodynamic and sediment transport Delft3D model to investigate the effects of different seagrass meadow characteristics on hydrodynamics and sediment transport processes. Our model is well calibrated using seasonal field hydrodynamic and suspended sediment data from the site. We use the model to explore the effects of different vegetation height, stem diameter, shoot density, and vegetation drag coefficients on flow and wave attenuation under seasonal wind conditions. Our results show that resuspension is sensitive to shoot density in winter when seagrass density is relatively low. In contrast, higher summer shoot densities inhibit most resuspension and further increases in density have little to no effect. The model is also sensitive to the drag coefficients associated with the interaction of flow and waves with vegetation, which we used as an effective calibration factor to match model results with seasonal field measurement. Our results provide practical guidelines for process-based modeling of flow-wave-vegetation-sediment interaction in shallow coastal environments.