Sand wave migration near the southeastern corner of Martha's Vineyard,Massachusetts, USA

Sand waves of approximately 2 m in height were observed to migrate nearly 40 m with counterclockwise rotation between two bathymetric surveys performed three months apart near the southeastern corner of Martha's Vineyard, Massachusetts. The region is characterized by strong tidal currents, intermittent energetic surface wave events, and shallow water with local depth ranging from 2 to 7 m. This study uses the process-based model, Delft3D, with a three-dimensional approach to examine the sand wave dynamics by incorporating surface waves, winds, currents, and bathymetric observations. The model successfully simulates sand wave migration in comparisons to observations. Model sensitivity analyses show that the sand wave migration reduces by 65% with the absence of the surface waves. The modeled sand wave migration speed is correlated with the tidal current Shields parameter, and sharp increases in migration speed occur when the wave-driven Shields parameter increases in response to energetic surface wave events. The combined effect of tides, surface waves, and bathymetry is the origin of the rotational aspect of the sand wave, using the Shields parameter as an indicator of tidal currents and surface wave influence on sand wave dynamics.