Laboratory investigation of bedform geometry under regular and irregular surface gravity waves

Bedform geometry is an important feature in the near-shore bottom profile that can effectively enhance wave energy dissipation. Bedform geometry will regulate wave transformations and influence the sediment transport phenomenon. We begin with a historical review of the available literature. Next, a laboratory investigation of bedform geometry under regular and irregular surface gravity waves was conducted for two different depths in Towing Tank III at Davidson Laboratory. This wave tank facility provided an ideal opportunity for investigating bedform features for a flat bed and enabled the novel study of a sloped sediment bed. Our results provide new data that strengthens prior relationships and demonstrate that a sloped surface may be modeled in similar fashion to a flat sediment bed. These results also suggest that ripple dimensions may be independent of water depth and bottom orbital excursion amplitude (Ab) which is in contrast to the continental shelf under equilibrium conditions where ripples scale with Ab. The evaluation of wave tank dynamics was also conducted using an Acoustic Doppler Velocimeter (ADV) and surface wave data. Velocity measurements were performed using the ADV, and the wave records were measured using wave wire devices. The resulting data provided the basis for evaluating the hydrodynamics within the wave tank. Data analysis includes measurements of residual velocity and return flows that are inherent in a laboratory facility in the presence of propagating waves. The higher order harmonics that occur in laboratory facilities in the presence of monochromatic waves were evaluated as well. This information provides a new assessment of the hydrodynamics within Davidson Laboratory.