Three-Dimensional Hydrodynamics Associated with a Solitary Wave Traveling over an Alongshore Variable Shallow Shelf

We investigated, from two laboratory experiments, the kinematic behavior and the three-dimensional turbulence that is generated due to a breaking solitary wave propagating over irregular shallow water bathymetry. The bathymetry was composed of a deep water region followed by a shallow shelf via a relatively steep slope. The offshore boundary of the shelf break varied in the longshore direction. The shelf had a triangular shape in plan view, with the widest part of the shelf located along the center of the basin. The first experiment used a planar shelf, while an obstacle in the shape of a conical island was placed near the shelf apex for the second experiment. Measurements of fluid velocities and free surface elevations were collected using three-dimensional acoustic Doppler velocimeters (ADVs) and wave gauges, respectively. In the first experiment, the inundating flow varied weakly in the alongshore direction, but demonstrated strong variations in the second experiment. A refraction-generated jetting mechanism caused by the convergence of water mass near the basin centerline characterized the run-up. The greatest cross-shore velocities were located near the basin's centerline and were triggered by the jetting mechanism. The greatest turbulent events were well correlated with four identified bore fronts. The bore fronts were generated by a combination of waves including the leading wave, beach reflections, and shelf oscillations. A primary conclusion of this study is that nonlinear long-wave transformation over irregular bathymetry can lead to a highly complex nearshore wave field with little apparent correlation to the offshore wave.