Exchange across the inner shelf influences the distribution of nutrients, harmful algal blooms, pollutants, larvae and sediment. It is not yet fully understood how surface waves influence this exchange. Recent advances have been made in the numerical modeling of wave-current interactions, but so far these modeling studies have focused on the surf zone. This study will extend these modeling capabilities to the inner shelf by testing model results in the context of laboratory and field observations. This research will drive further development of wave-current coupling in a modeling system that is freely available to the scientific community. The insight into wave-current interaction processes gained during this investigation will improve the development of realistic models used in practical sediment transport applications.
Most studies of inner-shelf circulation have focused on the role of wind stress. Surface waves have only recently been recognized as an important forcing mechanism over the inner shelf. Present understanding of the wave-driven inner-shelf circulation is based on analytical models with restrictive assumptions, such as constant turbulent mixing throughout the water column, and no spatial variations across the shelf. The model experiments in this study will allow for more realistic representations of turbulent mixing, and will include the effects of stratification, a sloping bottom and advection of momentum from the surf zone, where breaking waves generate strong along-shelf currents. Few previous studies have quantified the importance of momentum advection on the inner shelf, but it is potentially important near the boundary of the surf zone and will also be assessed in observations. Based on the model experiments, the relative importance of the hypothesized mechanisms under different environmental conditions will be scaled so that results can be applied generally at many locations.
The goal of this study is to identify the key processes that determine the observed spatial structure of the circulation driven by surface waves on the inner shelf, which is located offshore of the breaking surf. Previous observations have identified a surface-intensified offshore flow associated with surface waves over the inner shelf. In the direction parallel to shore, new observational analysis shows a complex response to wave forcing that varies with water depth. Two alternative hypotheses are formulated to account for these observations: one in which the Earth's rotation is necessary, and another that involves strong turbulent mixing and transport of momentum from the surf zone. Numerical modeling experiments, with complex physics but idealized geometry, will be carried out to determine the relative contribution of these two mechanisms to the observed wave-driven circulation during different forcing and environmental conditions. A new parameterization for the critical process of "wave streaming" near the bottom will be tested against field and laboratory observations. Model experiments, in combination with new analysis of existing observations, will identify processes that generate exchange between the surf zone and inner shelf during combined wind and wave forcing.
