Simulating wave-tide induced circulation in Bay St. Louis, MS with a coupled hydrodynamic-wave model

Abstract

Because tidal inlets are important areas with respect to biodiversity, sediment transport, freshwater river outflow, and pollutant transport, a comprehensive understanding of their circulation patterns is necessary for their management. This study focuses on modeling the 2D, depth-averaged circulation of Bay St. Louis in the northeastern Gulf of Mexico that is driven by waves and tides using a coupled hydrodynamic-wave model. The wave-tide coupled circulation within the inlet is examined during the flood, slack, and ebb phases of the tidal cycle. The wave height field, current velocity and sea surface elevation are analyzed to determine the effects of wave-current interaction. The influence of the various forcings on bay/inlet circulation is further investigated by the introduction of Lagrangian tracers. Lagrangian tracers are a reasonable indicator of how circulation patterns affect the motion of sediment particles or passive biological organisms such as fish larvae. Wave-current interaction is simulated by iteratively coupling the depth-integrated ADCIRC-2DDI hydrodynamic model to the phase-averaged spectral wave model SWAN. ADCIRC-2DDI is a fully developed, 2-dimensional, finite element, barotropic hydrodynamic model capable o f including wind, wave, and tidal forcing as well as river flux into the domain. The wave-hydrodynamic model coupling is captured through the following approach. First, radiation stress gradients, determined from the SWAN wave field, serve as surface stress forcing in ADCIRC. Elevation and currents computed from ADCIRC are subsequently input into the SWAN model. Between these iterations, the ADCIRC model is run for some appropriately small time interval during which the wave field is held constant. Presently there are no shelf-scale hydrodynamic models that incorporate waves, therefore a coupled model approach is one way of simulating wave-current interaction in bays and inlets. This approach is very flexible, making it possible to couple different wave models to ADCIRC depending on the relevant physics of the domain being studied (e.g. monochromatic wave diffraction vs. multi-spectral wave effects).