Simulating Wave-Driven Circulation in Tidal Inlets With Tide and River Forcing Using a Coupled Hydrodynamic-Wave Model

Tidal inlets are important areas with respect to bio-diversity, sediment transport, and fresh water river outflow. This study examines the 2-D depth-averaged circulation of inlets that are driven by waves, tides, and fresh water river inflow using a coupled hydrodynamic-wave model. The circulation patterns of an ideal embayment and Bay St. Louis, located in the northeastern Gulf of Mexico, are compared under the range of forcing conditions. Wave-current interaction is simulated by iteratively coupling the depth-integrated ADCIRC-2DDI hydrodynamic model to the phase-averaged spectral wave model SWAN. Radiation stress gradients are determined from the wave predictions of SWAN and used to force the circulation model. ADCIRC-2DDI is a fully developed, 2-dimensional, finite element, barotropic hydrodynamic model capable of including wind, wave, and tidal forcing as well as river flux into the domain. The circulation within each inlet is examined during the flood, slack, and ebb phases of the tidal cycles with and without river inflow under different wave conditions. The effects of including/excluding advection and varying the strength of the lateral mixing are examined as well. 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. Lastly, influence of the wave model itself in the hydrodynamic coupling, and in particular the effect of wave diffraction on the wave-induced circulation, is comparatively examined within the ideal inlet by separately coupling the REF/DIF1 and REF/DIFS wave models to ADCIRC-2DDI; REF/DIF1 is a monochromatic phase-resolving wave model capable of simulating wave diffraction and refraction and REF/DIF-S is a multi-spectral version of REF/DIF1.