Mechanistic analysis of the wave-current interaction in the plume region of a partially mixed tidal inlet

In this research, a three-dimensional coupled wave-circulation model, including meteorological forcing, freshwater inflow and time varying open boundary conditions, for New River Inlet is validated. A mechanistic approach is taken to investigate how various wave-current interaction mechanisms affect the nearshore circulation, plume expansion and surface wave field in the plume region of a relatively small partially mixed tidal estuarine system. More specifically, focus is comparing four different modeling cases including: (1) a three-dimensional ocean circulation model (no wave effects), (2) a coupled wave-circulation model, (3) a coupled wave and circulation model including vertical mixing enhancement due to wave breaking, and (4) a wave model without surface current effects. Findings reveal forces are applied by incoming waves due to various wave-current interaction mechanisms. Wave momentum released by incoming waves pushes the outgoing freshwater ebb plume back to the shoreline and prevents the plume from expanding freely towards the open ocean. Findings also reveals that releasing wave-dissipated energy in the expanding plume region enhances vertical mixing, mixes down freshwater, and therefore thickens the plume. These results are congruent with observations at the mouth of the Columbia River.