While estuarine salt plugs can develop worldwide in estuaries adjacent to buoyant coastal currents, their formation has been scarcely documented. This study aims to generalize a mechanism for salt plug formation that does not invoke evaporation processes but involves a buoyant coastal current modified by wind stresses. A numerical model, Delft3D, is used to simulate two idealized bays, one with a single inlet and another with two inlets. The numerical experiments are inspired by recent observations and simulate nine different scenarios of wind and tidal forcings under the influence of an along-shelf buoyant current. Results show that the salt plug induces an inverse circulation at the inlet with inflow at the surface and outflow underneath. This circulation is modified by wind action. The persistence of the salt plug depends on tidal flushing, as well as wind intensity and direction. A yearlong numerical experiment with non-stationary buoyant currents and non-stationary winds indicate that: (i) onshore winds transport oceanic waters into the bay, while offshore winds export estuarine water to the ocean; (ii) onshore winds enhance the inverse circulation at the inlet, while offshore winds stall it. The ratio between wind-driven and density-induced accelerations, given by the Wedderburn number, determines the dominant contribution to the along-estuary circulation in an along-estuary transect. In general, baroclinicity dominates over wind-stress at the inlet, while wind-stress governs the circulation along the estuary. This study represents the first attempt to identify the role of wind and buoyant coastal currents on the dynamics of salt plug formation.

The Glass Window Bridge Located in Eleuthera, The Bahamas, is the only bridge connecting Eleuthera’s northern and southern mainland, facing the Atlantic Ocean to the east and the Great Bahama Bank to the west. This bridge is under constant threat from hurricanes and large swells in the Atlantic Ocean. The existing bridge has been subject to severe damage arising from wave impact forces since its construction. In addition, severe overtopping of the cliffs near the Glass Window Bridge causes damage to the roads and severe erosion, that over the years has created unique geologic features. As the global climate warms and sea level rises (SLR), coastal areas will be subject to more extreme flooding and intense hurricanes. Therefore, assessing the impact of potential SLR on the GW bridge and guiding bridge wave mitigation measures are of crucial need. A 3D Digital Terrain Model (DTM) of the bridge site and adjacent ocean bathymetry is constructed from satellite data. This study develops a multiphase computational fluid dynamics (CFD) model based on the DTM to study the impact of wave-breaking for three major historical storm events, and for three different estimates of SLR for the year 2100. Our results suggest that, due to SLR, the islands are subjected to increased overtopping, which occurs even during normal wave conditions. Notably, nonlinear increases in wave splash extent and wave-induced bridge loads are observed as SLR increases. Our results indicate that SLR additionally magnifies the erosional energy, accelerating further changes in the geological features of the island.