Subtidal water flux through a multiple-inlet system: Observations before and during a cold front event and numerical experiments

This paper examines the net transport through a multiple-inlet bay under a combined force of strong wind and tide, with observations and a model experiment. The observations were made in central Georgia in Sapelo and Altamaha Sounds between 13 and 17 September 2000. Wind was weak in the beginning of the survey. An air pressure trough (as a weak cold front) passed the area on 16 September, when the wind changed to the northeast and increased in magnitude. This front was associated with a midlatitude cyclone in the New England area. This weather event with an episode of strong northeasterly winds prompted a numerical model experiment on an idealized three-inlet bay, with a set of nonlinear 2-D shallow water equations on an f plane, which provides some insight to the wind-driven circulation under the presence of tidal forcing. It is found that tidally induced currents are small compared to wind-induced flows. When the wind direction is not perpendicular to the alignment of the three inlets, the net outward flow tends to occur at the inlet farther away in the downwind direction. This is associated with a net inward transport in the inlet opposite of the downwind direction. As a result, the middle inlet has the minimum of the net flow. When the wind is perpendicular to the barrier islands, and if the three inlets have different maximum depth values, the deeper inlet tends to have a net flow against the wind, while the shallower inlet tends to have a net flow in the direction of the wind. Offshore (onshore) currents may develop outside of the inlet with outward (inward) flow, as an effect of fluxes through the inlets on the coastal ocean.