Tidal Hydrodynamics in a Multiple-Inlet Estuary: Apalachicola Bay, Florida

Abstract

Tidal hydrodynamics in a multiple inlet estuarine system, Apalachicola Bay, were investigated in this study. The estuary is connected to the Gulf of Mexico through five tidal inlets. From eastern inlets to western inlets, the tidal amplitude decreases and the dominant tidal constituents change from mixed diurnal and semi-diurnal to diurnal components. The tidal hydrodynamics in the bay are complex due to different tidal forcing from multiple tidal inlets in the estuary. In order to characterize the tidal forces in the boundary inlets, we applied harmonic analysis to determine the dominant tidal components at the inlets using field measurements of water levels. Then we applied a previously validated hydrodynamic model to investigate the 2-D tidal circulation during a twenty-four hour period. Snapshots of model simulations at high, mid-ebb, low, and mid-flood tidal conditions were used to characterize the propagation of tidal waves and vertically averaged currents in the bay. Model simulations indicated that currents in the bay were driven mainly by the surface gravity gradients corresponding to the propagation of the tidal waves in the bay. At high tide, the higher surface elevation in the eastern tidal inlets drove the bay water from east to west. At low tide, the lower water level in East Pass caused strong eastward currents in the eastern region of the bay. One of the interesting issues in Apalachicola Bay is the effect of an artificial inlet (Sikes Cut) on the estuary circulation and aquatic ecosystem. This study indicates that strong tidal currents occur in this inlet and allow an exchange of waters between bay and Gulf. The result s will benefit the biological research programs in this important estuarine system.