Circulation in a Tropical Embayment with Two Inlets and Complex Geometry: the Itamaracá-Itapessoca System, Brazil.

Along the northeast coast of Brazil, numerous estuaries with intricate morphologies, characterized by multiple channels, islands, and intertidal areas, are found. These estuaries undergo significant seasonal variations, experiencing pronounced wet and dry periods. While some of these systems have small drainage basins with minimal freshwater inflow and sediment production, they boast extensive intertidal mangrove areas. This study focuses on assessing the hydrodynamics and residual circulation of the Itamaracá-Itapessoca Estuarine System (IIES) to elucidate the impact of residual circulation on estuary-shelf exchange dynamics. The IIES comprises two main islands and two inlets surrounded by extensive intertidal areas. Field observations collected during the wet season were used to calibrate and validate a numerical model. Two model scenarios were examined: a 'dry' scenario, considering hydrodynamics driven solely by interactions between morphology and tides, and a 'wet' scenario, incorporating freshwater inflow. Key findings include: (a) the inclusion of freshwater inflow minimally alters system dynamics; (b) tidal dynamics are amplified within the system, resulting in a null zone between the inlets; and (c) residual circulation circulates around the islands, with net importation through the larger inlet and net exportation through the smaller one. The intensity of exchange is heightened under wet conditions.