Varying Patterns of water circulation in Canal de Cotegipe, Baía de Todos os Santos

The Canal de Cotegipe is a 30 m deep, 4 km long tidal channel in northeastern Brazil connecting the small Baía de Aratu (24.5 km²) to the much larger Baía de Todos os Santos (1223 km²). Several industrial and port facilities surround the channel and Baía de Aratu, and polluted riverine discharge as well as a direct release of toxic residuals by harbor operations makes the area one of the four polluted hot-spots within Baía de Todos os Santos. An analysis of current measurements, tidal elevation records and water quality monitoring has allowed for a preliminary understanding of the driving forces that affect the channel. Tidal flows are modulated by the extent of intertidal inundation in the channel and the bay, with stronger ebb-dominant flow conditions associated with neap tides at the seaward end of the channel and with spring tides at the landward end of the channel. Subtidal flows are mainly driven by density gradients normally oriented towards Baía de Todos os Santos, leading to a vertically stratified, estuarine like flow. This structure is strengthen in the wet season and weakened in the dry season when unstratified or evenand inverse estuarine stratification may develop as a result of higher evaporation rates