Abstract:
The water masses and residual circulation in the estuaries are part of the set of processes that
determine heat exchange, salt distribution and biological organisms adrift in this ecosystem. This
fact makes the study of water masses and residual circulation relevant for both the scientific
community and ecological processes. The main objective of the present work was to understand the
behavior of the water masses and the residual circulation pattern of the Bons Sinais estuary and to
classify it based on the Hansen and Rattray equation. For the materialization of the study, seasonal
data of water temperature, salinity and currents measured at a fixed station during a tide cycle and
data measured across the Estuary were used. The result obtained concerning the longitudinal
gradients in salinity and density indicated that the estuary was dominated by the river during the
rainy season and by the tide during the dry season, but the water column remained partially mixed
in both seasons. Tidally averaged vertical profiles of temperature and salinity of the fixed station of
the estuary revealed uniform temperature throughout the depth, warmer during the rainy season;
lower salinity and stratified in depth during the rainy season, vertical homogeneous during the dry
and transition seasons; and uniform density in depths but with high values during dry seasons. The
vertical velocity profile presented a classic two-layer circulation model, with downstream flow
intensifying on the surface and upstream flow at the bottom, during the rainy and transition seasons,
when fresh water is discharged into the estuary. The flow velocities obtained from the calibrated
Hansen and Rattray model adjusted to the observed data, confirming that the model proposed by
Hansen and Rattray is adequate to describe the residual flow of the Bons Sinais Estuary.
