The delta-front estuaries of large rivers are crucial interfaces between lands and oceans, being considered hotspots of vulnerability to the impact of climate changes due to several causes: sea level rise; changes in the river discharges driven by climatic alterations in the hydrographic basins; high human concentration and other anthropic factors. This study focuses on the hydrodynamics/circulation and T-S structure within the shelf regions and continental platform adjacent to two among the major rivers of Northeastern Brazil: the Sao Francisco and Parnaiba. We aim to qualitatively and quantitatively describe the physical dynamics typical of these coastal regions and try to relate their main alterations to the effects of local mechanisms as tidal forcing. The choice of these deltas was motivated by the great potential that such, biodiverse regions have in acting as important proxies of environmental modifications affecting the Brazilian tropical zone, allowing to investigate the role of geographical variability in response to these changes. A series of regional, modelling simulations was realized, at increasingly higher resolutions, in order to assess the mean and seasonal spatio-temporal variability of physical properties (T-S distribution, salt transport, hydrodynamical features of the local circulation). The identification and analysis of the major scales of variability was also used to evaluate the performance and applicability of our numerical tool, the Regional Ocean Modelling System, in the study areas. Preliminary results on mesoscales processes indicate that both deltas are modulated by an intense turbulent activity. The continental platform near the Sao Francisco estuary is marked by the presence of subsurface-intensified vortices, and the one in proximity of the Parnaiba mouth is characterised by the appearance of small vortices, fine meanders and filaments probably triggered by non-linear interactions between the river plume and the North Brazilian Current rings.