Avaliação dos principais forçantes responsáveis pela dinâmica da pluma do Rio São Francisco

Abstract

The São Francisco river is one of the main rivers in Brazil, originating in Serra da Canastra in the State of Minas Gerais, passing through six states and hundreds of towns until it reaches the Atlantic ocean, between the border of the States of Sergipe and Alagoas. It is an important river due to the fact that it transports a large volume of water through the semi-arid region of the country and has a large hydroelectric potential. Because the São Francisco river has a large discharge capacity, it also carries large amounts of dissolved and solid matter to the ocean as coastal plumes, being responsible for the input of sediments and nutrients to the continental shelf and adjacent coastal areas. Since the construction of hydroelectric power plants along the lower São Francisco, the river discharge has been reduced, as well as the amount of sediments and nutrients that would reach the ocean. Thus, the monitoring of the coastal plume generated by the São Francisco river should be conducted regularly so that it is possible to understand its contribution to the transport of dissolved and solid matter from the continent to the ocean; and this can be made through the analysis of the main hydrodynamic forcings controlling the plume dispersion over the continental shelf. Aiming to determine these hydrodynamic forcings, six scenarios were created and run in the numerical model Delft3D as an attempt to represent the discharge regime of the river. The results showed that the wind has an important role in the dispersion of the plume, pushing it towards the open ocean in the presence of northeasterly winds (summer) whereas the plume is confined to coast in the presence of southeasterly winds (winter). Finally, the results also showed that the construction of power plants along the river impacted directly on the extension of the coastal plume over the continental shelf, with consequences to the amount of sediments and nutrients transported to coastal areas.