Morphologically induced changes in the circulation of the patos lagoon estuary

Abstract

The Patos Lagoon estuary has one of the most important harbor complexes in Brazil. The increasing navigational activities observed in the last decade enhanced the dredging demand in the access channel of the lagoon. Developments have been proposed for the area, which include an extension of the jetties at the entrance of the estuary, as well as deepening the existing access channel. The objective of this study is to investigate the effect of the proposed developments on the circulation pattern of the estuary. Three scenarios are the focus of this study: a) original channel geometry and jetties length; b) original channel depth and extension of the jetties; c) modification of the channel depth and extension of the jetties. The TELEMAC flow model, based on the finite elements method, was used to carry out two-dimensional depthaveraged simulations to investigate the effect of such alterations on the hydrodynamics of the area. Results showed that the extension of the jetties would reduce flood and enhance ebb fluxes in the estuary. The scenario with the extension of the jetties without dredging, however, would lead to stronger velocities at the access channel causing stronger shear stresses over the bottom and potentially reducing the demand for dredging. The scenario considering the extention of the jetties with dredging would lead to weaker velocities, which could promote the siltation of the access channel. Moreover, the extension of the jetties seems to reduce salt-water intrusion, which could affect the entrance of commercial fish and shrimp species, harming the local fishery production.