Abstract. The Patos Lagoon estuary is a reservoir of fine sediments derived from the continental basin, which is exported to the coastal area through a narrow channel with average discharge of 2000 m³ s⁻¹. The Port of Rio Grande is located in this connection channel between the Patos Lagoon and the Atlantic Ocean, and recently received investments from the Brazilian Government to expand its draft and modify the configuration of the breakwaters located at the mouth. The objective of this study is to investigate changes in the fine sediment dynamics in the estuarine and coastal region, after the modernization work carried out at the Port of Rio Grande. The study was conducted using a three-dimensional numerical model (TELEMAC-3D) coupled with a sediment in suspension and morphological model (SediMorph). Results were analyzed in a comparative way in relation to the deposition pattern observed in these regions before and after the construction work. Results indicate that there was a change in the deposition pattern and redistribution of sediment at the bottom due to hydrodynamic changes resulting from the new configuration of the breakwaters and progressive deepening of the access channel.