Caracterização hidrodinâmica e fluxos de sedimentos em suspensão no complexo portuário de São Luís (Ma) durante a atividade de dragagem

Abstract

ABSTRACT The São Luís Port Complex (CPSL) is the largest and most important port complex on the North-Northeast coast of Brazil and the second largest in Latin America in terms of cargo handling. Therefore, its operational depth need to be maintained, through dredging activities, at depths compatible for the performance of the activities. The aim of this study was to characterize the hydrodynamic circulation and sediment transport in São Luis Port Complex (CPSL) in three different periods: pre-dredging, 25% and 75% of the dredged material and post-dredging. Current data were acquired using a 500 MHz ADCP (SONTEK / YSI) and the thermohaline structure and dissolved oxygen were acquired using a CTD (EXO2 / YSI) as the autonomous unit. The hydrodynamic circulation of the region presented max 2.68 m.s-1 to 3.76 m.s-1 during the rainy and dry periods, respectively. It was possible to identify in the presence of two water bodies, in the CPSL: estuarine water (EW) and coastal water (CW). The suspended sediment fluxes were directly associated to the evolution of the dredging activity, ranging from 40 mg.L-1 to 852 mg.L-1. The volume transport values ranged from 3.5 x 104 m3s-1 to 12.2 x 104 m3s-1, and the increase of the flows over the post-dredging is explained by the observed fluvial contribution. During the first three campaigns, it was possible to observe the loss of influence of the fluvial water mass, due to the minimization of precipitations, where the marine water mass had greater influence. The volume of wate 0.8 x 109 m3 to 2.3 x 109 m3 during the sampling period. The residence time (RT) during the rainy season (fourth season) reached 2 hours, while in the dry season RT values were approximately 0.5 hours. Density gradients cause a barrier that cannot be broken by the MPS, which, along with longer residence times and possible contaminant spills in the studied region, can cause irreversible ecological and socioenvironmental effects for the region.