Caracterização da hidrodinâmica e do transporte de sedimentos dos três principais afluentes do rio Doce

Abstract

On November 5, 2015, in the municipality of Mariana, Minas Gerais, there was the biggest tailings dam accident in Brazil. The Fundão dam collapsed, spilling 32 million cubic meters of waste, causing a severe socioeconomic and environmental impact on the Doce River. After the accident, much research has been carried out to understand and minimize the impacts. One of the ways to understand the dynamics of the Mariana – MG disaster, from the perspective of hydrodynamics, is through models. With the aim of understanding the role of tributaries in the recovery of the Doce River, hydrodynamic and sediment transport simulations were carried out in this work, using the two-dimensional version of the HEC-RAS model, at the confluences of the Gualaxo do Norte River with the Carmo River, of the do Carmo with the Piranga river, the Suaçuí Grande river with the Doce river and the Manhuaçu river with the Doce river. The results of the 2D hydrodynamic model showed the hydrographs and areas flooded by the disaster in Mariana – MG, that the reservoir of the Risoleta Neves Hydroelectric Plant would hypothetically hold the waste from the disaster if the floodgates had been kept closed, that the narrowing of the Doce river channel in the municipality of Governador Valadares – MG caused the flow speed to increase substantially, and the topographic conditions of the confluence of the Manhuaçu River with the Doce River meant that the simulation was varied with slow speeds in the reservoirs and high speeds in narrow stretches. The results of the 2D sediment transport model showed erosion and sedimentation in the studied areas, that the Carmo river exerts a mixing and dilution function of the sediments transported by the Gualaxo do Norte river, which the Suaçuí Grande river and the Manhuaçu river do not have capacity to perform a mixing and dilution function of the sediments transported by the Doce River in a short period, and that the dams interfere considerably with the sediment transport regime. In addition to these results, the sediment transport model showed that large amounts of sediment were retained on the banks of the rivers at the confluence of the Carmo River with the Piranga River and on the rock banks, which makes this confluence an important location for the retention of contaminated sediments, with significant influences on downstream water quality. However, these results can contribute to decision-making, to identify stretches with greater susceptibility to erosion and sediment deposition and to plan the restoration of these rivers.