Modeling the Sediment Load of the Doce River after the Fundão Tailings Dam Collapse, Brazil

Abstract

The collapse of the Fundão tailings dam in Brazil spilled 32 million cubic meters of mine waste, causing a severe socioeconomic and environmental impact in the Doce River. Approximately 90% of the spilled volume settled on floodplains, over 118 km downstream of Fundão Dam. A hyperconcentrated flow (≈400,000 mg/L) reached the Doce River, where the floodwave and sediment wave traveled at different celerities over 570 km until the Atlantic Ocean. The one-dimensional advection-dispersion equation with settling was solved and calibrated to fit the observed concentration using an analytical solution to determine the longitudinal dispersion coefficient and the settling rate, both along the river and in the reservoirs. The longitudinal dispersion coefficient ranged from 30 to 120 m2/s, and the sediment settling rate corresponded to particle sizes from 1.1 to 2.0 μm. Moreover, simulations with the calibrated model revealed that without the presence of three hydropower reservoirs on the Doce River, the sediment concentration at the watershed outlet would have been 64,000 mg/L instead of the observed 1,500 mg/L. The temperature effects were also examined, and a decrease from 30°C to 5°C in water temperature would have caused a concentration 12 times higher at the outlet.