TETRA TECH conducted a modeling study of Rio Doce (Doce River) and adjacent coastal region in order to assess the environmental impacts of the muddy material dispersion from a dam accident in Mariana (Minas Gerais, Brazil). The accident occurred at the end of 2015 and had a great repercussion, being considered the largest environmental disaster ever occurred in the country. Rio Doce is a water course of the Southeast Region of Brazil; it rises in Minas Gerais state and flows until the encounter with Atlantic Ocean near Linhares city, Espírito Santo state, Brazil. The study comprised the implementation of a hydrodynamic and sediment transport modeling with daily update and forecast for the next five days. Delft3D was selected to achieve the objectives proposed in this study, through modules Delft3D-FLOW and Delft3D-SED. The first requested result was to forecast the moment that the sediment plume would achieve the marine environment. The numerical grid comprised the entire length of the river, from the rupture of the dam to the encounter of the river with the sea. The boundaries were composed of river discharge and suspended sediments, which were measured and supplied daily by the contractor, and harmonic tide on the marine boundary. The meteorological forcing, i.e. wind and pressure fields, were obtained from operational forecasts generated by TETRA TECH. When the material reached the sea, another model was implemented to predict the plume behavior in the coastal zone, with higher resolution nearby the river mouth. The hydrodynamic boundaries were composed by TPXO harmonic tide and HYCOM current and elevation predictions. The composition between tide and current conditions was imposed on the numerical model boundary through a boundary condition called Riemann. Considering these conditions, the model adequately represents the continental shelf dynamics.and low frequency events that affect the direction of the marine currents. The current results generated by the hydrodynamic model were compared with data measured in field, and the elevation’s model results were compared with harmonic predictions. Results generated by the model concerning the transported sludge are compared with aerial photos of the plume. The major difficulty was the delay in receiving information that was being measured in the study area. Nonetheless, the implemented model matched the exact moment of the mud arrival in the coastal region, and the modelled sediment transport results in the coastal region showed good agreement with the satellite images.