Assessing sediment dynamics and erosion-deposition patterns after a dam break: Insights from the Brumadinho tailings dam failure in Brazil

Abstract

Dam break events cause disruptive scenarios, leading to the sudden release of large volumes of water and sediment downstream, resulting in significant geomorphic changes in the floodplain. Assessing the consequences of dam break events on floodplain geomorphology, including changes in channel morphology, erosion, and deposition patterns, is an emerging research field, with perspectives of understanding the potential for landform evolution concerning sediment transport and establish benchmarks for future impact assessments and event modeling. The main objective of this research is to quantitatively assess the sediment dynamics following the Brumadinho tailing dam failure, focusing on the released sediment, the bulk retained in the Ferro Carvão stream watershed, and the tailings that reached the Paraopeba River. The methodology involved geospatial evaluation and zonal statistics to calculate bulk volumes, account for uncertainties, and compare the results with available monitoring data. The results highlighted a significant uncertainty regarding the mass sediment discharge hydrograph due to particle's geotechnical properties variability. It was estimated that about half of the sediment volume released from the dam was retained in the event-scale tailing spread area, diverging from other reported values in the literature. Zonal statistics in the floodplain revealed a predominant tendency for deposition over erosion across most of the spread area, especially in downstream areas, attributed to the geomorphological characteristics of the terrain and flow characteristics. However, erosion was more prominent in areas closest to the dam, justified by the flow velocity and stream power in these areas. Additionally, a mass balance indicates that a significant amount of sediment particles is being constantly transported in Paraopeba river, driven mainly by flow regime in rainy periods.