Sediment Transport Assessment for Rio Gualaxo Do Norte After the Fundão Dam Failure

The debris flood created by the 5 November 2015 failure of the Fundão dam in Brazil injected a large amount of fine sediment in the Gualaxo do Norte River system. Although coarse and sand-sized sediment injections in rivers have been studied in relative detail, little is known about river response to overloading of mud-sized sediments (consisting of clay and silt). This paper presents an assessment of suspended sediment transport occurring in and along the Gualaxo do Norte River after the Fundão dam failure to contribute to the general understanding of how rivers recover following large inputs of mud-sized sediments (consisting of clay and silt). The average total sediment removal estimated based on the last 2 rainy periods is 54 466 tonnes, ranging from 37 385 to 71 546 tonnes according to the uncertainty analysis. The sediment transport analysis suggests that the Gualaxo do Norte River is returning to its pre-event morphological character in terms of sediment transport. However, the morphologic recovery of the system has been constrained in recent years by decreased stream power, the result of moderate wet seasons and limited large flood events. We anticipate that future larger flood events will transport most of the remaining available in-channel tailings, speeding up the physical morphologic recovery of the Gualaxo do Norte River, which is a key component of improving water quality and eventually the river ecology. Although the proposed approach for the sediment budget is simplified and has limitations and uncertainties, it provides a scientific basis to explain the natural fluvial processes that have been occurring in the river system. The approach used for the sediment budget presented in this paper could be applied to similar cases with limited data. Integr Environ Assess Manag 2020;16:572-582. © 2020 SETAC.