Simulating suspended sediment transport during the 2023–2024 floods in southern Brazil

Abstract

The most intense rainfall event in Brazil (> 950 mm during 14 days in May 2024) affected millions of people in the south of the country. The damage includes several deaths and other social issues, billions in economic losses, and massive environmental devastation with more than 15,000 landslides and sediments settling in flat areas. As intense floods are becoming more frequent in this region and there are no estimates of sediment transport during these events, we estimated the suspended sediments transport in the Guaíba River basin for three major recent floods (September and November 2023 and May 2024). We used the hydrological model MGB-SED and daily precipitation to compute sediment erosion, transport and deposition, with calibration focused on representing extreme events. Our model showed that around 5 million tons of suspended sediment were delivered to the Guaíba River during the 2024 event, followed by 2.3 million tons in September 2023 and 1 million tons in November 2023. When compared to the simulated long-term average between 1975 and 2015 (7.3 kt/day) the 2024 peak was around 63 times higher. The amounts of sediment coming from the Taquari-Antas River represented 58 % of the total for the November event and 66 % for the September and May events, while the Jacuí River contributed 27 % and 30 % respectively. The extreme rainfall and the topographic conditions made the 2024 event the one that transported the most sediment in the basin's recent history.