Drivers and Impacts of Sediment Deposition in Amazonian Floodplains

The Science

A major challenge in understanding large river dynamics, such as the Amazon, is a process-based understanding that controls the deposition of river sediment on floodplains. Sediment deposition significantly shapes landscapes and ecosystems. This research found that sediment deposition in Amazonian floodplains depends jointly on three key factors: river flooding (inundation), the amount of sediment carried by the Amazon River water, and how water moves within the floodplain. Human actions, like building dams and removing forests, also significantly affect sediment deposition, altering the natural balance of these important environments.

The Impact

This research develops an unprecedented high-resolution, hydrodynamic-sediment model for Amazonian floodplains. The model simulates how sediment moves and is deposited in Amazonian floodplains at high resolution. This is important for managing and preserving these unique ecosystems which isn’t achievable using only observations. It provides the first detailed picture of how flooding, sediment levels, and water movement together control sediment deposition. The Amazon floodplain serves as an ideal testbed due to its complex topography, extensive measurements, and critical sediment dynamics relevant to U.S. river systems. Findings from this study directly enhance scientists' understanding of how human activities—such as dam construction and land-use changes—shape these processes in the Amazon and similar regions worldwide, providing valuable insights for refining global Earth system models.  

Summary

The Amazon River carries massive amounts of sediment, much of which is deposited in its floodplains and shapes the region's unique landscapes and ecosystems. However, precisely quantifying this sediment deposition across time and space remains challenging. To address this gap, this study used a high-resolution numerical model that simulates sediment deposition in detail for a representative Amazonian floodplain, called Janauacá. Simulations showed that sediment deposition is driven jointly by river inundation, suspended sediment concentration in the Amazon River, and floodplain hydrodynamics. Sediment deposition showed a stronger relationship with sediment concentration in the river rather than with the flooding magnitude itself. Additionally, this study evaluated how human activities—particularly dam construction and deforestation—impact sediment dynamics. While dams reduce sediment supply, and thus sediment deposition, in the floodplain, widespread deforestation initially boosts sediment deposition but ultimately decreases floodplain trapping efficiency over time. This work advances scientists understanding of sediment dynamics in the Amazon Basin, providing important insights for managing river systems facing similar pressures worldwide.

Contacts

Funding

This work was supported by Scientific Discovery through Advanced Computing (SciDAC) partnership program, through the project “Capturing the Dynamics of Compound Flooding in E3SM”, funded by the Department of Energy, Office of Science, Biological and Environmental Research program, Earth System Model Development Program Area and the Office of Advanced Scientific Computing Research. Pacific Northwest National Laboratory is operated by Battelle for the Department of Energy.