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Sediment supply as a driver of river meandering and floodplain evolution in the Amazon Basin

2014; Nature Portfolio; Volume: 7; Issue: 12 Linguagem: Inglês

10.1038/ngeo2282

1752-0908

José Antonio Constantine, Thomas Dunne, Joshua Ahmed, Carl J. Legleiter, Eli D. Lazarus,

Geological formations and processes

Proposed engineering projects in the Amazon Basin would disrupt sediment supplies to lowland rivers. Landsat imagery of Amazonian tributaries reveals that lower sediment loads are associated with lower meander migration and cutoff rates. The role of externally imposed sediment supplies on the evolution of meandering rivers and their floodplains is poorly understood, despite analytical advances in our physical understanding of river meandering1,2. The Amazon river basin hosts tributaries that are largely unaffected by engineering controls and hold a range of sediment loads, allowing us to explore the influence that sediment supply has on river evolution. Here we calculate average annual rates of meander migration within 20 reaches in the Amazon Basin from Landsat imagery spanning 1985–2013. We find that rivers with high sediment loads experience annual migration rates that are higher than those of rivers with lower sediment loads. Meander cutoff also occurs more frequently along rivers with higher sediment loads. Differences in meander migration and cutoff rates between the study reaches are not explained by differences in channel slope or river discharge. Because faster meander migration and higher cutoff rates lead to increased sediment-storage space in the resulting oxbows, we suggest that sediment supply modulates the reshaping of floodplain environments by meandering rivers. We conclude that imposed sediment loads influence planform changes in lowland rivers across the Amazon.