Greater amounts of sediment carried by lowland rivers drive the reshaping of floodplains in the Amazon Basin, according to a study published online in Nature Geoscience. These findings are relevant as the Amazonian river system may be significantly altered by proposed mega-dams that would disrupt sediment supplies.
Jose Constantine and colleagues analysed Landsat satellite imagery from 1985 to 2013 to track the lateral migration of river bends in the Amazon. As rivers evolve, their meanders migrate outwards and the rivers become more sinuous. The researchers found that the speed at which the meanders migrated for each of the rivers studied depended on the river’s supply of sand and silt. The meanders of rivers carrying more sediment migrated faster than those carrying less sediment, and were also more frequently cut off and abandoned to form U-shaped lakes.
If sediment loads are reduced - by a dam, for example - meander migration is expected to slow, and thus the reshaping of the floodplain environment is affected.