Sediment supply drives floodplain evolution in Amazon Basin

The findings have implications for the Amazonian river system, which may be significantly altered by proposed mega-dams that would disrupt sediment supplies. The research project, led by José Constantine, examined 20 reaches within the Amazon Basin from Landsat imagery spanning nearly 30 years (1985 to 2013).

They found that rivers transporting larger amounts of sediment migrated more across floodplains and created more oxbow lakes than rivers carrying less sediment. They also noted that channel movement did not depend on either the slope of the channel or the river discharge.

The research gives scientists insight into the contrasting behavioural properties of rivers where sediment is an imposed variable – e.g. resulting from glacial, volcanic, or human activity – and rivers where the main sediment supply is from local bank erosion.

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.

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