The role of sediment supply in the adjustment of channel sinuosity across the Amazon Basin

Sediment supplies are a fundamental component of alluvial river systems, but the importance of sustained supplies of externally derived sediments for the evolution of meandering planforms remains unclear. Here we demonstrate the importance of sediment supply in enhancing the growth of point bars tha...

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Bibliographic Details
Published in:Geology (Boulder) 2019-09, Vol.47 (9), p.807-810
Main Authors: Ahmed, Joshua, Constantine, José Antonio, Dunne, Thomas
Format: Article
Language:English
Subjects:
Alluvial rivers
Amazon Basin
applied (geophysical surveys & methods)
Bars
Bends
channels
Curvature
Downstream
Evolution
fluvial features
Fluvial sediments
Geology
geomorphology
Geophysics
imagery
landform evolution
Landsat
Landsat satellites
Loads (forces)
Meandering
Meanders
Remote sensing
River basins
River meanders
River systems
Rivers
Rotation
Routing
Satellite imagery
satellite methods
Sediment
Sediment load
sediment supply
sediment transport
Sediments
Sinuosity
South America
Supplies
transport
Upstream
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Summary:Sediment supplies are a fundamental component of alluvial river systems, but the importance of sustained supplies of externally derived sediments for the evolution of meandering planforms remains unclear. Here we demonstrate the importance of sediment supply in enhancing the growth of point bars that influence the rate of sinuosity increase through flow deflections in meander bends. We use an archive of Landsat images of 16 meandering reaches from across the Amazon Basin to show that rivers transporting larger sediment loads increase their sinuosity more rapidly than those carrying smaller loads. Sediment-rich rivers are dominated by downstream-rotating meanders that increase their sinuosity more rapidly than both extensional and upstream-rotating meanders. Downstream-rotating meanders appear to establish larger point bars that expand throughout the meander, in contrast to extensional meanders, which have smaller bars, and upstream rotating meanders, which are characterized by deposition over the bar head. These observations demonstrate that the size and position of point bars within meander bends influences flow routing and thus controls the dominant direction of meander growth. Rivers with low sediment supplies build smaller point bars, which reduces their capacity to increase meander curvature and the resulting sinuosity.
ISSN:0091-7613
1943-2682
DOI:10.1130/G46319.1