Flow directionality of pristine meandering rivers is embedded in the skewing of high-amplitude bends and neck cutoffs

Xingyan Guo, Dong Chen, Gary Parker

Research output: Contribution to journalArticle

Abstract

Information concerning the dynamics of river meandering is embedded in their planforms. Here, we focus on how bend skewing varies with increasing sinuosity, and how flow direction is embedded in bend skewing. It has often been thought that upstream-skewed bends are dominant within a sufficiently long reach. These bends may allow a reasonable inference as to the direction of flow. Here we consider this issue using 20 reaches of freely meandering alluvial rivers that are in remote locations, generally far from human influence. We find that low-amplitude bends tend to be downstream-, rather than upstream-skewed. Bends with sinuosity greater than 2.6, however, are predominantly upstream-skewed. Of particular interest are the neck cutoffs, all chosen to be relatively recent according to their position related to the main channel: 84% of these are upstream-skewed. Neck cutoffs, which have likely evolved directly from bends of the highest sinuosity, represent the planform feature most likely to have flow direction embedded in them. The field data suggest that meander bends without external forcing such as engineering works tend to evolve from downstream-skewed low-sinuosity bends to upstream-skewed high-sinuosity bends before cutoff. This process can be reproduced, to some extent, using models coupling sedimentary dynamics with flow dynamics.

Original languageEnglish (US)
Pages (from-to)23448-23454
Number of pages7
JournalProceedings of the National Academy of Sciences of the United States of America
Volume116
Issue number47
DOIs
StatePublished - Jan 1 2019

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Rivers
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Keywords

  • Alluvial rivers
  • Bends
  • Flow direction
  • Meandering
  • Planform skewing

ASJC Scopus subject areas

  • General

Cite this

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abstract = "Information concerning the dynamics of river meandering is embedded in their planforms. Here, we focus on how bend skewing varies with increasing sinuosity, and how flow direction is embedded in bend skewing. It has often been thought that upstream-skewed bends are dominant within a sufficiently long reach. These bends may allow a reasonable inference as to the direction of flow. Here we consider this issue using 20 reaches of freely meandering alluvial rivers that are in remote locations, generally far from human influence. We find that low-amplitude bends tend to be downstream-, rather than upstream-skewed. Bends with sinuosity greater than 2.6, however, are predominantly upstream-skewed. Of particular interest are the neck cutoffs, all chosen to be relatively recent according to their position related to the main channel: 84{\%} of these are upstream-skewed. Neck cutoffs, which have likely evolved directly from bends of the highest sinuosity, represent the planform feature most likely to have flow direction embedded in them. The field data suggest that meander bends without external forcing such as engineering works tend to evolve from downstream-skewed low-sinuosity bends to upstream-skewed high-sinuosity bends before cutoff. This process can be reproduced, to some extent, using models coupling sedimentary dynamics with flow dynamics.",
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