Meandering rivers are common, esthetically pleasing, and of engineering and ecological importance. The bends of alluvial meandering rivers often double back on themselves, showing skewing. This skewing may be directed upstream or downstream. How skewing evolves as bends develop remains incompletely understood.

Scientists from the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences and University of Illinois at Urbana-Champaign consider this issue using 20 reaches of nearly pristine alluvial meandering rivers in the world.  

Their analysis shows that low-amplitude bends tend to be downstream-skewed, while upstream skewing increasingly dominates as bend sinuosity increases. Of particular interest are the neck cutoffs which have likely evolved directly from the bends of highest sinuosity: 84% of these are upstream-skewed.  

This provides a new guide for interpreting bend evolution and offers a useful comparison with numerical models.  

The results suggest that rivers often carry an imprint of the direction of the flow that created them, through the shape of their high-amplitude bends and oxbow lakes.  

“This study provides a reference tool for estimating paleoflow direction on Earth and other planets,” said Prof. CHEN Dong.  

The related results have been published in Proceedings of the National Academy of Sciences (Guo X., Chen D.*, Parker G.*, 2019. Flow directionality of pristine meandering rivers is embedded in the skewing of high-amplitude bends and neck cutoffs. Proceedings of the National Academy of Sciences: 201910874).  

This work was supported by the National Key R&D Program of China and the National Natural Science Foundation of China.