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Bank pull or bar push: What drives scroll-bar formation in meandering rivers?

van de Lageweg, Wietse I.; van Dijk, Wout M.; Baar, Anne W.; Rutten, Jantien; Kleinhans, Maarten G.


Wietse I. van de Lageweg

Wout M. van Dijk

Dr Anne Baar
Post-doctoral Research Associate

Jantien Rutten

Maarten G. Kleinhans


One of the most striking features of meandering rivers are quasi-regular ridges of the point bar, evidence of a pulsed lateral migration of meander bends. Scroll bars formed on the inner bend are preserved on the point-bar surface as a series of ridges as meanders migrate, and in the subsurface of the point bar as inclined heterolithic stratification with lateral accretion surfaces. It is necessary to understand the formation and sedimentary architecture of these point bars, which are fundamental geomorphic building blocks of meandering rivers and potential reservoirs for water, oil, and gas. However, it remains unresolved whether the scroll-bar pattern forms in response to outer bend bank erosion during floods (i.e., bank pull), or is forced by bank progradation (i.e., bar push). Here we use experimentally formed meandering rivers with a set of static and migrating bends to isolate the effects of sediment supply to the point bar, bank protection, and forced bank retreat. We find that channel widening caused by bank retreat near the bend apex causes deposition of new scroll ridges along the inner bend point bar, whereas scroll bars cannot be forced by sediment pulses. Thus channel width variations along meander bends cause bank pull, which is necessary for scroll-bar formation. Furthermore, we find that each newly attached scroll bar overlies a nonpermeable layer of finer grained sediment caused by the temporary flow expansion, which explains the fining-upward tendency of point bars.

Journal Article Type Article
Publication Date 2014-04
Journal Geology
Print ISSN 0091-7613
Electronic ISSN 0091-7613
Publisher Geological Society of America
Peer Reviewed Peer Reviewed
Volume 42
Issue 4
Pages 319-322
APA6 Citation van de Lageweg, W. I., van Dijk, W. M., Baar, A. W., Rutten, J., & Kleinhans, M. G. (2014). Bank pull or bar push: What drives scroll-bar formation in meandering rivers?. Geology, 42(4), 319-322.
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