Download
Abstract
Counter point bars are sedimentary deposits that form on the concave (outer) bank of river bends, opposite to the more common convex-bank point bars. Although their existence has been recognized for decades, counter point bars are often attributed to local bank resistance or channel confinement. Here we use a simple kinematic model of meandering to show that counter point bars can form through autogenic processes without variations in bank erodibility. The model predicts that counter point bars develop when the downstream translation rate of meander bends exceeds the lateral migration rate. This occurs when meander bends have high curvature and short wavelength, which are common characteristics of bends formed by neck cutoffs. Analysis of planform change along the Mamoré River in Bolivia confirms that counter point bars are associated with high-curvature bends that translate downstream. The grain size of counter point bar deposits is finer than that of adjacent point bars, which is consistent with deposition during the falling stage of floods when bedload transport rates are reduced. The presence of counter point bars in the stratigraphic record does not necessarily indicate channel confinement or lateral variations in substrate erodibility, but may simply reflect the natural evolution of meandering rivers.
Citation
Sylvester, Z., Durkin, P. R., Hubbard, S. M., & Mohrig, D. (2021). Autogenic translation and counter point bar deposition in meandering rivers. GSA Bulletin, 133(9-10), 1921-1938. doi: 10.1130/B35829.1
@article{sylvester2021counter_point_bars,
author = {Z. Sylvester and P. R. Durkin and S. M. Hubbard and D. Mohrig},
year = {2021},
title = {Autogenic translation and counter point bar deposition in meandering rivers},
journal = {GSA Bulletin},
volume = {133},
number = {9-10},
pages = {1921--1938},
url = {https://pubs.geoscienceworld.org/gsa/gsabulletin/article/doi/10.1130/B35829.1/595343/Autogenic-translation-and-counter-point-bar}}