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Emergence of abrupt gravel to sand transitions along rivers through sorting processes

Ferguson, R.I.


R.I. Ferguson


Gradual downstream fining along gravel-bed rivers is often followed by a relatively abrupt change to a sand bed. This has usually been explained by the breakdown of pebbles of certain lithologies to sand, but it is not restricted to particular rock types and can occur over distances too short for significant abrasion. An alternative explanation is that as shear stress declines downstream, size sorting is enhanced through nonlinearities and thresholds in bedload transport and deposition mechanisms. This hypothesis is tested by numerical modeling of an idealized channel with a mixed gravel and sand bed. Abrupt and persistent gravel fronts with associated breaks of slope develop from a range of smooth initial states when a new initial-motion equation is used, but not with a conventional equation. The results suggest an emergent phenomenon, but one that is sensitive to process specification rather than initial or boundary conditions.


Ferguson, R. (2003). Emergence of abrupt gravel to sand transitions along rivers through sorting processes. Geology, 31(2), 159-162.

Journal Article Type Article
Publication Date 2003-02
Deposit Date Mar 13, 2007
Journal Geology
Print ISSN 0091-7613
Electronic ISSN 1943-2682
Publisher Geological Society of America
Peer Reviewed Peer Reviewed
Volume 31
Issue 2
Pages 159-162
Keywords Geomorphology, Modeling, Gravel front, Bedload transport.