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River system discontinuities due to lateral inputs: generic styles and controls

Ferguson, R.I.; Cudden, J.R.; Hoey, T.B.; Rice, S.P.


R.I. Ferguson

J.R. Cudden

T.B. Hoey

S.P. Rice


In alluvial river systems, lateral inputs of water and/or sediment at junctions or undercut hillsides can disrupt what would otherwise be smooth downstream trends in mainstream bed elevation, channel gradient, and bed grain size. Generic styles of mainstream response to lateral inputs are investigated using a one-dimensional sediment routing model with multiple grain size fractions. Numerical experiments isolate the effects of three para-meters: ratio of tributary to mainstream water flux (QR), ratio of tributary to mainstream bedload flux (FR), and ratio of tributary to mainstream bedload diameter (DR). The findings are not unduly sensitive to the choice of initial conditions or to approximations made in the model. The primary distinction is between junctions that aggrade, causing local profile convexity with interrupted downstream fining, and junctions that degrade. The immediate effects of aggradation extend further upstream than downstream, whereas degradation is much more subdued and has no upstream impact. Aggradation is typical of coarse inputs (DR > 2), and degradation of fine inputs (DR < 1), but very high ratios of QR to FR also promote degradation. Both aggrading and degrading junctions can lead to a change in mainstream bed grain size well below the junction, with higher ratios of QR to FR producing a coarser distal bed. The effect of a tributary reflects the interplay between additional bed load and additional discharge to transport it.


Ferguson, R., Cudden, J., Hoey, T., & Rice, S. (2006). River system discontinuities due to lateral inputs: generic styles and controls. Earth Surface Processes and Landforms, 31(9), 1149-1166.

Journal Article Type Article
Publication Date 2006-03
Deposit Date Nov 9, 2006
Journal Earth Surface Processes and Landforms
Print ISSN 0197-9337
Electronic ISSN 1096-9837
Publisher British Society for Geomorphology
Peer Reviewed Peer Reviewed
Volume 31
Issue 9
Pages 1149-1166
Keywords Tributary junction, Aggradation, Degradation, Gravel-bed river, Sediment transport, Confluence.