Hydrodynamic controls on alluvial ridge construction and avulsion likelihood in meandering river floodplains

A. P. Nicholas, R. E. Aalto, Greg Sambrook-Smith, A. C. Schwendel

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)
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Existing models of alluvial stratigraphy often neglect the hydrodynamic controls on channel belt and floodplain sedimentation, and predict avulsion using topographic metrics, such as channel belt super-elevation. This study provides a first demonstration of the potential for simulating long-term river floodplain evolution (over >500 floods) using a process-based hydrodynamic model. Simulations consider alluvial ridge construction during the period leading up to an avulsion, and assess the controls on avulsion likelihood. Results illustrate that the balance between within-channel and overbank sedimentation exerts a key control on both super-elevation ratios and on the conveyance of water and sediment to the floodplain. Rapid overbank sedimentation creates high alluvial ridges with deep channels, leading to lower apparent super-elevation (the ratio of ridge height to channel depth), and implying reduced avulsion likelihood. However, channel deepening also drives a reduction in channel belt-floodplain connectivity, so that conveyance of water to the distal floodplain is concentrated in a declining number of channel breaches, which may favor avulsion. These results suggest that while super elevation ratios in excess of a threshold value may be a necessary condition for a meandering river avulsion, avulsion likelihood may not be greatest where the super elevation ratio is maximised. Instead, optimal conditions for avulsion may depend on channel-floodplain hydrodynamic connectivity, determined by the balance between coarse (channel bed forming) and fine (floodplain constructing) sediment delivery. These results highlight a need to rethink the representation of avulsion in existing models of alluvial architecture.
Original languageEnglish
Pages (from-to)639-642
Issue number7
Early online date12 Jun 2018
Publication statusPublished - Jul 2018


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