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

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Hydrodynamic controls on alluvial ridge construction and avulsion likelihood in meandering river floodplains. / Nicholas, A. P.; Aalto, R. E.; Sambrook-Smith, Greg; Schwendel, A. C.

In: Geology, Vol. 46, No. 7, 07.2018, p. 639-642.

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Nicholas, A. P. ; Aalto, R. E. ; Sambrook-Smith, Greg ; Schwendel, A. C. / Hydrodynamic controls on alluvial ridge construction and avulsion likelihood in meandering river floodplains. In: Geology. 2018 ; Vol. 46, No. 7. pp. 639-642.

Bibtex

@article{d584abf68e75426ea1295219af20ea61,
title = "Hydrodynamic controls on alluvial ridge construction and avulsion likelihood in meandering river floodplains",
abstract = "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.",
author = "Nicholas, {A. P.} and Aalto, {R. E.} and Greg Sambrook-Smith and Schwendel, {A. C.}",
year = "2018",
month = jul
doi = "10.1130/G40104.1",
language = "English",
volume = "46",
pages = "639--642",
journal = "Geology",
issn = "0091-7613",
publisher = "Geological Society of America",
number = "7",

}

RIS

TY - JOUR

T1 - Hydrodynamic controls on alluvial ridge construction and avulsion likelihood in meandering river floodplains

AU - Nicholas, A. P.

AU - Aalto, R. E.

AU - Sambrook-Smith, Greg

AU - Schwendel, A. C.

PY - 2018/7

Y1 - 2018/7

N2 - 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.

AB - 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.

U2 - 10.1130/G40104.1

DO - 10.1130/G40104.1

M3 - Article

VL - 46

SP - 639

EP - 642

JO - Geology

JF - Geology

SN - 0091-7613

IS - 7

ER -