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The planform mobility of river channel confluences: insights from analysis of remotely sensed

The planform mobility of river channel confluences: insights from analysis of remotely sensed
The planform mobility of river channel confluences: insights from analysis of remotely sensed
River channel confluences are widely acknowledged as important geomorphological nodes that control the downstream routing of water and sediment, and which are locations for the preservation of thick fluvial deposits overlying a basal scour. Despite their importance, there has been little study of the stratigraphic characteristics of river junctions, or the role of confluence morphodynamics in influencing stratigraphic character and preservation potential. As a result, although it is known that confluences can migrate through time, models of confluence geomorphology and sedimentology are usually presented from the perspective that the confluence remains at a fixed location. This is problematic for a number of reasons, not least of which is the continuing debate over whether it is possible to discriminate between scour that has been generated by autocyclic processes (such as confluence scour) and that driven by allocyclic controls (such as sea-level change). This paper investigates the spatial mobility of river confluences by using the 40-year record of Landsat Imagery to elucidate the styles, rates of change and areal extent over which large river confluence scours may migrate. On the basis of these observations, a new classification of the types of confluence scour is proposed and applied to the Amazon and Ganges-Brahmaputra-Meghna (GBM) basins. This analysis demonstrates that the drivers of confluence mobility are broadly the same as those that drive channel change more generally. Thus in the GBM basin, a high sediment supply, large variability in monsoonal driven discharge and easily erodible bank materials result in a catchment where over 80 % of large confluences are mobile over this 40-year window; conversely this figure is less than 40 % for the Amazon basin. These results highlight that: i) the potential areal extent of confluence scours is much greater than previously assumed, with the location ofsome confluences on the Jamuna (Brahmaputra) River migrating over a distance of 20 times the tributary channel width; ii) extensive migration in the confluence location is more common than currently assumed, and iii) confluence mobility is often tied to the lithological and hydrological characteristics of the drainage basins that determine sediment yield.
delta, FLOODING, REMOTE SENSING
0012-8252
1-18
Dixon, Simon J.
83eded54-415c-41a6-a016-ad186c675478
Sambrook Smith, Gregory H.
94a595d4-34e8-4045-b74c-17ce652f7898
Best, James L.
307c0d1d-bff5-459a-abcd-38a649ced8ef
Nicholas, Andrew P.
6406b349-a2c8-4dc6-9d13-6aa70154229a
Bull, Jon. M.
974037fd-544b-458f-98cc-ce8eca89e3c8
Vardy, Mark E.
8dd019dc-e57d-4b49-8f23-0fa6d246e69d
Sarkar, Maminul H.
473e1d46-92d2-4025-ae0d-b2d0b276bd1c
Goodbred, Steven
9a6c8a90-d932-467b-ad49-a81938f18f02
Dixon, Simon J., Sambrook Smith, Gregory H., Best, James L., Nicholas, Andrew P., Bull, Jon. M., Vardy, Mark E., Sarkar, Maminul H. and Goodbred, Steven (2018) The planform mobility of river channel confluences: insights from analysis of remotely sensed Earth-Science Reviews, 176, pp. 1-18. (doi:10.1016/j.earscirev.2017.09.009).

Dixon, Simon J., Sambrook Smith, Gregory H., Best, James L., Nicholas, Andrew P., Bull, Jon. M., Vardy, Mark E., Sarkar, Maminul H. and Goodbred, Steven (2018) The planform mobility of river channel confluences: insights from analysis of remotely sensed Earth-Science Reviews, 176, pp. 1-18. (doi:10.1016/j.earscirev.2017.09.009).

Record type: Article

Abstract

River channel confluences are widely acknowledged as important geomorphological nodes that control the downstream routing of water and sediment, and which are locations for the preservation of thick fluvial deposits overlying a basal scour. Despite their importance, there has been little study of the stratigraphic characteristics of river junctions, or the role of confluence morphodynamics in influencing stratigraphic character and preservation potential. As a result, although it is known that confluences can migrate through time, models of confluence geomorphology and sedimentology are usually presented from the perspective that the confluence remains at a fixed location. This is problematic for a number of reasons, not least of which is the continuing debate over whether it is possible to discriminate between scour that has been generated by autocyclic processes (such as confluence scour) and that driven by allocyclic controls (such as sea-level change). This paper investigates the spatial mobility of river confluences by using the 40-year record of Landsat Imagery to elucidate the styles, rates of change and areal extent over which large river confluence scours may migrate. On the basis of these observations, a new classification of the types of confluence scour is proposed and applied to the Amazon and Ganges-Brahmaputra-Meghna (GBM) basins. This analysis demonstrates that the drivers of confluence mobility are broadly the same as those that drive channel change more generally. Thus in the GBM basin, a high sediment supply, large variability in monsoonal driven discharge and easily erodible bank materials result in a catchment where over 80 % of large confluences are mobile over this 40-year window; conversely this figure is less than 40 % for the Amazon basin. These results highlight that: i) the potential areal extent of confluence scours is much greater than previously assumed, with the location ofsome confluences on the Jamuna (Brahmaputra) River migrating over a distance of 20 times the tributary channel width; ii) extensive migration in the confluence location is more common than currently assumed, and iii) confluence mobility is often tied to the lithological and hydrological characteristics of the drainage basins that determine sediment yield.

Text Dixon et al, postprint_Earth_Science_Reviews_2017 - Accepted Manuscript
Restricted to Repository staff only until 28 September 2018.
Text 1-s2.0-S0012825216303464-main - Version of Record
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Accepted/In Press date: 12 September 2017
e-pub ahead of print date: 28 September 2017
Published date: 1 January 2018
Keywords: delta, FLOODING, REMOTE SENSING

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Local EPrints ID: 414607
URI: http://eprints.soton.ac.uk/id/eprint/414607
ISSN: 0012-8252
PURE UUID: 0ebaa7ca-81d3-4dbd-b3e6-5397d3c36eaa

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Date deposited: 05 Oct 2017 16:30
Last modified: 08 Nov 2017 17:30

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Contributors

Author: Simon J. Dixon
Author: Gregory H. Sambrook Smith
Author: James L. Best
Author: Andrew P. Nicholas
Author: Jon. M. Bull
Author: Mark E. Vardy
Author: Maminul H. Sarkar
Author: Steven Goodbred

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