Integrating suspended sediment flux in large alluvial river channels: application of a synoptic rouse-based model to the Irrawaddy and Salween rivers
Integrating suspended sediment flux in large alluvial river channels: application of a synoptic rouse-based model to the Irrawaddy and Salween rivers
A large portion of freshwater and sediment is exported to the ocean by a small number of major rivers. Many of these megarivers are subject to substantial anthropogenic pressures, which are having a major impact on water and sediment delivery to deltaic ecosystems. Due to hydrodynamic sorting, sediment grain size and composition vary strongly with depth and across the channel in large rivers, complicating flux quantification. To account for this, we modified a semi-empirical Rouse model, synoptically predicting sediment concentration, grain-size distribution, and organic carbon (%OC) concentration with depth and across the river channel. Using suspended sediment depth samples and flow velocity data, we applied this model to calculate sediment fluxes of the Irrawaddy (Ayeyarwady) and the Salween (Thanlwin), the last two free-flowing megarivers in Southeast Asia. Deriving sediment-discharge rating curves, we calculated an annual sediment flux of (Formula presented.) Mt/year for the Irrawaddy and (Formula presented.) Mt/year for the Salween, together exporting 46% as much sediment as the Ganges-Brahmaputra system. The mean flux-weighted sediment exported by the Irrawaddy is significantly coarser (D
84 = 193 ± 13 μm) and OC-poorer (0.29 ± 0.08 wt%) compared to the Salween (112 ± 27 μm and 0.59 ± 0.16 wt%, respectively). Both rivers export similar amounts of particulate organic carbon, with a total of (Formula presented.) Mt C/year, 53% as much as the Ganges-Brahmaputra. These results underline the global significance of the Irrawaddy and Salween rivers and warrant continued monitoring of their sediment flux, given the increasing anthropogenic pressures on these river basins.
POC flux, hydrodynamic sorting, megarivers, particulate organic carbon, sediment flux, sediment transport
Baronas, J. Jotautas
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Stevenson, Emily I.
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Hackney, Christopher R.
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Darby, Stephen E.
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Bickle, Michael J.
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Hilton, Robert G.
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Larkin, Christina S.
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Parsons, Daniel R.
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Khaing, Aung Myo
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Tipper, Edward T.
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1 September 2020
Baronas, J. Jotautas
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Stevenson, Emily I.
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Hackney, Christopher R.
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Darby, Stephen E.
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Bickle, Michael J.
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Hilton, Robert G.
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Larkin, Christina S.
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Parsons, Daniel R.
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Khaing, Aung Myo
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Tipper, Edward T.
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Baronas, J. Jotautas, Stevenson, Emily I., Hackney, Christopher R., Darby, Stephen E., Bickle, Michael J., Hilton, Robert G., Larkin, Christina S., Parsons, Daniel R., Khaing, Aung Myo and Tipper, Edward T.
(2020)
Integrating suspended sediment flux in large alluvial river channels: application of a synoptic rouse-based model to the Irrawaddy and Salween rivers.
Journal of Geophysical Research: Earth Surface, 125 (9), [e2020JF005554].
(doi:10.1029/2020JF005554).
Abstract
A large portion of freshwater and sediment is exported to the ocean by a small number of major rivers. Many of these megarivers are subject to substantial anthropogenic pressures, which are having a major impact on water and sediment delivery to deltaic ecosystems. Due to hydrodynamic sorting, sediment grain size and composition vary strongly with depth and across the channel in large rivers, complicating flux quantification. To account for this, we modified a semi-empirical Rouse model, synoptically predicting sediment concentration, grain-size distribution, and organic carbon (%OC) concentration with depth and across the river channel. Using suspended sediment depth samples and flow velocity data, we applied this model to calculate sediment fluxes of the Irrawaddy (Ayeyarwady) and the Salween (Thanlwin), the last two free-flowing megarivers in Southeast Asia. Deriving sediment-discharge rating curves, we calculated an annual sediment flux of (Formula presented.) Mt/year for the Irrawaddy and (Formula presented.) Mt/year for the Salween, together exporting 46% as much sediment as the Ganges-Brahmaputra system. The mean flux-weighted sediment exported by the Irrawaddy is significantly coarser (D
84 = 193 ± 13 μm) and OC-poorer (0.29 ± 0.08 wt%) compared to the Salween (112 ± 27 μm and 0.59 ± 0.16 wt%, respectively). Both rivers export similar amounts of particulate organic carbon, with a total of (Formula presented.) Mt C/year, 53% as much as the Ganges-Brahmaputra. These results underline the global significance of the Irrawaddy and Salween rivers and warrant continued monitoring of their sediment flux, given the increasing anthropogenic pressures on these river basins.
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Accepted/In Press date: 28 July 2020
Published date: 1 September 2020
Additional Information:
Funding Information:
Funding was provided by NERC Standard Grant NE/P011659/1 to E.?T.?T., R.?G.?H., and M.?J.?B. We thank Si Thu, Charlie Eardley, Vivien Cumming, Luke Bridgestock, Hazel Chapman, and the staff of Directorate of Water Resources and Improvement of River Systems (Myanmar) for help in the field. Chris Parish helped develop and build the sediment sampling rig and filtration units. Tamsin O'Connell and Catherine Kneale (Department of Archaeology, University of Cambridge) are thanked for assisting with freeze drying. Olly Dawes and Laura Healy helped with sediment grain size analyses at the University of Hull and the University of Cambridge, respectively. We thank Maarten Lupker, an anonymous reviewer, and editor Noah Snyder for constructive and insightful comments.
Publisher Copyright:
©2020. The Authors.
Keywords:
POC flux, hydrodynamic sorting, megarivers, particulate organic carbon, sediment flux, sediment transport
Identifiers
Local EPrints ID: 444184
URI: http://eprints.soton.ac.uk/id/eprint/444184
ISSN: 2169-9003
PURE UUID: 7c74b24b-9654-43b2-85a7-f9532b801ce1
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Date deposited: 30 Sep 2020 16:31
Last modified: 17 Mar 2024 04:05
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Contributors
Author:
J. Jotautas Baronas
Author:
Emily I. Stevenson
Author:
Michael J. Bickle
Author:
Robert G. Hilton
Author:
Christina S. Larkin
Author:
Daniel R. Parsons
Author:
Aung Myo Khaing
Author:
Edward T. Tipper
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