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Flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone of the Three Gorges Reservoir, China

Flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone of the Three Gorges Reservoir, China
Flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone of the Three Gorges Reservoir, China
Since the launch of the Three Gorges Dam on the Yangtze River, a distinctive reservoir fluctuation zone has been created and significantly modified by regular dam operations. Sediment redistribution within this artificial landscape differs substantially from that in natural fluvial riparian zones, due to a specific hydrological regime comprising steps of water impoundment with increasing magnitudes and seasonal water level fluctuation holding a range of sediment fluxes. This study reinterpreted post-dam sedimentary dynamics in the reservoir fluctuation zone by stratigraphy determination of a 345-cm long sediment core, and related it to impact of the hydrological regime. Seasonality in absolute grain-size composition of suspended sediment was applied as a methodological basis for stratigraphic differentiation. Sedimentary laminations with relatively higher proportions of sandy fractions were ascribed to sedimentation during the dry season when proximal subsurface bank erosion dominates source contributions, while stratigraphy with a lower proportion of sandy fractions is possibly contributed by sedimentation during the wet season when distal upstream surface erosion prevails. Chronology determination revealed non-linear and high annual sedimentation rates ranging from 21.7 to 152.1cm/yr. Although channel geomorphology may primarily determine the spatial extent of sedimentation, seasonal sedimentary dynamics was predominantly governed by the frequency, magnitude, and duration of flooding. Summer inundation by natural floods with enhanced sediment loads produced from upstream basins induced higher sedimentation rates than water impoundment during the dry season when distal sediment supply was limited. We thus conclude that flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone, though little impact on total sediment retention rate was detected. Ongoing reductions in flow and sediment supply under human disturbance may have profound implications in affecting sedimentary equilibrium in the reservoir fluctuation zone. The results herein provide insights of how big dams have disrupted the sediment conveyance processes of large scale fluvial systems.
0048-9697
410-420
Tang, Qiang
eec1f05c-51c2-4801-ae81-da75d4923ca4
Bao, Yuhai
96f8861a-47ea-4319-8a37-a5881ff22944
He, Xiubin
65cdfb0b-bcb9-4c36-9b5f-8ec45a9cec1c
Fu, Bojie
ca2f7fa0-1a79-4321-a4ac-9b60f74676c3
Collins, Adrian L.
700e5f6a-4de3-4406-ad7a-d9d8ec0a5069
Zhang, Xinbao
ec78da65-783c-438e-a799-d67ff10f623b
Tang, Qiang
eec1f05c-51c2-4801-ae81-da75d4923ca4
Bao, Yuhai
96f8861a-47ea-4319-8a37-a5881ff22944
He, Xiubin
65cdfb0b-bcb9-4c36-9b5f-8ec45a9cec1c
Fu, Bojie
ca2f7fa0-1a79-4321-a4ac-9b60f74676c3
Collins, Adrian L.
700e5f6a-4de3-4406-ad7a-d9d8ec0a5069
Zhang, Xinbao
ec78da65-783c-438e-a799-d67ff10f623b

Tang, Qiang, Bao, Yuhai, He, Xiubin, Fu, Bojie, Collins, Adrian L. and Zhang, Xinbao (2016) Flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone of the Three Gorges Reservoir, China. Science of the Total Environment, 548-549, 410-420. (doi:10.1016/j.scitotenv.2015.12.158).

Record type: Article

Abstract

Since the launch of the Three Gorges Dam on the Yangtze River, a distinctive reservoir fluctuation zone has been created and significantly modified by regular dam operations. Sediment redistribution within this artificial landscape differs substantially from that in natural fluvial riparian zones, due to a specific hydrological regime comprising steps of water impoundment with increasing magnitudes and seasonal water level fluctuation holding a range of sediment fluxes. This study reinterpreted post-dam sedimentary dynamics in the reservoir fluctuation zone by stratigraphy determination of a 345-cm long sediment core, and related it to impact of the hydrological regime. Seasonality in absolute grain-size composition of suspended sediment was applied as a methodological basis for stratigraphic differentiation. Sedimentary laminations with relatively higher proportions of sandy fractions were ascribed to sedimentation during the dry season when proximal subsurface bank erosion dominates source contributions, while stratigraphy with a lower proportion of sandy fractions is possibly contributed by sedimentation during the wet season when distal upstream surface erosion prevails. Chronology determination revealed non-linear and high annual sedimentation rates ranging from 21.7 to 152.1cm/yr. Although channel geomorphology may primarily determine the spatial extent of sedimentation, seasonal sedimentary dynamics was predominantly governed by the frequency, magnitude, and duration of flooding. Summer inundation by natural floods with enhanced sediment loads produced from upstream basins induced higher sedimentation rates than water impoundment during the dry season when distal sediment supply was limited. We thus conclude that flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone, though little impact on total sediment retention rate was detected. Ongoing reductions in flow and sediment supply under human disturbance may have profound implications in affecting sedimentary equilibrium in the reservoir fluctuation zone. The results herein provide insights of how big dams have disrupted the sediment conveyance processes of large scale fluvial systems.

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e-pub ahead of print date: 1 April 2016
Organisations: Geography & Environment

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Local EPrints ID: 389584
URI: https://eprints.soton.ac.uk/id/eprint/389584
ISSN: 0048-9697
PURE UUID: 6e6cdeab-4519-49b8-86a3-924085ee3996

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Date deposited: 09 Mar 2016 11:57
Last modified: 15 Jul 2019 20:42

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Contributors

Author: Qiang Tang
Author: Yuhai Bao
Author: Xiubin He
Author: Bojie Fu
Author: Adrian L. Collins
Author: Xinbao Zhang

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