Bed load sediment transport and morphological evolution in a degrading uniform sediment channel under unsteady flow hydrographs

Le Wang, Alan Cuthbertson (Lead / Corresponding author), Gareth Pender, Deyu Zhong

Research output: Contribution to journalArticle

Abstract

Flume experiments are conducted to investigate the intrinsic links between time-varying bed load transport properties for uniform sediments and bed surface morphology under unsteady hydrograph flows, in the absence of upstream sediment supply. These conditions are representative of regulated river reaches (e.g. downstream of a dam) that are subject to natural flood discharges or managed water releases, resulting in net degradation of the river bed. The results demonstrate that the hydrograph magnitude and unsteadiness have significant impacts on sediment transport rates and yields, as well as hysteresis patterns and yield ratios generated during the rising and falling limbs. A new hydrograph descriptor combining the influence of total water work and unsteadiness on bed load transport is shown to delineate these hysteresis patterns and yield ratios, whilst correlating strongly with overall sediment yields. This provides an important parametric link between unsteady hydrograph flow conditions, bed load transport and bed surface degradation under imposed zero sediment feed conditions. As such, maximum bed erosion depths and the longitudinal bed degradation profiles along the flume, are strongly dependent on the magnitude of this new hydrograph descriptor. Similarly, non-equilibrium bed forms generated along the flume indicate that formative conditions for alternate bars, mixed bar/dunes or dunes are defined reasonably well by an existing morphological model and the new hydrograph descriptor. These findings provide a new framework for improved predictive capabilities for sediment transport and morphodynamic response in regulated rivers to natural or imposed unsteady flows, while their wider application to graded sediments are also considered.
Original languageEnglish
Pages (from-to)5431-5452
Number of pages22
JournalWater Resources Research
Volume55
Issue number7
Early online date7 Jun 2019
DOIs
Publication statusPublished - Jul 2019

Fingerprint

unsteady flow
bedload
hydrograph
sediment transport
sediment
hysteresis
degradation
dune
flume experiment
morphodynamics
bedform
river bed
sediment yield
river
limb
dam
erosion
water

Keywords

  • bed load
  • bed morphology
  • flood hydrographs
  • flume experiments
  • sediment transport
  • unsteady flow

Cite this

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title = "Bed load sediment transport and morphological evolution in a degrading uniform sediment channel under unsteady flow hydrographs",
abstract = "Flume experiments are conducted to investigate the intrinsic links between time-varying bed load transport properties for uniform sediments and bed surface morphology under unsteady hydrograph flows, in the absence of upstream sediment supply. These conditions are representative of regulated river reaches (e.g. downstream of a dam) that are subject to natural flood discharges or managed water releases, resulting in net degradation of the river bed. The results demonstrate that the hydrograph magnitude and unsteadiness have significant impacts on sediment transport rates and yields, as well as hysteresis patterns and yield ratios generated during the rising and falling limbs. A new hydrograph descriptor combining the influence of total water work and unsteadiness on bed load transport is shown to delineate these hysteresis patterns and yield ratios, whilst correlating strongly with overall sediment yields. This provides an important parametric link between unsteady hydrograph flow conditions, bed load transport and bed surface degradation under imposed zero sediment feed conditions. As such, maximum bed erosion depths and the longitudinal bed degradation profiles along the flume, are strongly dependent on the magnitude of this new hydrograph descriptor. Similarly, non-equilibrium bed forms generated along the flume indicate that formative conditions for alternate bars, mixed bar/dunes or dunes are defined reasonably well by an existing morphological model and the new hydrograph descriptor. These findings provide a new framework for improved predictive capabilities for sediment transport and morphodynamic response in regulated rivers to natural or imposed unsteady flows, while their wider application to graded sediments are also considered.",
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Bed load sediment transport and morphological evolution in a degrading uniform sediment channel under unsteady flow hydrographs. / Wang, Le; Cuthbertson, Alan (Lead / Corresponding author); Pender, Gareth; Zhong, Deyu.

In: Water Resources Research, Vol. 55, No. 7, 07.2019, p. 5431-5452.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Bed load sediment transport and morphological evolution in a degrading uniform sediment channel under unsteady flow hydrographs

AU - Wang, Le

AU - Cuthbertson, Alan

AU - Pender, Gareth

AU - Zhong, Deyu

N1 - China Postdoctoral Science Foundation (GrantNumber(s): 2017M610907; Grant recipient(s): Le Wang); National Natural Science Foundation of China (GrantNumber(s): 91547204); National Key Research and Development Program of China (GrantNumber(s): 2017YFC0404303)

PY - 2019/7

Y1 - 2019/7

N2 - Flume experiments are conducted to investigate the intrinsic links between time-varying bed load transport properties for uniform sediments and bed surface morphology under unsteady hydrograph flows, in the absence of upstream sediment supply. These conditions are representative of regulated river reaches (e.g. downstream of a dam) that are subject to natural flood discharges or managed water releases, resulting in net degradation of the river bed. The results demonstrate that the hydrograph magnitude and unsteadiness have significant impacts on sediment transport rates and yields, as well as hysteresis patterns and yield ratios generated during the rising and falling limbs. A new hydrograph descriptor combining the influence of total water work and unsteadiness on bed load transport is shown to delineate these hysteresis patterns and yield ratios, whilst correlating strongly with overall sediment yields. This provides an important parametric link between unsteady hydrograph flow conditions, bed load transport and bed surface degradation under imposed zero sediment feed conditions. As such, maximum bed erosion depths and the longitudinal bed degradation profiles along the flume, are strongly dependent on the magnitude of this new hydrograph descriptor. Similarly, non-equilibrium bed forms generated along the flume indicate that formative conditions for alternate bars, mixed bar/dunes or dunes are defined reasonably well by an existing morphological model and the new hydrograph descriptor. These findings provide a new framework for improved predictive capabilities for sediment transport and morphodynamic response in regulated rivers to natural or imposed unsteady flows, while their wider application to graded sediments are also considered.

AB - Flume experiments are conducted to investigate the intrinsic links between time-varying bed load transport properties for uniform sediments and bed surface morphology under unsteady hydrograph flows, in the absence of upstream sediment supply. These conditions are representative of regulated river reaches (e.g. downstream of a dam) that are subject to natural flood discharges or managed water releases, resulting in net degradation of the river bed. The results demonstrate that the hydrograph magnitude and unsteadiness have significant impacts on sediment transport rates and yields, as well as hysteresis patterns and yield ratios generated during the rising and falling limbs. A new hydrograph descriptor combining the influence of total water work and unsteadiness on bed load transport is shown to delineate these hysteresis patterns and yield ratios, whilst correlating strongly with overall sediment yields. This provides an important parametric link between unsteady hydrograph flow conditions, bed load transport and bed surface degradation under imposed zero sediment feed conditions. As such, maximum bed erosion depths and the longitudinal bed degradation profiles along the flume, are strongly dependent on the magnitude of this new hydrograph descriptor. Similarly, non-equilibrium bed forms generated along the flume indicate that formative conditions for alternate bars, mixed bar/dunes or dunes are defined reasonably well by an existing morphological model and the new hydrograph descriptor. These findings provide a new framework for improved predictive capabilities for sediment transport and morphodynamic response in regulated rivers to natural or imposed unsteady flows, while their wider application to graded sediments are also considered.

KW - bed load

KW - bed morphology

KW - flood hydrographs

KW - flume experiments

KW - sediment transport

KW - unsteady flow

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UR - https://discovery.dundee.ac.uk/en/publications/e4fcdc84-9c81-43e7-a397-d40b62a6fa5b

U2 - 10.1029/2018WR024413

DO - 10.1029/2018WR024413

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EP - 5452

JO - Water Resources Research

JF - Water Resources Research

SN - 0043-1397

IS - 7

ER -