Sediment Transport of Fine Sand to Fine Gravel on Transverse Bed Slopes in Rotating Annular Flume Experiments

Baar, Anne; Smit, Jeroen; Uijttewaal, W.S.J.; Kleinhans, Maarten G.

doi:10.1002/2017wr020604

Cited by 62 publications

(102 citation statements)

References 48 publications

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“…In contrast to ω diff bed slope results this contribution from bed load transport processes. Figure reveals that ω bl bed slope is much smaller than ω diff bed slope , which, based on the values from Table , directly follows from the fact that

\frac{μ w_{s} β_{b} {\tilde{C}}_{eq, 0} / κ_{v}}{normalΛ} \approx 5 .

The above gives a physical argument for using a larger bed load bottom slope parameter Λ than suggested by literature (Baar et al, ), when a total load formula is used. It then also represents the suspended load bed slope effect when this is not explicitly taken into account.…”

Section: Resultssupporting

confidence: 56%

Sensitivity of Tidal Bar Wavelength to Channel Width

2019

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Tidal bars are repetitive estuarine bedforms with heights of several meters and wavelengths in the order 1–15 km. Understanding their formation and sensitivity to changes in channel characteristics is important as they hamper marine traffic and play a crucial role in the local ecosystem. Recent observations suggest that the local width of the channel is dominant in determining the tidal bar wavelength. However, theoretical studies could not reproduce the sensitivity of the tidal bar wavelength to channel width. This discrepancy between theory and observations suggests that a mechanism is missing. In this study, one of the theoretical models is extended and results in tidal bar wavelengths, lateral mode numbers, and growth rates that agree fairly well with those of natural tidal bars, including the wavelengths dependency on estuary width. An important extension of the model concerns the bed slope induced diffusive suspended load transport of sediments. With this, it is explained why previously, the modelled tidal bar wavelengths depend only weakly on estuary width and why in the extended model it does. This has, from a modelling point of view, general implications for morphological models using a total load sediment transport formulation with a so‐called bed slope parameter.

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\frac{μ w_{s} β_{b} {\tilde{C}}_{eq, 0} / κ_{v}}{normalΛ} \approx 5 .

Section: Resultssupporting

confidence: 56%

Sensitivity of Tidal Bar Wavelength to Channel Width

2019

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“…, ; Baar et al. , ). Pre‐wetted nutshell was added to the system during ebb with the river discharge.…”

Section: Methodsmentioning

confidence: 99%

“…For such long timescales, only numerical modelling studies are available, but these may suffer from weaknesses such as neglected processes, numerical effects, imperfect transport predictors and the need for calibration of physics‐based parameters (Baar et al. ). Additionally, these studies rarely include mud because this has only become possible very recently (Le Hir et al.…”

Section: Introductionmentioning

confidence: 99%

Effects of estuarine mudflat formation on tidal prism and large‐scale morphology in experiments

Braat

Leuven

Lokhorst

et al. 2018

Earth Surf Processes Landf

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Human interference in estuaries has led to increasing problems of mud, such as hyper‐turbidity with adverse ecological effects and siltation of navigation channels and harbours. To deal with this mud sustainably, it is important to understand its long‐term effects on the morphology and dynamics of estuaries. The aim of this study is to understand how mud affects the morphological evolution of estuaries. We focus on the effects of fluvial mud supply on the spatial distribution of mudflats and on how this influences estuary width, depth, surface area and dynamics over time. Three physical experiments with self‐forming channels and shoals were conducted in a new flume type suitable for tidal experiments: the Metronome. In two of the experiments, we added nutshell grains as mud simulant, which is transported in suspension. Time‐lapse images of every tidal cycle and digital elevation models for every 500 cycles were analysed for the three experiments. Mud settles in distinct locations, forming mudflats on bars and sides of the estuary, where the bed elevation is higher. Two important effects of mud were observed: the first is the slight cohesiveness of mud that causes stability on bars limiting vertical erosion, although the bank erosion rate by migrating channels is unaffected. Secondly, mud fills inactive areas and deposits at higher elevations up to the high‐water level and therefore decreases the tidal prism. These combined effects cause a decrease in dynamics in the estuary and lead to near‐equilibrium planforms that are smaller in volume and especially narrower upstream, with increased bar heights and no channel deepening. This trend is in contrast to channel deepening in rivers by muddier floodplain formation. These results imply large consequences for long‐term morphodynamics in estuaries that become muddier due to management practices, which deteriorate ecological quality of intertidal habitats but may create potential area for marshes. © 2018 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.

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“…Physical scale experiments and numerical models complement observations in natural systems because they can provide higher temporal resolution, enabling detailed observation of the morphodynamic evolution of bars. In this study we use physical experiments, because the produced channel and bar patterns in numerical models (e.g., Braat et al, ; van der Wegen & Roelvink, ) depend on calibration parameters such as the transverse bed slope effect that strongly affect channel‐shoal interaction and bar dynamics (Baar et al, ; Schuurman et al, ).…”

Section: Introductionmentioning

confidence: 99%

Growing Forced Bars Determine Nonideal Estuary Planform

et al. 2018

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The planform of estuaries is often described with an ideal shape, which exponentially converges in landward direction. We show how growing topographically forced nonmigratory (i.e., anchored) bars determine the large‐scale estuary planform, which explains the deviations observed in the planform of natural estuaries filled with bars compared to the ideal planform. Experiments were conducted in a 20‐m long, 3‐m‐wide tilting flume, the Metronome. From a narrow, converging channel a self‐formed estuary developed characterized by multiple channels, braided bars, a meandering ebb channel, and an ebb delta. Bars hardly migrated due to the alternating current, but the bar width increased with increasing estuary width. At locations where the estuary width was narrow, major channel confluences were present, while the zones between the confluences were characterized by a higher braiding index, periodically migrating channels, and a relatively large estuary width. At the seaward boundary, confluences were forced in place by the presence of the ebb tidal delta. Between confluences, bars were topographically forced to be nonmigratory. Diversion of flow around forced midchannel bars caused bank erosion. This resulted in a planform shape with a quasiperiodic widening and narrowing at the scale of forced bars. Observations in natural systems show that major confluence locations can also be caused by inherited geology and human engineering, but otherwise the estuary outline is similarly affected by tidal bars. These observations provide a framework for understanding the evolution of tidal bar patterns and the planform shape of the estuary, which has wide implications for navigation, dredging, and ecology.

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Sediment Transport of Fine Sand to Fine Gravel on Transverse Bed Slopes in Rotating Annular Flume Experiments

Cited by 62 publications

References 48 publications

Sensitivity of Tidal Bar Wavelength to Channel Width

Sensitivity of Tidal Bar Wavelength to Channel Width

Effects of estuarine mudflat formation on tidal prism and large‐scale morphology in experiments

Growing Forced Bars Determine Nonideal Estuary Planform

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