Sediment heterogeneity and mobility in the morphodynamic modelling of gravel-bed braided rivers

Singh, Udita; Crosato, Alessandra; Giri, Sanjay; Hicks, Murray

doi:10.1016/j.advwatres.2017.02.005

Cited by 55 publications

(35 citation statements)

References 78 publications

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“…Sediment mobility, represented by the Shields number, is crucial for bar morphodynamics, and it depends on particle size and grain size distribution (GSD) of the mixture forming the river bed. Analytical studies (e.g., Lanzoni & Tubino, ), field and laboratory observations (e.g., Lanzoni, ; Lisle et al, ; Lisle & Madej, ; Powell, ), and numerical simulations (e.g., Hoey & Ferguson, ; Juez et al, ; Mosselman et al, ; Mosselman, ; Nelson et al, , ; Tritthart, Liedermann, et al ; Tritthart, Schober, & Habersack ; Qian et al, ; Siviglia & Crosato, , ; Wu, ) have shown that bars are affected by both size and heterogeneity of bed sediment. Lanzoni and Tubino () and Takebayashi and Egashira () state that sediment heterogeneity leads to the diminishing of free migrating bar amplitude and wavelength.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study of Alternate Bars in Alluvial Channels With Nonuniform Sediment

Cordier

Tassi

Claude³

et al. 2019

Water Resources Research

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Rivers typically present heterogeneous bed material, but the effects of sediment nonuniformity on river bar characteristics are still unclear. This work investigates the impact of sediment size heterogeneity on alternate bars with a morphodynamic numerical model. The model is first used to reproduce a laboratory experiment showing alternate bar formation with nonuniform bed material. Subsequently, the influence of sediment size heterogeneity on alternate bars is investigated distinguishing hybrid from free bars, definition based on the presence/absence of morphodynamic forcing, considering the results of nine scenarios. In four of them, a transverse obstacle is used to generate forcing. The computations are carried out with the Telemac‐Mascaret system solving the two‐dimensional shallow‐water equations with a finite element approach, accounting for horizontal and vertical sediment sorting processes. The results show that sediment heterogeneity affects free migrating and hybrid bars in a different way. The difference lies in the presence/absence of a migration front, so that distinct relations between bed topography, bed shear stress, and sediment sorting are obtained. Sediment sorting and associated planform redistribution of bed roughness only slightly modify free migrating bar morphodynamics, whereas hybrid bars are greatly impacted, with decreased amplitude and increased wavelength. Increased sediment size heterogeneity increases the degree of sediment sorting, while the sorting pattern remains the same for both free and hybrid bars. Moreover, it produces averagely higher, longer, and faster free bars, while in the case of hybrid bars their wavelength is increased but no general trend can be determined for their amplitude.

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Section: Introductionmentioning

confidence: 99%

Numerical Study of Alternate Bars in Alluvial Channels With Nonuniform Sediment

Cordier

Tassi

Claude³

et al. 2019

Water Resources Research

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“…The patterns of channels, bars, and braiding properties are highly sensitive to the bed slope parameterization, and particularly transverse slope affects the sediment transport in longterm simulations (Schuurman et al, 2013;Kasvi et al, 2014;Singh et al, 2017). Also, during these rather short-term flood event simulations at gravel bed Rambla de la Viuda, the ef-fects of the increasing transverse slope on channel evolution were evident, and the simulation results resembled the observed topographies more.…”

Section: Uncertainties Related To the Simulationsmentioning

confidence: 49%

“…Wang et al, 2013) from the surface layers, instead of lowerresolution site sampling such as the Wolman method. Earlier studies have stated that a calculation of the bedload transport rate of mixtures should be based on the availability of each size range in the surface layer (Parker, 1990), and that during the calibration of the Delft3D model uniform sediment cannot be an acceptable assumption to study the longterm response of natural gravel bed braided rivers (Singh et al, 2017). The best simulation results of Rambla de la Viuda were indeed gained when spatially varying upper surface layer sediment sizes were applied.…”

Section: Uncertainties Related To the Simulationsmentioning

confidence: 66%

“…These equations include MPM (1948) and Bagnold (1960) equations, which have been applied in ephemeral channels. In addition, Singh et al (2017) state that during variable discharge conditions, the MPM formula cannot produce the braided river pattern because MPM is not suitable if the value of the Shields parameter falls outside its applicability range. These above-mentioned facts could explain why the MPM equation did not move particles during the lower discharges and during the receding phase of the hydrographs of Rambla de la Viuda, where flow is temporally highly variable.…”

Section: Uncertainties Related To the Simulationsmentioning

confidence: 99%

“…In addition, the EH is a total load equation (Engelund and Hansen, 1967), whereas, for example, the MPM equation calculates bedload. There are no universal sediment transport formulas that can cover all coarse sediment transport conditions from low discharges to peak discharges (Li et al, 2016;Singh et al, 2017). The grain sizes, which had been moved by the 2013 discharge events, were on the upper limit of the available sediment transport equations.…”

Section: Uncertainties Related To the Simulationsmentioning

confidence: 99%

See 2 more Smart Citations

Topographical change caused by moderate and small floods in a gravel bed ephemeral river – a depth-averaged morphodynamic simulation approach

et al. 2018

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Abstract. In ephemeral rivers, channel morphology represents a snapshot at the end of a succession of geomorphic changes caused by floods. In most cases, the channel shape and bedform migration during different phases of a flood hydrograph cannot be identified from field evidence. This paper analyses the timing of riverbed erosion and deposition of a gravel bed ephemeral river channel (Rambla de la Viuda, Spain) during consecutive and moderate-(March 2013) and low-magnitude (May 2013) discharge events, by applying a morphodynamic model (Delft3D) calibrated with pre-and post-event surveys by RTK-GPS points and mobile laser scanning. The study reach is mainly depositional and all bedload sediment supplied from adjacent upstream areas is trapped in the study segment forming gravel lobes. Therefore, estimates of total bedload sediment mass balance can be obtained from pre-and post-field survey for each flood event. The spatially varying grain size data and transport equations were the most important factors for model calibration, in addition to flow discharge. The channel acted as a braided channel during the lower flows of the two discharge events, but when bars were submerged in the high discharges of May 2013, the high fluid forces followed a meandering river planform. The model results showed that erosion and deposition were in total greater during the long-lasting receding phase than during the rising phase of the flood hydrographs. In the case of the moderate-magnitude discharge event, deposition and erosion peaks were predicted to occur at the beginning of the hydrograph, whereas deposition dominated throughout the event. Conversely, the low-magnitude discharge event only experienced the peak of channel changes after the discharge peak. Thus, both type of discharge events highlight the importance of receding phase for this type of gravel bed ephemeral river channel.

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Rivers in the Landscape

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Sediment heterogeneity and mobility in the morphodynamic modelling of gravel-bed braided rivers

Cited by 55 publications

References 78 publications

Numerical Study of Alternate Bars in Alluvial Channels With Nonuniform Sediment

Numerical Study of Alternate Bars in Alluvial Channels With Nonuniform Sediment

Topographical change caused by moderate and small floods in a gravel bed ephemeral river – a depth-averaged morphodynamic simulation approach

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