Study on Hydraulic Resistance and Bed-Load Transport Rate in Alluvial Streams

Ashida, Kiwamu; Michiue, Masanori

doi:10.2208/jscej1969.1972.206_59

Cited by 307 publications

(261 citation statements)

References 7 publications

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“…The final parameter that appears in (2.23) is the critical Shields parameter θ b cr,n for each grain size class n. For this, we adopt the formulation of Ashida & Michiue (1972), which accounts for the hiding of small grains between the large grains.…”

Section: Bed Load Transportmentioning

confidence: 99%

Formation of rhythmic sorted bed forms on the continental shelf: an idealised model

2011

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An idealised model is presented to study the formation of sorted bed forms generated by a wind-driven along-shore current. The study employs a linear stability analysis to describe the time development of perturbations of both bottom composition and bed elevation, superimposed on a flat bed composed of a sediment mixture homogeneously distributed in space. The model considers both bed and suspended loads and takes into account the averaged influence of waves on the flow field and the transport of sediment. The results show that the positive coupling between waves, along-shore current and the erodible heterogeneous bed leads to the amplification of two modes, which exhibit distinct characteristics. A first mode is found to be dominant when moderate hydrodynamic conditions are considered and is primarily amplified by the convergence of sediment transport induced by the changes in the bed elevation. This mode has wavelengths of the order of hundred metres and has coarse (fine) sediments in its troughs (crests). By increasing the height of the waves and/or the strength of the steady current, the second mode can become dominant. This mode is characterised by shorter wavelengths and results from the interaction between the convergence of sediment transport related to changes in the bottom composition and that induced by perturbations of the bed elevation. These bed features can have an up-current or a down-current shift between the centre of the coarse-grained bands and the trough of the bottom wave. Typical growth times of the amplified features are of the order of hundreds of days and the migration rates, in the direction of the along-shore current, range between 0.1 and 10 m per day. A qualitative comparison of the model results with field observations indicates that the generation of two distinct modes provides a possible explanation for the broad range of characteristics of the natural bed features.

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Section: Bed Load Transportmentioning

confidence: 99%

Formation of rhythmic sorted bed forms on the continental shelf: an idealised model

2011

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“…The latter effect has been known as ''hiding'' since the time of Einstein (1950). Since the groundbreaking work of Egiazaroff (1965) and Ashida and Michiue (1972), it has been established that these two effects nearly cancel each other out [e.g., Wiberg and Smith (1987)] but nevertheless leave the finer grains exposed at the surface somewhat more mobile than neighboring coarser grains [e.g., Parker (1990)]. The residual difference in mobility tends to be small and, in particular, less than might be expected based on the scalings according to which particle weight increases with the cube of grain size whereas drag increases only with the square.…”

Section: Standard Model For Mobility Variation In Mixturementioning

confidence: 99%

“…The friction angle extracted from an extrapolation of mobile-bed conditions to the threshold of motion can be expected to be somewhat smaller than the static value [e.g., Ashida and Michiue (1972)]. With this in mind, a value of g of 0.5, corresponding to a friction angle of 26.6Њ, is employed here.…”

mentioning

confidence: 99%

The Curious Case of Mobility Reversal in Sediment Mixtures

Solari

Parker

2000

J. Hydraul. Eng.

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ABSTRACT:It is common for aggrading deposits of sediment mixtures to show a pattern of downstream fining, whereby characteristic grain size becomes finer in the streamwise direction. Although various factors may contribute to this phenomenon, it can often be explained largely or solely in terms of the variation of grain mobility with grain size in sediment mixtures. That is, finer grains exposed on the surface are typically somewhat more mobile than their coarser neighbors, resulting in preferential transport of finer grains. Experiments reported here, document a reversal in this familiar pattern at slopes in excess of 0.02-0.03. At these higher slopes aggrading and prograding deposits are observed to show downstream coarsening in geometric mean size, indicating a mobility reversal associated with preferential transport of the coarser grains. This rather curious behavior is explored herein.

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“…Indeed, in this type of model, the transit is a mixture of approximately 30% of material coming from the active layer (in our case the substratum) and 70% coming from the upstream i.e. the bed-load (Egiazaroff [15]; Ashida and Michiue [16]). The difference may result either from errors in the geochemical analyses and in transport capacity calculation within the hydraulic model.…”

Section: Application To the Loire Rivermentioning

confidence: 99%

Novel combined approach for bedrock incision analysis: geochemistry and hydraulic modelling. Loire River Application (France)

Tombozafy¹,

Mimoun²,

Batton‐Hubert³

et al. 2008

WIT Transactions on the Built Environment

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The goal is to accurately forecast or understand erosion and deposition in bedrock river channels. The Loire River (France) was chosen as a case study. Like most European major rivers, the Loire presents an accelerated incision (2.5m during the last 150 years). Current models are limited because they can only accurately simulate aggradation and degradation on alluvial river containing non-cohesive and cohesive sediments. In our case, these models are not efficient along the whole length of this river. This is because of the outcropping of bedrock. This obstacle led us to establish a new manner to characterize bedrock incision not only by particle impacts but also considering stream flow intensity. To complete this work, we use the geochemical signature of transported materials to quantify the amount of substratum eroded between two sampled areas. This allows us to validate the results of the hydraulic model.

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Study on Hydraulic Resistance and Bed-Load Transport Rate in Alluvial Streams

Cited by 307 publications

References 7 publications

Formation of rhythmic sorted bed forms on the continental shelf: an idealised model

Formation of rhythmic sorted bed forms on the continental shelf: an idealised model

The Curious Case of Mobility Reversal in Sediment Mixtures

Novel combined approach for bedrock incision analysis: geochemistry and hydraulic modelling. Loire River Application (France)

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