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Braid bar

About: Braid bar is a research topic. Over the lifetime, 44 publications have been published within this topic receiving 3964 citations.

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Journal ArticleDOI
TL;DR: In this article, a Froude-scaled physical model of a proximal gravel-bed braided river was used to connect the river morphological characteristics, and sedimentary processes and forms, to deposit geometry.
Abstract: A Froude-scaled physical model of a proximal gravel-bed braided river was used to connect the river morphological characteristics, and sedimentary processes and forms, to deposit geometry. High resolution continuous three-dimensional topographic data was acquired from sequential photogrammetric digital elevation models paired with grain-size surface maps derived from image analysis of textural properties of the surface. From these data the full three-dimensional development of the braided river deposit and grain-size sorting patterns was compiled over an experimental time period of 40 hours during which the model river reworked a large portion of the braided channel. The minimum surface of the deposit is developed progressively over time by erosion, migration and avulsion of channels, and by local scour at channel confluences. The maximum surface of the deposit is formed by amalgamation of braid bar surfaces and has less overall relief than the minimum surface. Confluence scour constitutes about 5% of the area of the minimum surface. Migration of individual confluences is limited to distances of the order of the width and length of the confluence so that confluences do not form laterally extensive deposits and basal surfaces. Maximum and minimum surfaces have very similar grain-size distributions, and there is no extensive basal coarse layer. Deposit maximum thickness is strongly associated with large channel confluences which occur as deeper areas along the main channel belt and make up a large proportion of the thickest portions of the deposit. This article is protected by copyright. All rights reserved.

25 citations

Journal Article
TL;DR: In this paper, an attempt has been made to identify recurring floods in the alluvial rivers based on architectural element analysis of Sandbar-Levee deposits, where the point bar deposits characterized by low-Angled lateral accretion(LA) elements exhibit some Channel-Ward steeply dipping (18-20°)discordant surfaces These high-Angeled surfaces are erosional and show change of facies across them.
Abstract: Based on architectural element analysis of Sandbar-Levee deposits an attempt has been made to identify recurring floods in the alluvial rivers Point bar deposits characterized by Low-Angled lateral accretion( LA) elements exhibit some Channel-Ward steeply dipping (18-20°)discordant surfaces These High-Angled surfaces are erosional and show change of facies across them Such discordant planes present within the point bar deposits most probably indicate phases of exceptional floods, when the bar was mostly eroded and remodelled under High-Energy conditions Similarly, in the braid bar deposits superimposed Bar-Building events separated either by mud drapes or marked erosional contacts are restimony to High-Energy floods At flood times, a new bar may form and can migrate over Pre-Existing sand bar, forming huge sandflat Alternatively, a new channel may develop cutting across the existing bar complex producing a channel bar having a different orientation Multi-Stoned levee deposits developed at the bank of the channels, and characterized by decimeter to meter scale Fining-Up sequences, are the best indicators of exceptionally large floods overtopping the channels The flood events are commonly separated by erosional contacts and mottled horizons containing organic matter, root burrows and Faecal-Pellet filled earthworm burrow network

19 citations

Journal ArticleDOI
TL;DR: In this article, a physically-based morphodynamic model was applied to simulate the evolution and alluvial architecture of large river junctions, where boundary conditions within the model were defined to approximate the junction of the Ganges and Jamuna rivers, with the model output being supplemented by geophysical datasets collected at this junction.
Abstract: Channel confluences are key nodes within large river networks, and yet surprisingly little is known about their spatial and temporal evolution. Moreover, because confluences are associated with vertical scour that typically extends to several times the mean channel depth, the deposits associated with such scours should have a high preservation potential within the rock record. Paradoxically, such scours are rarely observed, and their preservation and sedimentological interpretation are poorly understood. The present study details results from a physically-based morphodynamic model that is applied to simulate the evolution and alluvial architecture of large river junctions. Boundary conditions within the model were defined to approximate the junction of the Ganges and Jamuna rivers, Bangladesh, with the model output being supplemented by geophysical datasets collected at this junction. The numerical simulations reveal several distinct styles of sedimentary fill that are related to the morphodynamic behaviour of bars, confluence scour downstream of braid bars, bend scour and major junction scour. Comparison with existing, largely qualitative, conceptual models reveals that none of these can be applied simply, although elements of each are evident in the deposits generated by the numerical simulation and observed in the geophysical data. The characteristics of the simulated scour deposits are found to vary according to the degree of reworking caused by channel migration, a factor not considered adequately in current conceptual models of confluence sedimentology. The alluvial architecture of major junction scours is thus characterised by the prevalence of erosion surfaces in conjunction with the thickest depositional sets. Confluence scour downstream of braid bar and bend scour sites may preserve some large individual sets, but these locations are typically characterised by lower average set thickness compared to major junction scour and by a lack of large-scale erosional surfaces. Areas of deposition not related to any of the specific scour types highlighted above record the thinnest depositional sets. This variety in the alluvial architecture of scours may go some way towards explaining the paradox of ancient junction scours, that while abundant large scours are likely in the rock record, they have been reported rarely. The present results outline the likely range of confluence sedimentology and will serve as a new tool for recognizing and interpreting these deposits in the ancient fluvial record.

17 citations

Journal ArticleDOI
TL;DR: In this article, a ground-penetrating radar (GPR) survey of gravelly braid bars in the Abe River, central Japan, was conducted to clarify the three-dimensional (3D) variations in their depositional facies under various geomorphologic conditions.

14 citations

Journal ArticleDOI
TL;DR: In this article, a plot of stratification ratio versus bed relief index indicates a predominance of transverse bars over longitudinal bars for the Trujillo Sandstone, which indicates deposition in the distal portions of a braided stream system.
Abstract: Exposed within the Upper Triassic Trujillo Sandstone of the Texas Panhandle are excellent examples of transverse braid bar deposits. The bars are 0.3-1.0 m high with a distance of 5-10 m between bar crests. They are composed of fine- to medium-grained sand with planar cross stratification overlain by a thin layer of small-scale trough cross stratification or linguoid ripples. A plot of stratification ratio versus bed relief index indicates a predominance of transverse bars over longitudinal bars for the Trujillo Sandstone. This indicates deposition in the distal portions of a braided stream system.

7 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20212
20202
20192
20184
20171
20151