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Journal ArticleDOI

Morphological evolution and dynamics of a large, sand braid-bar, Jamuna River, Bangladesh

01 Jun 2000-Sedimentology (Wiley-Blackwell)-Vol. 47, Iss: 3, pp 533-555
TL;DR: The initiation and evolution of a kilometre-scale, sand braid-bar was monitored during a 28-month survey period from 1993 to 1996 in one of the world's largest braided rivers, the Jamuna River, Bangladesh as mentioned in this paper.
Abstract: The initiation and evolution of a kilometre-scale, sand braid-bar was monitored during a 28-month survey period from 1993 to 1996 in one of the world's largest braided rivers, the Jamuna River, Bangladesh. Repeated bathymetric surveys through two monsoon flood seasons, combined with bar-top surveys during exposure of the bar at low flow, provide the most detailed chronology of braid-bar growth yet compiled for a large sand-bed river. During rising and peak flow of the 1994 monsoon flood, a 1.5-km-long, 0.5-km-wide, 12-m-high, symmetrical mid-channel bar was deposited in the centre of a major channel downstream of a zone of flow convergence and significant bank erosion. Initial deposition and growth of the bar core were probably caused by amalgamation of dunes that are present in the Jamuna channels at all flow stages. Bar-top aggradation continued through downstream migration of an `accretionary dune front', a 3-m-high, angle-of-repose slipface that was composed of amalgamated, 0.5- to 1-m-high dunes. At waning and low flow, the mid-channel bar widened by up to 1 km through the lateral accretion of dunes onto the margins of the initial bar core. A low-velocity zone in the sheltered wake region of the bar-tail led to the accumulation of substantial volumes of silts and clays. During the rising and peak flows of the next monsoon flood, the mid-channel bar extended its bar-tail by up to 1.5 km, as one of the anabranches became dominant, and flow was deflected across the bar-tail. Accretion at the bar-tail generated a lobate, transverse bar-front with a 10-m-high, angle-of-repose avalanche face. Emergence of several smaller bars along this depositional front produced an overall reach morphology that more closely resembled an alternate bar rather than several mid-channel bars. The conversion of a mid-channel bar to an alternate bar is contrary to many previous descriptions of the braiding process.
Citations
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Journal ArticleDOI
TL;DR: In this article, the authors summarized the principal features of mean and turbulent flow over alluvial sand dunes and highlighted some possible focus areas for future research: (1) the influence of dune leeside angle upon flow processes in the dune wake and downstream flow field, (2) three-dimensionality in dune shape upon the generation of turbulence and distribution of bed shear stress, (3) flow field modification resulting from bed form superimposition and amalgamation, (4) the scale and topology of dunes-related turbulence and its interactions
Abstract: [1] Dunes are present in nearly all fluvial channels and are vital in predicting flow resistance, sediment transport, and deposition within many rivers. Progress in understanding the fluid dynamics associated with alluvial dunes has been significant in the last 15 years and has witnessed huge advances in field, laboratory, and numerical investigations. Progress has been made in detailing the principal features of mean and turbulent flow over asymmetric dunes that possess flow separation in their leesides and how these forms affect both downstream boundary layer structure and stress partitioning over the dune. Additionally, the links between sediment transport over dunes and instantaneous coherent flow structures are being increasingly understood, with the feedback of dune three-dimensionality upon flow and sediment dynamics over these bed forms beginning to be recognized as vital. Such research now provides an outstanding background for beginning to address areas of greater complexity that will enable a fuller understanding of these important natural features. This review paper summarizes the principal features of mean and turbulent flow over alluvial sand dunes. Five areas are then highlighted and discussed as a possible focus for future research: (1) the influence of dune leeside angle upon flow processes in the dune wake and downstream flow field, (2) the influence of three-dimensionality in dune shape upon the generation of turbulence and distribution of bed shear stress, (3) flow field modification resulting from bed form superimposition and amalgamation, (4) the scale and topology of dune-related turbulence and its interactions with sediment transport and the flow surface, and (5) the influence of suspended sediment on the dune flow field and dune morphology.

414 citations


Cites background from "Morphological evolution and dynamic..."

  • ...…such as Bangladesh, where riverbank erosion, often driven by within-channel aggradation that is linked to the growth of dunes and larger bar forms [Ashworth et al., 2000; Best et al., 2005], can lead to very significant population displacement and loss of infrastructure and agricultural land…...

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Journal Article
TL;DR: In this paper, the authors summarized the principal features of mean and turbulent flow over alluvial sand dunes and highlighted some possible focus areas for future research: (1) the influence of dune leeside angle upon flow processes in the dune wake and downstream flow field, (2) three-dimensionality in dune shape upon the generation of turbulence and distribution of bed shear stress, (3) flow field modification resulting from bed form superimposition and amalgamation, (4) the scale and topology of Dune-related turbulence and its interactions
Abstract: [1] Dunes are present in nearly all fluvial channels and are vital in predicting flow resistance, sediment transport, and deposition within many rivers. Progress in understanding the fluid dynamics associated with alluvial dunes has been significant in the last 15 years and has witnessed huge advances in field, laboratory, and numerical investigations. Progress has been made in detailing the principal features of mean and turbulent flow over asymmetric dunes that possess flow separation in their leesides and how these forms affect both downstream boundary layer structure and stress partitioning over the dune. Additionally, the links between sediment transport over dunes and instantaneous coherent flow structures are being increasingly understood, with the feedback of dune three-dimensionality upon flow and sediment dynamics over these bed forms beginning to be recognized as vital. Such research now provides an outstanding background for beginning to address areas of greater complexity that will enable a fuller understanding of these important natural features. This review paper summarizes the principal features of mean and turbulent flow over alluvial sand dunes. Five areas are then highlighted and discussed as a possible focus for future research: (1) the influence of dune leeside angle upon flow processes in the dune wake and downstream flow field, (2) the influence of three-dimensionality in dune shape upon the generation of turbulence and distribution of bed shear stress, (3) flow field modification resulting from bed form superimposition and amalgamation, (4) the scale and topology of dune-related turbulence and its interactions with sediment transport and the flow surface, and (5) the influence of suspended sediment on the dune flow field and dune morphology.

402 citations

Journal ArticleDOI
Abstract: This review and commentary sets out the need for authoritative and concise information on the expected error distributions and magnitudes in observational data We discuss the necessary components of a benchmark of dominant data uncertainties and the recent developments in hydrology which increase the need for such guidance We initiate the creation of a catalogue of accessible information on characteristics of data uncertainty for the key hydrological variables of rainfall, river discharge and water quality (suspended solids, phosphorus and nitrogen) This includes demonstration of how uncertainties can be quantified, summarizing current knowledge and the standard quantitative results available In particular, synthesis of results from multiple studies allows conclusions to be drawn on factors which control the magnitude of data uncertainty and hence improves provision of prior guidance on those uncertainties Rainfall uncertainties were found to be driven by spatial scale, whereas river discharge uncertainty was dominated by flow condition and gauging method Water quality variables presented a more complex picture with many component errors For all variables, it was easy to find examples where relative error magnitudes exceeded 40% We consider how data uncertainties impact on the interpretation of catchment dynamics, model regionalization and model evaluation In closing the review, we make recommendations for future research priorities in quantifying data uncertainty and highlight the need for an improved ‘culture of engagement’ with observational uncertainties Copyright © 2012 John Wiley & Sons, Ltd

315 citations

Journal ArticleDOI
TL;DR: In this article, a comprehensive review of 144 Cambrian to Devonian alluvial successions documented in published literature was combined with original field data from 34 alluvian successions across Europe and North America.

270 citations

Book
18 Apr 2022
TL;DR: Goodbred et al. as discussed by the authors studied the Ganges-brahmaputra river sediment in the Indian Ocean and found evidence for highstand dispersal to flod-plain, shelf and deepsea depocenters.
Abstract: . Gilbert, G.K. (1885) The topographic features of lake shores. US Geol. Surv., 5th Ann. Rept, 69–123. Gilbert, G.K. (1890) Lake Bonneville. US Geol. Surv. Monogr. 1. Goodbred, S.L., Jr and Kuehl, S.A. (1998) Floodplain processes in the Bengal Basin and the storage of Ganges-Brahmaputra river sediment: an accretion study using Cs and Pb geochronology. Sediment. Geol., 121, 239–258. Goodbred, S.L., Jr and Kuehl, S.A. (1999) Holocene and modern sediment budgets for the Ganges-Brahmaputra River system: evidence for highstand dispersal to fl ood-plain, shelf, and deepsea depocenters. Geology, 27, 559–562. Goodbred, S.L., Jr and Kuehl, S.A. (2000a) The signifi cance of large sediment supply, active tectonism, and eustasy on margin sequence development: Late Quaternary stratigraphy and evolution of the Ganges-Brahmaputra delta. Sediment. Geol., 133, 227–248. Goodbred, S.L., Jr and Kuehl, S.A. (2000b) Enormous GangesBrahmaputra sediment discharge during the strengthened early Holocene monsoon. Geology, 28, 1083–1086. Gould, H.R. (1970) The Mississippi delta complex. In: Deltaic Sedimentation: Modern and Ancient (J.P. Morgan, Ed.). SEPM Spec. Publ. no. 15, pp. 3–30. Harris, P.T., Baker, E.K., Cole, A.R. and Short, S.A. (1993) A preliminary study of sedimentation in the tidally dominated Fly River Delta, Gulf of Papua. Cont. Shelf Res., 13, 441– 472. Harris, P.T., Pattiaratchi, C.B., Keene, J.B., Dalrymple, R.W., Gardner, J.V., Baker, E.K., Cole, A.R., Mitchell, D., Gibbs, P. and Schroeder, W.W. (1996) Late Quaternary deltaic and carbonate sedimentation in the Gulf of Papua foreland basin: response to sea-level change. J. Sediment. Res., 66, 801–819. Harris, P.T., Heap, A.D., Bryce, S.M., Porter-Smith, R., Ryan, D.A. and Heggie, D.T. (2003) Classifi cation of Australian clastic coastal depositional environments based upon a quantitative analysis of wave, tidal, and river power. J. Sediment. Res., 72, 858–870. Haruyama, S. and Phai, V.V. (2002) Coastal change in the Southern Song Hong Delta. J. Geogr., 111, 124–132 (in Japanese with English abstract). Hayes, M.O. (1979) Barrier island morphology as a function of tidal and wave regime. In: Barrier Islands from the Gulf of St Lawrence to the Gulf of Mexico (S.P. Leatherman, Ed.). Academic Press, New York, pp. 1–27. Hori, K. and Saito, Y. (2003) Morphology and sediments of large river deltas, J. Geogr., 112, 337–359 (in Japanese with English abstract). Hori, K., Saito, Y., Zhao, Q., Cheng, C., Wang, P., Sato, Y. and Li, C. (2001a) Sedimentary facies and Holocene progradation rates of the Changjiang (Yangtze) delta, China. Geomorphology, 41, 233–248. Hori, K., Saito, Y., Zhao, Q., Cheng, C., Wang, P., Sato, Y. and Li, C. (2001b) Sedimentary facies of the tide-dominated paleoChangjiang (Yangtze) estuary during the last transgression. Mar. Geol., 177, 331–351. Hori, K., Saito, Y., Zhao, Q. and Wang, P. (2002) Architecture and evolution of the tide-dominated Changjiang (Yangtze) River delta, China. Sediment. Geol., 146, 249–264. Hori, K., Tanabe, S., Saito, Y., Haruyama, S., Nguyen, V. and Kitamura, A. (2004) Delta initiation and Holocene sea-level change: example from the Song Hong (Red River) delta, Vietnam. Sediment. Geol., 164, 237–249. Hovius, N. (1998) Controls on sediment supply by large rivers. In: Relative Role of Eustasy, Climate, and Tectonism in Continental Rocks (K.W. Shanley and P.J. McCabe, Eds.). SEPM Spec. Publ. no. 59, pp. 3–16.

260 citations


Cites background or methods from "Morphological evolution and dynamic..."

  • ...For example, changes in water surface elevation of up to 8 m are common in the Brahmaputra/Jamuna River of Bangladesh (Coleman, 1969; Bristow, 1987; Ashworth et al., 2000), and up to 12 m in the Amazon (Mertes et al., 1996; Archer, 2005)....

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  • ...Together with the survey data presented in Ashworth et al. (2000), this example of channel evolution near Bahadurabad illustrates that kilometre-scale bars may have a life-cycle of about 5 years (i.e. more than one fl ood season but then of limited duration)....

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  • ...Scours up to 40 m deep have been recognized from the Brahmaputra (Bristow, 1987, 1993; Best and Ashworth, 1997; Ashworth et al., 2000) and lower Amazon Rivers (Vital et al., 1998), and an extraordinary 80 m deep in the Yangtze (Saito et al., 2001) and 100 m deep in the middle Amazon (Sioli, 1984)....

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  • ...…of detailed ground penetrating radar (Figure 19.22) and trench/core logging tied into surveys over an evolving, newly formed mid-channel braid bar (Ashworth et al., 2000), document four principal depositional facies: (1) large bar-margin slipfaces, up to 8 m high, that are generated as steep…...

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  • ...Ashworth et al. (2000) tracked the development of a 1.5 km long, 0.5 km wide, 12 m high, symmetrical mid-channel bar over a 28- month period in a major anabranch of the Jamuna near Bahadurabad (Figures 19.1 and 19.15) and noted that the bar was probably initiated by the stalling and amalgamation of…...

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References
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OtherDOI
01 Jan 1957

1,595 citations


"Morphological evolution and dynamic..." refers background or result in this paper

  • ...…dune amalgamation and braid-bar initiation in sand-grade material has been invoked to explain the cause of gravel-bed mid-channel bar deposition, where a `chance stalling' of sediment caused by a local drop in ¯ow competence can provide the initial impetus for bar growth (Leopold & Wolman, 1957)....

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  • ...This pattern of bar growth is consistent with the classic description of braiding by Leopold & Wolman (1957), who observed that bar emergence is usually aided by anabranch incision after initial central bar deposition....

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  • ...The occurrence and morphology of mid-channel bars in the Jamuna is strongly stage dependent, although bars can also become emergent without a change in ¯ow stage or discharge because of anabranch incision (Leopold & Wolman, 1957; Ashmore, 1982)....

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Journal ArticleDOI
TL;DR: The Ganges and Brahmaputra rivers combined have formed one of the largest deltas in the world, comprising some 23,000 sq. miles as discussed by the authors, and the large discharge and heavy sediment load cause the rivers to be extremely unstable, and the channels are constantly migrating laterally.

1,030 citations


"Morphological evolution and dynamic..." refers background or methods in this paper

  • ...A range of micro- and mesoscale bedforms (terminology after Jackson, 1975) is present in the Jamuna, including ripples, dunes and upper-stage plane beds (Coleman, 1969; Klaassen et al., 1988; Bristow, 1993; Julien & Klaassen, 1995; Roden, 1998)....

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  • ...The Jamuna is the name given to the braided river downstream of the Old Brahmaputra distributary (see Fig....

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  • ...…of studies of modern rivers, such as the River Platte (Smith, 1971; Blodgett & Stanley, 1980; Crowley, 1983), South Saskatchewan (Cant & Walker, 1976; Cant, 1978; Cant & Walker, 1978), Calamus (Bridge et al., 1986, 1998; Bridge & Gabel, 1992) and Brahmaputra (Coleman, 1969; Bristow, 1987, 1993)....

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  • ...This paper will use the local river name, the Jamuna, but this is essentially synonymous with the Brahmaputra described in past work (e.g. Coleman, 1969; Bristow, 1987, 1999; Thorne et al., 1993)....

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  • ...Estimates of the total sediment load in the Jamuna range between 500 and 725 ´ 106 tons per year (Coleman, 1969; Thorne et al., 1993; Schumm & Winkley, 1994), the majority of which is transported as suspended load (Klaassen et al., 1988)....

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Journal ArticleDOI
TL;DR: A Symposium entitled "Classification of Large-Scale Flow-Transverse Bedforms" was convened at the 1987 Mid-Year Meeting of SEPM in Austin, Texas with the purpose of examining the problems involved in classifying large subaqueous flow-transverse bedforms developed in fluvial, intertidal, and marine environments, and recommending changes in nomenclature.
Abstract: A Symposium entitled "Classification of Large-Scale Flow-Transverse Bedforms" was convened at the 1987 Mid-Year Meeting of SEPM in Austin, Texas with the purpose of examining the problems involved in classifying large subaqueous flow-transverse bedforms developed in fluvial, intertidal, and marine environments, and recommending changes in nomenclature. The consensus of the participants is that despite the wide spectrum of morphologies of large-scale flow-transverse bedforms (excluding antidunes), they all occupy a similar position in the lower-flow-regime sequence between ripples and upper plane bed. The wide variety of forms is a reflection of secondary effects such as channelization, fluctuating water levels, and unsteady and reversing flows. The bedforms appear not to fall into size classes with naturally occurring boundaries but rather form a continuum with spacing from just under 1 m to over 1,000 m. The symposium panel proposes, therefore, that they should have only one name, DUNE. Dune is preferred as it has historical precedence over other terms in use, such as megaripple and sand wave. The term "dune" should be modified by primary descriptors of shape (i.e., 2-D or 3-D) and size based on spacing (small (0.6-5 m), medium (5-10 m), large (10-100 m) or very large (> 100 m) and the adjective subaqueous when it is important to distinguish them from eolian dunes. The panel recommends a morphologically based classification that is descriptive, with an underlying genetic rationale. Second order descriptors such a sediment size and bedform superposition may be used to describe more thoroughly the variety of subaqueous dunes in nature.

1,022 citations


"Morphological evolution and dynamic..." refers methods in this paper

  • ...The term dune is used here to encompass the bedforms previously described as megaripples in the Jamuna (e.g. Coleman, 1969; Klaassen et al., 1988), which are dynamically analogous to dunes and scale with ¯ow depth (Ashley, 1990)....

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Journal ArticleDOI
TL;DR: The South Saskatchewan River has a long term average discharge of 275 m3/sec, with flood peaks in the range of 1500 to 3800 m 3/sec as discussed by the authors, and the dominant channel bedforms are dunes, which deposit trough cross bedding.
Abstract: The South Saskatchewan River has a long term average discharge of 275 m3/sec, with flood peaks in the range of 1500 to 3800 m3/sec. South of Saskatoon, the four major types of geomorphological elements recognised are channels, slipface-bounded bars, sand flats and vegetated islands and floodplains. Major channels are 3-5 m deep, up to 200 m wide, and flow around sand flats which are 50-2000 m long, and around vegetated islands up to 1 km long. At areas of flow expansion, long straight-crested cross-channel bars form. During falling stage, a small part of the crest of the cross-channel bar may become emergent, and act as a nucleus for downstream and lateral growth of a new sand flat. The dominant channel bedforms are dunes, which deposit trough cross bedding. Cross-channel bars deposit large sets of planar tabular cross bedding. Sand flats that grow from a nucleus on a cross-channel bar are mostly composed of smaller planar tabular sets, with some parallel lamination, trough cross-bedding, and ripple cross-lamination. A typical facies sequence related to sand flat growth would consist of in-channel trough cross-bedding, overlain by a large (1-2 m) planar tabular set (cross-channel bar), overlain in turn by a complex association mostly of small planar tabular cross-beds, trough cross-beds and ripple cross-lamination. By contrast, a second stratigraphic sequence can be proposed, related only to channel aggradation. It would consist dominantly of trough cross-beds, decreasing in scale upward, and possible interrupted by isolated sets of planar tabular cross-bedding if a cross-channel bar formed, but failed to grow into a sand flat. During final filling of the channel, ripple cross-lamination and thin clay layers may be deposited. In the S. Saskatchewan, these sequences are a minimum of 5 m thick, and are overlain by 0.5-1 m of silty and muddy vertical accretion deposits.

535 citations

Journal ArticleDOI
TL;DR: In this article, a detailed field and laboratory studies of the geometry, flow and sedimentary processes in braided rivers of simple geometry, in single river bends, in channel confluences, and using some theoretical reasoning, it has been possible to construct fully 3D qualitative and quantitative models of braided river deposits.
Abstract: Abstract Models of braided-river deposition must be detailed, fully 3D, and preferably quantitative to be of use in understanding and predicting the nature of ancient deposits. In order to construct and validate adequate predictive models it is necessary to have information on: (1) variation and interaction of channel geometry, water flow and sediment transport in time and space in modern channel belts, as these control erosion and deposition, the formation and migration of channels and bars, and channel abandonment and filling; (2) 3D variation of bed geometry, texture, sedimentary structures and paleocurrents throughout modern channel-belt deposits, including the age and spatial arrangement of preserved parts of bars and channel fills; (3) long-term (more than hundreds of years) trends in channel and floodplain geometry, flow and sedimentary processes in order to understand channel-belt movements such as avulsions, and the spatial arrangement of channel-belt deposits relative to overbank deposits. Such information is rare because: (1) it is difficult to study modern braided-river geometry, flow and sedimentary processes throughout a range of the all-important high discharges; (2) detailed reconstructions of braided channel and bar geometry and movement are only available for the past half-century and cannot readily be linked to causative mechanisms; (3) 3D documentation of modern deposits below the water table (especially large scale features like lateral-accretion bedding) requires extensive coring and dating of the deposits, and geophysical profiling. As a result of this lack of information, and because of the quality of analysis and presentation of the information available, existing braided-river facies models are virtually useless as interpretive and predictive tools. The nature of the information available is critically reviewed. Using information from recent detailed field and laboratory studies of the geometry, flow and sedimentary processes in braided rivers of simple geometry, in single river bends, in channel confluences, and using some theoretical reasoning, it has been possible to construct fully 3D qualitative and quantitative models of braided river deposits. These models can be used to provide sophisticated quantitative interpretations of palaeochannel geometry, hydraulics and migration, as illustrated by comparison with some particularly well described examples of ancient braided river deposits.

445 citations


"Morphological evolution and dynamic..." refers background in this paper

  • ...…Church & Jones, 1982) that are Ó 2000 International Association of Sedimentologists 533 strongly stage dependent (Rust, 1978; Mosley, 1982) and, through a combination of lateral, upstream and downstream accretion, produce a heterogeneous and complex alluvial architecture (Bridge, 1985, 1993b)....

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  • ...…trough cross-strati®cation in view of the ubiquitous presence of curvedcrested dunes', although he also suggests that the initial core of a braid-bar is associated with deposition as a `unit bar' that, in turn, is related to a double row of alternate bars (see Bridge, 1993a, his ®g. 1, p. 16)....

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  • ...One of the major constraints in producing realistic facies models for braided alluvium is the paucity of primary data from modern rivers, such that existing ®eld, theoretical and experimental facies models are `virtually useless as interpretative and predictive tools' (Bridge, 1993a)....

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  • ...Braided rivers are characterized by relatively high stream power, rapid rates of erosion and depos- ition and frequent channel and braid belt avulsion (Bridge, 1993a; Ferguson, 1993)....

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  • ...5a and b), there is no evidence to suggest that the Jamuna braid-bar grew from back-to-back double-row alternate bars (e.g. Bridge, 1993a, his ®g. 1c, p. 16; Ferguson, 1993, his Fig....

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