Secondary Currents around Braid Bar in Brahmaputra River, Bangladesh

Richardson, William R.; Thorne, Colin R.

doi:10.1061/(asce)0733-9429(1998)124:3(325)

Cited by 65 publications

(40 citation statements)

References 15 publications

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“…In the case of the Calamus River, data collection was facilitated by the operation of measuring equipment from bridges built across the channel (Bridge & Gabel, 1992;Gabel, 1993). In the case of the Brahmaputra River, high-stage flow data (and suspended sediment concentration) were collected using an acoustic Doppler current profiler operated from a boat, positioned using differential global positioning systems (GPS) (Richardson et al, 1996;Richardson & Thorne, 1998;McLelland et al, 1999).…”

Section: Methodsmentioning

confidence: 99%

“…However, studies of processes of fluid flow, sediment transport, erosion and deposition in braided rivers during flood stages are rare (Bridge & Gabel, 1992;Richardson et al, 1996;Richardson & Thorne, 1998;McLelland et al, 1999). Therefore, there has been little progress in the generation of realistic empirical models that link bed topography, fluid flow, sediment transport, erosion and deposition in braided rivers.…”

Section: Introductionmentioning

confidence: 99%

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Depositional Models of Braided Rivers

2006

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Depositional models of braided rivers are necessary for rational interpretation of ancient deposits, and to aid in the characterization of subsurface deposits (e.g. aquifers, hydrocarbon reservoirs). A comprehensive depositional model should represent bed geometry, flow and sedimentary processes, and deposits accurately, quantitatively, and in detail. Existing depositional models of braided rivers do not meet these requirements, and there are still many misconceptions about braided rivers and their deposits that need to be expunged. Over the past decade, there have been major advances in our understanding of braided rivers, making it possible to develop new and improved depositional models. First, the use of groundpenetrating radar in combination with cores and trenches has allowed detailed description of the different scales of deposit in braided rivers that vary widely in channel size and sediment size. Second, the study of braided channel geometry and kinematics has been facilitated by the use of aerial photographs taken at short time intervals. In some cases, these photographs have been analysed using digital photogrammetry to produce digital elevation models. Third, water flow and sediment transport at the all-important flood stages have been studied using new equipment and methods (e.g. acoustic Doppler current profilers, positioning using differential global positioning systems). However, such high-flow studies are rare, which is one reason why there has not been much progress in development of realistic theoretical models for the interaction between bed topography, water flow, sediment transport, erosion and deposition. Laboratory experimental studies of braided rivers have continued to be useful for examining the controls on channel geometry and dynamics, but have not been able to generate all of the different types and scales of strata observed in natural braided river deposits.New depositional models for sand-bed and gravel-bed braided rivers are presented here based mainly on studies of natural rivers. They comprise: 1 maps showing idealized active and abandoned channels, compound bars and lobate unit bars; 2 cross-sections showing large-scale inclined strata and their internal structures, associated with migration of compound bars, unit bars and their superimposed bedforms; 3 vertical logs of typical sedimentary sequences through different parts of compound bar deposits and channel fills.Compound bars migrate laterally and downstream, associated mainly with accretion of lobate unit bars. Abandoned channels are mainly filled with unit-bar deposits. The geometry of the different scales of strataset is related to the geometry and migration of the bedform associated with deposition of the strataset. In particular, the length-to-thickness ratio of stratasets is similar to the wavelength-to-height ratio of associated bedforms. Furthermore, the wavelength and height of bedforms such as dunes and bars are related to channel depth and width. Therefore, the thickness of a particular scale of strataset ...

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Depositional Models of Braided Rivers

2006

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“…Most of the bar studies were carried out in fl umes (SMITH, 1974;LEOPOLD and WOLMAN, 1957;ASHMORE, 1982;ASHWORTH, 1996;LANZONI, 2000;LUI, 2009;CROSATO et al, 2012), braided (JACKSON, 1975;BRIDGE, 1985;ASHMORE, 1993;RICHARDSON et al, 1998;ASHWORTH et al, 2011) or meandering rivers (LEVEY, 1978;KLEINHANS et al, 2008;PARKER, et al, 2011;SLOFF et al, 2012). As for anastomosing rivers, there have recently been some studies on the mechanisms of bar formation and heterogeneity FRANZINELLI 2002, 2005;SARMA, 2005;LATRUBESSE, 2008;ROZO et al, 2012, NICHOLAS et al, 2012NICHO-LAS et al, 2013;REESINK et al, 2014).…”

Section: Introdutionmentioning

confidence: 99%

Fluvial Processes in Attachment Bars in the Upper Paraná River, Brazil

Santos

Stevaux

Assine

2017

Rev. Bras. Geomorfol.

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Abstract:Bars are semi-submerged fluvial forms associated with the availability of sediments and a temporal dynamic, whose dimensions are controlled by the fl ow and depth of the channel. Attachment bars are very common in large anabranching river systems and play an important role in island formation and ecology. The Upper Paraná River exhibits an anabranching pattern characterized by channels of diff erent sizes, separated by islands and bars. The objective of this work is to present the processes involved in the formation and development of attachment bars in Santa Rosa Island, situated in Porto Rico, State of Parana, Southern Brazil. Acquisition campaigns were performed to obtain data on channel hydraulics (ADCP equipment), morphometry (Echo-sound profi les) and textural parameters (grain-size analyses) at high and medium water levels. Santa Rosa Island divides the fl ow into two channels of distinct hydraulic and sedimentary dynamics. Flow diversion produces a decrease in fl ow velocity and consequent sediment deposition near the upstream end of Santa Rosa Island. The formation and maintenance of attachment bars in Santa Rosa Island is related to fl ow competence reduction and the occurrence of divergent currents. Vegetation cover and fl ow regime control its permanence.

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“…[3] Local hydraulic conditions at bifurcations are influenced by secondary flow patterns related to local topography [Richardson and Thorne, 1998], affecting suspended load sediment transport. Both in tropical meandering rivers and in deltaic systems, the suspended-load is often dominant over bed load.…”

Section: Introductionmentioning

confidence: 99%

Sediment discharge division at two tidally influenced river bifurcations

Sassi

Hoitink

Vermeulen

et al. 2013

Water Resources Research

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[1] We characterize and quantify the sediment discharge division at two tidally influenced river bifurcations in response to mean flow and secondary circulation by employing a boatmounted acoustic Doppler current profiler (ADCP), to survey transects at bifurcating branches during a semidiurnal tidal cycle. The ADCP collecting flow velocity and acoustical backscatter data was used to quantify suspended sediment discharge, adopting a recently introduced calibration procedure. Measured profiles of flow velocity and sediment concentration allowed us to compute spatiotemporal distributions of the shear velocity, the roughness length and the Rouse number. Spatiotemporal distributions of the settling velocity were obtained by combining the Rouse number and shear velocity estimates with in situ measurements from a laser particle size analyzer. Bed-load transport rates were inferred from shear stress estimates. The concentration field shows a direct response to bed shear stress, stressing the alluvial context of the system. The flow in the bifurcation regions is characterized by counter rotating secondary-flow cells, which stretch over the full width and depth of the cross sections in the downstream branches, and persist throughout the entire tidal cycle. The pattern of secondary flow suggests the flow approaching the bifurcation is concentrated in two independent threads. A two-cell structure inhibits the exchange of sediment that would occur in case a single cell would stretch over the full channel width. The division of suspended sediment primarily depends on the upstream transverse profile of the suspended sediment concentration, which is in turn dependent on geometrical factors such as upstream curvature.

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Secondary Currents around Braid Bar in Brahmaputra River, Bangladesh

Cited by 65 publications

References 15 publications

Depositional Models of Braided Rivers

Depositional Models of Braided Rivers

Fluvial Processes in Attachment Bars in the Upper Paraná River, Brazil

Sediment discharge division at two tidally influenced river bifurcations

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