Modelling Hydraulics and Sediment Transport at River Confluences

Biron, Pascale M.; Lane, Stuart N.

doi:10.1002/9780470760383.ch3

Cited by 43 publications

(37 citation statements)

References 74 publications

(234 reference statements)

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“…These results, hence, suggest that the higher mixing rates under nonneutrally buoyant conditions are largely the result of a higher level of distortion of the mixing layer. This conclusion is consistent with simulations [ Bradbrook et al ., ; Biron and Lane , ] and field observations [ Rhoads and Kenworthy , ; Rhoads and Sukhodolov , ] of river confluences reported earlier. The mechanisms causing distortion in Ribarroja, though, are not the same as those reported earlier.…”

Section: Resultsmentioning

confidence: 99%

“…They could also be the result of differences in the thermal inertia between the mainstream and the tributary, and, in this case, one would expect the temperature‐driven variations in density to occur at hourly scales, as a result of diurnal variations in insolation. The contribution of small density differences to mixing dynamics in confluences has not been addressed before, with the exception of the numerical study of Biron and Lane [] in a simplified 90° junction of two rectangular channels with density differences of O(1) kg m −3 . In that study, Biron and Lane [] demonstrated that mixing rates increased if the mixing layer distorted as a result of density differences.…”

Section: Introductionmentioning

confidence: 99%

“…The contribution of small density differences to mixing dynamics in confluences has not been addressed before, with the exception of the numerical study of Biron and Lane [] in a simplified 90° junction of two rectangular channels with density differences of O(1) kg m −3 . In that study, Biron and Lane [] demonstrated that mixing rates increased if the mixing layer distorted as a result of density differences. It is not clear, however, whether weaker or stronger density differences, or hourly scale variations in density, will have an effect or not on the mixing rates in river confluences.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Mixing dynamics at the confluence of two large rivers undergoing weak density variations

Ramón

Armengol

Dolz

et al. 2014

J. Geophys. Res. Oceans

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Simulations of tracer experiments conducted with a three-dimensional primitive-equation hydrodynamic and transport model are used to understand the processes controlling the rate of mixing between two rivers (Ebro and Segre), with distinct physical and chemical properties, at their confluence, upstream of a meandering reservoir (Ribarroja reservoir). Mixing rates downstream of the confluence are subject to hourly scale oscillations, driven partly by changes in inflow densities and also as a result of turbulent eddies that develop within the shear layer between the confluent rivers and near a dead zone located downstream of the confluence. Even though density contrasts are low-at most O(10 21 ) kg m 23 difference among sources-and almost negligible from a dynamic point of view-compared with inertial forces-they are important for mixing. Mixing rates between the confluent streams under weakly buoyant conditions can be of up to 40% larger than those occurring under neutrally buoyant conditions. The buoyancy effects on mixing rates are interpreted as the result of changes in the contact area available for mixing (distortion of the mixing layer). For strong density contrasts, though, when the contact area between the streams becomes nearly horizontal, larger density differences between streams will lead to weaker mixing rates, as a result of the stabilizing effect of vertical density gradients.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Mixing dynamics at the confluence of two large rivers undergoing weak density variations

Ramón

Armengol

Dolz

et al. 2014

J. Geophys. Res. Oceans

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“…The tributary channels were straight, shallow ( b / h = 12.5), and long enough for establishing fully developed flow ( l / h = 25) near the confluence apex, where b and l are the width and length of the tributary sections, respectively. This configuration of the inlet tributary sections was expected to eliminate the possible influence of the upstream planform on the structure of secondary flow (Biron & Lane, ). The equality between the total cross‐sectional area and width of the tributary channels with that of the postconfluence channel allows for direct comparison between parallel (0° junction angle) and converging channels (40° and 70° junction angles).…”

Section: Field Experimentsmentioning

confidence: 99%

Dynamics of Flow at Concordant Gravel Bed River Confluences: Effects of Junction Angle and Momentum Flux Ratio

Sukhodolov

Sukhodolova

2019

JGR Earth Surface

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Although the dynamics of secondary flow at river confluences have received considerable attention, a lack of theoretical insight in exploratory field and experimental research has led to different conclusions about the mechanisms driving these dynamics. This study revisits the problem of secondary flow at confluences by examining responses of the flow to controllable variations in curvature of flow trajectories in a series of field‐based experiments. The experiments were performed in a physical model designed to eliminate the influence of bed morphology, while using a large width‐to‐depth ratio to enable proper identification of flow structures at different scales. The results show that no secondary flow is detectable in runs with parallel merging flows irrespective of the momentum ratio. In runs with converging channels the secondary flow is represented by large‐scale motions consisting either of a pair of counterrotating helixes or a single helix depending on the momentum ratio. Comparison of scaled measured and theoretically predicted vertical profiles of lateral velocity shows that the helical secondary flow is primarily driven by the curvature of flow trajectories. This study also indicates that small‐scale secondary motions that have the same sense of rotation as the large‐scale helixes may develop in the immediate margins of the mixing interface. Differing only slightly from the flow depth in size, they are manifested by local upwelling within the large‐scale secondary motions. Several reasons to believe that interactions of large‐scale motions with opposing sense of rotation drive these small‐scale secondary flow cells are discussed in the paper.

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“…Rice et al, 2008). Even at confluences that possess a relatively stable planform location, the hydraulic processes at junctions are still highly complex, which makes understanding of pollutant pathways, for example, problematic (Biron and Lane, 2008). In the present paper, we focus on exploring the planform morphodynamics of large confluences and linking this to the subsurface sedimentology.…”

Section: Introductionmentioning

confidence: 99%

The Planform Mobility of River Channel Confluences: Insights from Analysis of Remotely Sensed Imagery

Dixon¹,

Smith²,

Best³

et al. 2017

Preprint

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A B S T R A C TRiver channel confluences are widely acknowledged as important geomorphological nodes that control the downstream routing of water and sediment, and which are locations for the preservation of thick fluvial deposits overlying a basal scour. Despite their importance, there has been little study of the stratigraphic characteristics of river junctions, or the role of confluence morphodynamics in influencing stratigraphic character and preservation potential. As a result, although it is known that confluences can migrate through time, models of confluence geomorphology and sedimentology are usually presented from the perspective that the confluence remains at a fixed location. This is problematic for a number of reasons, not least of which is the continuing debate over whether it is possible to discriminate between scour that has been generated by autocyclic processes (such as confluence scour) and that driven by allocyclic controls (such as sea-level change). This paper investigates the spatial mobility of river confluences by using the 40-year record of Landsat Imagery to elucidate the styles, rates of change and areal extent over which large river confluence scours may migrate. On the basis of these observations, a new classification of the types of confluence scour is proposed and applied to the Amazon and Ganges-Brahmaputra-Meghna (GBM) basins. This analysis demonstrates that the drivers of confluence mobility are broadly the same as those that drive channel change more generally. Thus in the GBM basin, a high sediment supply, large variability in monsoonal driven discharge and easily erodible bank materials result in a catchment where over 80% of large confluences are mobile over this 40-year window; conversely this figure is < 40% for the Amazon basin. These results highlight that: i) the potential areal extent of confluence scours is much greater than previously assumed, with the location of some confluences on the Jamuna (Brahmaputra) River migrating over a distance of 20 times the tributary channel width; ii) extensive migration in the confluence location is more common than currently assumed, and iii) confluence mobility is often tied to the lithological and hydrological characteristics of the drainage basins that determine sediment yield.

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Modelling Hydraulics and Sediment Transport at River Confluences

Cited by 43 publications

References 74 publications

Mixing dynamics at the confluence of two large rivers undergoing weak density variations

Mixing dynamics at the confluence of two large rivers undergoing weak density variations

Dynamics of Flow at Concordant Gravel Bed River Confluences: Effects of Junction Angle and Momentum Flux Ratio

The Planform Mobility of River Channel Confluences: Insights from Analysis of Remotely Sensed Imagery

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