Three-dimensional flow structure, morphodynamics, suspended sediment, and thermal mixing at an asymmetrical river confluence of a straight tributary and curving main channel

Rhoads, Bruce L.; Johnson, Kevin K.

doi:10.1016/j.geomorph.2018.09.009

Cited by 65 publications

(41 citation statements)

References 61 publications

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“…Baranya and Józsa (2013) proposed a method to define the relationship between suspended sediment concentration and the variable RB which is derived from the acoustic backscatter intensity. Past work has shown that using the information of the backscatter intensity signal of ADCPs is a useful method for characterizing spatial patterns of suspended sediment within confluences (Konsoer & Rhoads, 2014; Rhoads & Johnson, 2018; Zinger et al., 2013). Hence, patterns of RB were used here as a surrogate for suspended sediment concentration.…”

Section: Study Site Field Procedures and Methodsmentioning

confidence: 99%

Hydrodynamics, Sediment Transport and Morphological Features at the Confluence Between the Yangtze River and the Poyang Lake

Yuan

Tang

et al. 2021

Water Resources Research

102

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Confluences are critical nodes in a river network and affect flow, sediment transport, water quality, and ecological patterns. Significant changes in hydrodynamics, bed morphology as well as environmental and ecological features occur at the confluence, where the flows from two tributaries combine and adjust to the postconfluence planform geometry. Confluence of two flows with different momentum and velocity ratios (the ratio of the variable of one channel to that of the other) often results in a downstream shear layer driven by the Kelvin-Helmholtz (KH) instability. It enhances turbulent mixing and exchange of momentum and other matter (e.g., sediment and pollutants;

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Section: Study Site Field Procedures and Methodsmentioning

confidence: 99%

Hydrodynamics, Sediment Transport and Morphological Features at the Confluence Between the Yangtze River and the Poyang Lake

Yuan

Tang

et al. 2021

Water Resources Research

102

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“…On the other hand, many authors have recently investigated the mixing processes downstream of confluences of small (Rhoads & Sukhodolov, 2001), medium (Herrero et al, 2018), to very large (Gualtieri et al, 2019; Lane et al, 2008; Laraque et al, 2009) rivers using modern measurement techniques, especially high‐resolution multibeam echosounders and hydroacoustic velocity profilers. However, no reliable and accurate tracing of the waters is available with high resolution: Mixing was assessed either from sky based on spectral response (Umar et al, 2018), using low‐resolution tracer sampling (Bouchez et al, 2010) or vertical electrical conductivity profiles (Herrero et al, 2018) over a few locations throughout each cross section, or based on acoustically derived suspended sediment concentration with high spatial resolution but usually large uncertainties and difficult interpretation due to local bed‐material resuspension (Gualtieri et al, 2019; Lane et al, 2008; Rhoads & Johnson, 2018). Such research efforts have provided extremely valuable insights on the mixing processes downstream of river confluences and on the typical values of complete mixing lengths.…”

Section: Introductionmentioning

confidence: 99%

Predicting Transverse Mixing Efficiency Downstream of a River Confluence

Pouchoulin

Coz

Mignot

et al. 2020

Water Resources Research

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Predicting mixing processes, especially transverse mixing, downstream of river confluences, is necessary for assessing and modeling the fate of pollutants transported in river networks, but it is still challenging. Typically, there is a lack of transverse mixing solutions implemented in 1-D hydrodynamical models widely used in river engineering applications. To investigate the mixing processes developing downstream of a medium-sized river confluence, three high-resolution in situ surveys are conducted at the Rhône-Saône confluence in France, based on geolocated specific conductivity and hydroacoustic measurements. Contrasting mixing situations are observed depending on hydrological conditions. In some cases, the two flows mix slowly due to turbulent shear at their vertical interface. This can be modeled by an analytical solution of the advection-diffusion equation. In other cases, the waters from one of the two tributaries move under the waters of the other tributary. The induced local circulation enhances transverse mixing but not vertical mixing and the flow remains stratified vertically, which may be missed when surface or satellite images are analyzed qualitatively. Stratification may be predicted by comparing the time scales for shear and density-driven adjustment. Shear-dominated transverse mixing of depth-averaged concentrations can be predicted analytically and implemented in 1-D hydrodynamical models. However, the initiation of apparently rapid transverse mixing due to density-driven circulation remains to be better understood and quantified. Plain Language Summary Predicting how waters mix downstream of river confluences is necessary for assessing and modeling the fate of pollutants transported in river networks, but it is still challenging. Typically, there is a lack of transverse mixing solutions implemented in models widely used in river engineering applications. To investigate the mixing processes developing downstream of a medium-sized river confluence, three high-resolution in situ surveys are conducted at the Rhône-Saône confluence in France. Contrasting slow or rapid mixing situations are observed depending on hydrological conditions. The transverse mixing of depth-averaged concentrations can be predicted analytically and implemented in 1-D hydrodynamical models. However, the initiation of rapid transverse mixing due to difference in fluid density remains to be better understood and quantified.

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“…Current advance in remote sensing and GIS enables us understand the extent to which river confluences are dynamic, planform characteristics and decadal evolution of the confluence points (Trigg et al 2012;Lewin and Ashworth, 2014;Mount et al 2013). In recent time, many aspects of river confluence like sediment, flow structure, and morpho-dynamics are being focused throughout the world to understand the process and mitigate the possible hazards (Ali et al 2019;Szupiany et al 2019;Sankey et al 2018;Rhoads and Johnson 2018). In the river confluence zone, erosion-accretion is considered a prime focal point.…”

Section: Introductionmentioning

confidence: 99%

Assessment of Morpho-Dynamics through Geospatial Techniques within the Padma-Meghna and Ganges-Jamuna River Confluences, Bangladesh

Gazi

Roy

Mia

et al. 2020

KN J. Cartogr. Geogr. Inf.

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Bangladesh is a low-lying riverine country with the mighty Ganges–Brahmaputra–Meghna (GBM) major river system including their abundant tributaries and distributaries. Land erosion–accretion is a very common phenomenon in this riverine country. This process extensively erodes huge productive landmasses at the river confluence zones every year. The main objective of this study was to understand the confluence morpho-dynamics and identify the vulnerable areas near the Padma–Meghna Confluence (PMC) and Ganges–Jamuna confluence (GJC) due to confluence shifting and erosion–accretion phenomenon of those rivers. The present study utilized multi-temporal Landsat satellite images from 1972 to 2019 approximately ten years of interval. Results showed that the PMC indicated frequent variation in migration trend towards NW from 1972 to 1980, SE from 1980 to 2010, and then reversed towards NW direction from 2010 to 2019. On the other hand, the GJC confluence point moved NW direction (2.37 km) from the year 1972 to 1980, but from 1980 to 2019, the confluence shifted towards the SE direction. Due to the migration dynamics, huge changes happened in width and sand bars area of both confluences. In PMC, confluence width increased remarkably indicating erosive flow during 1972–1980, then progressively shortened up to 2019, indicating accretion. In contrast, GJC shows a significant accretional trend over the 47 years. The sand bar area of the PMC increased about 147.09 km2 throughout the study period. But, GJC shows an opposite scenario where the total sand bar area decreased about 51.02 km2 in the same period. From the vulnerability study of erosion–accretion scenarios, it is predicted that Paturia Ferry Ghat area, Aricha Ferry Ghat area, Arua, Baruria, Dashkin Saljana, Bhadiakola, Masundia, Khanganj and Nyakandi areas near GJC and Chandpur sadar, Srimandi, Sakhua, Bilaspur and char Atra near PMC are highly vulnerable zones. The outputs of the study will enable policy makers to take necessary measures to reduce the erosional severity on both confluence zones and could also provide a basis for proper land management.

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Three-dimensional flow structure, morphodynamics, suspended sediment, and thermal mixing at an asymmetrical river confluence of a straight tributary and curving main channel

Cited by 65 publications

References 61 publications

Hydrodynamics, Sediment Transport and Morphological Features at the Confluence Between the Yangtze River and the Poyang Lake

Hydrodynamics, Sediment Transport and Morphological Features at the Confluence Between the Yangtze River and the Poyang Lake

Predicting Transverse Mixing Efficiency Downstream of a River Confluence

Assessment of Morpho-Dynamics through Geospatial Techniques within the Padma-Meghna and Ganges-Jamuna River Confluences, Bangladesh

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