Flow structure through a fluvial pool-riffle sequence – Case study

Najafabadi, Elham Fazel; Afzalimehr, Hossein; Rowiński, Paweł M.

doi:10.1016/j.jher.2018.01.001

Cited by 18 publications

(16 citation statements)

References 42 publications

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“…Chartrand et al (2018) reported that the values of average shear velocity and the flow velocity in each section decrease separately, decreasing the incipient motion in the widening sections (decelerating flow region), and increasing for the narrowing sections of the channel (accelerating flow region). Fazel et al (2018) stated in their study that the values of average velocity during upstream riffle in the flow direction were generally lower than the downstream riffle and also the maximum value of average velocity in the flow direction occurred in downstream riffle, confirming the findings of the present study.…”

Section: Chronological Order Of Incipient Motion Of the Particle Unde...supporting

confidence: 90%

Incipient motion of sediment particles in the presence of bed forms under decelerating and accelerating flows

Dodangeh

Afzalimehr

2022

Journal of Hydrology and Hydromechanics

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This paper investigates the incipient motion of sediment particles under non-uniform flow in river and laboratory. In rivers, the non-uniform flow is often observed due to the presence of various bed forms. Threshold condition has been examined by using the Shields diagram based on the uniform flow assumption, however, this approach can be led to fallacious results for non-uniform flows where the effect of pressure gradient is significant due to bed forms. This study investigates the chronological order of incipient motion of the particles, the average threshold velocity (Ucr ), and Shields parameter for non-uniform flows. River data collection with gravel is used for investigating the incipient motion of surface layer of river bed and the laboratory data collection is considered studying the incipient motion of sub-surface layer of river. Both river and laboratory data collections are conducted in the presence of bed forms. Results reveal that the Shields diagram underestimates the particle incipient motion under accelerating and decelerating flows for the both case of laboratory and river. In both weak and general motion in the laboratory, the values of the critical Shields parameter are located below the Shields diagram, showing no particle motion. Our analysis shows that the incipient motion in river is affected by the presence of bed forms, river width changes, and flow non-uniformity conditions. The results show that in the accelerating flow (the bed form exit with a negative slope), the incipient motion is greater than the decelerating flow (the bed form entrance with a positive slope).

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Section: Chronological Order Of Incipient Motion Of the Particle Unde...supporting

confidence: 90%

Incipient motion of sediment particles in the presence of bed forms under decelerating and accelerating flows

Dodangeh

Afzalimehr

2022

Journal of Hydrology and Hydromechanics

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“…The trend of changes in velocity averaged in depth in the transverse direction shows that the velocities are higher near the central axis than those in the channel bank, indicating the flow's convergence upon entering the pool part. Furthermore, the results indicate that the highest Reynolds shear stress occurs at the entrance slope of the pool, and the lowest turbulence intensity was observed in the middle of the pool [24].…”

Section: Introductionmentioning

confidence: 89%

Effects of Channel Width Variations on Turbulent Flow Structures in the Presence of Three-Dimensional Pool-Riffle

2023

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Changes in the width of channels or rivers that have three-dimensional pool-riffle can affect the key parameters of river engineering and flow resistance. Understanding the effect of width changes on flow structures helps to control erosion and sedimentation in coarse-bed rivers and better design ecological restoration projects. The present study investigates the effect of the sequential pool-riffle and its interaction with the bank narrowness on the turbulent flow characteristics. For this purpose, an experimental study was conducted in variable and fixed width flume with an aspect ratio greater than five. The results showed that when the flow decelerates (entrance of the pool), the negative and low longitudinal velocities expand as the flow depth increases. From both sides of the central axis, longitudinal velocities decreased when entering the middle part of the pool and reduced the flow width. The changes in the maximum turbulence intensity values, from the central axis towards the channel bank, in the variable and fixed width modes had an increasing trend. In all three longitudinal directions along the flume, the maximum turbulence intensity and the maximum Reynolds shear stress in the variable width mode were larger than those in fixed one. Knowledge of the flow pattern along a variable width stream and better understanding of velocity and Reynolds stress distribution will help engineers to better estimate the controlling parameters in river restoration and improve hydraulic models’ performance.

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“…Three regions were distinguished in both rivers: The relatively flat, deepest region with vegetation, a middle region without plants but with sand forms, and a shallow region opposite the deep one (Figure 4), which in the Jeziorka River was also vegetated. This pattern of deep and shallow fragments of a channel, a sequence of pools and riffles, is typical for natural meandering rivers [57][58][59]. However, the pattern of plant patches in a channel varies not only yearly but also seasonally, changing the bed shear stress over time [18,24].…”

Section: Discussionmentioning

confidence: 84%

“…Obtained results indicate that there was a connection between the height of sand dunes and Reynolds shear stress in the water layer above. However, in the pool region, Reynolds stress distribution might be not correlated with sediment size or flow characteristics [59].…”

Section: Discussionmentioning

confidence: 99%

Experimental Investigations of Interactions between Sand Wave Movements, Flow Structure, and Individual Aquatic Plants in Natural Rivers: A Case Study of Potamogeton Pectinatus L.

Przyborowski

Łoboda

Bialik

2018

Water

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Long-duration measurements were performed in two sandy bed rivers, and three-dimensional (3D) flow velocity and bottom elevation changes were measured in a vegetated area and in a clear region of a river. Detailed flow velocity profiles downstream and upstream of a single specimen of Potamogeton pectinatus L. were obtained and the bed morphology was assessed. Potamogeton plants gathered from each river were subjected to tensile and bending tests. The results show that the existence of the plants was influenced by both bottom and flow conditions, as the plants were located where water velocity was lower by 12% to 16% in comparison to clear region. The characteristics of the flow and sand forms depended on the cross-sectional arrangement of the river, e.g., dunes were approximately four times higher in the middle of the river than in vegetated regions near the bank. Furthermore, the studied hydrophytes were too sparse to affect water flow and had no discernible impact on the sand forms’ movements. The turbulent kinetic energy downstream of a single plant was reduced by approximately 25%. Additionally, the plants’ biomechanical characteristics and morphology were found to have adjusted to match the river conditions.

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Flow structure through a fluvial pool-riffle sequence – Case study

Cited by 18 publications

References 42 publications

Incipient motion of sediment particles in the presence of bed forms under decelerating and accelerating flows

Incipient motion of sediment particles in the presence of bed forms under decelerating and accelerating flows

Effects of Channel Width Variations on Turbulent Flow Structures in the Presence of Three-Dimensional Pool-Riffle

Experimental Investigations of Interactions between Sand Wave Movements, Flow Structure, and Individual Aquatic Plants in Natural Rivers: A Case Study of Potamogeton Pectinatus L.

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