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

Sanaz Hadian, Hossein Afzalimehr () and Sajjad Ahmad
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Sanaz Hadian: School of Civil Engineering, Iran University of Science and Technology, Tehran 16846-13114, Iran
Hossein Afzalimehr: School of Civil Engineering, Iran University of Science and Technology, Tehran 16846-13114, Iran
Sajjad Ahmad: Department of Civil and Environmental Engineering and Construction, University of Nevada Las Vegas, Las Vegas, NV 89154, USA

Sustainability, 2023, vol. 15, issue 10, 1-20

Abstract: 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.

Keywords: three-dimensional pool-riffle; width variations; accelerating and decelerating flows; turbulence intensity; Reynolds shear stress (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2023
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