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Journal ArticleDOI

Experimental observation of turbulent structure at region surrounding the mid-channel braid bar

TL;DR: In this paper, it was shown that the braiding of marine waterways of the estuary zone occurs at an unknown time and place in the evolution of river morphological processes, which is among the most complex and least understood phenomenon in nature.
Abstract: River morphological processes are among the most complex and least understood phenomenon in nature. Recent research indicates that the braiding of marine waterways of the estuary zone occurs at an ...
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TL;DR: In this article , the authors synthesize the knowledge on braided rivers and an extensive review of the bio-morphological processes in the Brahmaputra River and integrate field investigated datasets along with geo-spatial imageries and Google Earth Engine computed fluvial information to conceptualize and understand the complex underlying processes.
Abstract: The spatio‐temporal heterogeneity in process–form–vegetation interactions has enabled the Brahmaputra river system to dissipate the fluvial energy at hierarchical scales. The present review article synthesizes the knowledge on braided rivers and an extensive review of the bio‐morphological processes in the Brahmaputra River. In addition, field investigated datasets along with geo‐spatial imageries and Google Earth Engine computed fluvial information are integrated to conceptualize and understand the complex underlying processes in the river. The review can be further used to propose rejuvenation frameworks and research directions concerning the implication of hierarchical energy dissipation potential in the Brahmaputra River.

4 citations

Journal ArticleDOI
TL;DR: In this paper , the authors developed and experimentally verified a novel method for suspended-sediment-discharge quantification in estuaries and coasts using underwater imaging, where red clay samples with different particle sizes were introduced into separate tanks containing clean water, and the concentration, particle size, turbidity, and water quality were measured and analyzed using LISST-200x and EXO2 multiparameter Sonde sensors.
Abstract: The amount of suspended sediment transported from rivers to the ocean fluctuates over time, with a substantial increase occurring during storm events. This surge in sediment poses numerous challenges to coastal areas, highlighting the importance of accurately assessing the sediment load to address these issues. In this study, we developed and experimentally verified a novel method for suspended-sediment-discharge quantification in estuaries and coasts using underwater imaging. Specifically, red clay samples with different particle sizes were introduced into separate tanks containing clean water. After adequate mixing, the concentration, particle size, turbidity, and water quality were measured and analyzed using LISST-200x and EXO2 Multiparameter Sonde sensors. To maintain constant lighting conditions, a camera box was created for filming. Based on the experimental results, a turbidity–concentration relationship formula was derived. The proposed regression equation revealed that the relationship between the turbidity and estimated suspended-sediment concentration was significantly affected by the particle size, and the prediction results were underestimated under high-concentration conditions. Using blue, green, and gray band values, a multiple regression model for estimating suspended-sediment concentrations was developed; its predictions were better than those obtained from the turbidity–concentration relationship. Following efficiency improvements through additional approaches considering underwater-image filming conditions and characteristics of actual streams, estuaries, and coasts, this method could be developed into an easily usable technique for sediment-discharge estimation, helping address sediment-related issues in estuaries and coastal regions.

1 citations

Journal ArticleDOI
TL;DR: In this paper , a comparison between the conventional triangular/tetrahedral porcupines and a relatively new prismatic design has been made in between the two species of porcupine.
Abstract: Erosion of bed and banks of rivers is a problem of great concern in India and abroad. A meandering river generally erodes the outer bank and deposits the sediments on the inner bank. Protection of riverbank, also termed as river restoration, thus becomes a necessity in such reaches of a river where scouring of banks and bed material leads to change of course of the river, thereby causing loss not only to land and property, but also to flora and fauna of the region. Porcupine systems have been found to be successful in big Indian rivers such as Ganga, Brahmaputra and Kosi as a cost-effective measure for river restoration. In this chapter, sediment trap efficiency of porcupine systems has been studied with laboratory experiments. Sediment trap efficiency of porcupines is found to be higher for low submergence and high sediment concentration. A comparison has been made in between the conventional triangular/tetrahedral porcupines and a relatively new prismatic design. Various configurations of layout of porcupines have been investigated to gain an insight into the sediment deposition pattern for a particular discharge, water depth and sediment concentration of the river. Performance of prismatic porcupines is found to be almost similar to that of conventional porcupines, although they comprise nine members in contrast with the triangular porcupines, which consist of six members only. Trap efficiency of conventional porcupines in capturing sediment is found to be as much as 82%, whereas in case of prismatic porcupines, maximum trap efficiency is found to be 74.26%, other parameters being the same. Therefore, the use of prismatic porcupines is rather not advantageous for erosion control or reclamation. Also, they are economically more expensive since they require nine members instead of six. However, they can prove to be safer and better at trimmed bank slopes of rivers.
Journal ArticleDOI
TL;DR: In this paper , the authors introduce the readers to the changes occurring in such properties due to vegetation; found by various experiments over the years, in a detailed manner, such as Flow velocity, Reynolds Shear Stress (RSS), and Turbulent Intensities, etc.
Abstract: Vegetation such as submerged, emergent, and floating plays an essential role in altering the flow characteristics through a channel. Moreover, vegetation serves as a means for the ecological restoration of a river and the prevention of erosion. Hence, understanding the changes that take place in the flow as it flows through vegetation forms the crux of the river restoration and erosion prevention works to name a few. For understanding the hydrodynamics of vegetation, various experiments have been carried out throughout the years along with the arrangements of numerous models. Properties such as Flow velocity, Reynolds Shear Stress (RSS), and Turbulent Intensities, etc. are extensively studied to understand this complex flow-vegetation interaction in a much better way. This chapter aims to introduce the readers to the changes occurring in such properties due to vegetation; found by various experiments over the years, in a detailed manner. Studies and results based on the different experimental set-ups in terms of vegetation type, arrangement, etc. have been put forward in the study such that the readers can gain an insight into the comparative study in this field of research. The chapter concludes by highlighting the important results as well as the research gaps in this field of study.
References
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Journal ArticleDOI
TL;DR: In this article, the velocity at the edge of the viscous sublayer is used as a detector signal for bursts and sweeps, and the scaling of the mean time interval between bursts with outer flow variables is confirmed.
Abstract: Additional experimental studies of the structure of Reynolds stress which supplement our previous work (Willmarth & Lu 1971) are reported. The velocity at the edge of the viscous sublayer is again used as a detector signal for bursts and sweeps. The signal uv obtained from an X-wire probe at various locations is conditionally sampled and sorted into four quadrants of the u, v plane. Using this method it is found that, when the velocity uw at the edge of the viscous sublayer becomes low and decreasing, a burst occurs. On the other hand, a sweep occurs when uw becomes large and increasing. The convection speeds of the bursts and the sweeps are found to be equal and are about 0·8 times the local mean velocity and 0·425 times the free-stream velocity at a distance y ≈ 0·15δ* from the wall (δ* is the displacement thickness). Throughout the turbulent boundary layer, the bursts are the largest contributors to from different events. Both mean time intervals are approximately equal and constant for most of the turbulent boundary layer. The scaling of the mean time interval between bursts with outer flow variables is confirmed. It is suggested that many of the features of the fluctuating flow revealed by the measurements may be explained by convection past the measuring station of an evolving deterministic flow pattern such as the hairpin vorticity model of Willmarth & Tu (1967).

1,050 citations

Journal ArticleDOI
TL;DR: In this article, the accuracy of the acoustic Doppler velocimeter (ADV) is evaluated in a 17m flume using an ADV and a laser DOF.
Abstract: Accuracy of the acoustic Doppler velocimeter (ADV) is evaluated in this paper. Simultaneous measurements of open-channel flow were undertaken in a 17-m flume using an ADV and a laser Doppler velocimeter. Flow velocity records obtained by both instruments are used for estimating the true (“ground truth”) flow characteristics and the noise variances encountered during the experimental runs. The measured values are compared with estimates of the true flow characteristics and values of variance (〈u′2〉, 〈w′2〉) and covariance (〈u′w′〉) predicted by semiempirical models for open-channel flow. The analysis showed that the ADV sensor can measure mean velocity and Reynolds stress within 1% of the estimated true value. Mean velocities can be obtained at distances less than 1 cm from the boundary, whereas Reynolds stress values obtained at elevations greater than 3 cm above the bottom exhibit a variation that is in agreement with the predictions of the semiempirical models. Closer to the boundary, the measure...

566 citations


"Experimental observation of turbule..." refers background in this paper

  • ...McLelland and Nicholas (2000), Voulgaris and Trowbridge (1998) observed that the sampling frequency range of (25-30) Hz is best for measuring velocity by Acoustics Doppler Velocimetry....

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  • ...ADV can measure velocity accurately up to 100Hz frequency (Voulgaris and Trowbridge 1998)....

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  • ...The “white noise” can be identified as an added noise floor in the high frequency region of the spectrum (Voulgaris and Trowbridge 1998)....

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Book
01 Jan 1993
TL;DR: Part I presents the statistical theory of turbulence, and Part 2 the coherent structures in open-channel flows and boundary layers.
Abstract: Part I presents the statistical theory of turbulence, and Part 2 the coherent structures in open-channel flows and boundary layers. The book is intended for advanced students and researchers in hydraulic research, fluid mechanics, environmental sciences and related disciplines. References Index.

371 citations

Journal ArticleDOI
TL;DR: In this article, a simple model of the flow structure and flow evolution of turbidity currents traversing submarine channels is proposed, based on theoretical, experimental, and field-derived concepts, which predicts that submarine channel flows are highly stratified, have significant supra-levee thicknesses, and form broad overbank bodies of low-concentration fluid moving along the entire channel length.
Abstract: Although analogies have been drawn between some types of meandering rivers and medium- to high-sinuosity, aggradational, leveed submarine channels, a number of different or additional processes operate in submarine channels. Analysis of several individual submarine channels suggests that they undergo much slower bend growth than alluvial rivers and may reach a planform equilibrium, in contrast to meandering rivers, in which bends progressively migrate downstream. Sinuous leveed submarine channels should therefore aggrade to produce isolated ribbons of thalweg deposits (of predictable 3D geometry), in contrast to the stacked channel belts characteristic of most alluvial meandering rivers. A simple model of the flow structure and flow evolution of turbidity currents traversing submarine channels is proposed, based on theoretical, experimental, and field-derived concepts. It predicts that submarine channel flows are highly stratified, have significant supra-levee thicknesses, and form broad overbank bodies of low-concentration fluid moving along the entire channel length. The interaction between the broad body of overbank fluid and within-channel flow is controlled by the processes of towing and angular shear, whose possible effects on channel sedimentation and planform stability are explored.

369 citations

Journal ArticleDOI
TL;DR: In this paper, the evolution and morphology of the confluences of model channels in a small flume were documented, showing that scour holes were maintained by turbulence and helicoidal flow cells generated by converging flows; their depths and cross-sectional areas increased as turbulence increases.
Abstract: The evolution and morphology of the confluences of model channels in a small flume were documented. Scour holes developed that were similar to features described at the confluences of branch channels in the braided North Saskatchewan River, North Platte River, and Medano Creek. The scour holes were maintained by turbulence and helicoidal flow cells generated by the converging flows; their depths and cross-sectional areas increase as turbulence increases. Scour hole depth increases rapidly as confluence angle increases from 15° to 90°, and more slowly up to 180°. Depth also increases as the difference between the discharges of the two confluent tributaries declines, and is a maximum when discharges are precisely equal. Depth decreases, other things being equal, as total sediment load increases. Apparently, an increase in sediment load requires an increase in shear stress for it to be transported, and therefore a constriction of flow and commensurate increase in flow velocity. Scour at the confluences of no...

363 citations


"Experimental observation of turbule..." refers background in this paper

  • ...In the past, a lot of work has been done on braided rivers and their channel pattern forms by many researchers (Leopold and Wolman 1957; Mosley 1976, Sharma 2004;Thorne, Russell, and Alam 1993) etc. and yet, when compared to the wealth of literature upon meandering systems, the braided rivers have…...

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