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Journal ArticleDOI

Methods to control bed erosion at 90° river confluence: an experimental study

10 Apr 2017-International Journal of River Basin Management (Taylor & Francis)-Vol. 15, Iss: 3, pp 297-307

Abstract: Confluence is a common occurrence in rivers. The convergence of flows often leads to erosion of the river bed and formation of a deep scour-hole at the confluence. In the present experimental study, vanes and circular piles are proposed as scour mitigation measures. Experiments are performed in a distorted mobile bed model (d50 = 0.28 mm) with 90° confluence angle. Three different discharge ratios (Qr = ratio of lateral to main flow discharge) of 0.33, 0.50 and 0.75 are used. Vanes (1.5 cm width and 1 mm thick) or piles (ɸ = 8 mm and 12 mm) are arranged in a row perpendicular to the lateral flow at a spacing of 5, 10 or 15 cm. Three vane angles of 15°, 30° and 60° with respect to the main flow are used. The experimental results show that scour depth (Sd) increases with an increase of Qr. Sd reduces by 33%, 50% and 47% with vanes for Qr = 0.33, 0.50 and 0.75, respectively. Sd reduces by 43%, 55% and 55% with 12 mm piles and by 70%, 60% and 59% with 8 mm piles, for the corresponding discharge ratios...
Citations
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01 Jan 2004-
Abstract: On the basis of energy and continuity equations a simple one-dimensional formulation was proposed to predict the transitional flow at an open-channel junction. An empilical relation between the junction losses, the junction angle, and the discharge ratio was suggested which agrees well with the experimental results. The results calculated by the present formulation for the depth ratio were compared with the results of earlier one-dimensional formulations and experiments. It is found that the present results coincide better with experiments than those of others.

24 citations


Journal ArticleDOI
14 Jun 2018-
Abstract: A confluence is a place where two flows with different flow and sediment characteristics merge together. Confluences are common occurrences along the natural rivers as well as artificial open channels. In general, a lateral flow confluences into a main flow at various angles. The confluence angle influences the flow and sediment transport at the confluence region. The bed erosion occurs because of turbulence at the confluence. Sometimes, the bank opposite to the direction of lateral flow fails due to the increase in lateral momentum. In addition, the main flow width in the downstream of the confluence increases due to increase of discharge. A confluence is characterized by the presence of a stagnation zone, a separation zone, a mixing layer and the recovered flow in the downstream. A secondary circulation (helicoidal flow cells) induced by the centrifugal action of the lateral flow when merging with the main flow leads to formation of a scour-hole along the central portion of the confluence. The eroded soil from the confluence poses problems by deposition in the downstream locations such as check dams, barrages and reservoirs resulting in reduction of water storage capacity as well as water quality. Hence, this necessitates studies on control of bed erosion at the confluence.

5 citations


Journal ArticleDOI
Abstract: Tributaries play a significant role in changing flow structure of the main river through their additional discharge. A study was conducted at the point of convergence of the River Deo with the River Manu using simple geospatial technique and field work to justify the hydrological and morphological changes in downstream of the confluence point. The spatio-temporal change of both the river channels for 10 km length in upstream and downstream of the confluence point was considered. Moreover, field measurements and post-field work were carried out to examine the spatial variation of hydrodynamic characteristics like flow velocity, depth, water discharge, wetted perimeter and hydraulic radius of the selected stretches. Sieving method was applied for grain size analysis of river bed sediment samples. The result revealed that both the aggradation and degradation processes were equally active in the upstream segment of the Manu River but in downstream segment aggradation exceeded the degradation activity, though all the hydrodynamic variables were boosted up in downstream, except flow velocity. The present research highlighted that the steeper gradient of the R. Deo had enhanced its competency to transport medium-sized grains to the R. Manu, where fine grains were commonly found. Moreover, increased wetted perimeter in downstream specified more friction between channel bed and its flow consequent upon reduced flow velocity with extra sediment load accumulation.

5 citations


Journal ArticleDOI
01 Jan 2019-Resources
Abstract: Controlling the flow and bed morphology in a river confluence is important in training and navigation works. The flow in river confluence is highly complex due to crucial and rapid changes associated with flow dynamics, sediment transport, and geomorphology. The flow in Malaysia’s rivers has many confluence junctions in natural drains of catchment areas. The confluence between Kurau and Ara Rivers, in Perak, Malaysia, is selected to investigate the scour hole that usually forms in the erosion zone and the bar that forms in the deposition zone. A 2D numerical model is used in simulating hydro-morpho dynamics in the rivers confluence to mitigate the erosion and deposition zones by adopting vanes as control structures. Simulation results suggest that the most effective location, dimension, and angle of vanes can be decided based on their performance in scouring and deposition zones. The distribution velocity and flow vectors can help in deciding the location of the vanes.

4 citations


Cites background from "Methods to control bed erosion at 9..."

  • ...Two recent studies were conducted on a laboratory scale with 60◦ and 90◦ confluences [38,39], in which a set of vanes and piles were proposed to control bed erosion....

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Journal ArticleDOI
Abstract: Controlling erosion and deposition zones that are usually forming at rivers confluences are important for improving river hydraulic efficiency. The flow in rivers confluences is highly complex, due to rapid changes associated with the river flow dynamics, sediment transport, and morphology. A two-dimensional (2D) numerical model was used to simulate the confluence between Kurau and Ara rivers, Perak, Malaysia. The numerical model has been calibrated and validated by using field data. The model was used to investigate the effectiveness of different shapes and sizes of 30o obstacles/vanes in controlling erosion and deposition zones at the confluence of Kurau and Ara rivers. The simulation results show that the best performance of 30o obstacles/vanes was found when a single obstacle/vane was introduced in the flow.

4 citations


Additional excerpts

  • ...[45] Wuppukondur, A., & Chandra, V. (2017)....

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  • ..., [49] and Wuppukondur and Chandra, [45]....

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  • ...In addition, the optimum angle of the obstacle was taken as 30° as recommended by Odgaard and Spoljaric, [48], Barkdoll et al., [49] and Wuppukondur and Chandra, [45]....

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References
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Journal ArticleDOI
Abstract: A method is presented which enables the computation of the bed-load transport as the product of the saltation height, the particle velocity and the bed-load concentration. The equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity. Experiments with gravel particles (transported as bed load) are selected to calibrate the mathematical model using the lift coefficient as a free parameter. The model is used to compute the saltation heights and lengths for a range of flow conditions. The computational results are used to determine simple relationships for the saltation characteristics. Measured transport rates of the bed load are used to compute the sediment concentration in the bed-load layer. A simple expression specifying the bed-load concentration as a function of the flow and sediment conditions is proposed. A verification analysis using about 600 (alternative) data shows that about 77% of the predicted bed-load-transport rates are within 0.5 and 2 times the observed values.

1,561 citations


"Methods to control bed erosion at 9..." refers background in this paper

  • ...Critical shear velocity (u*c) and particle Reynolds number (Re*) describe various conditions for incipient motion of the particles and ensure the sediment entrainment in the model for a given flow and sediment characteristics (van Rijn 1984)....

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Journal ArticleDOI
Michael Church1Institutions (1)
Abstract: The morphology of an alluvial river channel is the consequence of sediment transport and sedimentation in the river. Morphological style is determined chiefly by the caliber and quantity of sediment delivered to the channel, although modulated by channel scale. Yet the relations between sediment transport and river morphology have received only limited, qualitative attention. In this review, the problem is studied by defining sediment transport regimes on the basis of the Shields number, a nondimensional measure of the capacity of the channel to move sediment of a given caliber. The problem is also approached from an inverse perspective by which the quantity and character of sediment deposits are used to infer details about the variation of sediment transport and sedimentation along a channel. Coupling the two approaches establishes a basis to gain new insights into the origins of alluvial channel morphology.

525 citations


"Methods to control bed erosion at 9..." refers background in this paper

  • ...In alluvial rivers, channel morphology and sediment transport processes are inevitably linked (Church 2006)....

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Book
01 Jan 1989-

496 citations


"Methods to control bed erosion at 9..." refers methods in this paper

  • ...The critical shear velocity for d50 = 0.28 mm was obtained as 0.011 m/s from Shields number threshold value of 0.056 for present particle Reynolds number, Re* = 233 which indicated sediment entrainment (Re* > 40) (Ponce 1989, Jayaraman 1995)....

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Journal ArticleDOI
Abstract: A design method for the estimation of equilibrium depths of local scour at bridge piers is presented. The method is based upon envelope curves drawn to experimental data derived mostly from laboratory experiments. The laboratory data include wide variations in flow velocity and depth, sediment size and gradation, and pier size, shape, and alignment. Local scour depth estimation is based upon the largest possible scour depth that can occur at a cylindrical pier, which is 2.4D, where D=thepierdiameter. According to the method, this depth is reduced using multiplying factors where clear‐water scour conditions exist, the flow depth is relatively shallow, and the sediment size is relatively coarse. In the case of nonrectangular piers, additional multiplying factors to account for pier shape and alignment are applied. The method of estimation of local scour depth is summarized in a flow chart.

493 citations


"Methods to control bed erosion at 9..." refers background in this paper

  • ...Since σg > 1.3 and Vm/Vc 1 (Vc = 0.195 m/s) for all discharge ratios, clear-scour conditions prevailed (Melville and Sutherland 1988)....

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  • ...The flow velocity observed is less than the threshold mean flow velocity (Vc) but it is sufficient (Vm > 0.5Vc) for sediment entrainment (Melville and Sutherland 1988)....

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  • ...In addition, the pile diameter influences the local scour around the piles and the local scour increases with an increase of pile diameter (Melville and Sutherland 1988, Subhasish et al. 2014)....

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Journal ArticleDOI
James L. Best1Institutions (1)
01 Jan 1988-Sedimentology
Abstract: River channel confluences form important morphological elements of every river system, being points at which rapid changes in flow, sediment discharge and hydraulic geometry must be accommodated. This article presents results of a quantitative investigation of sediment transport at channel confluences accomplished through both scaled laboratory flume simulation and complementary monitoring of a natural channel confluence. Bed morphology at channel confluences is characterized by three distinct elements: avalanche faces at the mouth of each confluent channel, a deep central scour and a bar within the separation zone formed at the downstream junction corner. These elements are controlled predominantly by the confluence angle and the ratio of discharges between the tributary and mainstream channels. As confluence angle and discharge ratio increase, the sediment contributions from the confluent channels are progressively segregated in their paths through the junction, with sediment being transported around rather than through the centre of the confluence. This segregation of sediment loads is accompanied by the retreat of the main channel avalanche face from the confluence, an increase in the scour depth, a change in the orientation of the scour and an increase in the size of the separation zone bar. Field measurements closely replicate the flume simulation. A model of sediment transport and bed morphology links these features to the fluid dynamics of these sites. An understanding of confluence dynamics is important not only in considerations of channel morphology and design criteria but must form the basis for the interpretation of confluence sediments in the ancient record.

361 citations


"Methods to control bed erosion at 9..." refers background in this paper

  • ...For Qr = 0.50, Best (1988) obtained highest values of Srmax, may be due to the small channel width (15 cm) which increases velocity and leads to high scour....

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  • ...Furthermore, the size and location of scour-hole are studied in natural confluences by Rhoads and Sukhodolov (2001), Riley and Rhoads (2012), Riley et al. (2015), and experimental studies are conducted by Best (1988), Biron et al. (1993), Boyer et al. (2006), etc....

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