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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
TL;DR: In this article, vanes and circular piles are proposed as scour mitigation measures in a distorted mobile bed model with 90° confluence angle and three discharge ratios (Qr = 0.33, 0.50 and 0.75) are used.
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
TL;DR: In this article, a simple one-dimensional formulation was proposed to predict the transitional flow at an open-channel junction, based on energy and continuity equations, and an empilical relation between the junction losses, the junction angle, and the discharge ratio was suggested which agrees well with the experimental results.
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
TL;DR: In this article, 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.
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.

9 citations

Journal ArticleDOI
TL;DR: In this paper, experiments were conducted to control sediment entry into an intake channel using submerged vanes in a physical model with a rectangular mobile-bed main channel and a trapezoidal rigid-bed intake channel diverting at an angle of 45°.
Abstract: Intake canals are used to withdraw water from rivers for various purposes. Sedimentation in the intake canal reduces the quality and quantity of water being delivered. In this study, experiments were conducted to control sediment entry into an intake channel using submerged vanes in a physical model with a rectangular mobile-bed main channel and a trapezoidal rigid-bed intake channel diverting at an angle of 45°. The variables in the study included vane angle, number of vane rows, and vane spacing in terms of mean flow depth in the main channel. In addition to the commonly used vane array with uniform vane heights, three other vane-height configurations were also tested. The least local scour around vanes and highest sediment reduction (~70%) were observed for vanes oriented at a 15° vane angle with an increasing vane-height configuration placed in two rows. It was also observed that control of sediment entry into the intake canal increased with an increase of both vane spacing and number of vane rows.

7 citations

Journal ArticleDOI
14 Jun 2018
TL;DR: A confluence is a place where two flows with different flow and sediment characteristics merge together as discussed by the authors, which is a common occurrence along the natural rivers as well as artificial open channels.
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.

6 citations

Journal ArticleDOI
TL;DR: In this article, a 2D numerical model is used in simulating hydromorpho dynamics in the rivers confluence to mitigate the erosion and deposition zones by adopting vanes as control structures.
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.

5 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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References
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Journal ArticleDOI
TL;DR: Submerged vanes as mentioned in this paper are small flow-training structures (foils), designed to modify the near-bed flow pattern and redistribute flow and sediment transport within the channel cross section.
Abstract: Recent research results with the submerged‐vane technique for sediment control in rivers are described. Submerged vanes are small flow‐training structures (foils), designed to modify the near‐bed flow pattern and redistribute flow and sediment transport within the channel cross section. The structures are installed at an angle of attack of 15–25° with the flow, and their initial height is 0.2–0.4 times local water depth at design stage. The vanes function by generating secondary circulation in the flow. The circulation alters magnitude and direction of the bed shear stresses and causes a change in the distributions of velocity, depth, and sediment transport in the area affected by the vanes. As a result, the river bed aggrades in one portion of the channel cross section and degrades in another. The vanes can be laid out to develop and maintain any desired bed topography. Vanes have been used successfully for protection of stream banks against erosion and for amelioration of shoaling problems at water inta...

139 citations


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

  • ...Vanes of width 0.3Hm (1.5 cm) and thickness of 1 mm are used (Odgaard and Wang 1991)....

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  • ...Similarly, vanes are flow training structures designed to modify the near-bed flow pattern and redistribute flow and sediment transport (Odgaard and Kennedy 1983, Odgaard and Spoljaic 1986, Odgaard and Wang 1991)....

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  • ...5 cm) and thickness of 1 mm are used (Odgaard and Wang 1991)....

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Journal ArticleDOI
TL;DR: In this article, it was shown that short, vertical, submerged vanes installed at incidence to the channel axis in the outer half of a river-bend channel significantly reduce the secondary currents and the attendant undermining and high-velocity attack of the outer bank.
Abstract: It is shown, theoretically and by a physical model, that short, vertical, submerged vanes installed at incidence to the channel axis in the outer half of a river-bend channel significantly reduce the secondary currents and the attendant undermining and high-velocity attack of the outer bank. The effect of the vanes on the secondary flow is estimated by a simple torque calculation using the Kutta-Joukowski theorem. A design relation for the vane spacing is derived by equating the torque, about the channel centroid, produced by the flow curvature to that resulting from the lateral force exerted on the vanes. The relation is verified in an idealized, physical model of a bend of the Sacramento River, California.

133 citations


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

  • ...Similarly, vanes are flow training structures designed to modify the near-bed flow pattern and redistribute flow and sediment transport (Odgaard and Kennedy 1983, Odgaard and Spoljaic 1986, Odgaard and Wang 1991)....

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Journal ArticleDOI
TL;DR: The first measurements of mixing processes at a large river junction (Rio Parana and Rio Paraguay, Argentina, combined width ∼2.8 km) are presented at two occasions: first when they mix in >400 km, and second when mixing is complete in only 8 km downstream of the junction as discussed by the authors.
Abstract: [1] Airborne and satellite observations show that when large rivers join they can take hundreds of kilometers to mix completely but, on occasion, may mix very rapidly. Application of established semitheoretical analyses shows that long mixing lengths should be expected. The first measurements of mixing processes at a large river junction (Rio Parana and Rio Paraguay, Argentina, combined width ∼2.8 km) are presented at two occasions: first when they mix in >400 km, and second when mixing is complete in only 8 km downstream of the junction. For the case of slower mixing, at-a-point surveys showed that mixing driven by turbulent shear associated with a near-vertical shear layer was restricted to close to the junction (to 0.272 multiples of the postconfluence width downstream). Transect surveys showed penetration of more turbid water from the Rio Paraguay underneath the Rio Parana, but this was insufficient to promote more rapid mixing. There was no clear channel-scale circulation present and slow mixing was compounded by reverse topographic forcing on the mainstream Rio Parana side of the river. This kept more turbid water on the Rio Paraguay side of the river, close to the bed. In the case of rapid mixing, we found clear channel-scale circulation. The momentum ratio between the combining flows reinforced the effects of the discordance in bed height between the tributaries at the confluence and allowed penetration of more turbid Rio Paraguay water further across the channel width deeper within the flow. The importance of the interaction between momentum ratio and bed morphology at channel junctions makes mixing rates at the confluence dependent upon basin-scale hydrological response, which is more likely to differ between large confluent rivers than small rivers, as a result of the different climatic/topographic zones that they may capture.

129 citations

Journal ArticleDOI
TL;DR: In this article, the authors show that the rise in the upstream flow depth due to the effect of lateral inflow from the branch channel can be significant for rightangled, sharpedged junctions of rectangu...
Abstract: In combining open channel flow, the rise in the upstream flow depth due to the effect of lateral inflow from the branch channel can be significant. For rightangled, sharpedged junctions of rectangu...

121 citations


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

  • ...This results in the conversion of velocity head to hydraulic head, that is, rise in flow depth at upstream sections (Taylor 1944, Ramamurthy et al. 1988, Hsu et al. 1998, Wang et al. 2007, Coelho 2015) and this afflux gets conveyed to the upstream sections (Greated 1968)....

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  • ...The studies on river confluences were carried out in laboratory experiments by Taylor (1944), Ramamurthy et al. (1988), Best and Roy (1991), Escauriaza et al. (2012) and field studies at river confluences are conducted by Best (1985), Rhoads (1987), Biron et al. (2002), Lane et al. (2008), etc....

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Journal ArticleDOI
TL;DR: In this article, the authors used eddy resolving simulations to predict details of flow structure for both Kelvin-Helmholtz (KH) and wake-mode conditions at a confluence for which field measurements are available.
Abstract: [1] The flow and turbulence structure at stream confluences are characterized by the formation of a mixing interface (MI) and, in some cases, of streamwise-oriented vortical (SOV) cells flanking the MI. Depending on the junction angle and planform symmetry, as well as the velocity ratio across the MI, the MI can be in the Kelvin-Helmholtz (KH) mode or in the wake mode. In the former case, the MI contains predominantly co-rotating large-scale quasi two-dimensional (2-D) eddies whose growth is driven by the KH instability and vortex pairing. In the latter case, the MI is populated by quasi 2-D eddies with opposing senses of rotation. This study uses eddy resolving simulations to predict details of flow structure for KH- and wake-mode conditions at a confluence for which field measurements are available. Results indicate that SOV cells at this confluence, which occur in both modes, redistribute momentum and mass, enhancing the potential for entrainment of bed material beneath the cells and for extraction of fluid and suspended sediment from the MI. The simulations predict that the cores of some of the primary SOV cells are subject to large-scale bimodal oscillations toward and away from the MI that contribute to amplification of the turbulence close to the MI and enhance the capacity of the SOV cells to entrain sediment. At this confluence, which has a concordant bed and a large angle between the incoming streams - conditions that generate strong adverse lateral pressure gradients adjacent to the MI - the oscillating SOV cells interact with MI eddies to generate large bed friction velocities in the zone of scour immediately downstream of the confluence.

115 citations