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Journal ArticleDOI

Control of Bed Erosion at 60° River Confluence Using Vanes and Piles

01 Jun 2018-International Journal of Civil Engineering (Springer International Publishing)-Vol. 16, Iss: 6, pp 619-627
TL;DR: In this article, the authors used a distorted model with a non-uniform sediment of mean particle size d¯¯ 50672 ǫ = 0.28mm with a confluence angle of 60°.
Abstract: River confluences have complex hydrodynamics than ambient flows due to different flow characteristics of the two merging flows. Secondary circulation develops due to merging of two flows which leads to bed erosion. The eroded sediment gets deposited at various locations in the downstream of the confluence. It is reported in the literature that major reservoirs in India will lose 50% storage capacity by 2020 and reservoirs all over the world lose storage capacity by as much as 5% every year. In view of controlling bed erosion at the confluence, vane and circular pile models are used as scour mitigation structures and experimental results are presented. Experiments are performed in a distorted model with a non-uniform sediment of mean particle size d 50 = 0.28 mm with a confluence angle of 60°. Two different discharge ratios (Q r = ratio of lateral flow discharge to main flow discharge) of 0.5 and 0.75 are used with a constant flow depth (H m) of 5 cm in the main channel. Vanes of width 0.3H m (1.5 cm), thickness of 1 mm are placed at 15°, 30° and 60° vane angles with respect to main flow. Circular pile models of 8 and 12 mm diameter are also used. Two different spacing of 2H m and 3H m (10 and 15 cm) between the vanes or piles are used to perform the experiments. For Q r = 0.5 and 0.75 using vanes, scour depth reduces by 25 and 34%, respectively. When circular pile models of 8 and 12 mm are used, the scour depth reduces by 25, 38 and 27, 43%, for Q r = 0.5 and 0.75, respectively. The scour depth decreases with an increase of vane angle and pile diameter, but increases with an increase of spacing. Therefore, piles have better performance over vanes in reducing scour at the confluence.
Citations
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Journal ArticleDOI
TL;DR: In this article, the authors compared the scour pattern upstream of square and circular orifices with equal opening areas of 38.45 cm2 and found that the influence zone area upstream of the square orifice is 1.46 times larger than the circular orifice.
Abstract: Scour pattern upstream of square and circular orifices with equal opening areas of 38.45 cm2 are compared experimentally. A total of 16 tests for four constant heads, two initial conditions of fixed bed versus mobile bed and two non-cohesive sediments used as the bed layer are performed. The bed profile is surveyed by an acoustic bed profiler and the velocity distribution is measured using an ADV instrument. In the fixed-bed tests the thickness of sediment layer below the orifices’ invert is 2 mm and the observations show that the influence zone, which is the zone exposed to excess shear stress in which particles are removed, is elliptically shaped in both orifices with larger ellipse radius in transverse direction. The influence zone area upstream of square orifice is 1.46 times larger than the circular orifice. Observations of the mobile-bed tests indicate that the geometrical scour parameters, namely maximum depth of scour, length and width of the scour hole increase with the head of water upstream of both orifices. It is also found that the maximum scour depth upstream of square orifice is approximately two times deeper than that of circular orifice. Meanwhile, scour length and width, upstream of square orifice are, respectively, 10–15 and 20–33% larger than those of circular orifice. Finally, the measurements of the longitudinal velocity profiles along the centrelines of the orifices for both orifices are performed. The results indicate the existence of three separate zones of velocity distribution upstream of the orifices.

8 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
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 "Control of Bed Erosion at 60° River..."

  • ...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
TL;DR: In this article, the scour hole depth at the downstream of cross-vane structures with different shapes (i.e., J, I, U, and W) is simulated utilizing a modern artificial intelligence method entitled "Outlier Robust Extreme Learning Machine (ORELM)".
Abstract: Due to the vital role of rivers and canals, the protection of their banks and beds is critically important. There are various methods for protecting beds and banks of rivers and canals in which “cross-vane structures” is one of them. In this paper, the scour hole depth at the downstream of cross-vane structures with different shapes (i.e., J, I, U, and W) is simulated utilizing a modern artificial intelligence method entitled “Outlier Robust Extreme Learning Machine (ORELM)”. The observational data are divided into two groups: training (70%) and test (30%). After that, the most optimal activation function for simulating the scour depth at the downstream of cross-vane structures is selected. Then, using the input parameters including the ratio of the structure length to the channel width (b/B), the densimetric Froude number (Fd), the ratio of the difference between the downstream and upstream depths to the structure height (Δy/hst) and the structure shape factor $$ \left( \phi \right) $$ , eleven different ORELM models are developed for estimating the scour depth. Subsequently, the suitable model and also the most effective input parameters are identified through the conduction of an uncertainty analysis. The suitable model simulates the scour values by the dimensionless parameters b/B, Fd, Δy/hst. For this model, the values of the correlation coefficient (R), Variance accounted for (VAF) and the Nash-Sutcliffe efficiency (NSC) for the suitable model in the test mode are obtained 0.956, 91.378 and 0.908, respectively. Also, the dimensionless parameters b/B, Δy/hst. are detected as the most effective input parameters. Furthermore, the results of the suitable model are compared with the extreme learning machine model and it is concluded that the ORELM model is more accurate. Moreover, an uncertainty analysis exhibits that the ORELM model has an overestimated performance. Besides, a partial derivative sensitivity analysis (PDSA) model is performed for the suitable model.

5 citations

References
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Journal ArticleDOI
TL;DR: Wang et al. as mentioned in this paper proposed an ensemble empirical mode decomposition (EEMD)-ARIMA model for forecasting annual runoff time series from Biuliuhe reservoir, Dahuofang reservoir and Mopanshan reservoir in China.
Abstract: Hydrological time series forecasting is one of the most important applications in modern hydrology, especially for effective reservoir management. In this research, the auto-regressive integrated moving average (ARIMA) model coupled with the ensemble empirical mode decomposition (EEMD) is presented for forecasting annual runoff time series. First, the original annual runoff time series is decomposed into a finite and often small number of intrinsic mode functions (IMFs) and one residual series using EEMD technique for a deep insight into the data characteristics. Then each IMF component and residue is forecasted, respectively, through an appropriate ARIMA model. Finally, the forecasted results of the modeled IMFs and residual series are summed to formulate an ensemble forecast for the original annual runoff series. Three annual runoff series from Biuliuhe reservoir, Dahuofang reservoir and Mopanshan reservoir, in China, are investigated using developed model based on the four standard statistical performance evaluation measures (RMSE, MAPE, R and NSEC). The results obtained in this work indicate that EEMD can effectively enhance forecasting accuracy and that the proposed EEMD-ARIMA model can significantly improve ARIMA time series approaches for annual runoff time series forecasting.

432 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

Journal ArticleDOI
TL;DR: In this article, it was shown that the width and length of the separation zone increase systematically with an increase in confluence angle, though the values of width are much less than predicted by recent mathematical modelling.
Abstract: The configuration of open-channel junctions controls local sedimentary processes, channel scour, and sidewall erosion through its influence on the flow patterns established as confluent streams compete for limited channel capacity. Entry of a tributary into a mainstream ensures detachment of flow from the channel sidewall immediately downstream from the junction, and flume experiments show well-defined relationships between the dimensions of the separation zone and discharge from the tributary. Other things equal, both the width and length of the separation zone increase systematically with an increase in confluence angle, though it is shown that values of width are much less than predicted by recent mathematical modelling. The zone grows at the expense of the proportion of the channel occupied by the immediate post-confluence flow with the consequence that near-bottom velocity increases by a factor of 1.3 as confluence angle is increased from 15°–90°. The implications for sediment entrainment are reviewed briefly.

285 citations

Journal ArticleDOI
TL;DR: In this paper, the authors measured downstream and cross-stream velocities at a small, asymmetrical stream confluence and found that the structure of low-stage flows is influenced by the tributary/main stem momentum flux ratio, the total discharge of the incoming flows, and the bed morphology.

245 citations

Journal ArticleDOI
TL;DR: In this article, the authors examined a 90°, sharp-edged, open-channel junction for channels of equal width using a point gauge and an acoustic doppler velocimeter over a grid defined throughout the junction region.
Abstract: Although open-channel junctions are common in many hydraulic structures, no comprehensive data set has been compiled that describes the 3D flow field within the junction itself. This physical model study examined a 90°, sharp-edged, open-channel junction for channels of equal width. Depth measurements were made using a point gauge while velocity measurements were taken using an acoustic doppler velocimeter over a grid defined throughout the junction region. The average velocity and turbulence intensity were calculated from a time series of velocities that was recorded at each location. In addition, a 2D mapping of the water surface was performed on a 76.2 mm square grid throughout the channel junction. This paper presents the details of the experimental procedure and the general flow characteristics observed. The full data set generated during this experimental work is available for downloading on the Internet. Using a small portion of the data recorded, an evaluation of several previously proposed theori...

232 citations