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The loss of spur dike rootstones in the lower reaches of the Yellow River is an increasingly frequent problem, and traditional monitoring methods have limited effectiveness. In order to improve the accuracy and scientificity of the early warning of missing root-stones, the micro-core pile monitoring equipment was innovatively applied in the No.13, No.14, No. 15 and No.20 spur dikes of the Yellow River Shendi control works to monitor the missing root-stones as well as the changes of the tilting angle of spur dike body, vibration impact and acceleration. The micro-core pile monitoring system utilized IOT integrated sensing technology to realize 24 hours all-weather monitoring of underwater root- stone operation status through sensing terminal. The application shows that when the foundation stone of spur dike slips under the action of water flow or external force, causing slight displacement, tilting or vibration of spur dike, the micro-core pile can sensitively capture the in- formation of these indexes, and the monitoring accuracy is high. [ABSTRACT FROM AUTHOR]

A comprehensive understanding of velocity distribution is the fundamental information hydraulic engineers need to estimate an alluvial channel's discharge and stage characteristics. This study examines the Tsallis entropy approach for estimating streamwise velocity patterns in open channels. Entropy, which quantifies system uncertainty, has been applied in hydraulic research to account for variables such as shear strength, silt content, and flow velocities. However, its applicability to non-uniform channel sections remains unexplored. In the current work, the velocities estimation under various experimental conditions was calculated using the Tsallis entropy approach, wherein the random variable employed for constructing the velocity estimations was the time-averaged normalised velocity. This study considered two experimental conditions: (1) channels with attached spurs under seepage and non-seepage conditions and (2) channels with a 31-degree bank slope with and without an upstream pit. The velocity pattern obtained closely corresponds to the experimental data, exhibiting significant accuracy. However, it should be noted that the accuracy of the velocity pattern is slightly diminished in the region near the spur field when the y / D value is below 0.3. The difference can be caused by factors such as the area's non-uniform cross-section, sediment interaction along the bed, and secondary currents, which ultimately affect the velocity profile. [ABSTRACT FROM AUTHOR]

In this research, complementary numerical and experimental physical models were conducted to investigate flow parameters around an isolated permeable spur dike using ANSYS FLUENT ver. 16.1 software. The volume of fluid method VOF with the help of CFD technique and the κ − ε turbulence model was used to simulate the complex free-surface flow by applying a geometric reconstruction scheme. Two different mediums with different porosities were used, namely, gravel and glass beads. It was found that, for low flow rate values, there are no significant changes in the water profiles in both longitudinal and lateral directions for both media. Although for high flow rate values, the differences tend to be clearer. Results showed that there is a slight effect of the medium's properties if the dike width is less than 1/3 of width of the channel, in particular with low flow rate values. Good agreement was observed between the computational and the measured results for the water surface profiles. Also, there is an exact match between the lateral velocity distribution of gravels and glass beads. Downstream the dike, the lateral velocity profiles exhibit an S shape curve due to high velocity in the free flow and small flow velocity behind the porous dike. The results show good agreement between the CFD results and the experimental observations of the water surface profiles and velocity distribution according to the statistical analysis using some standard indexes error. [ABSTRACT FROM AUTHOR]

One of the most significant problems faced by hydraulic engineers is the local scouring of in-stream structures. The optimal design of scour protection methods requires time consuming, laborious and costly studies. Fractional factorial methods have been provided to formulate experimental designs which can optimize designs with fewer experiments and high accuracy. Therefore, this study aimed at using Taguchi and grey relational analysis (GRA) methods to investigate the effect of three factors: (1) spur dike angle, (2) size of riprap stones, and (3) riprap extent on the local scouring. An additional goal was to achieve an economical pattern for the riprap apron so that it delivers the best performance in protecting spur dikes with different angles. The results show that the riprap apron decreases the scouring depth and moves the scouring hole away from around the structure. However, increasing the spur dike angle decreases its performance in scouring reduction. Increasing the area of the riprap apron protected the downstream walls better and reduced the edge failure of the riprap; however, the erosion in the opposite wall increased. In addition, analysis of variance showed that the riprap extent and the spur dike angle, respectively, have the highest effects on the riprap performance, respectively. The comparison of the predictions of the Taguchi and GRA methods with observed values showed that these two methods have high capabilities to predict the results of scouring studies. [ABSTRACT FROM AUTHOR]

A 3D numerical model is developed to investigate the flow motion and sediment transport around a spur dike. In this model, fluid motion is described by the Navier–Stokes equations, adopting large eddy simulation to capture turbulent transport and dissipation. The spur dike and sand bed are treated by the porous media method. The suspended load concentration and the bed load transport rate is calculated separately, and then the bed variation is updated using the mass-balance equation. A series of flume experiments are employed to validate the model's performance before being applied for the case of partially emergent spur dikes and submerged spur dikes, respectively. Detailed analyses on the spatial-temporal variation of flow intensity, sediment concentration and shapes of scour holes are made, based on which some innovative findings are discussed such as the scouring process patterns, as well as the influence of flow conditions on the maximum scour depth and location, and then useful engineering suggestions are provided to improve structural safety. [ABSTRACT FROM AUTHOR]

• Modelling hydrodynamic-microplastic (MP) transport at the confluence. • Higher retention of PE and PS pellets with a diameter of less than 1 mm. • The motion patterns of MPs at the confluence with spur dike. • The spur dike layout will decrease the amount of MPs by 85% in flow separation. The issue of microplastic pollution is an urgent and undeniable global ecological concern. Due to the intricate three-dimensional (3D) hydrodynamic properties, the confluence is highly susceptible to microplastic contamination, particularly in the presence of spur dike disturbance. The present research goal is to elucidate the underlying mechanism governing the impact of the spur dike on transport and retention fate of microplastic at the confluence. A 3D hydrodynamic-microplastic transport model was developed at the confluence, and the Computational Fluid Dynamics (CFD) coupled with Discrete Element Method (DEM) method was employed to conduct the simulation. The concentration distribution, residence time, and trajectory of microplastics with different sizes and materials, as well as the effect of various angles of the spur dike on them were explored. The results indicate that (i) Large quantities of polyamide and polystyrene microplastics (less than 1 mm in diameter) with a residence time greater than 70 s are present in the flow stagnation zone, flow separation zone, the vicinity of spur dike, and downstream of the flow separation. (ii) The layout of the spur dike will lead to an increase in microplastic concentrations upstream of the spur dike and downstream of the flow separation. (iii) Vorticity and mixing layer thickness play crucial roles in the retention of microplastics within the flow separation and spur dike field. (iv) The dimensionless angles of the spur dike (α N) exhibit a linear and inverse relationship with the dimensionless standard deviations (σ N) within the spur dike field. This study will expand our understanding of the transport and retention mechanisms of microplastics, and provide valuable insights for accurately identifying pollution hotspots of microplastic pollution at confluences with spur dikes. [ABSTRACT FROM AUTHOR]

The scouring process near spur dikes could jeopardize the stability of riverbanks. Thus, accurate estimation of the maximum scour depth near spur dikes is crucial in river engineering. However, due to the complexity of the scour phenomenon around these structures, it has been a challenge to accurately estimate the maximum scour depth. Few efforts have been made to develop a machine learning (ML) approach for such a purpose. In this study, two novel multilayer stacked generalization frameworks are developed to model the scour depth near a spur dike in a uniform sediment condition. Stacked tree-based frameworks consist of three standalone ML approaches, including multivariate adaptive regression spline, multigene genetic programming, and kernel extreme learning machine as the first layer and the boosting regression tree (BRT) and bagging regression tree (BGT) as meta learners. A total of 186 data points were collected from previous experimental studies, and 32 flume experiments were further conducted under clear water conditions at the Indian Institute of Technology (IIT) Roorkee Laboratory in this study. The performances of the models were assessed using various statistical metrics [e.g., correlation coefficient (R), root-mean-square error (RMSE), and mean absolute percentage error (MAPE)], graphical criteria, and some existing empirical equations. The modeling results demonstrated that the stacked BRT and BGT frameworks were superior to all the standalone ML approaches (R=0.9786 , RMSE=0.1654 , and MAPE=11.68 for BRT; and R=0.9742 , RMSE=0.1831 , and MAPE =11.29 for BGT). This finding was also confirmed by a comparison between the empirical correlations and the artificial intelligence models. In addition, the sensitivity analysis proved that the mean sediment size ratio (L/d50) was the most influential variable in estimating the scour depth near spur dikes. [ABSTRACT FROM AUTHOR]

With the advancement in the science of engineering, bridge piers scouring has become a well-known phenomenon, and engineers have always been making efforts to counter such a destructive phenomenon. One of the methods used to reduce scouring around the bridge pier is application of other hydraulic structures which influence the amount of scouring in the flow path, such as submerged vanes, collars, riprap, and spur dike. This study aims to analyse the efficiency of rigid T-shaped spur dike in decreasing the scouring around bridges with a 90° pier in a 180° channel with a sharp bend. Experiments were carried out with the installation of a spur dike at the upstream pier on both inner or outer banks, in different positions, under clear water conditions, and the efficiency of the spur dike for reducing the scouring was compared with the control experiments. The results showed that the installation of the T-shaped spur dike on the outer bank significantly augmented the bridge pier scour reduction, and the greatest influence resulted from installation of a spur dike at 70° position on the outer bank, which reduced the scouring by 50% compared to a case of no spur dike installed. [ABSTRACT FROM AUTHOR]

• A dedicated standalone piece of software for fish habitat simulation was constructed. • Spur dike deployment enhances physical habitat quality and quantity in bends. • The deployment of dike group reduces ecological flow demand by 25%. • Combination of spur dikes and bend flow optimizes habitat improvement. Although channel meandering is currently a popular approach for river ecological restoration, the spiral flow formed in bends may lead to fragmentation of aquatic habitats due to the concave bank erosion and convex bank sedimentation. The aforementioned issue motivated this study, which aims to mitigate the adverse effects of curved flow on aquatic habitats within bends. We proposed a placement strategy of dike group within the curved channel to adjust the water–sediment structure of meandering rivers, thereby safeguarding against bank erosion and the fragmentation of river habitats. The effectiveness of this strategy has been validated by the development of numerical models based on 2D depth-averaged water–sediment equations, coupled with the IFIM method. These models investigate the mechanism of aquatic habitat enhancement achieved by deploying groups of submerged and non-submerged dikes on the convex and concave banks of the Fuhe River in Chengdu, China. The findings indicate that the implementation of dike groups resulted in an enhancement of approximately 30% in the weighted usable area (WUA) of the specific river. This improvement was accompanied by a 25% decrease in the ecological flow threshold (WUAmax). Furthermore, subsequent comprehensive comparative analyses under various conditions revealed that the fluctuations in enhancement effects were mitigated by flow increases. The degree of submergence parameter exhibits heightened sensitivity to enhancement effects, especially when the flow remains below the ecological threshold. The findings of this study can serve as a reference for the ecological restoration of river systems. [ABSTRACT FROM AUTHOR]

This work has compared the performance of three well-known artificial neural network (ANN) approaches in turbulent flow pattern modeling based on geometric characteristics of the channel (angle of horizon, distance from outer bank of the bend, and distance from the bed) in a 180° sharp bend with and without a T-shaped spur dike. ANN methods discussed in this work are feed-forward neural network, cascade feed-forward neural network, and extreme learning machines. Acoustic Doppler velocimetry is used to measure the velocity components in x, y, and z directions. Conducting this research is innovative and significant from three aspects: First, the data of the flow pattern around T-shaped spur dikes in a 180° bend, given its high importance in rivers in nature, are very rarely available; second, application of neural network models for understanding the flow nature is highly efficient at other bend points where no experimental or field measurements have been conducted; and third, with these models, the cost and time required for conducting numerical and experimental modeling for prediction of the flow velocity significantly decrease. Outliers (abnormalities or anomalies) may be generated by various factors in the measured velocities. Before modeling by ANNs, the self-organizing map clustering method is used to detect outliers to obtain more accurate models. Performance of ANN models is evaluated using correlation coefficient (R) and root mean squared error criteria. In order to compare the performance of ANNs in flow velocity modeling at different locations of the bend, seven different data groups are considered using different combinations of samples by random sampling. Results of comparison of ANN models with experimental data indicate that ANNs provide reasonable results in most cases and may be employed successfully in estimating the velocity in sharp bends with and without the presence of a spur dike. Moreover, it may be concluded that ANN models without spur dikes are more accurate than those with spur dikes due to creating less turbulence flow. [ABSTRACT FROM AUTHOR]

Spur dike is a typical river regulation building. It is widely used in control work. The research on scouring and protection of spur dike is especially important in practical engineering, which is related to the stability and safety of spur dike. This paper systematically reviews the research progress of scour and protection safety of spur dike at home and abroad.The research progress on mechanism research, prototype observation, physical modelling, numerical simulation and protective measure of scour at spurdike is introduced and discussed.The theoretical research trends and shortcomings of spur scouring at home and abroad, and put forward the general research ideas to provide scientific advice for the subsequent research on spur scouring and protection related issues. [ABSTRACT FROM AUTHOR]

In this study, the performance of slot in the spur dike was evaluated as a way to reduce the scouring around the installed flat spur dike in a 180 degree bend and the development of scouring in the slotted spur dike was compared with that of the spur dike with no slot. To evaluate the effect of the slot on the development of scouring around it, a flat spur dike made of Plax Glass was installed in a position of 70 degrees from a bend (180 degrees) in the flume bed. After determining the maximum of scouring depth at the tip, to reduce the scouring around the spur dike, two slots with the determined height were placed in 4 different positions in the spur dike. Experiments with 4 different discharges and constant flow depth in clear water conditions were conducted. The results of the experiments showed that the created the slot reduced the scouring depth toward the spur dike. In both slots, the minimum of scouring depth was seen in a model with the closest position of the slot toward tip, and its maximum was seen in a model with the farthest position from the slot. [ABSTRACT FROM AUTHOR]

Based on the heavy equipment installation complete basement project in Xiaoyangkou ( Yangkou Town) of Rudong County, we conducted the application research of stability and safety of approach dike maintenance and cofferdam during the construction of the seaport in the radial sand ridge region. The results show that the construction of the spur dike has promoted the deposition and protected the beach, prevented the horizontal migration of tidal creeks, stopped the impact and erosion of current in the tidal creeks on the cofferdam, and changed the current direction along the cofferdam so that to maintain a certain distance with the cofferdam which has played an role of great importance in safely constructing the project. [ABSTRACT FROM AUTHOR]

• The influence of different hydraulic conditions on the hyporheic exchange. • The temperature distribution law in the hyporheic zone is analyzed. • The degree of hyporheic exchange under the action of spur dike is quantified. It is important to understand heat transfer changes in the hyporheic zone of spur dikes when assessing ecological restoration and sustainability in rivers. To reveal the rule of hyporheic exchange under the action of a spur dike, the sinusoidal temperature change of surface water was set with a period of 24 h. The porous subsurface flow paths under different riverbed forms were plotted through dye tracing. In addition, the influences of surface water velocity (U), river width narrowing ratio (L/B), the number of spur dikes and riverbed shape on hyporheic exchange were also studied using the temperature tracing method. The results show that the hyporheic exchange path presents a trend of diagonal flow downstream, first conducting turbulent diffusion upstream and then sinking, with different riverbed morphologies having different path lengths. The temperature of surface water has a significant controlling effect on the temperature field of the riverbed. The sediment temperature change from the water–sediment interface to 0.3 m depth is closer to the sinusoidal trend. The change in surface water velocity (U) has the most significant effect on the temperature amplitude ratio. The temperature field below spur dikes is more susceptible to the impact of spur dikes and usually presents a "semielliptical" high-temperature area. With the increase in surface water velocity (U), river width narrowing ratio (L/B), and the number of spur dikes, the range of hyporheic exchange under the dam head also increases, which is positively related to the vertical section hyporheic exchange flux at the dam head. The local backwater area generated by spur dikes also affects pressure field distribution near spur dikes, but the changes caused by the fluctuation of the riverbed itself are greater than the impact of spur dikes on the riverbed. The water–sediment interface velocity at the spur dike increases sharply, and the upstream 1 m of the dam head gradually experiences upflow, drops sharply after reaching the maximum at the dam head, and then approaches zero after 1 m. There is no obvious upwelling and downwelling at the whole interface. [ABSTRACT FROM AUTHOR]

• Spur dikes alter flow regime and may improve physical habitat. • Different preferences of target fish urge spur dikes distinct contribution to physical habitat. • Artificial water level fluctuations promote carps reproduction in the study reach. Spur dikes, mainly for regulating water flow and protecting river banks in the past, were found recently to have the ability to increase the fish physical habitat and improve aquatic system. However, the effect of spur dikes on aquatic system was generally ignored previously, and the studies on the influence of spur dikes on improving specific native fish physical habitat are still rare. This study reports a numerical investigation for the effects of spur dikes on the physical habitat and the minimum ecological flow in the Jinjiang River. Three spur dikes are placed along the inner bend in the study reach and two fish species of the Pelteobagrus fulvidraco and carps are selected as the target species. Two-dimensional water depth and velocity field are simulated in different discharges and the results are used to predict the corresponding weight use area (WUA). The differences of WUA before and after the building of spur dikes for the two selected fish species show that spur dikes have a significant effect on the physical habitats. And the minimum ecological flows from the instream flow increment approach are different for the two objective fish species and are also considerably impacted by spur dikes. [ABSTRACT FROM AUTHOR]

• The accuracy of the numerical model is verified by physical test data. • The influence of geometric parameters of the model on exchange degree is revealed. • The temperature response law of the hyporheic zone driven by spur dike is analyzed. The study of hyporheic exchange and the temperature response law driven by spur dikes is helpful to promote the protection of ecological river environments. Taking the river channel course with a spur dike as the research object, the numerical simulation method was used to study the influence of the river width narrowing rate (L/B), spur dike angle (θ), surface water velocity (U), and hydraulic conductivity (K) on the hyporheic exchange characteristics and the temperature response of the hyporheic zone. Research shows that the degree of hyporheic exchange and the spatial range of the temperature response of the hyporheic zone are positively correlated with the river width narrowing rate, surface water velocity and hydraulic conductivity and negatively correlated with the spur dike angle. The temperature response law of the hyporheic zone is affected by spur dikes in different spatial locations in the following ways, from the cross-section, the upstream response area of the spur dike deepens near the dam bank, while the downstream response area deepens on the other side of the spur dikes, and the downstream response area affected by spur dikes is significantly larger than the upstream response area in the vertical range. From the side section, the response area of the curved boundary appears around the spur dike in the central section of the river, and the curvature radius of the response area of the curved boundary around the spur dike in the side section near the dam is smaller. From the longitudinal section, the sensitivity of the temperature response of the shallow section is significantly stronger than that of the deep section. Consequently, we found that the hyporheic exchange law driven by spur dikes. We offer recommendations for future studies seeking to choose the reasonable structure of the spur dam in practical engineering, and optimize the design of the spur dam. [ABSTRACT FROM AUTHOR]

Scour is a natural phenomenon in rivers caused by the erosive action of the flowing water on the bed and banks. Spur dikes are constructed across the flow to protect the bank from erosion by shifting of the river away from the bank. The spur dike undermines due to river-bed erosion and scouring, which is generally recognized as the main cause of spur dike failure. In this study, accuracy of existing equations for the computation of maximum scour depth has been checked with available data in the literature and data collected in the present study using graphical and statistical performance indices. Three new relationships are also proposed to estimate the maximum scour depth and maximum scour length upstream and downstream of spur dike. This new relationship for maximum scour depth is shown to perform better than other existing equations. [ABSTRACT FROM AUTHOR]

In estuaries with strong tidal bore, the scour behind the spur dike induced by tidal bore overflow has significant influence on the dike safety. In this study, an experiment study of the local scour induced by tidal bore overflow behind the spur dike was carried out in a physical flume. In addition, the process of the tidal bore overflow on the dike was numerically simulated with the boundary generation method. The stable overflow water depth on the spur dike (h ts), unit overflow discharge (q ts) and the scour hole characteristics were analyzed based on the experimental and numerical results. It is found that the relative stable overflow water depth (h ts / h 1) increases with the increase of the F roude number after bore (F r 1) and decreases with the increase of relative dike height (h d / h 1). While the relative stable unit overflow discharge (q ts / q 1) is mainly affected by the relative dike height. Additionally, the results of scour pit behind the spur dike show that the scour depth (s / h 1) is directly proportional to the relative current intensity (u 1 / u c) and the dike height (h d / h 1), but inversely proportional to the water depth before bore (h 0 / h 1). An empirical equation for predicting relative maximum scour depth is obtained by fitting the experimental results and the field measured data, and the prediction accuracy is within 30%. The conclusions of this paper can provide technical support for the engineering design and operation evaluation of spur dikes in estuaries with the strong tidal bore. • The tidal bore overflow and scour behind the spur dike are investigated. • The overflow water depth under tidal bore is affected by dike height and Froude number after bore. • The scour depth behind the spur dike is mainly influenced by the flow intensity, dike height and water depth before bore. • An empirical equation predicting scour depth behind the spur dike is established. [ABSTRACT FROM AUTHOR]

Totally, spur dike is an economical way to preserve morphology of rivers. Numerical methods can be useful for evaluating hydraulic parameters for spur dike because of their reduced simulation time, while experimental ones take a long time and need lots of tools to simulate any models. In this paper, flow patterns around a T-shape spur dike and a support structure, which is located upstream of the T-shape spur dike, is analyzed in 90° bend channel by Flow-3D model. The numerical and laboratory data are compared in longitudinal section to verify numerical model. The results show very good correspondence between numerical and laboratory data. After verification numerical model, a support structure has been installed upstream of the T-shape spur dike with 3, 5, 7 and 9 times distance longer than the length of the T-shape spur dike. The support structure altered flow patterns and hydraulic parameters such as power of secondary flow and separation zone in all of sections. By increasing support structure distance from 3L up to 9L, the power of secondary flow around main spur dike decreases by 40-120% and the length of separation zone increases from 0.8 to 2.5 times bigger than the length of T-shape spur dike. [ABSTRACT FROM AUTHOR]

Turbulent flow structures forming around isolated spur dikes in a horizontal channel are investigated in this study. In the analysis detached eddy simulation is used under fully turbulent incoming flow conditions at a channel Reynolds number of 45,000. Changes in the structure of the horseshoe vortex system, bed shear stress and pressure standard deviation on the bed are investigated for three different spur dike lengths. In all of the cases the main horseshoe vortex undergoes bimodal oscillations, which leads to an amplification in the turbulence quantities such as turbulent kinetic energy and pressure fluctuations along its axis. The main horseshoe vortex disappears over a much shorter distance in the flow direction for the short spur dike than those of medium and long spurs. Large bed shear stress values and pressure standard deviation values observed around the tip of the spur dike, beneath the upstream part of the main horseshoe vortex and beneath the separated shear layers increase with the increasing length of the spur dike. Different from the long and medium spur dike, in the short spur dike case, it is shown that the secondary horseshoe vortex is as coherent as the main horseshoe vortex and it contains bimodal oscillations together with the main horseshoe vortex. [ABSTRACT FROM AUTHOR]

Industrial contaminants and chemicals adversely impact surface water quality and may lead to serious health risks to human and ecosystems. Rivers as one of the major surface water resources receive wastewaters and transport dissolved pollutions in water through Advection-Dispersion processes. A minimum distance known as the mixing length is required for complete mixing and dispersion of the pollutants. Since the concentration of pollutants often exceeds the self-purification capacity of rivers within this distance, reducing it decreases the negative impacts on the aquatic ecosystems. Creating turbulent flows with inherent mixing characteristics is an efficient measure in decreasing the mixing length. Spur dikes that are widely used in river engineering are able to reduce the mixing length by virtue of the turbulence made in a stream. Given the fact that entry of pollutants into the surface water is inevitable and the influence of spur dikes on the characteristics of pollution transport has not been meticulously investigated, this study aimed at the numerical simulation of pollution transport in a rectangular channel adjacent to a spur dike. We thus invoked Flow-3D to simulate flow and transport characteristics around an impermeable and non-submerged rectangular spur dike. The findings of this study enhance our understanding of spur dike effects on pollution transport. Notwithstanding the fact that the spur dike effectively decreased the mixing length of the pollution, the location of the pollutant entry also played a prominent role in reducing the length of this region. • Exploitation of spur dikes could reduce the extent of the pollution zone • The pollutant entry points must be set at the location of rotation zone in the flow • Pollution entry from lower water depths reduces the length of the pollution zone [ABSTRACT FROM AUTHOR]

The weighted usable area (WUA) is one of the popular metrics to quantify the stream physical habitat and the effects of instream structures. However, most habitat studies only considered existing or proposed channel geometries in their WUA computations and not how the channel will evolve over time. This study reports a numerical investigation for the effects of spur dikes on WUA along the Juanchiao levee, Touchien River, Taiwan. Seven virtual dikes were placed along the outer bend in the study reach and the Rhinogobius candidianus was selected for target species. The horizontal two-dimensional (2D) flow fields at various flows and the corresponding WUAs for R. candidianus were computed under four channel bathymetry configurations, including: (1) existing; (2) immediately after dikes are implemented; (3) after 10-year channel migration without dikes; and (4) 10 years after dikes are implemented. The WUA obtained from the first two bathymetry configurations aimed to investigate the short-term spur dikes effect, whereas the last two examined the long-term effect. The channel geometry after 10 years channel migration under the conditions of both with and without spur dikes were simulated through a 2D mobile bed model. The analyses of short-term effect showed the WUA of R. candidianus, shortly after the virtual dikes were placed, increases due to increased water depth near the dikes, especially in low-flow conditions. As for long-term effects, however, the WUA in the case with spur dikes are lower than the case without spur dikes, especially in relatively high-flow conditions. The adverse effects of spur dikes on WUA appeared in the long-term investigation and resulted from the ever-increasing water depth and flow velocity around the tip of spur dikes and the main channel. This study showed that the habitat quality and availability might be overestimated if the channel bed changes over time. When using the WUA approach to evaluate the effects of instream structure on physical habitat prior to actually placing them in the river, quantitative predictions of the long-term variation of channel geometry and the associated physical habitat conditions are important. [ABSTRACT FROM AUTHOR]

The turbulent flow structures around an isolated spur dike located at three different approach flow angles are investigated. Detached eddy simulation is used at a channel Reynolds number of 45,000. Experimental velocity measurements were also conducted using acoustic Doppler velocimetry for validating the simulations. It is found that the size and orientation of the horseshoe vortex system change considerably with the approach flow angle. The main necklace vortex is largest in size and most coherent for 90°. Within this orientation it has larger amplitude bimodal oscillations compared to the 60° and 120° cases. A new scour mechanism is defined for the 60° case which is expected to generate more scour upstream of the spur dike. The possible scour area around the spur dike is found to be the maximum in the 90° case which is roughly by 15% larger than that of the 120° case. [ABSTRACT FROM PUBLISHER]

In the present study, flow patterns around a single spur dike (also termed a groyne) with free-surface flow was simulated using a numerical model known as Fluent. The model solved the fully three-dimensional, Reynolds-averaged Navier-Stokes equation to predict flow near the structure where three-dimensional flow is dominant. To treat the complex free-surface flow, the volume of fluid method with geometric reconstruction scheme was applied and turbulence was simulated using standard [image omitted] equations. In this research work, both a structured and an unstructured mesh were used and the density of the mesh spacing was selected the highest near the walls and also free surface to obtain more accurate results. Comparison of free surface and velocities of 3D model showed good agreement with three experimental flume data obtained by other researchers. The reattachment length for various conditions was computed using the numerical results and flow pattern was presented for repelling, attracting and vertical spur dikes together. Also, bed-shear stress distribution was presented and the effects of flow discharge and the length and angle of the spur dike upon the bed shear-stress distribution were evaluated. [ABSTRACT FROM AUTHOR]

Abstract: An acoustic Doppler velocimeter was used to measure flow and turbulence around an experimental spur dike in a flat and a scoured bed. Differences of mean velocity, turbulent intensity and Reynolds stresses between these two flow fields were analyzed. Upon the formation of scour hole, mean flow velocities in the downstream and lateral directions were reduced, but increased in the vertical direction. The turbulence intensities ( and ) are much larger, and the vertical component is smaller than that in the flat bed. Among three Reynolds stresses, the and components are much smaller than the . Bed shear stress near the dike can be 6 to 8 times as large as that of the approaching flow so that a local scour is developed near the dike without the shear stress of approaching flow exceeding the critical shear stress of bed material. The local scour initiated at the upstream of the dike and then extends to downstream from the dike tip. These results indicated that the development of local scour synchronizes to high shear stresses resulted from the horseshoe vorticies on a mobile bed surface. [Copyright &y& Elsevier]

• Scour estimation around the submerged spur dike in cohesive sediment mixtures. • Examination of three novel AI based models for the nose and wake scenarios. • GBDT outperformed the CFNN and KRR models. • Application of the best subset regression to select the best input combination. Spur dike has been widely used as one of the river training structures to increase the stability of riverbanks and embankments. Scour around spur dikes affects their hydraulic performance and stability. Hence, the precise calculation of scour depth variation with time at spur dikes is essential to the design of safe and economical spur dikes. This study focuses on assessing the scour depth variation with time around a vertical wall spur dike in cohesive sediment mixtures using soft computing techniques based on 26 experiments performed and the data collected from existing literature. Specifically, three novel machine learning techniques including Gradient Boosting Decision Tree (GBDT), Cascaded Forward Neural Network (CFNN), and Kernel Ridge Regression (KRR) were developed for accurate prediction of scour depth at the nose and wake zones of spur dikes. An efficient best subset regression (BSR) was implemented to identify the best input combinations for two different scenarios (nose and wake scenarios). The results demonstrated that the GBDT model outperformed the CFNN and KRR models in both scenarios. In addition, the sensitivity analysis based on mutual information of datasets indicated that the clay percentage (P c) and the ratio of cohesion to frictional angle of sediment mixture (C*/ ϕ *) were the most effective variables in the nose and wake scenarios, respectively. [ABSTRACT FROM AUTHOR]

Spur dikes are river engineering structures that project from the bank of a stream at some angle to the main flow direction. They are principally used for river training and protection of the riverbank from erosion. A spur dike might be considered a form of macroscale boundary roughness, which produces a backwater effect upstream from the spur dike location. Despite this impact, spur dike design often proceeds without regard to the effect that the spur dike might have on the stream system. The work presented herein is on the backwater effect due to a single, vertical-walled spur dike. It is based on a momentum analysis in which the resistance offered by the spur dike is represented by a drag equation, for which the key parameter is the spur dike drag coefficient. Experimental data acquired for various configurations of a single spur dike within fixed-bed flumes have been used to calibrate and validate the proposed backwater model. The results show that the spur dike drag coefficient, hence the computed backwater effect, depends on the channel contraction caused by the spur dike, the degree of spur dike submergence, the aspect ratio of the spur dike, and the Froude number of the flow. [ABSTRACT FROM AUTHOR]