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This study numerically investigates a pile-supported pier, which comprises a column with a partially buried pile cap and a group of piles, recognizing that partially buried pile caps lead to the highest scour depth. Most research has focused on equilibrium scour conditions in laboratory settings, overlooking the detailed dynamics of horseshoe vortices around pile groups. This study aims to clarify the flow structure and vortex dynamics at a pile-supported pier during local scour hole development stages using an in-house developed numerical model. The model's accuracy is validated against flat-channel and compound pier reference cases. For the pile-supported pier, fixed bed geometry was used in flow simulations at selected scouring stages. Results show significant changes in flow structure and vortex formation with scour hole time development, particularly as the bed surface moves away from the pile cap. The study reveals variations in vortex size, number, and positioning, alongside turbulent kinetic energy and Reynolds shear stress distributions over time. High positive Reynolds shear stress near the bed during intermediate scouring stages highlights the complex interactions within the flow field. This research provides the first detailed visualization of flow structure evolution within a scour hole at a pile-supported pier. [ABSTRACT FROM AUTHOR]

This study numerically investigates a pile-supported pier, which comprises a column with a partially buried pile cap and a group of piles, recognizing that partially buried pile caps lead to the highest scour depth. Most research has focused on equilibrium scour conditions in laboratory settings, overlooking the detailed dynamics of horseshoe vortices around pile groups. This study aims to clarify the flow structure and vortex dynamics at a pile-supported pier during local scour hole development stages using an in-house developed numerical model. The model’s accuracy is validated against flat-channel and compound pier reference cases. For the pile-supported pier, fixed bed geometry was used in flow simulations at selected scouring stages. Results show significant changes in flow structure and vortex formation with scour hole time development, particularly as the bed surface moves away from the pile cap. The study reveals variations in vortex size, number, and positioning, alongside turbulent kinetic energy and Reynolds shear stress distributions over time. High positive Reynolds shear stress near the bed during intermediate scouring stages highlights the complex interactions within the flow field. This research provides the first detailed visualization of flow structure evolution within a scour hole at a pile-supported pier.

Balancing between sediment removal discharge and dam reservoir storage loss considering river environmental impact is of major and practical concern. The paper presents indices for evaluating the sediment removal performance of a Vertical Multi-hole Hydrosuction System (VMHS) in view of environmental impacts. A new hole arrangement on the vertical pipe of VMHS was experimentally examined. The compiled data of the temporal variations of the sediment concentration and the cumulative volume of removed sediment demonstrated that the arrangement of the holes on the vertical pipe of VMHS has profound impact on the speed of sediment removal and on the reservoir water loss. The high concentration of the outflow from the reservoir, however, might affect the downstream water course environment. The proposed indices could be applied to determine the proper duration for terminating the hydrosuction process in order to obtain a balance between the storage capacity and the downstream water course environment. [ABSTRACT FROM AUTHOR]

Reservoir sediment flushing, one of the most effective strategies for alleviating reservoir sedimentation, involves discharging sediment-laden flows downstream through bottom tunnels. However, whether flushing can be accomplished if the intake of a bottom tunnel is initially covered by cohesive sediment remains poorly understood. Here, flume experiments were done to investigate cohesive sediment flushing in a reservoir. It is demonstrated that cohesive sediment in a reservoir is harder to flush than non-cohesive sediment. A higher water level in the reservoir, initially smaller cover layer thickness, and lower dry density of the sediment favor the occurrence of sediment flushing. The flushing process of cohesive sediment is significantly affected by seepage. Under the combined action of gravity erosion and water erosion, the scour hole upstream of the dam is characterized by angular and broken edges. The threshold conditions for flushing of non-cohesive and cohesive sediments are evaluated. Empirical formulas applicable to both non-cohesive and cohesive sediment are proposed to estimate the equilibrium scour depth immediately upstream of the bottom tunnel intake. Also, empirical models are proposed for the time variation of sediment position in the bottom tunnel. The current findings are significant for informing the design and operation of reservoirs on rivers carrying fine-grained cohesive sediment in support of reservoir benefits and capacity preservation. [ABSTRACT FROM AUTHOR]

This paper presents the results of bed scouring near an abutment that spans the entire floodplain width and terminates at the edge of the main channel, termed here as the bankline abutment. The cross section can be divided into a scoured section and an un-scoured section. The scoured bed profile can be approximated using a power function. An analytical method has been suggested to predict the maximum scour depth at bankline abutment. This method is valid irrespective of whether the original bed is at or below the threshold condition of sediment motion. The proposed method is consistent with the experiments from this study and previous studies. [ABSTRACT FROM AUTHOR]

Studying the influences of the debris settled by the flood upstream of the bridge pier on the scour is important. In the present study, experimental tests were performed as four models including the bridge pier, the bridge pier with buried debris, the bridge pier with the free debris, and the bridge pier with free debris and the bed sill with the downstream gap equal to 0, 1, 2, 3, and 4 times of pier diameter. The results showed that buried debris increased the maximum length of the scour hole (ls), and the maximum width of the scour hole (ws) by about 50, and 180% respectively in comparison with the alone pier. It resulted that buried debris has a more increased effect than free debris. Free debris at low submergence ratios reduces ls by up to 27%, and in high submergence ratios increases it by up to 37%. Also, free debris increases ws in all submergence ratios, which is by up to 127% for the critical case compared to the case without debris. At all distances, the bed sill reduces ls and ws, and the best performance for reducing ls and ws is when it is attached to the bridge pier. HIGHLIGHTS Predicting length and width of the scour hole.; Effect of debris blockage on pier scour was evaluated.; Utilizing bed sill for protecting pier with debris blockage.; Experimental approach was suggested for scour hole of bridge pier.;

Effects of bed material and downstream flow depth on bed evolution in a right-angled channel confluence were studied through laboratory experiments. Velocity field, water surface elevation, and bed profile were measured intermittently until the flow attained equilibrium. Sediment discharges at various locations of the confluence were estimated from bed levels. Six prominent bedforms were identified, and their characteristics were quantified. The sediment discharges from different channels were initially high but decreased to approximately zero as the flow attained equilibrium. Downstream flow depth influenced overall sediment transport in the system, including the main features of bed morphology. Overall erosion in the confluence reduced as the particle size of the bed material increased. In addition, the maximum scour depth occurred at the confluence edge, and, due to the sharp corner of the confluence, its location did not change with time. Results from the present experimental study can help validate numerical models and assist in the design of a right-angled confluence. This study is related to the hydraulics of man-made confluences with mobile beds and can be useful in the following practical applications. More accurate numerical models to predict maximum scour, bed morphodynamics, and sediment transport in man-made confluences can be developed using the detailed bed profile measurements at different time instants presented in this study. Note that available numerical models use sediment discharge formulas (e.g., Meyer-Peter-Muller, Van Rijn), which are for sediment flows in straight channels. The interplay between the three-dimensional flow field, developed bed shear stress, and sediment discharge can be explored. In addition, A man-made confluence with the mobile bed can be designed with findings from the present study. The bedforms corresponding to equilibrium flow depend on discharge ratio, confluence angle, flow conditions at the exit channel, and bed material characteristics. The major bedforms can be incorporated into the confluence geometry. [ABSTRACT FROM AUTHOR]

The piano key weir is a unique new geometric type that can have a linear (rectangular or trapezoidal) or arc (trapezoidal) layout. Depending on the flow hydraulics and the bed type, different shapes of scour holes can form downstream of these weirs. Two types of piano key weirs—rectangular, and trapezoidal with an arced plan—were built to investigate the sediment transport patterns. The bed material comprised sand (d50=1.25 mm) and gravel (d50=8.9 mm). The results revealed that the scour hole dimensions and bed topography patterns depend on hydraulic conditions, crest geometry, and bed material gradation. Analysis of the data suggested that local scour depths behind a piano key weir with a rectangular crest might be as much as 12% larger than those for other configurations in sand or gravel. [ABSTRACT FROM AUTHOR]

Abstract The confluence of rivers is an important phenomenon that is really vital for irrigation and water transmission networks. Investigation on bed morphology at the junction of two streams is of great importance. Flow complexity at confluences, as well as being at risks of rising water levels and flooding, interfering with the use of bridges, filling the inlets of the ponds and reducing the efficiency of water transport are resulted by this phenomenon. The purpose of this research is to investigate the effect of geometric and hydraulic parameters, such as junction angle, width ratio of two intersected canals, and Froude number on the bed morphology at intersection, using SSIIM2. Validation of the results of numerical model in terms of hydraulic and morphology parameters indicated good correlations coefficients of 0.9 and 0.68, respectively. In the next step, the effect of intersection angle (45, 60, 75, 90 and 105 degrees) on the scour depth was investigated. By decreasing the junction angle from 105° to 45°, the maximum scour depth reduced to about 96% and the scour hole dimensions were smaller and moved toward the confluence shore. Furthermore, the results showed that by increasing the width ratio from 0.5 to 1, and also, decreasing the Froude number ratio of tributary to main channel from 3 to 0.68, maximum scour depth decreased by 25% and 30%, respectively.

The confluence of rivers is an important phenomenon that is really vital for irrigation and water transmission networks. Investigation on bed morphology at the junction of two streams is of great importance. Flow complexity at confluences, as well as being at risks of rising water levels and flooding, interfering with the use of bridges, filling the inlets of the ponds and reducing the efficiency of water transport are resulted by this phenomenon. The purpose of this research is to investigate the effect of geometric and hydraulic parameters, such as junction angle, width ratio of two intersected canals, and Froude number on the bed morphology at intersection, using SSIIM2. Validation of the results of numerical model in terms of hydraulic and morphology parameters indicated good correlations coefficients of 0.9 and 0.68, respectively. In the next step, the effect of intersection angle (45, 60, 75, 90 and 105 degrees) on the scour depth was investigated. By decreasing the junction angle from 105° to 45°, the maximum scour depth reduced to about 96% and the scour hole dimensions were smaller and moved toward the confluence shore. Furthermore, the results showed that by increasing the width ratio from 0.5 to 1, and also, decreasing the Froude number ratio of tributary to main channel from 3 to 0.68, maximum scour depth decreased by 25% and 30%, respectively. [ABSTRACT FROM AUTHOR]

This paper presents the results of bed scouring near an abutment that spans the entire floodplain width and terminates at the edge of the main channel, termed here as the bankline abutment. The cross section can be divided into a scoured section and an un-scoured section. The scoured bed profile can be approximated using a power function. An analytical method has been suggested to predict the maximum scour depth at bankline abutment. This method is valid irrespective of whether the original bed is at or below the threshold condition of sediment motion. The proposed method is consistent with the experiments from this study and previous studies.

The sky-jump spillway is an economical solution to return water to rivers, but an unsuitable flip bucket design might jeopardize the spillway, the dam, or other appurtenant works. Characterizing in advance, during the design phase, the position, size, and shape of the erosion basin would be useful to ensure that water flow is returned to the river in a safe way. Also, it would be useful for the safety assessment throughout the exploitation phase when erosion has not yet reached its maximum extension. Here, based on experimental laboratory work, the location, size, and shape of the erosion basin are analyzed, and a procedure is given for its characterization according to the design of the sky-jump spillway. [ABSTRACT FROM AUTHOR]

The complex flow structure around bridge piers is challenging for both experimental and numerical studies. Therefore, investigating the capabilities of Computational Fluid Dynamics (CFD) tools in resolving the flow structure and the mechanism of sediment entrainment into and out of the scour hole remains a challenging task. In this study, the scour depth around an oblong bridge pier and the bed shear stress distributions in time and space were numerically investigated using the Computational Fluid Dynamics (CFD) tool Sediment Simulation In Intakes with Multiblock option (SSIIM). Clear water scour conditions and sand of known granulometric composition were considered in accordance with the experimental study carried out. Laboratory data and the results of a scour characterization around a 0.11 m wide oblong bridge pier were considered to calibrate and validate the numerical model. The averaged form of the Navier–Stokes equations was considered to simulate the turbulent flow fields in anticipation of long time scales. The results show that calibrated numerical models can reproduce measured scour depths in the laboratory environment with considerable accuracy, with an average relative error of less than 3%, especially around oblong bridge piers. [ABSTRACT FROM AUTHOR]

Reservoir sedimentation is of worldwide concern, involving not only reservoir benefits, but environmental and ecological issues. Sediment flushing is one of the most common and effective methods for alleviating sedimentation and its negative impacts. To date, however, it has remained unknown whether sediment flushing can be accomplished through a bottom tunnel once its intake has been covered by sediment deposits. Here, a total of 65 runs of flume experiments were conducted to investigate the threshold conditions for occurrence of sediment flushing. The results demonstrate that higher water level, smaller cover layer thickness, shorter tunnel length, and steeper tunnel slope favor the occurrence of sediment flushing. Physically, as the gate located at the tunnel intake is opened, the sediment deposits immediately upstream of the intake collapse and enter the tunnel, entraining water. A mass of hyperconcentrated water-sediment mixture is generated, in which the amount of sediment depends on the cover layer thickness. If the water level is sufficiently high, the cover layer thickness is low, the tunnel slope is steep, or the tunnel is short, the pressure difference between the inlet and outlet of the tunnel suffices to drive the water-sediment mixture to move down to the outlet, overcoming the resistance due to the tunnel boundary. This way, sediment flushing is accomplished. Based on dimensional analysis of the observed data, a threshold condition is proposed for the occurrence of sediment flushing. It is also shown that an equilibrium scour hole is formed immediately upstream of the tunnel intake, and an empirical model for the scour hole geometry is proposed. The present findings can be exploited to improve sediment-rich reservoir planning, design, and operation for benefit maximization and eco-environmental wellbeing. [ABSTRACT FROM AUTHOR]

Sumps are commonly used in urban stormwater systems, which can be considered as a simple pretreatment device for stormwater quality control. However, they may function as pollution sources due to sediment washout under high flow conditions. An experimental study was conducted to investigate the scour process of predeposited sediments from a sump and its influencing parameters. Under conditions with large inflows or high sediment deposit, the sediment particles could be resuspended, entrained and flushed out. The washout mass decreased exponentially with time if the sediment bed surface depth was larger than a threshold value; otherwise, the amount of washout would be much smaller. The same scour pattern was observed for all the testing cases, of which the largest scour depth always occurred below the outlet. The deposit below the inlet might increase under conditions with high flow rates and low levels of sediment bed. Dimension analysis was performed and principal non-dimensional parameters were found, including the Péclet number, the pipe Froude number, and the dimensionless particle diameter, which can be used to determine whether the washout would occur and its intensity in a stormwater sump under given conditions. HIGHLIGHTS Maximum scour depth always occurs at the downstream side of stormwater sumps.; Sediment bed surface depth, discharge and particle size affect the washout process.; Péclet number, pipe Froude number and dimensionless particle size are most important to assess sump washout.;

Bridges are one of the important structures in the field of land communication. With the construction of these structures in the river, a flow pattern with a three-dimensional structure is formed in the vicinity of its piers, and as a result of increasing the flow speed and the formation of horseshoe vortex and wake vortices, part of the sediments around the piers and foundation will be washed away, and if the sufficient depth of foundation is not taken into account, the destruction of the bridge will result especially during floods. Road or railway crossing over the rivers is limited to the particular reach of the rivers which is determined by the general direction of the road or railway. Moreover, the general direction of the road or railway determines the position of the bridge over the river. Selection of the bridge path angle relative to the river flow direction is very important. Sometimes, due to the geographical conditions of the region and the general direction of the road or railway, the bridge crossing directly perpendicular to the flow direction is impossible. In this case, the bridge deck diagonally crosses over the river and the bridge group piers are angled relative to the flow direction. In such case, the distance between the piers, the flow direction relative to the piers and the piers submergence are very important parameters which affect the scour depth.

Submerged vanes are used as an eco-friendly low-cost measure for the management of river bed sediment. The performance of the vane is more sensitive to its angle of installation. A high angle increases the vane's nose scour which results in its failure, and a lower angle reduces the vane's performance. The design angles for the impenetrable vane are known, whilst for the impermeable vane are not clear. Therefore, it is our goal to experimentally examine the performance of permeable submerged gabion vane (SGV) with different permeability and different installed angles (α) in two conditions of clear water (CW) and live bed (LB). Experiments were performed in an 11-m-long and 0.66-m-wide bed flume. A SGV with a size 0.16-m wide, 0.80-m high, and 0.20-m thick was installed in the center of the flume with the submergence ratio (T/do = 0.5). The flow depth was 0.16 m, and the flume bed was covered with uniform sand bed (d50 = 0.48 mm). The SGV was filled with four different sizes of very fine, fine, medium, and coarse gravels and installed at different angles: α =10°, 15°, 20°, 25°, 30°, and 35°. Comparing the maximum scour depth around the SGV at the end of each experiment, it shows that the vane's nose scour is minimum at α = 20°, whilst for the LW condition, the minimum scour depth occurs at α = 25°. Moreover, under all hydraulic conditions, the results reveal that the permeability of the gabion can reduce the vane's scour depth and the minimum scour depth was for gabion filled with gravel (D50 = 4 mm). [ABSTRACT FROM AUTHOR]

Laboratory experiments were carried out to investigate the hydraulics, turbulence structure, and sediment removal capacity of bridge pier with different adjusted roughness. Four experimental models of the roughness were employed to measure the effect of the geometry of the roughness on the scour hole formation and depth. The effects of roughness geometry on the turbulence structure and local erosion through the bridges were studied for one sand sediment size. The three-dimensional velocity profiles and turbulence characteristics of flow downstream and upstream of the bridge pier were measured by Acoustic Doppler velocimetry (ADV) technique due to different adjusted roughnesses. After filtration process by WinADV software, the contour plots of the turbulence kinetic energy were depicted due to triangular roughness. The maximum longitudinal eroded section, which is commonly located by bridge pier corners, was measured through the experiments. The results of the scour hole measurements indicate that due to increasing the length of the roughness, the scour hole depth values decreased; however, increasing the vertical distance has the same effect on the scour hole formation. Furthermore, different geometries of the employed roughness illustrate that the triangular roughness has less scour hole depth than other experimental models with the same hydraulic condition. The detailed information of the magnitude, distribution, and probability of turbulence structures was extracted from time-series data using power spectra. The turbulence data were compared with the topography of upstream erosion. Analysis of the power spectrum density function indicated that the discontinuous adjusted roughness remarkably reduced the downward energy level of vortexes at the upstream of bridge pier, which is supposed that the gap opening through the roughness can increase downward jets impact. It appears that this condition reduces the turbulence kinetic energy near the bed elevation at the upstream face of squire bridge pier.

The depths and areas of the scour holes around spur dikes are the most concerning issues regarding spur dike design. In this study, using a moving bed experiment, the influence of traditional rock-fill spur dikes and new permeable spur dikes with different permeabilities on riverbed scour under unsteady flow was studied, and the spatial characteristics of scour holes at dike heads were analyzed. The results show that with increases in the permeability coefficient of the spur dike, the depth and area of the scour hole at the dike head gradually decreases; however, when the permeability coefficient is more than 17.6%, the depth and area of the scour hole downstream of the dike body increases with an increase in the permeability coefficient. According to comprehensive evaluation, when the water permeability is 17.6%, the stability of the spur dike is at its best. The maximum depth of the scour hole at the dike head is affected by factors such as the spur dike permeability coefficient, effective scouring time, and width bottom protection structure. On this basis, a new formula for calculating the maximum depth of the scour hole at a dike head is proposed. These research results will be beneficial to the reliability of spur dikes and the sustainability of navigation channels. [ABSTRACT FROM AUTHOR]

An experimental investigation on flow fields within the scour holes upstream and downstream of circular piers positioned in tandem and staggered arrangements is reported and compared with isolated piers on mobile beds with uniform sediment. The instantaneous bed elevations and instantaneous three dimensional (3D) velocities were measured using a 5 MHz Ultrasonic Ranging system and 16 MHz micro down looking acoustic Doppler velocimeter, respectively. The velocity and flow depth were measured at different locations under near equilibrium bed scour conditions. The measured 3D velocities were processed for the computation of flow parameters, such as velocity fields, streamline patterns, vorticity fields, and circulation. Furthermore, turbulence intensities, turbulent kinetic energy, Reynolds shear stresses, and bed shear stresses around the piers for all three pier configurations were computed from the detrended velocity signals to identify significant differences in the flow parameters and turbulence in the tandem and staggered pier arrangements as compared to those for an isolated pier. A recirculation zone was found near the bed in front of the rear pier in the tandem case from the streamline patterns. The vortices in the bi-vortex system were observed to be opposite to each other in the gap between the three piers in the staggered case. A strong secondary vortex also was observed apart from the primary vortex at the foot of the pier (θ = 0°) in all the three configurations. The strength of the horseshoe vortex (combination of primary and secondary vortices) was found to be higher at the front piers of the staggered arrangement as compared to those of the tandem piers, followed by the isolated pier. The bed shear stresses were found to be higher for the staggered piers than for the tandem piers in the direction of flow (θ = 0°). However, a 50% reduction in the bed shear stresses was observed behind the tandem piers at θ = 180°. The study reported in this paper provides the foundation for further investigation of countermeasures against local scour around tandem and staggered bridge piers on a mobile bed with non-uniform sediment. [ABSTRACT FROM AUTHOR]

The bed formations of submarine pipelines models were measured to investigate the effect of design parameters such as the distance between two submarine pipelines and also the effect of adjusted rectangular spoiler due to different angles of adjustment. To investigate the hydraulic parameters, three experimental models of parallel pipelines with three distances were made through the hydraulic laboratory. By considering the threshold velocity, the bed profiles were measured experimentally by employing the point gauge apparatus due to changing the angle of considered spoilers. Results indicate that increasing the distance between two submarine pipelines is the reason why that the downstream scour hole was formed independently from the upstream scour hole, which was developed under the upstream pipelines. Also, due to different angles of spoilers, the scour hole of spoiler with angle 90o formed the same as the witness model (with no spoiler), showing that angle 90o has no marginal effect on scour hole formation process. However, the angle of 180o adjusted on two submarine pipelines made the maximum scour hole under the upstream and downstream pipelines. It is assumed that the spoiler 180o affects the downstream flow of the pipelines and by creating the region with low pressure behind the pipelines, the scour holes were plunged to the bed and the depth of the scour holes increased significantly. Also, the investigation of spoiler position on the two pipe lines illustrates that by adjusting the spoiler on the downstream pipelines, the downstream pipe was buried under the sediment. These conditions were observed by angles of 135o, 180o, and 225o. It is assumed that increasing the distance between two submarine pipelines diminishes the rate of self-burial conditions. It appears that by increasing the distance between two pipelines, the effect of the upstream pipeline was omitted because the downstream and upstream pipelines were scoured as two single pipes; thus, the upstream pipelines did not affect the downstream pipelines.

Scouring holes under the oil, gas, and water pipelines threaten their stability by bending and demolishing. This phenomenon can cause damage to the environment and the oil and gas industry. The present study investigated the effect of the pipe diameter, the height of support, and the angle of the pipeline with flow direction by applying the experimental aspects to the cohesive sediments. The experiments were carried out by considering three angles of deviation as zero,15, and 30 degree based on the flow direction. Three opening gaps were considered through the experiments based on the pipe height as 0, D/2, and D/4 from the sand bed. Furthermore, three pipe diameters were employed to investigate the effect of diameter size. The results indicated that by increasing the angle of deviation, the height of scour hole decreased significantly, however, the raising the opening gap between pipe and bed increased the sediment deposition and it causes the height of scour hole is decreased consequently which was constituted approximately 18 percent. Moreover, the pipe diameter affects the scour hole formation and its effect on a downward jet and horseshoe vortexes and the result indicate by increasing the piper diameter the scour hole is increased based on its effect on the flow configuration. Finally, based on the experimental data, an equation was estimated to predict the scour depth by employing the non-linear regression technique.

Submarine pipeline is one of the most popular research filed that many researchers focus on solving the issue of buckling of pipeline. The snaked laying is an effective method to control the lateral buckling. The scour below offshore pipeline may affect the efficiency and performance of the snake lay pipeline. The objective of this study was to investigate the effect of scour hole on the buckling of seawater pipelines. A three-dimensional numerical model developed to investigate the effect of scour below offshore pipeline subjected to wave and current by using Abaqus software and Aqua Module. The results indicated that vertical deformation of straight pipeline increased by increasing scour hole depth. This value changed 4.85 cm to 32.87 for holes 11 to 200 cm respectively, but these parameters of the snake lay pipelines were not affected by the presence of scour hole. Moreover, the effective axial force of snacked lay pipelines reduced 5 times in comparison to straight pipeline by applying wave and current. The results indicated that the value of stress of snaked-lay pipeline was independent on scour hole depth. Therefore, this pipeline was effective method to limit and control buckling even in the presence of scour below it

• On-wall flow allocation and erosion of vegetation-covered gully heads were investigated. • The on-wall flow proportion decreased as the inflow rate and upstream slope gradient increased. • The Fr of the upstream flow played a critical role in the on-wall and jet flow allocation. • On-wall flow was responsible for scour hole development in the gully headwall. • On-wall flow contributed 17.6 %–64.9 % of the sediment yield during gully head retreat. On-wall flow and jet flow converted from upstream flow at the gully brink play important but differential roles in gully head erosion. However, on-wall flow allocation at gully brinks and its erosive effects on vegetation-covered loess gully heads remain unclear. Simulated flow scouring experiments were conducted on grass-covered gully heads under different inflow rates (3.0–7.2 m3/h) and upstream slope gradients (1–7°) to investigate the on-wall flow proportion and relationships with the hydraulic parameters of upstream flow, as well as erosion and sediment yield characteristics. The results showed that the on-wall flow rates linearly increased with increasing inflow rate (P < 0.01) but decreased as the slope gradient increased, whereas the jet flow rate increased as the inflow rate or slope gradient increased. The on-wall flow proportions ranged from 24.6 % to 58.7 % and decreased with increasing inflow rate or slope gradient, whereas the jet flow proportions exhibited the reverse trend. The on-wall and jet flow proportions had the most significant correlations with the Froude number, following a negative power function and positive logarithmic function (P < 0.01), respectively. The breadth and depth of the scour hole that developed on the gully headwall increased linearly with the on-wall flow rate (P < 0.01). Jet flow had a limited effect of accumulation on scour hole development, with average increases of 13.5 % and 8.6 % in the breadth and depth, respectively. On-wall flow generally contributed 17.6 %–48.4 % of the sediment driven by on-wall and jet flows but played a dominant role under 1° upstream slope gradient and 3.6 m3/h inflow rate in which the contribution reached 64.9 %. On-wall flow might have dominated the runoff volume and played a dominant role in the sediment yield under low upstream slope gradients and inflow rates and was essentially responsible for scour hole development, which could destabilize and retreat the gully head. [ABSTRACT FROM AUTHOR]

In this paper, a series of numerical experiments are carried out on the anti-scour device combined with perforated baffle and ring-wing plate. In addition, the optimal dimensions and location of the combined device are obtained: The perforated ratio of the baffle is S = 20%, the distance from the center of the bridge pier is L = 2d (d is the diameter of the bridge pier), and the ring-wing plate is located at H = 1/3h (h is the water depth). To verify the effect of the anti-scour device, the scour characteristics and flow field are further investigated. Compared with single pier and single ring-wing plate, the results revealed that the combined device with the optimal dimensions is of great anti-scour performance. Moreover, the maximum scour depth at the front and side of the pier reduced by 84.20% and 78.95%, which is better than the single ring-wing plate and other combined conditions in the orthogonal experiments. Due to the diversion of perforated baffle and ring-wing plate, the flow velocity at the pier side near the bed surface decreases by 30.7%, and the down-flow is almost eliminated on the vertical plane. Furthermore, the turbulent kinetic energy at different horizontal and vertical planes is reduced due to the reduction in horseshoe vortex and wake flow. Based on the investigation presented herein, the combined device is a promising tool for mitigating scour around the bridge pier. [ABSTRACT FROM AUTHOR]

To prevent demolishing bridge piles due to developing the scour hole under the foundation of these piles some solution has been proposed in the literature. One of the important approaches could be installing different geometric of roughness at the downstream and upstream piles sections. This causes the downward flows which are performing the main role in developing scour holes to be marginally decreased. The present study explores the effect of geometric roughness and also, continuity and un-continuity of roughness length on maximum scour holes around bridge pile. Results indicate that due to increasing the length of roughness the developed scour holes were formed by less scour hole depths. Furthermore, continuity of roughness increases the scour hole depths; however, un-continuity causes the height of scour holes to be developed by fewer values. Also, the comparison shows that the length of installed roughness in maximum value is decreasing the scour hole depth constitute 34 percent. Based on the non-linear regression technique an equation has been proposed to predict the maximum scour hole due to different conditions. Comparison between experimental and proposed values shows that the accuracy of the proposed equation has an acceptable error which has been calculated less than 11 percent.

The complex flow structure around bridge piers is challenging for both experimental and numerical studies. Therefore, investigating the capabilities of Computational Fluid Dynamics (CFD) tools in resolving the flow structure and the mechanism of sediment entrainment into and out of the scour hole remains a challenging task. In this study, the scour depth around an oblong bridge pier and the bed shear stress distributions in time and space were numerically investigated using the Computational Fluid Dynamics (CFD) tool Sediment Simulation In Intakes with Multiblock option (SSIIM). Clear water scour conditions and sand of known granulometric composition were considered in accordance with the experimental study carried out. Laboratory data and the results of a scour characterization around a 0.11 m wide oblong bridge pier were considered to calibrate and validate the numerical model. The averaged form of the Navier–Stokes equations was considered to simulate the turbulent flow fields in anticipation of long time scales. The results show that calibrated numerical models can reproduce measured scour depths in the laboratory environment with considerable accuracy, with an average relative error of less than 3%, especially around oblong bridge piers.

The sky-jump spillway is an economical solution to return water to rivers, but an unsuitable flip bucket design might jeopardize the spillway, the dam, or other appurtenant works. Characterizing in advance, during the design phase, the position, size, and shape of the erosion basin would be useful to ensure that water flow is returned to the river in a safe way. Also, it would be useful for the safety assessment throughout the exploitation phase when erosion has not yet reached its maximum extension. Here, based on experimental laboratory work, the location, size, and shape of the erosion basin are analyzed, and a procedure is given for its characterization according to the design of the sky-jump spillway.

The interaction between the evolution of an ice jam and the local scour at bridge piers becomes much more complicated due to the evolution of both the channel bed and ice jam. Thus, research work regarding this topic has been hardly conducted. In the present study, experiments under different flow conditions with three different pier shapes were carried out. Through laboratory experiments, the development of scour holes around bridge piers under open flow, ice-covered, and ice-jammed flow conditions was compared. The results show that under the same hydraulic condition and with the same ice discharge rate (Qi/Q), the development of an initial ice jam with a local scour around bridge piers along the entire flume takes a relatively short time. However, it takes a longer time for an ice jam to achieve an equilibrium state. With the presence of a local scour at bridge piers, after an ice jam reaches an equilibrium state, the ice jam thickness, water level, and water depth for flow are relatively larger compared to that without a local scour at the pier. The equilibrium ice jam thickness around the pier is negatively correlated with the initial flow Froude number. When the development of an initial ice jam is dominated by a mechanical thickening process, the rate of the development of a scour hole around a pier is faster. On the other hand, when the development of an initial ice jam is dominated by a hydraulic thickening process, the development of a scour hole around a pier can be treated as a scour process under an ice-covered flow condition. An equation was developed to determine the scour depth around a pier under an ice-jammed flow condition by considering related factors such as the flow Froude number, ice jam thickness, and ice discharge rate. The results of this research can provide a reference for bridge design and safety protection, as well as the interaction mechanism of local scour and ice jam evolution. [ABSTRACT FROM AUTHOR]

The main goal of this study was comparing the performance of an open-source code OpenFOAM and a commercial software Ansys Fluent in simulating the turbulent flow through a scour hole developed in a sand bed channel, which helps to give a hint in choosing the appropriate calculating tool. Both models were set with the same mesh and as similar as possible numerical settings, with RANS turbulence modeling, applying the k-ωSST model, in transient simulations. The results of flow pattern, velocity, and turbulence properties were collected and compared with laboratory experimental data. The analyzed results showed that, although both of the two models cannot perfectly reproduce the values from a laboratory experiment, they can quite well capture the flow in scour hole near the wall, with a bit higher performance coming from the OpenFOAM model application. [ABSTRACT FROM AUTHOR]

Scouring holes under the oil, gas, and water pipelines threaten their stability by bending and demolishing. This phenomenon can cause damage to the environment and the oil and gas industry. The present study investigated the effect of the pipe diameter, the height of support, and the angle of the pipeline with flow direction by applying the experimental aspects to the cohesive sediments. The experiments were carried out by considering three angles of deviation as zero,15, and 30 degree based on the flow direction. Three opening gaps were considered through the experiments based on the pipe height as 0, D/2, and D/4 from the sand bed. Furthermore, three pipe diameters were employed to investigate the effect of diameter size. The results indicated that by increasing the angle of deviation, the height of scour hole decreased significantly, however, the raising the opening gap between pipe and bed increased the sediment deposition and it causes the height of scour hole is decreased consequently which was constituted approximately 18 percent. Moreover, the pipe diameter affects the scour hole formation and its effect on a downward jet and horseshoe vortexes and the result indicate by increasing the piper diameter the scour hole is increased based on its effect on the flow configuration. Finally, based on the experimental data, an equation was estimated to predict the scour depth by employing the non-linear regression technique. [ABSTRACT FROM AUTHOR]

Submarine pipeline is one of the most popular research filed that many researchers focus on solving the issue of buckling of pipeline. The snaked laying is an effective method to control the lateral buckling. The scour below offshore pipeline may affect the efficiency and performance of the snake lay pipeline. The objective of this study was to investigate the effect of scour hole on the buckling of seawater pipelines. A three-dimensional numerical model developed to investigate the effect of scour below offshore pipeline subjected to wave and current by using Abaqus software and Aqua Module. The results indicated that vertical deformation of straight pipeline increased by increasing scour hole depth. This value changed 4.85 cm to 32.87 for holes 11 to 200 cm respectively, but these parameters of the snake lay pipelines were not affected by the presence of scour hole. Moreover, the effective axial force of snacked lay pipelines reduced 5 times in comparison to straight pipeline by applying wave and current. The results indicated that the value of stress of snaked-lay pipeline was independent on scour hole depth. Therefore, this pipeline was effective method to limit and control buckling even in the presence of scour below it. [ABSTRACT FROM AUTHOR]

Accurate prediction of the scour hole depth and dimensions downstream of ski-jump spillways has been an important issue among hydraulic researchers for decades. In recent years, computing methods such as Artificial Neural Networks (ANNs), Adaptive Neuro-Fuzzy Inference Systems (ANFISs) and Support Vector Regression (SVR) have shown a powerful performance in the prediction of scour characteristics owing to their flexibility and learning nature. In the present paper, a new hybrid approach has been proposed for the first time in order to improve the estimation power of the SVR tool for scour hole geometry prediction below ski-jump spillways. The principal characteristics of the scour hole pattern in the equilibrium phase have been predicted using SVR optimized with Fruitfly Optimization Algorithms (FOAs). The hybrid model is compared with the corresponding simple SVR model. To evaluate the proposed hybrid model further, it is also compared with other machine learning and empirical methods, such as ANNs, ANFISs and regression equations. The results show that the proposed SVR-FOA method performs well, improves remarkably on Support Vector Machines (SVMs) results, estimates scour hole geometrical parameters more accurately than the simple SVR model, and can be applied as an alternative reliable scheme for estimations on which simple SVR and other methods demonstrate shortcomings. The proposed hybrid method improves the precision level for scour depth prediction by about 8% compared with simple SVM in terms of the correlation coefficient.

This study focuses on scour depth development around 45° wing‐wall setback abutments in a compound channel. The results show that the scour development curves almost have similar shape and they can be described using exponential function. It is generally observed that the scour hole achieved 80% of the equilibrium scour depth at a scour time equals to 25% of the equilibrium scour time. Additionally, an increase in the relative abutment length and the contraction ratio causes an increase in the equilibrium time. However, this time decrease with increasing flow depth ratio. Finally, new empirical equations are proposed to predict the development of scour depth and the time to reach the equilibrium state. These equations will be useful to predict these characteristics of scour hole especially for setback abutments in compound channel and predict the temporal development scour depth for previous studies that have available data related to maximum scour depth. [ABSTRACT FROM AUTHOR]

Understanding hydro‐morphological characteristics in mountain river confluences is significant in flood disaster mitigation and mountain river restoration, which is still poorly explored. This study employed a 2D hydro‐morphological model based on the finite element method to simulate the major bed morphological features in a mountainous‐type flume confluence and evaluate the effects of main controlling factors on these features. The modelling results show that the dominant bed morphological features in mountain river confluences can be well produced by the 2D model. Five controlling factors including downstream water level (H), branch discharge ratio (Qr), main channel sediment supply ratio (ψ), tributary slope (St) and confluence angle (α) reflecting different flow‐sediment‐geometry scenarios were adopted into a sensitive study. The upstream reach of the main channel is controlled by H and ψ and their decreases lead to bed degradation. The increase in Qr, St, and α mainly results in bed aggradation and steepening in the tributary, attaining a higher sediment transport rate. This contrasts the existing experimental results, due to the difference in sediment feeding. The size of the bank‐attached bar is promoted by the increase in Qr, St, and α and the decrease in H and ψ. A quantitative analysis shows that the water surface slope well correlates with various dimensions of the scour hole and bar morphology (correlation = 0.58–0.8). Meanwhile, the bank‐attached bar displays a strong self‐similarity (correlation = 0.84–0.98) regarding its geometric dimensions. This study provides new insights into the existing knowledge of the hydro‐sediment‐morphodynamics of mountain river confluences obtained from laboratory studies and field investigations. [ABSTRACT FROM AUTHOR]

An artificial chute cutoff was implemented to eliminate the danger caused by the lateral migration of meandering river in the upper Yellow River in 2018. However, the earlier studies on chute cutoff have not provided a clear understanding of the hydrodynamic and morphodynamic characteristics of this artificial chute cutoff. In this study, three field measurements have been conducted to reveal the channel morphology and flow structure of the artificial chute channel. The results show that, compared with the natural chute cutoff, a 20-m-deep scour hole and a 2.26-km-long scour belt formed in the diversion channel are the significant features of this artificial cutoff. Further, a dual counter-rotating helical cell separated by a distinct shear layer is observed at the scour hole. Therefore, the formation of scour hole is likely related to the helical cells. However, flow stagnation was not observed in the chute channel, but the flow recirculation and separation zones were observed. Among them, the flow separation zone observed on the right bank of the diversion channel promoted the formation of bar. The observed counterclockwise single helical cells aggravated the erosion of the left bank. These findings provide useful insights on the artificial chute cutoff with complex flow structure and channel morphology characteristics, which can be used to improve the conceptual models of chute cutoff. [ABSTRACT FROM AUTHOR]

Accurate prediction of the scour hole depth and dimensions downstream of ski-jump spillways has been an important issue among hydraulic researchers for decades. In recent years, computing methods such as Artificial Neural Networks (ANNs), Adaptive Neuro-Fuzzy Inference Systems (ANFISs) and Support Vector Regression (SVR) have shown a powerful performance in the prediction of scour characteristics owing to their flexibility and learning nature. In the present paper, a new hybrid approach has been proposed for the first time in order to improve the estimation power of the SVR tool for scour hole geometry prediction below ski-jump spillways. The principal characteristics of the scour hole pattern in the equilibrium phase have been predicted using SVR optimized with Fruitfly Optimization Algorithms (FOAs). The hybrid model is compared with the corresponding simple SVR model. To evaluate the proposed hybrid model further, it is also compared with other machine learning and empirical methods, such as ANNs, ANFISs and regression equations. The results show that the proposed SVR-FOA method performs well, improves remarkably on Support Vector Machines (SVMs) results, estimates scour hole geometrical parameters more accurately than the simple SVR model, and can be applied as an alternative reliable scheme for estimations on which simple SVR and other methods demonstrate shortcomings. The proposed hybrid method improves the precision level for scour depth prediction by about 8% compared with simple SVM in terms of the correlation coefficient. [ABSTRACT FROM AUTHOR]

Artificial chute cutoff can fundamentally eliminate the threat of flood caused by the meandering river, but it significantly changes its morphodynamic characteristics. Channel adjustments after cutoff are rapid, which makes it difficult to study the interaction between river morphology and flow structure only through field measurement. However, numerical simulations can provide insights into the hydrodynamic characteristics after artificial chute cutoffs. In this study, both field measurement and numerical simulation are employed to investigate the flow structure and bed morphology caused by an artificial chute cutoff in Sipaikou area of the Upper Yellow River in 2018. The measured hydrological data provide boundary conditions and initial values for the numerical model. The field measurement results reveal that the concave bank of the study area is severely scoured up to 270 m after the artificial cutoff, and a 20 m deep scour hole and a 2.26 km long pool are formed at the entrance and near the left bank of the chute channel. The numerical simulation results of velocity at typical cross-sections are in good agreement with the measurement results. Flow separation and stagnation zones are observed near the right bank during the low flow conditions (discharge of at least 902 m3/s), but this phenomenon is not seen during larger flow conditions (discharge exceeds 2000 m3/s). Interestingly, flow recirculation zones are also found near the left and right banks of the scour hole. Further, a long flux belt is formed at the scour hole and the pool. Consequently, the impact of the bed topography on the hydrodynamic characteristics is relatively prominent when the discharge is small, while the impact on the river banks and river bed is more noticeable when the water discharge is large. In addition, high shear stress is observed near the left bank at the downstream of the studied area, which indicates that the left bank at the downstream is still being scoured. These results suggest that bank protection measures along the left bank are required to maintain the effectiveness of the artificial chute cutoff. [ABSTRACT FROM AUTHOR]

Estimation of scour dimensions below submarine pipelines is a vital step in designing offshore infrastructure. Extreme events like tsunami waves produce strong erosive forces below the underwater pipes, apt to create scour holes, jeopardizing the safety of the structure. Despite the importance of this issue, previous studies have mainly focused on steady flow cases, and the scour pattern below submarine pipes induced by high-amplitude transient waves has rarely been investigated. This paper reports the results of 40 experimental runs on transient wave-induced scour below a model pipe in a laboratory flume under a variety of initial conditions. The variables included the bed particle size and gradation, initial water depth, wave height, and slope of the bed layer. Waves were generated by a sudden release of water from a sluice gate, installed in the middle of the flume. A pressure transducer data acquisition system was used to record the wave heights at different time steps. The results indicate that, with a shallower initial depth of flow, the scour depth is relatively large. It was also found that there exists a direct correlation between the induced wave height and the size of the scour hole. It was observed that, in clear water conditions, the size of the scour hole in coarse sediments is smaller, while in live-bed conditions, larger scour holes are created in coarser sediments. It was also observed that at high wave amplitudes, the live-bed conditions are dominant, and consequently the bed elevation is altered.

In this paper, a series of numerical experiments are carried out on the anti-scour device combined with perforated baffle and ring-wing plate. In addition, the optimal dimensions and location of the combined device are obtained: The perforated ratio of the baffle is S = 20%, the distance from the center of the bridge pier is L = 2d (d is the diameter of the bridge pier), and the ring-wing plate is located at H = 1/3h (h is the water depth). To verify the effect of the anti-scour device, the scour characteristics and flow field are further investigated. Compared with single pier and single ring-wing plate, the results revealed that the combined device with the optimal dimensions is of great anti-scour performance. Moreover, the maximum scour depth at the front and side of the pier reduced by 84.20% and 78.95%, which is better than the single ring-wing plate and other combined conditions in the orthogonal experiments. Due to the diversion of perforated baffle and ring-wing plate, the flow velocity at the pier side near the bed surface decreases by 30.7%, and the down-flow is almost eliminated on the vertical plane. Furthermore, the turbulent kinetic energy at different horizontal and vertical planes is reduced due to the reduction in horseshoe vortex and wake flow. Based on the investigation presented herein, the combined device is a promising tool for mitigating scour around the bridge pier.

To prevent demolishing bridge piles due to developing the scour hole under the foundation of these piles some solution has been proposed in the literature. One of the important approaches could be installing different geometric of roughness at the downstream and upstream piles sections. This causes the downward flows which are performing the main role in developing scour holes to be marginally decreased. The present study explores the effect of geometric roughness and also, continuity and un-continuity of roughness length on maximum scour holes around bridge pile. Results indicate that due to increasing the length of roughness the developed scour holes were formed by less scour hole depths. Furthermore, continuity of roughness increases the scour hole depths; however, un-continuity causes the height of scour holes to be developed by fewer values. Also, the comparison shows that the length of installed roughness in maximum value is decreasing the scour hole depth constitute 34 percent. Based on the non-linear regression technique an equation has been proposed to predict the maximum scour hole due to different conditions. Comparison between experimental and proposed values shows that the accuracy of the proposed equation has an acceptable error which has been calculated less than 11 percent. [ABSTRACT FROM AUTHOR]

Coastal engineers are deeply concerned about wave-induced seabed instability around monopile foundations. Most prior studies have primarily focused on the seabed response around monopiles on flat seabeds, often neglecting the presence of scour holes commonly found in engineering practice. This study thoroughly investigates seabed response and liquefaction around monopiles of scour holes. The examination involves analyzing 3D flow velocities, dynamic wave loads, pore pressures, soil effective stresses, and wave forces around a monopile with a scoured profile. The analysis uses a model that integrates the interactions between waves, seabed, and structures, and it is implemented within the OpenFOAM framework. The study meticulously assesses the impact of scour holes on seabed responses and liquefaction zones around monopile foundations. Numerical results reveal that: (1) The magnitude of the pore pressure within the scoured seabed is reduced relative to a flat seabed; (2) Considering the scour hole effect leads to a more uniform distribution of liquefaction depth around the monopile; (3) This effect intensifies with a higher saturation degree, while it exhibits a pattern of increase, followed by a decrease with an increase in permeability. • An integrated model for wave–monopile–scour seabed is developed on OpenFOAM. • Results of wave forces, pile responses, pore pressure, and liquefaction are analyzed. • The effects of the scour hole on the soil response and liquefaction are investigated. [ABSTRACT FROM AUTHOR]

The aim of the present study is to numerically investigate the scouring phenomenon downstream of a stilling basin for a wide range of Froude number and size of bed material. The numerical model was first verified. The results obtained from the numerical model concerning the maximum depth and profiles of the scoured hole were in agreement with the long-term experimental data. Thereupon, the verified numerical model was employed to simulate the profile of the scour hole for various Froude numbers and bed material sizes downstream of the stilling basin. According to the results of the numerical model as well as experimental data, it was revealed that by using dimensionless scour depth, the upstream profile of the scour hole is independent of time and size of the material. Results show that the bottom of the scour hole in the oscillating jump is of greater length than the steady jump. Moreover, both the numerical and available experimental data were used to propose a relationship for calculation of long-term maximum scour depth in a wide range of affecting parameters. Article highlights: Scour hole depth and geometry downstream of a stilling basin were studied with a verified numerical model. Numerical simulations were made in a wide range of Froude number and bed material size which were not available in the literature. Using available experimental data and numerical model results, an equation was developed for estimating the scour depth. [ABSTRACT FROM AUTHOR]

The interaction between the evolution of an ice jam and the local scour at bridge piers becomes much more complicated due to the evolution of both the channel bed and ice jam. Thus, research work regarding this topic has been hardly conducted. In the present study, experiments under different flow conditions with three different pier shapes were carried out. Through laboratory experiments, the development of scour holes around bridge piers under open flow, ice-covered, and ice-jammed flow conditions was compared. The results show that under the same hydraulic condition and with the same ice discharge rate (Qi/Q), the development of an initial ice jam with a local scour around bridge piers along the entire flume takes a relatively short time. However, it takes a longer time for an ice jam to achieve an equilibrium state. With the presence of a local scour at bridge piers, after an ice jam reaches an equilibrium state, the ice jam thickness, water level, and water depth for flow are relatively larger compared to that without a local scour at the pier. The equilibrium ice jam thickness around the pier is negatively correlated with the initial flow Froude number. When the development of an initial ice jam is dominated by a mechanical thickening process, the rate of the development of a scour hole around a pier is faster. On the other hand, when the development of an initial ice jam is dominated by a hydraulic thickening process, the development of a scour hole around a pier can be treated as a scour process under an ice-covered flow condition. An equation was developed to determine the scour depth around a pier under an ice-jammed flow condition by considering related factors such as the flow Froude number, ice jam thickness, and ice discharge rate. The results of this research can provide a reference for bridge design and safety protection, as well as the interaction mechanism of local scour and ice jam evolution.