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Examining scouring around bridge piers is crucial for ensuring water-related infrastructure's long-term safety and stability. Accurate forecasting models are essential for addressing scour, especially in complex water systems where traditional methods fall short. This study investigates the application of the HEC-RAS 2D sedimentation model, which has recently become available for detailed sediment analysis, to evaluate its effectiveness in predicting scoring around various pier shapes and under different water conditions. This study offers a comprehensive assessment of the model's predictive capabilities by focusing on variables such as water velocity, shear stress, and riverbed changes. Particular attention was paid to the influence of factors like floating debris and different pier geometries on scour predictions. The results demonstrate that while the HEC-RAS 2D model generally provides accurate predictions for simpler pier shapes—achieving up to 85% precision—it shows varied performance for more complex designs and debris-influenced scenarios. Specifically, the model overpredicted scouring depths by approximately 20% for diamond-shaped piers and underpredicted by 15% for square piers in debris conditions. Elliptical piers, in contrast, experienced significantly less erosion, with scour depths up to 30% shallower compared to other shapes. This study highlights the novel application of the HEC-RAS 2D model in this context and underscores its strengths and limitations. Identified issues include difficulties in modeling water flow and debris-induced bottlenecks. This research points to the improved calibration of sediment movement parameters and the development of advanced computational techniques to enhance scour prediction accuracy in complex environments. This work contributes valuable insights for future research and practical applications in civil engineering, especially where traditional scour mitigation methods, such as apron coverings, are not feasible. [ABSTRACT FROM AUTHOR]

Scouring is one of the most important factors in the destruction of bridge piers. One of the ways to reduce scouring depth is to use a slot in the bridge pier. In this research, the Flow 3D model was used to simulate the effect of a slot with the same dimensions in two positions parallel to the bed and close to the water surface. The tests were performed at two relative speeds of 0.87 and 0.92. Uniform and non-cohesive bed sediments with a geometric standard deviation of 1.4 and an average diameter of 1 mm were used. The results showed that the slot created in the pier of the bridge weakens the eddies around the pier and is effective in reducing scour depth. The slot close to the surface, on average, about 6%, and the slot parallel to the bed, about 26%, are effective in reducing the maximum scour depth compared to the control pier. Also, with the increase of Froud number from 0.376 to 0.380, scour depth has increased by 11% on average.

Due to scouring problems in impermeable spur dikes, which compromise structural strength and stability and as a result repair and maintenance costs increase, an alternative method of scouring is needed to protect the river bank. In this area, bandal-like structure can be used. This structure is a combination of an impermeable spur dike and a permeable spur dike. The upper part is impermeable causes the upper half of the flow run towards the center and the inner wall and the lower part is permeable enabling the lower half of the stream passes through it (Rahman et al., 2003a, b). The lower part causes the flow to slow down and reduces speed, and because the flow near the bed has a higher concentration, it leads to settling sediments in the downstream of the river near the coast. On the other hand, because of the flow through the lower half, the power of downstream flows are reduced compared to the impermeable spur dike and the horseshoe vortices are vanished. Therefore, the scouring rate in the bandal-like structure is less than the impermeable spur dike (Zhang et al., 2010; Teraguchi et al., 2011b)Regarding that the scouring rate, the bandal-like structure is less than an impermeable spur dike therefore, its use has been suggested by some researchers. Since the sedimentation rate behind the bandal-like structure is less than the impermeable spur dike, in the present study, a new structure called the wedge bandal-like is proposed to enhance the sedimentation of the bandal-like. Wedge bandal-like structure is constructed of a bandal-like structure and a repellent impermeable triangular spur dike. The purpose of using this structure is to use both the advantages of the bandal-like structure as well as the benefits of repellent impermeable triangular spur dike, for deviation of flow and sediment transport to the back of the structure and sedimentation. Both structures cause the secondary flow of the surface to move towards the outer arc before moving to the outer shore down the bottom and practically shore the coastal tail into middle areas.

In this study, variations in water surface profile and bed topography along a meandering path were examined under different experiment durations. Although several studies have been conducted on sediment and scour in open channels, addressing temporal variations in meandering channels requires independent, merely experimental research. In this regard, a meandering laboratory flume consisting of two consecutive 180-degree bends was used in this study. The test was conducted under clear water conditions and in 6 different durations equal to 0.2, 0.4, 0.5, 0.6, 0.8, and 1 times the equilibrium time (240 minutes). Results indicated that at the downstream bend, lengthening the test time from 0.2 to 0.4, 0.5, 0.6, 0.8, and 1 times the equilibrium time added to the maximum scour by 70, 100, 115, 120, and 165%, and also increased the maximum sedimentation by 30, 25, 45, 45, and 45%, respectively. Moreover, with a comparison made between the average transversal water surface profile for 0, 120, and 240-minute duration tests, it was observed that when these transversal profiles were displaced from 45 degrees to 90, 135, and 180 degrees, the water surface at the inner bank was lowered by 2, 5, and 7% and that at the outer bank decreased by 2, 6, and 12%, respectively.

Barges offer a safe and cost-effective means for transporting commodities in inland waterway systems. This, however, comes with the risk of barge collision into bridge piers that span navigable waterways. While the vulnerability of such bridges has been investigated in an intact condition under vessel collision, the existing assessment methods fail to capture how scour events that bridge piers often experience during their service life can affect their response to vessel-induced impact loads. To address this gap, three bridge structures were modeled in this study, and a fully loaded barge traveling at 0.5, 1.0, 1.5, 2.0, and 2.5 m/s was allowed to collide into each of them after they underwent various scour scenarios. The scour scenarios under consideration were developed, following the procedure provided in Hydraulic Engineering Circular No. 18, for both 100- and 500-year floods. Based on the obtained results, the impact force, maximum shear, and maximum bending moment that the bridge piers experienced were found to decrease as the scour depth increased, mainly because the bridge piers gained flexibility. On the other hand, the maximum force that the bridge ends witnessed were determined to increase, indicating that the bridge structure can become vulnerable to failure at locations other than bridge piers as the scour depth increases. With an in-depth understanding of the magnitudes and trends of key structural response measures, the outcome of this study provided a rigorous multihazard perspective to improve the safety and performance of bridges built on navigable waterways. [ABSTRACT FROM AUTHOR]

This study examines the relations of structures and shapes of streambed evolution after dam break floods. A flume was used to simulate dam-break floods with variations of initial upstream water levels and variance, from uniform to graded, of the bed sediments. Detailed measurements of the evolution and composition were made during these experiments. The data indicate that intense scour occurred immediately downstream of the “dam break” in both uniform and graded sediments. The resulting bed surfaces of graded sediments showed coarse-fine-coarse structures in the areas with the lowest scour and highest deposition and various type of cluster (i.e. line and heap). This pattern was not observed in beds of uniform sediment. The scour hole changes from circular to oval-shaped in both uniform and graded sediments with increasing bed slopes. Keywords: Dam break, Experimental, Bed-surface composition, Graded and uniform sediment, Scour.

Destruction of bridges caused by scour and other natural phenomenon brings about financial and life losses. Hence, researchers have been studied extensively the scour mechanism and methods of scour countermeasure. Usually scour at bridge occurs both around piers and abutments. Melville (1992)'s study showed that 70 percent of the failure of bridges in New Zealand was due to the abutment scour. Studies conducted on the failure of 383 bridges in the United States showed that in 25% of them the pier scour, and in 72% of them the damage was due to abutment scour (Kayatrak, 2005). The main cause of the abutment scour is due to complex flow vortices which developed around the abutment. Therefore, during the past decades many measures have been developed to protect the bed material against erosion. These techniques can be categorized in two types of covering methods and flow altering techniques. Design guidelines for some of these mitigation techniques can be found in Melville and Coleman (2000). For existing bridges the common practice is to use armoring materials around bridge abutment. Riprap, gabions, rectangular concrete blocks and tetrahedron frames concrete elements are the most effective material for covering and stabilizing the bed around the bridge abutments. In rivers with high flood discharge, the covering material are subject to high flow velocities and therefore large size of rocks have to be used. When the site construction is far away from mountain area or large sizes of the rocks are not available or too costly to transport, other material should be applied. In the present study, a new concrete element-six –legs concrete (SLC)- beside using of smaller size of rocks have been studied to find out the best combination for protecting bridge abutments against scour.

Hydraulic structures that change the flow pattern around themselves may cause local scouring, since changing the flow characteristics (velocities or turbulence) can lead to changes in sediment transport capacity. The difference in height between the upstream and downstream bed levels of the river-intersecting structures will form a vertical waterfall in the tail-water that plays an important role in grade-control structures. An example of these structures is the Balaroud inverted siphon structure in Dez irrigation and drainage network in the south of Andimeshk county, Khuzestan province, Iran. Various experimental studies on downstream scour of hydraulic structures are available in the literature. The main objectives of this study were to investigate the scour process, estimating the maximum depth and location of the scour hole, and evaluating the maximum height and location of the sedimentary mound at the downstream of the grade-control structure. In this study, the experimental data obtained by the previous researchers was used, and the equations were reviewed and re-written using the D’Agostino and Ferro (2004) studies in order to improve the accuracy of the existing relationships. In the next step, the hydroinformatic science and the soft computing technique were used to achieve more accuracy for the relationships of the hole’s characteristic and the sedimentary mound in alluvial ducts containing non-cohesive sediments.

Chancy-Pougny is a run-of-river dam on the Swiss–French border constructed in the early 1920s. Since its commissioning, the operation of the four spillway gates has been responsible for a progressive erosion of the stilling basin. The future scour potential of the unlined stilling basin of the Chancy-Pougny dam was assessed by hybrid modeling, combining both a physical and a numerical model. The physical model investigated the flow structure in the basin as well as the dynamic pressure fluctuations exerted by the flow on the rocky bottom of the stilling basin. The presence of a large gyre, generated by a flow recirculation in the nonsymmetrical basin, was found to be one of the main causes of significant scour formation. The numerical model used the pressure recordings to reconstitute the observed scour since 1924, predicting significant additional long-term erosion in the stilling basin. As such, a series of scour mitigation measures, including a free-standing wall and various configurations of concrete prisms for scour protection, were tested on both models. A tailor-made solution containing a layer of randomly distributed concrete prisms laid on the basin's current bottom was identified through this study, proving the importance of both numerical and physical approaches in hydraulic engineering. [ABSTRACT FROM AUTHOR]

Protection of water pipelines - wastewater or fuel materials - on the bed of erosion of the sea and rivers against such factors as bending, slipping and even fracture are important and costly issues in ocean engineering. In order to protect the potential destruction and fracture of these pipelines due to hydrodynamic forces of flow-waves or human activities. It is necessary to be covered with a concrete-coat or buried at an appropriate depth of bed with trenching.Objective observations showed that the pipelines that are located on the erosion bed of the sea and the rivers have the potential to produce a natural burial (self-burial pipe) in a bed of sediment, due to localized scouring.But in natural conditions, the burial process takes place with little speed. Therefore, by installing the spoiler on the pipelines, it is attempting to increase the Perpendicular cross-section of the flow (making changes in the pattern of flow around the pipeline) and, finally, the occurrence of erosion and self-burial inlower environmental velocities, but more intense. Therefore, it is necessary to first investigate the factors affecting for erosion sediment bed and estimate the dimensions of scour hole under pipelines, to study the accelerating factors and its effects on ocean engineering. Themost of researchers considered the local scouring around the pipelines relatede to be rapid, the depth of the flow, the pipe diameter and the particle size of the bed. Moncada-M and Aguirre-Pe (1999) describe that, the scour depth below the pipeline as a function of the flow loss number and the dimensionless distance between the pipe and the intact bed. Cheng and Chew (2003) and Zhao and Wang (2009), by simulating the flow area around the pipeline with the mounted fin on it, found that the lifting force and shear stress in the bed and the scour depth increased with the fin. (2012), by using laboratory results, showed that the flow loss number and the height of the fin had a significant effect on the depth of scouring under the horizontal pipelines. Shan et al. (2015) with numerical evaluation of self-burial of tube with the fin mounted on it, and in displacement mode, with Fluent software, found that increasing the flow loss number in near of the bed would help to increase the burial speed of the tube. recently studies showed that the mounting of the fins on the pipeline lead to increasing the amount of erosion around the tube. The application of mounted Piggyback line with cross sectional and different angles on the main pipelines can be a major difference with previous research.

Water passage from steep slopes in river engineering issues and the design of water transfer structures is inevitable. Because of the steep slope of the surface, the surface velocity and surface erosion rates are high. Energy control in high-speed flows is one of the challenges of designing hydraulic structures. These flows, for example, occur in places such as dam overhead structures, drainage systems of urban areas and Mountain Rivers with a steep slope. One of the ways to reduce dimensions or eliminate energy depreciating structures is to use methods to reduce the kinetic energy of flow over the weir, including using of stairs or blocks on the overflow. The use of large-sized stairs or blocks will cause the passing jets of flow to be separated and as a result turbulent, which can effectively deplete the kinetic energy of the current. The problem with using a staircase or block is a huge cost of built and a high risk of cavitation. Another method of energy depreciation is to apply roughness at the overflow bed, which may be an efficient way to reduce energy. Roughness can dramatically reduce the flow turbulence, and thus reduces the risk of cavitation. Also, roughness can reduce the flow power over the overflow and reduce the depth of the lower erosion pit by removing or reducing the dimensions of the relaxation basin. Most studies in this field have investigated the effect of these roughs on the amount of energy depletion, which in addition to energy depletion is also important for lowering the erosion of the structure. However, for the economic design of hydraulic structures, designers need to have full knowledge of the particle mechanics and the dimensions of the scour hole, so that they can consider the requirements for the stability of the structure, which has so far been investigated insufficiently. Therefore, the present study aimed to investigate the effect of roughness density on sloped bed surface on its downstream scour depth.

draining the flood of enormous dams and transmitting the procedure to the downstream is one of the important issues regarding hydraulic structures. Plunge pools are the main structures to dissipate the high rate of energy. The amount of energy at an outlet jet depends on various parameters such as the dropping height, the thickness of the jet, and other environmental conditions. Local erosion in plunge pools with alluvial beds is a complex phenomenon and determining the geometric features of the scour hole is really difficult. The outlet flow mixes with the turbulence factor and hits the bed of the plunge pools with a semi-perpendicular condition. Therefore, the present study was conducted to determine the scour which was caused by inlet air along the middle water jet on the bottom of the plunge pools. Xu et al. (2004) tested the aeration effects on the scouring caused by the falling jet and obtained a small relationship between the percentage of air jet density and the relative scour depth. The results informed that aeration affects the shape of the scour hole and essentially reduces the scour depth. Manso et al. (2004) investigated the interaction of the geometric shape of the submerged pond with rocky bedding on the rate of diffusion of the falling jet. They tested various diameters of jets,5.5, 11 and 16.5 times the diameter of falling jet, on the smooth and rough beds to investigate the dynamic pressures with frequencies between 1 to 2 KHZ. Their findings showed that the geometric shape of the pond has a direct impact on the jet diffusion rate. Duarte et al. (2015) studied the effects of air inlet to jet on the dynamical pressure on the floor of the submerged pond. They increased the jet's velocity to 22 m/s. The final results showed that the air inlet to the jet led to a decline in the total pressure on the floor of the pond.

Providing safe conditions for water pipelines or other fluids on erodible beds is an important issue in the field of hydraulic engineering. Studies show that the installation of a plate called Spoiler on top of the pipeline increases the amount of the erosion around the pipe and its self burial stimulation. Most studies about spoiler have been done on a fixed pipe, but in reality, when the scouring hole underneath the pipe is deep enough, the pipe begins to lower as a result of the weight, at when the pipe reaches the bottom of the scour hole, the erosion process stops and then the pipe is covered with sand and buried. The self burial phenomenon has not been studied with the use of a spoiler in the case of actual displacement of the pipe, and due to the fact that the studied pipes have been fixed, the transitional and sedimentary phases have not been observed. Considering the role of pipe displacement in changing the scouring profile, the study of the spatial phenomenon of the pipe during displacement and observing the actual effect of the spoiler on the self burial performance and its effective parameters are necessary. In this study, this phenomenon has been studied experimentally.

The most common way to dissipate the water kinetic energy at the downstream of weirs , gates at chutes is to use the hydraulic jump. Hydraulic jump is a phenomenon that alters the flow regime of the state of supercritical to the subcritical with dissipating much of the flow kinetic energy and to prevent possible downstream scour of the structure. Development of the downstream scour hole of the hydraulic jump stilling basins can cause failure of the structure itself , which has been the interest of the researchers in the past. The extension of new roughened bed basin is essential to pursue and complete what previous researchers concluded for these basins.Safe and an economical design of hydraulic structures, an estimation of the maximum scour depth, and to minimization the scour dimensions is the interest of the researchers. Therefore, in this study the effect of placing the six-legged concrete elements under different lengths was investigated investigated. Covering the river bed downstream of the spillways and gates with these roughened and permeable elements can decrease the stilling basin length and expected less scour depth. These elements are tight together and placed on the bed. The covered length of the bed is equal to the length of jump on these elements. However, there is possibility in which few rows of the downstream elements are escaped because of the edge failure and therefore the roughened bed length is shortened. The main purpose of this study was to see how much exactly would be the magnitude of downstream scour depth if the covered length is decreased. .

Base-level fall in river beds occurs due to varying natural or unnatural causes. Base-level fall causes the change in the behavior of flow at the location of drop in base-level. In such situations, most of scour occur at the foot of the slope, and slope wall retreats in the upstream direction. This phenomenon widens the wall of the river bank, thus leading to its destruction. The amount of bed topography variations and scour around a rectangular bridge pier with an oblong nose located in the 90 degree angle of a 180 degree sharp bend was studied in this work by generating base-level fall at the beginning of the 180 degree sharp bend, and it was compared with a case without a base-level fall. The results indicated that in the case of base-level fall at the upstream side of the bridge pier, increase in flow depth, as well as reduction in velocity at the area around the pier, is observed, and the maximum depth of scour hole and the volume of scour hole around the pier respectively reduce by 73 and 97% in comparison with those in the case where no base-level fall occurs.

Local scouring in the downstream of hydraulic structures is one of the important issues in river and hydraulic engineering, which involves a lot of costs every year, so the prediction of the rate of scour is important in hydraulic design. Side weirs are the most important of hydraulic structures that are used in passing flow. This study investigate the scouring due to falling jet from side weir in downstream in side channel numerically. The simulation was done with finite volume method. The comparison of numerical and experimental results of flow fields shows agreement. Results show that from upstream to downstream of side weir located in side channel, scoring is increased and the dimensions of the scour hole in the downstream of the rectangular side weirs increase along it. In fact, at the downstream of the lower edge of side weirs in side channel, scouring has the greatest dimensions; in particular the depth.

Scouring downstream of grade control structure is a common problem. W-weir structures are recommended for controlling, reducing soil erosion, and development aquatic organisms habitat. W-weir structures can provide energy dissipation, increased aquatic habitat, grade-control, and bank and bed stabilization through the diversion of conveyance with the river-channel center. The current study aimed at analyzing the scour geometry downstream of W-weirs in the sinuous channels using heuristic gene expression programming (GEP) and support vector machine (SVM) models. A comparison was also made between the GEP and SVM with traditional multi variable linear regression (MLR) technique. The cross-validation technique (i.e. k-fold testing) was used to assess the developed models. Observations revealed that the scour typology affects the maximum scour depth value. The obtained results showed that both the GEP and SVM models give promising results in simulating the scour depth and scour length magnitudes. Assessing the models confirmed that using the k-fold testing cross validation is very necessary as all the available patterns can participate in training and testing stages, which reduces the risk of over fitting. [ABSTRACT FROM AUTHOR]

Abstract Monopile foundations are the most common foundation type of offshore wind turbines. In the ocean environment, in addition to threats related to scour of the foundation, offshore monopiles of wind turbines also are subjected to lateral vibrations induced by waves and winds. Over the past decades, the scour process induced by flow and pile-soil interactions has been independently investigated by researchers from the fields of hydraulic/coastal engineering and soil mechanics, respectively. Very few studies can be found in the published literature on lateral vibration effects on scour at monopile foundations. The objective of this experimental study is to improve understanding of the mechanics of current-induced scour at monopiles subjected to lateral vibrations with a non-cohesive bed. When compared to a non-vibrating monopile, the results show that scouring around its vibrating counterpart is comparatively faster during the first few hours of the test. This is primarily due to soil densification and the subsidence process induced by monopile-seabed interactions. Increasing both the frequency and amplitude of the monopile vibration would decrease the equilibrium scour depths and scour hole slopes. The reduction of equilibrium scour depth likely is due to the effect of sediment ratcheting motions on the surface of the scour hole. An empirical dimensionless equation is proposed to estimate equilibrium scour depth at monopiles subjected to lateral vibrations. Highlights • New experimental results of temporal evolution of scour depth and final scour geometry at vibrating monopiles. • New conceptual model of scour mechanism around monopile foundations subjected to lateral vibrations. • New relationship between scour reduction and vibration properties of a monopile. [ABSTRACT FROM AUTHOR]

Scouring at coastal structures is a serious issue that threatens structures. Previous research, focused on scour around vertical breakwaters, has shown that scour is mainly brought on by standing waves in front of structures. Scours caused by flow may be the dominating factor for breakwaters, which are composed of caisson breakwater suspended on piles. However, many breakwaters lose their stability and function due to scour. In the present study, a three-dimensional numerical model is developed to investigate modifying the caisson’s cross section for different four scenarios on controlling the scour progress around a semi-immersed caisson suspended on piles under wave action. Also, the consequence of reinforcing the piles by slotted with different heights was examined. The Reynolds-Averaged Navier – Stokes (RANS) equations, coupled with the Renormalization Group (RNG) turbulence model, are formulated to simulate the morphological performance surrounding the caisson breakwater. A numerical contour map was assessed for scour and deposition progress under the breakwater and around the piles. The simulation results are compared to the previous experimental data, showing a satisfactory level of agreement. A significant correlation was observed between the maximum relative hole length around the piles and the dimensionless wave number, particularly as the breakwater draft increased. Furthermore, for a large-spaced pile, the results demonstrated a high level of convergence between the numerical and experimental findings, with a low mean square error. The maximum scour depth decreased by 30% by increasing the base of the barrier by 0.50W as W is the breakwater width from both sides, compared to increasing the base of the barrier by 0.50W from only one side. The attempt to increase the overall width of the breakwater by 0.25W successfully moved scour away from the breakwater and the piles while maintaining its constant value. A minor effect is observed when increasing the caisson’s front wall for different heights in controlling the scour process. The impact of the pile system strengthening with different slotted heights led to changing the scour location from seaward to shoreward.

Pieve scour is one of the most important cause of bridge failure. Covering methods such as using riprap is among techniques which are widely applied for the existing bridges. For those places where the stones of adequate size are not available, use of six-legged elements which is the subject of this, study is a good choice. In this study the effect of placement of a single row six- legged around a rectangular bridge with 100% density in three different cases of above, mid and below the bed under five different Froude numbers of 0.24, 0.22, 0.19, 0.17 and 0.16 have been experimentally investigated. Comparison of the bed topography withmean measure of bed deposit of 0.7 mmof tests with six- legged and tests without elements showed that generally the elements can reduce the scour depth significantly. The elements placed on the mid of bed have shown better performance with maximum reduction of about 57%. The general recommendation is to use these elements with geo-syntactic filter or placed in more rows.

Two major factors causing of scour around bridge piers are the down flow occurred in upstream part of the piers and separation of streamlines from piers called horseshoe vortex. Installation of a collar on a pier will reduce the power of the down flow and horseshoe vortex. In this study, the effects of placement of collar and netted collars on scour depth of cubic pier are investigated. The experimental flume was rectangular with the length of 7.3 meters, width of 0.56 m and a depth of 0.6 m. For this propose four collars included, one simple and three netted (with opening parts equal to 15percent, 30percent and 40percent), are tested under clear water condition. The experiments were performed in laboratory flume on Hydraulics Laboratory of Shahid Chamran University. The collars were installed in three levels equal to 0.5B, 0.25B and on the bed. The results were compared with the pier without the collar, and showed that the netted collar reduce the maximum scour depth between 34percent to 97percent in comparison with the case of no collar used. Also in low Froude Numbers, the netted collars showed better protection in comparison with the simple one.

One of the most effective techniques for removing the deposited sediments from reservoirs is pressure flushing which has only much local effects. It is often applied as a clearing process to remove sediment saround the entrance of intakes.In order to make rational design of bottom outlets and other sediment flushing structures, the understanding of the characteristics of a scour funnel in under pressure flushing is significant. The physical model was constructed in the Hydraulic Laboratory at the Water Sciences Engineerin Faculty of Shahid Chamran University of Ahvaz and by performing various experiments on the effect of bottom outlet shape on the volume and dimensions of flushing cone was experimentally investigated. For this purposes, the experiments on 4 bottom outlets with a circular, semicircular, rectangular and square cross-sectional area equal to 18 cm2, five water levels of 30, 45, 55, 65, 78 cm, resulting in five different discharges on the bottom outlet, was performed. The results of this survey revealed that the shape of the lower opening is an important parameter in hydraulic flushing, changing of which results in change of scouring diameter. Results also showed that for a specific water level in the reservoir and for a specific time the scouring dimension for square valves and semicircle valves are more than one of rectangular valves. The scouring dimensions of rectangular valves are more than one of circular valves. The difference is more perceptible in lower water heights (i. e. lower discharge). The length of scouring and the volume of flushing cone increases with incrsing head and is the least for circular valves.

The local scour around bridge pier and abutment in recent years has been widely studied by different authors. Scant information exists as to how bridge pier proximity to abutment affects scour depth at an abutment and at a pier. Due to the fact that many bridges have a pier located close to an abutment, therefore, it is necessary to be study. This paper presents the effect of abutment length and pier shape on scour depth of them, by using wing-wall abutments with lengths 25, 37.5 and 50cm and circular, round edge and sharp edge piers in two distance, 17.5 and 35cm from the bank wall at the flood plain. The results of experimental study showed that the proximity pier to abutment, increases scour depth of them and the minimum scour depth related to the circular pier and maximum scour depth related to the sharp edge pier. For example, the sharp edge pier in distance 17.5cm from the bank wall at the flood plain, for abutment with length 50cm, increases scour depth of abutment and pier 50% and 61% respectively, compared with scour depth of them in isolation.

Scour downstream of hydraulic jump stilling basins can damage the surrounding area and can cause failure of the structure itself. Because of the study of such phenomenon has attracted the attention of researchers in the past. In the present study by constructing a model of spillways and stilling basin, The effect of B-jump characteristics on downstream scour was investigated. A total of 20 tests under 4 different Froude numbers and 5 different of jump position were carried out. The results indicated that at any discharge, the scour depth and length is decreased as the B-jump started at higher level. When the B-jump started at 14% of spillway depth, the non-dimensional scour depth and scour length decrease 7% and 19% respectively. The non-dimensional height of point bar downstream of scour hole was increased by 49%. Comparison of the results obtains in this study with other investigators finding shows good agreement for the case of B-jump scour.

Spur dike is a hydraulic structure which has an essential role in reducing the shear force on river banks. The interaction between the structure and flow makes vertical and horizontal vortices, which are the main reason for producing a local scour hole around spur dike and finally damaging it. The behavior of the flow around a spur dike and the intensity of degradation and aggradation depend on different factors such as the type of the spur dike, its position, its angle with the bank, and some other parameters. One of the most important factors is the permeability of the spur dike. This experimental study focuses on the effect of spur dike’s angle and its permeability on scour hole dimensions in non-submerged conditions. According to the results, when permeability increased up to 50%, scouring decreased significantly. For Fr=0.24, and in the vertical position of spur dike (90 degrees) with 50% permeability, relative depth, length, and width of the scour hole decreased 67%, 75.3% and 45.5%, respectively in comparison with impermeable spur dike. Also for the angle of 120 degrees, relative depth, length and width of the scour hole declined 64.1%, 72.1% and 35.4%, respectively. Similar results were obtained for the angle of 60 degrees with the reduction of relative depth, length and width of the scour hole being measured 60.2%, 68.7% and 38.8%, respectively. In addition, for 50% permeability, the highest level of scouring was for the angle of 60 degrees, whose average relative depth, length, and width were 0.19, 0.7 and 1.2, respectively.

Spur dike is one of the conventional structures in organizing and controlling erosion on the river side slopes. It causes the strong flows to be taken away of coastal and flow is guided towards river axis. On the other hand, changes in the flow pattern cause scour around spur dike. This study tries to evaluate the effect of increasing length in spur dike wing on the scour depth. Experiments were performed in the 90 degree meander with three different wing length, three different discharges and fixed depth. In addition L– shape spur dike was compared with ordinary spur dike. The result indicates that the scour depth and volume decreases with increase in wing length of spur dike. Comparing L-shape spur dike to ordinary spur dike show to be increase 3.25% up to 23.85%. Finally, an experimental predictor is presented for scouring in L-shape spur dike. This predictor has shown significant correlation with observation data in scour depth prediction.

Already many studies have been done on the mechanism of scour around hydraulic structure especially bridges and methods for control or reduction of scour around them have been investigated and evaluated. In the field of scour around bridges, researches are more focus on scour of piers in compare with abutment. While the review of available information on the bridge required cost, the major problems are related to abutment. There fore most costs has spent in this part. One of the methods used to reduction of scour is collar. Collar is the flat plate with small thickness that can be installed around the piers or abutment. In this research 93 set of experiments are performed to find the effect of different dimensions of symmetrical and unsymmetrical collars on reduction of scour around bridge abutment. Results show that increasing dimensions of both collars will increase the efficiency of performance. Comparing of both collars indicated, when the upstream width of collar was larger than its downstream width, its performance will be better than the symmetrical collar with uniform area. The influences of installing elevation of symmetrical collars were also investigated. The results show that the collars installed bellow the bed level have less scour in compare with the one installed on the bed or above the bed.

This research presents an experimental study on the scouring mechanism at semi-integral bridge piers. Based on laboratory experiments, this study focuses on the relationship between scour depth in complex pier groups and combined piles bridge and various parameters including the variation of inflow velocity, distance, and time. 1 200 data were collected for flow velocity and scour. The flow pattern and scour were analyzed for different flow discharges and flow depths. The results showed that the scour development with respect to time was greater for higher flow depth and bigger flow discharge at semi-integral bridges. In addition, the equilibrium scour depth increased with the approach flow depth around piers at semi-integral bridges. Velocity distribution also affected the scour development. It decreased when approaching the bridge but increased from upstream to downstream of the flume.

Unsteadiness of the vertical velocity profile and secondary flow in open channel bends poses serious problems in hydraulic engineering design. Insertion of vertical submerged vanes in the channel bend at an optimum angle with the tangential component of flow can minimize the unsteadiness and generation of secondary flow resulting in the reduction of scour depth at the outer bank. A series of experiments were conducted in a 180° bend laboratory channel to study flow erosion and effective ness of the submerged vane in reducing scour depth. The average approach to flow velocity at 0.20 m flow depth above the lowest initial bed level was 25 cm/s. An Acoustic Doppler Velocimeter (ADV) was used to measure the three-dimensional time-averaged velocity components at different azimuthal sections on stabilized nonscoured beds without vane. Scour bed profile without vanes shows that bank erosion in a 180° parabolic-shaped bed channel occurs mostly at the zone from bend angles 120° to 140°. Vanes were installed at angles of 10°, 15°, 20°, 30°, and 40° to the tangential flow component maintaining a spacingof 75 cm distance from one vane to another. Experimental results show that a 15° vane angle produces best result in reducing outer bank scour in a parabolic-shaped channel. The data presented in this paper can also be used for validating three-dimensional turbulence models for simulating flows in a curved channel. [ABSTRACT FROM AUTHOR]

The local scour around a bridge pier in recent years has been widely studied by different authors. They proposed different methods to control the scouring depth. Until now, many of authors have studied to find out how to control scouring around a pier along the straight stream. However, it may be required to construct a bridge across a bend of a river due to the some constraints. The objective of this research is to study a scour pattern around such piers on a bend due to the fact that there may be a difference between a flow pattern on a straight stream and the meander. Thus, this study tries to check whether the use of collar and cable together effects on scouring around bridge pier constructed on river meander. The results showed that as cable diameter increases and pitch of helix decrease, scouring depth will be decreased. The reduction of scouring depth by using cable does not exceed from 59% and alone collar reduces scour depth up to 55%. Using collar and cable together is reduced scour depth to 69.7%.

Scour caused by a water jet impinging the bed-sediment layer is a significant concern for hydraulic engineers. Although several studies investigated the maximum scour depth on the non-cohesive bed-sediment layer, the effect of the bed-sediment layer's thickness on the scour was not studied. This study investigated the effect of the thickness of the non-cohesive sediment layer at the canal bed on the depth of the scour caused by a water jet. The dimensionless parameters affecting the depth of the scour were obtained via dimensional analysis. Experiments were conducted on two different, non-cohesive bed-sediment layers at the bottom of a rectangular canal for different jet Froude numbers. Experimental results indicated that the depth of the scour increases with the thickness of the bed-sediment layer; this is because as the thickness of the sediment layer increases, the penetration depth of the air bubbles (dragged and enforced by the impinging water jet) through the sediment layer just under the scour hole increases. Due to the buoyancy force, as the air bubbles rise upward, they apply uplift forces and dynamic effects onto sediment particles, dislodging, suspending, and carrying the sediment particles away from the bed. If the thickness of the sediment layer is increased beyond a limiting value for a given flow condition, the maximum depth of the scour does not change (it remains almost constant). The effect of the thickness of the bed-sediment layer on the depth of the scour is present but not excessively large. [ABSTRACT FROM AUTHOR]

An analysis is presented of the 309 known laboratory data for local scour depth developed by two-dimensional (2D) horizontal jets, which leads to development of a new comprehensive prediction equation. The new equation comprises a number of mutually independent multiplying factors, which account for the effects on local scour depth of the characteristics of the applied jet flow and the bed sediment, as well as the extent of a downstream protective apron. When unitized in terms of the jet thickness, the equation shows that the maximum possible dimensionless local scour depth is equal to three times the jet Froude number expressed in terms of jet velocity and jet thickness. The equation is compared to most of the existing predictive equations by applying each equation to the existing data, the comparison indicating that the new method has superior performance. Indeed, many of the existing predictive equations are shown to perform poorly when judged against the known laboratory data. The known existing equations are listed in the paper. [ABSTRACT FROM AUTHOR]

Scour due to wall jet is one of the important problems in hydraulic engineering field. Prediction of the scour hole dimensions with acceptable accuracy is necessary for the structures around the jets. In this issue, use of soft computing (SC) methods is unavoidable due to the complex process of jet scour. In this research, SC techniques such as random forests (RF), particle swarm optimization based fuzzy inference system (PSOFIS), slime mould algorithm based fuzzy inference system (SMAFIS) and adaptive neuro fuzzy inference system (ANFIS) were implemented for predicting temporal variation of the scour hole dimensions due to plane wall jets for the first time. The performance indices and the data distribution showed that among the above-mentioned methods, the RF could predict the scour hole dimensions with the highest accuracy. This is attributed to this fact that RF which is a substantial modification of Bootstrap averaging, increases the precision of estimated prediction by a collection of de-correlated regression trees. The hybrid methods, PSOFIS, SMAFIS and ANFIS were ranked from the best to the worst based on the performance indices of the test data. The sensitivity analysis showed that among the effective parameters, the scouring time and sediment standard deviation had the most and the least effects on the temporal variation of scour hole dimensions, respectively. Use of channel width ratio and jet Reynolds number along with other effective parameters such as densimetric Froude number, tailwater depth ratio, sediment size ratio in the models are recommended to reach appropriate accuracies. Comparison with the existing literature indicated that the accuracy of the proposed methods is considerably better than the previous researches. • By using the soft computing methods, the temporal variation of the scour hole dimensions due to wall jets is analyzed for the first time. • RF is the superior method to estimate the scour hole dimensions as it increases the precision of estimated prediction by a collection of de-correlated regression trees. • The hybrid methods, PSOFIS, SMAFIS and ANFIS were ranked from the best to the worst for predictions of the temporal variation of scour hole dimensions. • Using the channel width ratio and jet Reynolds number along with other effective parameters are recommended to reach appropriate accuracies in the methods. • The accuracy of the proposed methods is considerably better than the previous researches. [ABSTRACT FROM AUTHOR]

The sediment erosion rate flume (SERF) device was computationally modeled using CD-adapco's Star-CCM+ at varying flow rates and sample roughnesses so that wall shear stresses could be evaluated during a piston-style erosion test. Shear stress data were matched between the model and data from previous physical tests. Pressure differential upstream and downstream from an eroding specimen displayed similar behavior during both physical and modeled tests in that as eroding sample roughness increased, pressure differential did not appear to change. A series of complicated bed configurations were added to the computational model to quantify the effects of blocking, chunking, or sample overadvancement during an erosion test. Results appeared to indicate that small deviations in sample geometry may have large effects on localized shear stresses. Another series of models was run to provide an explanation for the beginning of blocking or chunking as a result of shear stress development over a rough sample. Results showed that relatively large localized shear stresses may develop simply because of the introduction of roughness. Finally, results also indicated that the most conservative method for future testing is to keep the bottom edge of an eroding sample flush with a flume bottom. [ABSTRACT FROM AUTHOR]

The experimental study investigates how the application of point suction at different bed locations affects local scour around a cylindrical bridge pier under clear-water conditions. The results show that suction has a profound effect on pier-scour development, and the extent of the influence is related to the location of the suction source. When the suction source is located at or upstream of the pier, the equilibrium scour depth is reduced by up to 50%, with , where and = suction flow rate and undisturbed approach flow rate, respectively. The data also show that for the suction source that is located downstream of the pier, the equilibrium scour depth is reduced by up to 30% with the same suction flow rate. The extent of pier-scour depth reduction at different locations from the suction source is closely associated with changes to the local effective shear and critical shear velocity. Results of this study show that bed suction may be used as an effective pier-scour countermeasure. [ABSTRACT FROM AUTHOR]

Bridge piers having a nonuniform cross section over their height are termed as compound bridge piers. Mostly circular piers resting on large diameter wells or caissons (termed here as a circular compound bridge pier) are adopted for use in the Indian subcontinent for the road and railway bridges. In the present study, a new mathematical model is proposed for computation of temporal variation of scour depth at circular compound bridge piers. Two series of laboratory experiments were conducted to collect data for model application. In the first series of experiments, the data on temporal variation of scour depth were collected, albeit up to the transient (developing) stage of scour, around the circular uniform piers and circular compound piers for the clear-water scour condition. The second series of experiments was carried out to measure the size and hence the area of the principal vortex of the horseshoe vortex system and to determine the bed shear stress at the upstream face of the scour hole around the circular uniform piers and the circular compound piers. The mathematical model proposed in this paper has the capability to compute the temporal variation of scour depth around circular compound piers for all possible cases of footing position with respect to bed level, i.e., footing above the bed level, footing at the bed level, and footing below the bed level. [ABSTRACT FROM AUTHOR]

The ability of catchbasin sumps and hydrodynamic separators to remove sediment must be balanced with their ability to retain the previously captured material by preventing scour. The sediment scour process in these storm-water structures differs from the unidirectional scour and sediment transport process that occurs in pipes and channels. The hydrodynamics is affected by the particular characteristics of the hydraulic structure. The study of sediment scour in these devices requires incorporation of all the factors involved in the scour phenomenon and is best supported through computational fluid dynamic modeling (CFD) verified experimentally. Scour can be documented in the effluent as suspended sediment or total suspended solids concentration, a parameter of critical importance in storm-water quality management. This paper presents two simplified models for estimating effluent suspended sediment concentration attributable to scour of previously captured sediment. These models are based on results obtained from full-scale physical experimentation and calibrated and validated CFD modeling over a wide range of operating conditions where different particles sizes would be scoured. This paper also shows the effects of the armoring layer and of homogeneous and heterogeneous sediment sizes on the effluent concentration patterns. [ABSTRACT FROM AUTHOR]

Plunge pool scour is an important topic in hydraulic structures design. Numerous studies have been done in past years to understand the scour phenomenon due to plunging jets. These studies finally aimed at reducing the risk of structural undermining and collapse. Scour holes created under various hydraulic and geometrical conditions were analyzed for both two-dimensional and three-dimensional cases, and methods to reduce the scour were also investigated. In the current study, an attempt was made to quantify the feasibility of using crossing jets. The scour process was analyzed, and various relationships were presented to predict the main geometrical parameters, i.e., maximum scour hole depth, scour hole length, and scour hole width. Scour profiles were also compared with those due to an equivalent single jet. The main parameters on which the scour geometry depends were found as the densimetric Froude number of the jet, the crossing angle between the jets, the distance between the crossing point and the water surface level, and the water depth. All experiments have been carried out for a fixed vertical angle of 45°. [ABSTRACT FROM AUTHOR]

High bed-shear stress resulting from secondary flows and velocity increase at a channel junction cause local erosion and deposition in natural rivers and earth-lined channels. Herein, the scour patterns at the junction of two loose bed channels were studied under clear-water conditions. The main dimensionless variables are the angle between the two approach flow branches, the discharge and width ratios of the tributary to the downstream channel branches, and the ratio of the mean downstream velocity to the threshold velocity. The results indicate that the position of the maximum scour depth temporally moves to the outer wall and upstream to the main channel, as affected by the dimensionless variables. The effects of these variables are given in graphs and are expressed with a formula for maximum scour depth. [ABSTRACT FROM AUTHOR]

Various methods to control scour around bridge piers have been proposed, including application of riprap and installing a collar around piers. In the present study application of riprap alone and a combination of riprap and collar were examined experimentally for scour control around rectangular bridge piers. Piers aligned with the flow and skewed at 5, 10, and 20° to the flow were tested. Piers with three different aspect ratios equal to 1:3, 1:5, and 1:7 were used in this study. A collar three times wider than the piers’ width was installed around the piers at the streambed level. All experiments were conducted at the threshold of motion of the bed material. The size and extent of stable riprap stones for prevention of scouring around the piers was found by experiment with and without the collar. A method previously given for calculating stable riprap size around circular piers is extended for rectangular piers with different aspect ratios and skew angles with and without collar protection. The extent of stable riprap layer in all tests is also presented. [ABSTRACT FROM AUTHOR]

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Abstract: Genetic programming (GP) has nowadays attracted the attention of researchers in the prediction of hydraulic data. This study presents linear genetic programming (LGP), which is an extension to GP, as an alternative tool in the prediction of scour depth around a circular pile due to waves in medium dense silt and sand bed. Field measurements were used to develop LGP models. The proposed LGP models were compared with adaptive neuro-fuzzy inference system (ANFIS) model results. The predictions of LGP models were observed to be in good agreement with measured data, and quite better than ANFIS and regression-based equation of scour depth at circular piles. The results were tabulated in terms of statistical error measures and illustrated via scatter plots. [Copyright &y& Elsevier]

The temporal effect of hydrograph on local scour depth is investigated under clear-water scour condition. By analyzing the characteristics of scour-depth evolutions at bridge piers for different rising hydrographs, a relation for estimating the maximum scour depth in uniform sediment is proposed. In the relation, the flow unsteadiness effect is taken into account by an unsteady flow parameter combining the peak-flow intensity and time-to-peak factors. For nonuniform sediment with d84 employed as the effective sediment size, this relation can yield reasonably good results of the maximum scour depth under rising hydrograph. [ABSTRACT FROM AUTHOR]