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Piano key weirs are a type of non-linear weir that have a higher discharge coefficient than similar linear weirs. These hydraulic structures have a lightweight foundation and a simple structure is designed and installed on dams and drainage channels. Due to the high efficiency of these weirs, the investigation of downstream scour and ways to reduce it has been the focus of engineers in recent years. In the present study, a trapezoidal type C piano key weir, three discharges, and three tailwater depths were used. Two obstacles with heights of 0.02 and 0.04 meters were also used at the end of the weir exit keys. The results showed that the presence of an obstacle reduces scour at the toe of the weir. The amount of reduction in scour at the toe of the weir was greater in the weir with a larger obstacle height than in the weir with a smaller obstacle height, and in both cases was less than in the simple weir. The presence of an obstacle reduces the maximum depth of scour and moves the distance of the maximum depth of scour away from the toe of the weir. In the weir with obstacle heights of 0.02 and 0.04 meters, compared to the weir without an obstacle, the amount of maximum scour depth is approximately 16.4% and 26.9% less, and the distance of the maximum scour depth is approximately 8.7% and 19.1% more than the weir without an obstacle. The scour index in weirs with obstacles is less than in weirs without obstacles, which can reduce the risk of weir overturning. The lowest value of the scour index was observed in the weir with an obstacle height of 0.04 meters, which is approximately 41.2% less than the weir without an obstacle.

In the past, various methods have been proposed to control beach heel scouring. For shallow rivers (such as mountain rivers), various types of overflows are used. Therefore, the development of scour in cross-vane and w-weir structures for coastal protection was investigated in this study. The results showed that by installing a w-weir structure in a 90-degree position compared to a 30 and 60-degree position, a 37.9% and 19.7% reduction of scouring was observed, respectively. Also, by installing the cross vane structure in the 90-degree position compared to the 30 and 60-degree position, a 35.4% and 21.2% reduction of scouring was observed, respectively. With increasing width (L / B) (ratio of the width of structure to the width of flume), the w-weir structure decreased from 1.5 to 2, scour rate of 7.9%. Also, with increasing width (L / B) (ratio of the width of structure to the width of flume), the cross-vane structure has decreased from 1.3 to 1.7, and the scour rate has decreased by 4.7%. The w-weir structure had an average of 7.3% less scouring than the cross-vane structure.

In the past, various methods have been proposed to control beach heel scouring. For shallow rivers (such as mountain rivers), various types of overflows are used. Therefore, the development of scour in cross-vane and w-weir structures for coastal protection was investigated in this study. The results showed that by installing a w-weir structure in a 90- degree position compared to a 30 and 60-degree position, a 37.9% and 19.7% reduction of scouring was observed, respectively. Also, by installing the cross vane structure in the 90-degree position compared to the 30 and 60-degree position, a 35.4% and 21.2% reduction of scouring was observed, respectively. With increasing width (L / B) (ratio of the width of structure to the width of flume), the w-weir structure decreased from 1.5 to 2, scour rate of 7.9%. Also, with increasing width (L / B) (ratio of the width of structure to the width of flume), the cross-vane structure has decreased from 1.3 to 1.7, and the scour rate has decreased by 4.7%. The w-weir structure had an average of 7.3% less scouring than the cross-vane structure. [ABSTRACT FROM AUTHOR]

Today, abutments disrupt the normal flow of rivers and cause scouring and erosion of sedimentary materials around them, creating holes and resulting in much damage every year. Researchers have proposed various methods to reduce the power of water erosion. One of the essential methods in this regard is creating slots in abutments. Since the expansion of the scour hole endangers the stability of the bridge structure, this study examined the effect of slot dimensions in the support on the scour hole dimensions. The findings demonstrated that the presence of slots in abutments effectively reduces the dimensions of scour holes. With the slot, the volume of the scour hole can be reduced by up to 50%. Furthermore, as the relative speed of scouring increases by 75%, the depth of the scour hole also increased up to 140%. An increase in slot depth leads to a decrease in scour hole depth of up to 85%. [ABSTRACT FROM AUTHOR]

Today, abutments disrupt the normal flow of rivers and cause scouring and erosion of sedimentary materials around them, creating holes and resulting in much damage every year. Researchers have proposed various methods to reduce the power of water erosion. One of the essential methods in this regard is creating slots in abutments. Since the expansion of the scour hole endangers the stability of the bridge structure, this study examined the effect of slot dimensions in the support on the scour hole dimensions. The findings demonstrated that the presence of slots in abutments effectively reduces the dimensions of scour holes. With the slot, the volume of the scour hole can be reduced by up to 50%. Furthermore, as the relative speed of scouring increases by 75%, the depth of the scour hole also increased up to 140%. An increase in slot depth leads to a decrease in scour hole depth of up to 85%.

Maintaining the level of rivers bed, especially in a reach where their’s slope increased due to many reasons specifically sand and gravel mining is an essential issue to the conservation of rivers. Grade control structures are eco-friendly structures that are common to stabilize river’s beds and banks. Control and reduction of scour hole at the downstream basin is an important issue in the prevention of undercut and failure. In the current research, the effect of installation level of the apron on the variation of scour depth at downstream of the block ramp with slopes of 1:3 and 1:5 was considered experimentally under a range of flow discharges, the block ramp's surface roughness size and configuration. The comparison of the results indicated that there is a direct relationship between the level of the apron level and the scour depth so that by reducing the level of the apron to 1/10 and 1/6 of the block ramp height, the maximum scour depth increases in an average 36 and 41 for slope of 1:3 and 32 and 35 for slope of 1:5, respectively. By increasing the size of surface roughness such that the overpass flow regime changes to nappe flow, the reduction of installation of the level of block ramp does not noticeable effect on the increase of the scour depth. [ABSTRACT FROM AUTHOR]

Abstract Introduction: A physical model was prepared to investigate the effect of the geometric shape of the bridge pier with the abutment attached to it on the reduction of scour depth. This model was made of a laboratory flume with a length of 7.5 meters, a width of 30 cm, a depth of 45 cm with a variable slope and a glass body with bridge pier width of 4 cm were used. For bed sediments, a layer of natural river sand with an average diameter of 0.9 mm and a standard deviation coefficient of 1.1 and a uniformity coefficient of 1.25 were selected and used in a layer with a thickness of approximately 14 cm for experiments. Methods: The geometric shape of the bridge piers, as well as the presence of the footing, prevents direct contact of the descending current, reduces the activity of horseshoe vortices and thus reduces the scouring speed, and delays the scouring start time. Findings: According to the results of the experiments, the greatest decrease in scour depth was related to (0.26 descent and p1 base). The results showed that in the same condition, the relative scour depth at p1 base was less than other bases and reached its maximum in the control base. Also, the relative scour depth increased with increasing the number of landings in the same position. The abutment attached to the bridge base has reduced the scour depth by 29.6%.

Abstract Introduction: In free overfall spillways, waterfalls over the crown of the spillway almost vertically and impacts the downstream bed of the dams. Due to the high velocity and energy of the flow which impacts the erodible downstream bed, it may cause scouring close to the foundation of the dam and consequently threaten the stability of the dam. Methods: In this study, artificial intelligence methods were used to estimate the scour depth of slope control structures with sharp-crested weir due to the complexity of the phenomenon. Three models including neural network, adaptive fuzzy neural system, and support vector machine (SVM) were used as artificial intelligence or black-box model to solve the problem.. Findings: The results showed that artificial intelligence methods are more efficient than conventional experimental methods in estimating the depth of downstream scours of slope control structures with sharp-crested weir. Using more parameters in the input of artificial intelligence models does not increase the accuracy of these models. It is because of increasing errors as a result of using more parameters in these models. In estimating the downstream scour depth of slope control structures with the sharp-crested weir in both calibration and validation stages, an adaptive fuzzy neural system model is up to 20% more reliable than the artificial neural network model and up to 8.5% than the support vector machine model.

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.

A side weir is a hydraulic control structure used in irrigation and drainage systems and combined sewer systems. The Piano Key Weir (PKW) is a new type of long crest weirs that have a relatively simple structure and high economic efficiency structures. Due to the advantages of this weirs, it is necessary to study and investigate the Scour around of these structures as a side-weir. The present study focuses on investigate the scouring around the piano key Side weirs of the Type A at a 30° Section of a 180° Alluvial curved channel for clear water conditions. The results showed that at the end of the Side weir, longitudinal bar in the middle of the main channel and a scour hole close to the outer bank are formed because of the changes in shear stress field. The depth of clear-water scour increases by time and approaches the equilibrium state asymptotically depending on approach flow velocity. The equilibrium depth of scour depends on the dimensionless parameters of flow intensity, flow shallowness, weir crest height, side weir length and the maximum value of scour depth occurs at a depth when the approach flow intensity is equal to 1.0. Also, the scour equilibrium depth in the dimensionless ratio increased L/rc = 0.175 compared to L/rc = 0.125 in different flow velocity of 12 to 35%, 10 to 39% and 18 to 26%, respectively.

In this research, the scour hole depth at the downstream of cross-vane structures with different shapes (i.e., J, I, U, and W) was simulated utilizing a modern artificial intelligence method entitled "Outlier Robust Extreme Learning Machine (ORELM)". The observational data were divided into two groups: training (70%) and test (30%). Then, using the input parameters including the ratio of the structure length to the channel width (b/B), the densimetric Froude number (Fd), the ratio of the difference between the downstream and upstream depths to the structure height (Δy/hst), and the structure shape factor (φ), eleven different ORELM models were developed for estimating the scour depth. Subsequently, the superior model and also the most effective input parameters were identified through the conduction of uncertainty analysis. The superior model simulated the scour values by the dimensionless parameters b/B, Fd, Δy/hst. For this model, the values of the correlation coefficient (R), the variance accounted for (VAF), and the Nash-Sutcliffe efficiency (NSC) for the superior model in the test mode were obtained 0.956, 91.378, and 0.908, respectively. Also, the dimensionless parameters b/B and Δy/hst were detected as the most effective input parameters. Furthermore, the results of the superior model were compared with the extreme learning machine model and it was concluded that the ORELM model was more accurate. Moreover, an uncertainty analysis exhibited that the ORELM model had an overestimated performance. Besides, a partial derivative sensitivity analysis (PDSA) model was performed for the superior model.

One of the most common and practical methods in controlling the local scour around bridge pier is to place a protective riprap layer. Due to various uncertainties in the design of this countermeasure method, in the present study, the reliability analysis method was applied for the design of a riprap size around a real bridge pier as a case study. Therefore, four different methods including First Order Second Moment, First Order Reliability Method, Spread Sheet and Monte Carlo Simulation Technique were used to quantify the uncertainties and design of riprap size. The results showed that the probability of riprap size failure, which was calculated by the empirical equation and the use of the mean value of effective parameters in the case study, was very high, nearly 34%. In the following, the relationship between safety factor and the reliability index at the site of this case study was determined. Finally, in order to achieve more realistic results, the hydraulic correlation coefficient between depth and flow velocity parameters and its effect on the probability of the riprap failure were studied. It was shown that the correlation coefficient between these two hydraulic parameters was very high and more than 90%, and its maximum effect on the probability of the riprap failure was less than 10%.

Optimization of artificial intelligence (AI) models is a significant issue because it enhances the performance and flexibility of the numerical models. In this study, scour depth around bridge abutments with different shapes was estimated by means of ANFIS and ANFIS-Genetic Algorithm. In other words, the membership functions of the ANFIS model were optimized using the genetic algorithm, finding that the performance of ANFIS model was increased. Firstly, effective input parameters on the scour depth around bridge abutments were defined. Then, by using the input parameters, eleven ANFIS and ANFIS-GA models were produced. Next, the superior ANFIS and ANFIS-GA models were introduced by analyzing the numerical results. For example, the correlation coefficient and scatter index for ANFIS model were calculated to be 0.979 and 0.070; for ANFIS-GA, these were 0.986 and 0.056, respectively. In addition, the average discrepancy ratio (DRave) for ANFIS and ANFIS-GA models was 0.984 and 0.988, respectively. Also, it was shown that the ANFIS-GA models had more accuracy, as compared to the ANFIS models. Moreover, a sensitivity analysis showed that Froude number (Fr) and ratio of flow depth to radius of scour hole (h/L) were the most influential input parameters for simulating the scour depth around bridge abutments.

Introduction:The leading cause of damages on bridge is local scouring around piers. Many studies were carried out to control and reduce this phenomenon and suggested more solution methods to protect bridge piers. Protection is divided into direct and indirect methods. In this study, to reduce scouring depth around the pier, an indirect method is used by changing the pier's head angle in a flow direction.Materials and Methods:An experimental study on clear-water at a different angle of piers head under steady flow is presented. Experiments were used to assess the ability to change the head angle of piers to protect them. Toward this end, five angles (α) 90, 85, 80, 75, 70-degree with the flow direction were considered. The bed material size d50 was 0.9 mm and all experiments were done in Gunt hydraulic standard flume.Findings:The results showed that the pier with a 70-degree attack angle could reduce the scour depth more than others. This happens due to diverting part of streamlines to downstream, and it can have a 36 per cent reduction overall.Conclusion:The scouring depth and sediment point bar created around the pier with an inclined head compared with the control pier (α=90-degrees) have less scouring depth due to minor deviation of flow streamlines and reduction of disturbances around the pier.

A side weir is a hydraulic control structure used in irrigation and drainage systems and combined sewer systems. The Piano Key Weir (PKW) is a new type of long crest weirs that have a relatively simple structure and high economic efficiency structures. Due to the advantages of this weirs, it is necessary to study and investigate the Scour around of these structures as a side-weir. The present study focuses on investigate the scouring around the piano key Side weirs of the Type A at a 30° Section of a 180° Alluvial curved channel for clear water conditions. The results showed that at the end of the Side weir, longitudinal bar in the middle of the main channel and a scour hole close to the outer bank are formed because of the changes in shear stress field. The depth of clear-water scour increases by time and approaches the equilibrium state asymptotically depending on approach flow velocity. The equilibrium depth of scour depends on the dimensionless parameters of flow intensity, flow shallowness, weir crest height, side weir length and the maximum value of scour depth occurs at a depth when the approach flow intensity is equal to 1.0. Also, the scour equilibrium depth in the dimensionless ratio increased L/rc= 0.175 compared to L/rc= 0.125 in different flow velocity of 12 to 35%, 10 to 39% and 18 to 26%, respectively. [ABSTRACT FROM AUTHOR]

In this research, the scour hole depth at the downstream of cross-vane structures with different shapes (i.e., J, I, U, and W) was simulated utilizing a modern artificial intelligence method entitled "Outlier Robust Extreme Learning Machine (ORELM)". The observational data were divided into two groups: training (70%) and test (30%). Then, using the input parameters including the ratio of the structure length to the channel width (b/B), the densimetric Froude number (Fd), the ratio of the difference between the downstream and upstream depths to the structure height (Δy/hst), and the structure shape factor (φ), eleven different ORELM models were developed for estimating the scour depth. Subsequently, the superior model and also the most effective input parameters were identified through the conduction of uncertainty analysis. The superior model simulated the scour values by the dimensionless parameters b/B, Fd, Δy/hst. For this model, the values of the correlation coefficient (R), the variance accounted for (VAF), and the Nash-Sutcliffe efficiency (NSC) for the superior model in the test mode were obtained 0.956, 91.378, and 0.908, respectively. Also, the dimensionless parameters b/B and Δy/hst were detected as the most effective input parameters. Furthermore, the results of the superior model were compared with the extreme learning machine model and it was concluded that the ORELM model was more accurate. Moreover, an uncertainty analysis exhibited that the ORELM model had an overestimated performance. Besides, a partial derivative sensitivity analysis (PDSA) model was performed for the superior model. [ABSTRACT FROM AUTHOR]

Local scouring around the pier is one of the main reasons for the instability of the bridges. Providing appropriate methods for predicting and controlling scour depth is one of the important issues that have been considered. Various methods have been proposed to control the scouring around the bridge pier. In this study, the effect of using the bed sill on scouring around the cylindrical bridge pier under clear water conditions has been investigated and compared in non-cohesive sediments. The bed sill has been placed at the downstream of the pier and its effect on reducing the scouring has been evaluated by changing distance between and the pier and sill geometry. In this research, a pier with 50 mm diameter was used. The results showed that bed sill setting has effect on scour reducing. Also, the distance and the shape of the sill have the greatest effect on reducing the scour. The placement of the straight and oblique bed sill at the backside of the pier resulted in a decrease of 11% and 16%, respectively, in the maximum of scour depth. By increasing the distance of sill to the oblique pier, its protective effect was reduced. Also the oblique bed sill more reduces the amount of scour around the pier relative to the straight bed sill and prevents the scour hole from developing to upwards.

Erosion under the conveying pipeline affected by river flow at the cross to rivers is one the important reasons for breaking the pipelines that can lead to leakage. While the mechanism of erosion under the conveying pipeline in steady flow has been studied by many researchers, studies have shown the importance of scouring research in flood times under unsteady conditions. So, this study has been concerned with the investigation of bed river erosion under the conveying pipeline at the conflict of river in unsteady condition. To achieve this aim, some effective hydrograph’s parameters were changed in different scenarios and the results were compared to the steady condition. The result showed the erosion’s ratio of unsteady condition to steady one was 34 to 69 percent. Also, the rise of flood hydrograph’s peak led to increasing depth erosion from 7% to 22%.

Occurrence of local scour is one of the most significant causes of damage to the pipes. Therefore, safe and economical design of pipes in the flow path requires a good estimate. In this study, based on the important and effective parameters in the scouring phenomenon, in order to develop educational patterns according to the data obtained in the laboratory of Ahvaz Islamic Azad University, models based on artificial neural networks were created with the NeuroSolution5 software. MLP, GFF and RBF were the models used in this study; after comparing, MLP was selected as the basis for our study. Finally, the effect of each parameter on scouring was determined using the artificial neural networks technique, based on which the shields parameter with a very high effect (more than 95 percent) was determined as one of the most effective causes of the local scour.

Experimental and numerical study of scouring pattern on the direct and polo-shaped groynes have been investigated in this paper. In this study, direct and polo-shaped groynes models with a length of 0.12 meter have been used in discharges of 10.5, 15, 20 liters per second in a direct flume. The results showed that the maximum scour depth formed around the groyne head of direct and polo-shaped types has increased with augmentation of flow discharge, which was 0.095 and 0.104 meter in the case of 20 L/s discharge respectively. Also, the width of scour hole was 2.25 and 2 times of effective length of the groyne in direct and polo-shaped groynes respectively. In this regards, maximum scour depth around the head of groyne was seen 0.87 and 0.79 times of the effective length of the groyne. Sand form located at downstream of the direct groyne at the distance of 0.09 and 0.15 meters from the side wall of direct groyne was stretched and extended to about 1.3 times of the channel width as well. While the length of the sand form for direct groyne was 1.15 times of the channel width. Overall, the dimensions of the scour hole around the polo-shaped groyne, was less than the direct groyne. In addition to understanding the hydraulic behaviour around the groyne, Flow3D software was used. Statistical survey of the results obtained by experimental and numerical models attested that the relative error of the numerical model could be about 20%, which shows an appropriate performance of using Flow3D for predicting the maximum scour depth.

Rivers accumulate huge amounts of floating debris including the trunk, branches and leaves during the floods, leading to increase the depth of local scour around bridge piers. A large number of the laboratorial and field studies have been performed to understand the mechanism of scouring phenomenon under floating debris. Over two past decades, different types of the artificial intelligence methods have been used to estimate the maximum scour depth around bridges piers. In this study, the Neuro-Fuzzy model based on group method data handling (NF-GMDH) was used to estimate the scour under effect of debris accumulations. The NF-GMDH network was developed using evolutional algorithms: genetic algorithm (GA), particle swarm optimization (PSO), and gravitational search algorithm (GSA). Parameters effective on the maximum scour depth included average velocity of upstream flow of the bridge pier, critical velocity of river bed sediments, depth of flow in section without debris, thickness of submerged debris, debris diameter, average particle size, pier diameter, and channel width. After training and experiencing each NF-GMDH models, the performances of each one was evaluated through statistical parameters. The results showed that the models proposed had better performance compared with emperical relationships. NF-GMDH-PSO (R=0.8413 and RMSE=0.37) and NF-GMDH-GA (R=0.8407 and RMSE=0.3640) had relatively similar performance. Finally, sensitivity analysis indicated that the ratio of pile diameter (D) to mean diameter of bed sediments (d50) has the most influence on determination of maximum scour depth.

Flow pattern around the bridge piers includes water surface profile, velocity profile, shear velocity, shear stress distribution, etc. In this research, the effects of the base shape along with scale effects on the flow pattern around the rectangular bridge piers were numerically calculated through "Fluent Software", using Horizontal Velocity Distribution (Vx) and Vertical Velocity Distribution (Vy) criteria. The results showed that in studying the horizontal component of velocity (Vx) for the rectangular bridge piers, the vortices activity radius was 8 times of the length of the pier, and the minimum channel width for vortices activity was 16 times of the length of the Bridge pier; also, the minimum channel length in front of the pier was 4 times of the length of the pier and behind which, it was 25 times more than the bridge pier. Finally, the minimum channel length for the vortexes activity was calculated to be 29 times more than the bridge pier length. Furthermore, for the vertical component of velocity, the flow pattern around the base of the bridge cannot be an appropriate parameter for checking the effects of the length and width of the channel.

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.

One of the most common and practical methods in controlling the local scour around bridge pier is to place a protective riprap layer. Due to various uncertainties in the design of this countermeasure method, in the present study, the reliability analysis method was applied for the design of a riprap size around a real bridge pier as a case study. Therefore, four different methods including First Order Second Moment, First Order Reliability Method, Spread Sheet and Monte Carlo Simulation Technique were used to quantify the uncertainties and design of riprap size. The results showed that the probability of riprap size failure, which was calculated by the empirical equation and the use of the mean value of effective parameters in the case study, was very high, nearly 34%. In the following, the relationship between safety factor and the reliability index at the site of this case study was determined. Finally, in order to achieve more realistic results, the hydraulic correlation coefficient between depth and flow velocity parameters and its effect on the probability of the riprap failure were studied. It was shown that the correlation coefficient between these two hydraulic parameters was very high and more than 90%, and its maximum effect on the probability of the riprap failure was less than 10%. [ABSTRACT FROM AUTHOR]

Optimization of artificial intelligence (AI) models is a significant issue because it enhances the performance and flexibility of the numerical models. In this study, scour depth around bridge abutments with different shapes was estimated by means of ANFIS and ANFIS-Genetic Algorithm. In other words, the membership functions of the ANFIS model were optimized using the genetic algorithm, finding that the performance of ANFIS model was increased. Firstly, effective input parameters on the scour depth around bridge abutments were defined. Then, by using the input parameters, eleven ANFIS and ANFIS-GA models were produced. Next, the superior ANFIS and ANFIS-GA models were introduced by analyzing the numerical results. For example, the correlation coefficient and scatter index for ANFIS model were calculated to be 0.979 and 0.070; for ANFIS-GA, these were 0.986 and 0.056, respectively. In addition, the average discrepancy ratio (DRave) for ANFIS and ANFIS-GA models was 0.984 and 0.988, respectively. Also, it was shown that the ANFIS-GA models had more accuracy, as compared to the ANFIS models. Moreover, a sensitivity analysis showed that Froude number (Fr) and ratio of flow depth to radius of scour hole (h/L) were the most influential input parameters for simulating the scour depth around bridge abutments. [ABSTRACT FROM AUTHOR]

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.

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.

The local scour around the piers is an important factor that causes of the destruction of the bridges. Therefore, to avoid this phenomenon there is scientific solutions to protect the pier against scour. some of the most effective techniques you can use ,are using the collars or threading or slots on the pier. Therefore using the slots is not practical or not suitable to consider as permanent solution and threading is not so effective method so there is an idea to compose threading and slots with collars together in this experimental work that can make slots and threading so more practical and useful in pier scour reduction . there have been created some new tools which name jet-collar , slot-veneer and thread-veneer. at the best condition results shows that some of the collars which have a jagged side as a jet and a collar at other side , so this jet-collar could reduce local scour by 83% at pier side.

One of the main reasons of bridge destruction is the bridge piers scour. A more accurate computation of scour depth would lead to a more solid design of bridge piers. Empirical equations can be applied to compute the scour depth. In this study, the coefficients of 17 empirical equations were optimized using genetic algorithm and fieldwork values. 80% of the field data were used to optimize the equations and the rest were used to verify them. The RMSE, MAE, E and R2 criteria were applied to evaluate the optimization method where the results showed the ability of genetic algorithm in empirical equations optimization. The (Froehlich 1988) equation had the highest degree of precision among the empirical equations, so the genetic algorithm has had the least effect on the optimization of this equation. The optimized (Neill 1964), (Melville 1975), (Laursen & Toch 1956), (Blench II 1962) and (Hancu 1971) equations with respectively, 75, 72, 71, 71 and 71 percent showed the highest reduction in RMSE error criteria. The optimized (Blench II 1962) equation with RMSE, MAE, E and R2 criteria equal to 0.57m, -0.085m, 62 percent and 0.65 respectively, presented the highest correlation coefficient and lowest error. In the end, more equations were proposed to predict the bridge piers 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.

O‌n‌e o‌f t‌h‌e i‌s‌s‌u‌e‌s i‌n r‌i‌v‌e‌r e‌n‌g‌i‌n‌e‌e‌r‌i‌n‌g i‌s b‌r‌i‌d‌g‌e p‌r‌o‌t‌e‌c‌t‌i‌o‌n i‌n a w‌a‌y t‌h‌a‌t b‌r‌i‌d‌g‌e‌s s‌u‌f‌f‌e‌r t‌h‌e m‌i‌n‌i‌m‌u‌m d‌a‌m‌a‌g‌e d‌u‌r‌i‌n‌g a f‌l‌o‌o‌d. I‌n m‌a‌n‌y c‌a‌s‌e‌s, d‌u‌e t‌o t‌h‌e l‌i‌m‌i‌t‌a‌t‌i‌o‌n‌s, b‌r‌i‌d‌g‌e‌s a‌r‌e c‌o‌n‌s‌t‌r‌u‌c‌t‌e‌d o‌n a r‌i‌v‌e‌r b‌e‌n‌d. T‌h‌e p‌u‌r‌p‌o‌s‌e o‌f t‌h‌i‌s r‌e‌s‌e‌a‌r‌c‌h i‌s t‌o i‌n‌v‌e‌s‌t‌i‌g‌a‌t‌e t‌h‌e e‌f‌f‌e‌c‌t o‌f c‌o‌n‌s‌t‌r‌u‌c‌t‌i‌n‌g c‌o‌n‌v‌e‌r‌g‌e‌n‌t a‌n‌d d‌i‌v‌e‌r‌g‌e‌n‌t (V-s‌h‌a‌p‌e‌d \& A-s‌h‌a‌p‌e‌d) c‌o‌u‌p‌l‌e‌d b‌r‌i‌d‌g‌e p‌i‌e‌r‌s a‌n‌d t‌h‌e‌i‌r p‌o‌s‌i‌t‌i‌o‌n i‌n p‌a‌r‌a‌l‌l‌e‌l t‌o t‌h‌e f‌l‌o‌w o‌n a s‌t‌e‌e‌p 180-d‌e‌g‌r‌e‌e b‌e‌n‌d b‌e‌d t‌o‌p‌o‌g‌r‌a‌p‌h‌y. T‌h‌i‌s r‌e‌s‌e‌a‌r‌c‌h w‌a‌s p‌e‌r‌f‌o‌r‌m‌e‌d o‌n a l‌a‌b‌o‌r‌a‌t‌o‌r‌y c‌h‌a‌n‌n‌e‌l a‌t P‌e‌r‌s‌i‌a‌n G‌u‌l‌f U‌n‌i‌v‌e‌r‌s‌i‌t‌y o‌f B‌u‌s‌h‌e‌h‌r, I‌r‌a‌n. T‌h‌e c‌h‌a‌n‌n‌e‌l h‌a‌s a w‌i‌d‌t‌h o‌f 1 m‌e‌t‌e‌r, a‌n‌d a s‌t‌e‌e‌p b‌e‌n‌d w‌i‌t‌h a c‌e‌n‌t‌r‌a‌l r‌a‌d‌i‌u‌s t‌o c‌h‌a‌n‌n‌e‌l w‌i‌d‌t‌h r‌a‌t‌i‌o o‌f 2 a‌n‌d a 180-d‌e‌g‌r‌e‌e b‌e‌n‌d. I‌n t‌h‌e u‌p‌s‌t‌r‌e‌a‌m a‌n‌d d‌o‌w‌n‌s‌t‌r‌e‌a‌m o‌f t‌h‌e b‌e‌d, t‌h‌e‌r‌e a‌r‌e d‌i‌r‌e‌c‌t r‌o‌u‌t‌e‌s w‌i‌t‌h l‌e‌n‌g‌t‌h‌s o‌f 6.5 a‌n‌d 5.1 m‌e‌t‌e‌r‌s, r‌e‌s‌p‌e‌c‌t‌i‌v‌e‌l‌y. F‌o‌r t‌h‌e e‌x‌p‌e‌r‌i‌m‌e‌n‌t‌s, P‌V‌C p‌i‌e‌r‌s w‌i‌t‌h 5 c‌m d‌i‌a‌m‌e‌t‌e‌r a 21-d‌e‌g‌r‌e‌e a‌n‌g‌l‌e t‌o t‌h‌e v‌e‌r‌t‌i‌c‌a‌l a‌x‌i‌s, m‌a‌t‌e‌r‌i‌a‌l‌s w‌i‌t‌h a‌n a‌v‌e‌r‌a‌g‌e d‌i‌a‌m‌e‌t‌e‌r o‌f 1.5 m‌m a‌n‌d s‌t‌a‌n‌d‌a‌r‌d d‌e‌v‌i‌a‌t‌i‌o‌n o‌f 1.14 w‌e‌r‌e u‌s‌e‌d. A‌l‌l t‌h‌e e‌x‌p‌e‌r‌i‌m‌e‌n‌t‌s w‌e‌r‌e p‌e‌r‌f‌o‌r‌m‌e‌d w‌i‌t‌h f‌l‌o‌w v‌e‌l‌o‌c‌i‌t‌y t‌o c‌r‌i‌t‌i‌c‌a‌l v‌e‌l‌o‌c‌i‌t‌y r‌a‌t‌i‌o o‌f 0.98 (U/U‌c=0.98) a‌n‌d c‌o‌n‌s‌t‌a‌n‌t d‌e‌p‌t‌h o‌f 18 c‌m a‌t t‌h‌e b‌e‌g‌i‌n‌n‌i‌n‌g o‌f t‌h‌e b‌e‌n‌d a‌n‌d 70 l/s d‌i‌s‌c‌h‌a‌r‌g‌e. T‌h‌e r‌e‌s‌u‌l‌t‌s s‌h‌o‌w t‌h‌a‌t t‌h‌e m‌a‌x‌i‌m‌u‌m d‌e‌p‌t‌h o‌f t‌h‌e s‌c‌o‌u‌r h‌o‌l‌e o‌c‌c‌u‌r‌s a‌d‌j‌a‌c‌e‌n‌t t‌o t‌h‌e V-s‌h‌a‌p‌e‌d c‌o‌u‌p‌l‌e‌d p‌i‌e‌r‌s e‌s‌t‌a‌b‌l‌i‌s‌h‌e‌d a‌t t‌h‌e p‌o‌s‌i‌t‌i‌o‌n o‌f 90 d‌e‌g‌r‌e‌e. B‌y c‌h‌a‌n‌g‌i‌n‌g t‌h‌e p‌i‌e‌r‌s f‌r‌o‌m V-s‌h‌a‌p‌e‌d t‌o A-s‌h‌a‌p‌e‌d a‌t 60 a‌n‌d 90 d‌e‌g‌r‌e‌e‌s p‌o‌s‌i‌t‌i‌o‌n‌s, t‌h‌e m‌a‌x‌i‌m‌u‌m s‌c‌o‌u‌r h‌o‌l‌e i‌s t‌r‌a‌n‌s‌f‌e‌r‌e‌d f‌r‌o‌m t‌h‌e a‌d‌j‌a‌c‌e‌n‌c‌y o‌f t‌h‌e u‌p‌s‌t‌r‌e‌a‌m p‌i‌e‌r t‌o t‌h‌e a‌d‌j‌a‌c‌e‌n‌c‌y o‌f t‌h‌e d‌o‌w‌n‌s‌t‌r‌e‌a‌m p‌i‌e‌r, a‌n‌d b‌y c‌h‌a‌n‌g‌i‌n‌g t‌h‌e p‌o‌s‌i‌t‌i‌o‌n o‌f t‌h‌e p‌i‌e‌r‌s f‌r‌o‌m t‌h‌e b‌e‌n‌d's u‌p‌s‌t‌r‌e‌a‌m t‌o‌w‌a‌r‌d‌s t‌h‌e d‌o‌w‌n‌s‌t‌r‌e‌a‌m, t‌h‌e d‌e‌v‌e‌l‌o‌p‌m‌e‌n‌t o‌f t‌h‌e m‌a‌x‌i‌m‌u‌m s‌c‌o‌u‌r h‌o‌l‌e d‌e‌c‌r‌e‌a‌s‌e‌s. T‌h‌e h‌i‌g‌h‌e‌s‌t s‌c‌o‌u‌r d‌e‌p‌t‌h‌s w‌e‌r‌e m‌e‌a‌s‌u‌r‌e‌d i‌n t‌h‌e m‌a‌i‌n h‌o‌l‌e a‌n‌d t‌h‌e s‌e‌c‌o‌n‌d s‌c‌o‌u‌r h‌o‌l‌e a‌n‌d a‌l‌s‌o t‌h‌e h‌i‌g‌h‌e‌s‌t s‌e‌d‌i‌m‌e‌n‌t‌a‌t‌i‌o‌n w‌e‌r‌e m‌e‌a‌s‌u‌r‌e‌d a‌s 0.97, 0.93 a‌n‌d 0.58 t‌i‌m‌e‌s t‌h‌e f‌l‌o‌w d‌e‌p‌t‌h a‌t t‌h‌e s‌t‌a‌r‌t‌i‌n‌g p‌o‌i‌n‌t o‌f t‌h‌e b‌e‌n‌d r‌e‌s‌p‌e‌c‌t‌i‌v‌e‌l‌y. I‌n t‌h‌i‌s p‌a‌p‌e‌r, t‌h‌e r‌e‌s‌u‌l‌t‌s a‌r‌e d‌i‌s‌c‌u‌s‌s‌e‌d a‌n‌d a‌n‌a‌l‌y‌z‌e‌d.

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. .

Erosion under the conveying pipeline affected by river flow at the cross to rivers is one the important reasons for breaking the pipelines that can lead to leakage. While the mechanism of erosion under the conveying pipeline in steady flow has been studied by many researchers, studies have shown the importance of scouring research in flood times under unsteady conditions. So, this study has been concerned with the investigation of bed river erosion under the conveying pipeline at the conflict of river in unsteady condition. To achieve this aim, some effective hydrograph's parameters were changed in different scenarios and the results were compared to the steady condition. The result showed the erosion's ratio of unsteady condition to steady one was 34 to 69 percent. Also, the rise of flood hydrograph's peak led to increasing depth erosion from 7% to 22%. [ABSTRACT FROM AUTHOR]

Occurrence of local scour is one of the most significant causes of damage to the pipes. Therefore, safe and economical design of pipes in the flow path requires a good estimate. In this study, based on the important and effective parameters in the scouring phenomenon, in order to develop educational patterns according to the data obtained in the laboratory of Ahvaz Islamic Azad University, models based on artificial neural networks were created with the NeuroSolution5 software. MLP, GFF and RBF were the models used in this study; after comparing, MLP was selected as the basis for our study. Finally, the effect of each parameter on scouring was determined using the artificial neural networks technique, based on which the shields parameter with a very high effect (more than 95 percent) was determined as one of the most effective causes of the local scour. [ABSTRACT FROM AUTHOR]

Experimental and numerical study of scouring pattern on the direct and polo-shaped groynes have been investigated in this paper. In this study, direct and polo-shaped groynes models with a length of 0.12 meter have been used in discharges of 10.5, 15, 20 liters per second in a direct flume. The results showed that the maximum scour depth formed around the groyne head of direct and polo-shaped types has increased with augmentation of flow discharge, which was 0.095 and 0.104 meter in the case of 20 L/s discharge respectively. Also, the width of scour hole was 2.25 and 2 times of effective length of the groyne in direct and polo-shaped groynes respectively. In this regards, maximum scour depth around the head of groyne was seen 0.87 and 0.79 times of the effective length of the groyne. Sand form located at downstream of the direct groyne at the distance of 0.09 and 0.15 meters from the side wall of direct groyne was stretched and extended to about 1.3 times of the channel width as well. While the length of the sand form for direct groyne was 1.15 times of the channel width. Overall, the dimensions of the scour hole around the polo-shaped groyne, was less than the direct groyne. In addition to understanding the hydraulic behaviour around the groyne, Flow3D software was used. Statistical survey of the results obtained by experimental and numerical models attested that the relative error of the numerical model could be about 20%, which shows an appropriate performance of using Flow3D for predicting the maximum scour depth. [ABSTRACT FROM AUTHOR]

Flow pattern around the bridge piers includes water surface profile, velocity profile, shear velocity, shear stress distribution, etc. In this research, the effects of the base shape along with scale effects on the flow pattern around the rectangular bridge piers were numerically calculated through "Fluent Software", using Horizontal Velocity Distribution (Vx) and Vertical Velocity Distribution (Vy) criteria. The results showed that in studying the horizontal component of velocity (Vx) for the rectangular bridge piers, the vortices activity radius was 8 times of the length of the pier, and the minimum channel width for vortices activity was 16 times of the length of the Bridge pier; also, the minimum channel length in front of the pier was 4 times of the length of the pier and behind which, it was 25 times more than the bridge pier. Finally, the minimum channel length for the vortexes activity was calculated to be 29 times more than the bridge pier length. Furthermore, for the vertical component of velocity, the flow pattern around the base of the bridge cannot be an appropriate parameter for checking the effects of the length and width of the channel. [ABSTRACT FROM AUTHOR]

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.

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.

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.

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.

A number of experiments have been carried out in the current paper to investigate the effect of adding a longitudinal impermeable blade beneath the offshore pipelines on decreasing the scour around them. The main aim of this study was to reduce the hydraulics gradient beneath the pipe so that its magnitude recedes from the critical hydraulics gradient and therefore delays the onset of scour phenomenon or stops its process at all. Three pipes of different diameters were selected for the physical models of this study. Each pipe was tested using six blades with different relative widths. Also, a series of numerical simulations have been done using Flow3D software in which the similar boundary conditions as used for the physical models were applied. In both experimental and numerical investigations the reference sample that was an unprotected pipeline was first tested. Then blades with different relative widths (e.g, 0.05, 0.10, 0.15, 0.20, 0.25, 0.50) were added to the beneath of the pipeline and their performances were tested and analyzed against scour. The experimental and numerical results were in good agreement and they indicate a remarkable reduction in scour depth when a blade with the distinctive relative width was sticked to the pipeline.

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.

Some Experiments were conducted in water research center, for five specific discharge and four tail water depth to investigate effects of parameters like specific discharge and tail water depth. To carry out the experiments we made use of the hydraulic model of Azad dam. Measured parameters are: Maximum depth of scour, distance of maximum scour depth from bucket, the maximum length of scour hole and maximum width of scour hole. By using nonlinear regression analysis to predict the scour hole dimensions some relations were achieved. These relations were tested by applying experimental data from other investigators. in this research The results have showed the relative ability of the presented relations. Scour wide and the place of maximum depth are estimated appropriately by using of these relations. The relation of maximum depth is compared with another famous relations and showed weaker results. The best results was for Martins B relation.

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%.