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Most previous laboratory studies of local scour at bridge abutments were performed in rectangular channels in which the distributions of flow velocity and bed shear stress were considered uniform in the transverse direction. In reality however, bridge abutments are usually located in the floodplain zone of rivers where velocity and shear stress distributions are directly affected by the lateral momentum transfer. The influence of channel geometry and lateral momentum transfer in compound flow field on scouring phenomenon, however, has not been fully investigated and understood as yet. This paper presents the results of an experimental study performed to investigate the impact of both sediment size and lateral momentum transfer on local scour at abutments terminating in the floodplain of a compound channel. It is shown that, by accounting for lateral momentum transfer at small floodplain/main channel depth ratios (yalH<0.3), estimates of maximum local scour depth are increased by up to 30% . In relation to the sediment size, earlier studies of scouring around circular bridge piers proposed a limit for the relative size of sediment (pier diameter/median size of bed material) beyond which the sediment size has no effect on the equilibrium scour depth (Ettema, 1980; Chiew, 1984). The results of the current laboratory studies, however, indicated that the limit established for circular bridge piers might not be appropriate for the abutment case installed in the floodplain zones; further studies are required to draw a more general conclusion regarding the effects of relative grain size in the abutment case.

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Grade-control structures are aimed at preventing excessive channel-bed degradation in alluvial channels and at the outlet of a grassed waterway to stabilize the waterway outlet. The erosive action of the weir overflow may, however, cause significant local scour downstream and may endanger the stability of these structures. The scour process can be split up into different time phases. In the beginning the development of scour is very fast, and eventually an equilibrium situation is reached depending on clear water or live bed flow condition. Appropriate design of grade-control structures requires estimate geometric characteristics of the downstream scour. The local scour downstream of a grade-control structure located on an alluvial bed is a very complex and dynamic phenomenon which is influenced by many parameters. Most of these parameters are related to each other and determination of them is difficult. The estimation of maximum scour depth is very important in planning, design and management of hydraulic structures. Therefore, there is a great need to develop good prediction methods for geometric characteristics of scour hole downstream of grade control structures. Some of researchers studied scour downstream of grade-control structures and presented different empirical equations for estimation of maximum scour depth based on experimental data. The results of literatures show that the equation of D'Agostino and Ferro (2004) can be used as one of the most important empirical equations to estimate the maximum scour depth. In this study, coefficients of D'Agostino and Ferro (2004) equation to estimate of the maximum scour depth, horizontal distance between the weir crest and the maximum scour depth position, horizontal distance between the weir crest and sand deposition and maximum height of sediment deposition, were optimized by applying genetic algorithm. For this purpose, the field and laboratory data of Veronese (1937), Bormann and Julien (1991), D’Agostino(1994), Mossa (1998), Lenzi et al. (2000), Missiaga stream (2004), Falciai and Giacomin (1978), Some large-scale data ((Veronese 1937), Scimemi (1939), Whittaker and Schleiss (1984)) and shahabi (2010) were used for training and validation of the equations. The efficiency and accuracy of each equations were examined based on statistical Analyses such as percent error, root mean square error, mean bias error and correlation coefficient using independent data sets of training data and were compared with the results obtained from the equations proposed by D'Agostino and Ferro (2004). The results show that the value of percent error, root mean square error, mean bias error and correlation coefficient for maximum scour depth, horizontal distance between the weir crest and the maximum scour depth position, horizontal distance between the weir crest and sand deposition and maximum height of sediment deposition were 46.09, 11.78, 10.28 and 118.05, respectively. The corresponding values are 128.1, 27.73, 15.23 and 194.46 by using D'Agostino and Ferro relation. The results showed that the root mean square error and mean bias error are decreased by using proposed equations and the accuracy of obtained results by presented equations is higher than D'Agostino and Ferro (2004) equations. So it is recommended to use the proposed relations for assessing the characteristics of scour hole downstream of grade control structures.

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One of the most frequently encountered cases of rapid varied flow is the hydraulic jump. Stilling basins are used to dissipate the excess kinetic energy of flow to ensure the safety of overflow spillway, chutes, sluices, pipe outlets etc. in this study the topic of block in stilling basins is investigation in a general approach and it’s effect on energy dissipation and downstream scouring are analyzed. In the present research, the energy dissipation and scouring phenomenon were studied in different hydraulic and geometric conditions. Moreover, the present paper was focused on the effect of presence of blocks as an effective parameter on energy dissipation on stilling basin performance. To analyze and assessment of formed hydraulic jump in the stilling basins, the experimental data of many recent researches were achieved and compared. It was concluded that presence of blocks has significant effect on energy dissipation from 1% to 34%. It is also shown that with increasing the Fr Number, the secondary depth increases and the using a rough bed causes reducing the secondary depth between 18% to 37% in comparison with smooth one. Moreover, installing a rough bed also reduced the length of hydraulic jump between 27% to 67%. Using block in the stilling basins, reduces the scouring depth from USBR standard recommendation. Finally, it was concluded that using blocks increased the efficiency of the stilling basin performance.

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Submerged vanes are simple structures that can be used to control the sediment and redistribute the flow and sediment in open channels. Submerged vanes are low aspect ratio flow-training structures mounted vertically on the riverbed at an angle to the prevailing flow. The technique of submerged vanes is a new and efficient sediment management method in rivers. Odegard and et al (1991) are the creators of the idea of using vanes, they have chosen the angle of the vanes between 15 to 25 degrees and found that the vortex created by the vanes causes a change in the amount and direction of shear stress and dispersion velocity and depth,is resulting in sediment transport. When a submerged vane is installed in the river bed with a small angle to the flow direction, due to the pressure difference on either side of the vane, vortex and induced circulation is created around the vane. as a result of this vortex, at the downstream of vane, sediment are taken from the suction side of the vane and are deposited on the pressure side of the vane. So by installing a row of vanes on the riverbed, sediment can be distributed over a larger surface. In river meandering, when flow passes through a bend, reduction of flow velocity and rising hydrostatic pressure cause super elevation phenomena at outer side and reduction of water surface at inner-side of the bend. A helical motion results, causing erosion of the outer side of the bend. Installation of submerged vanes on the stream bed can reduce erosion of the outer bank significantly. Most of previous studies in this regard have been tasted in a rectangular flume cross section. In this research use of submerged vane and its influence on the bed topography changes, especially around the bridge pier is studied. Experiments were conducted in the laboratory flume with a 180 degree bend with rational curvature of 2 , height of 90 cm, width of 100 cm and a length of straight direction upstream and downstream of the bend respectively 6.5 m and 5 m, material with specific gravity of 1.5 and a cylindrical pier of 5 cm diameter, With clear water conditions u_*/u_(*c) =0.97 ,the water discharge of 70 liters per second, with a depth of 18 cm was tested. The vane was made of 10 mm thick plaxi glass. The height of the vane above the streambed level was 4.5 cm, 75% of the flow depth. and its length is 7.5 cm (1.5 D, D= pier`s diameter). Dissimilar arrays of vanes with same angles (25 degree) to main flow direction were employed. Five experiments were carried out considering various positions of the submerged vanes and one experiment was done without the presence of vanes, only with a bridge pier located at 90 degrees. The performance and efficiency of a submerged vane is related to its position. The results illustrate that the experiment with vanes in parallel, by overlapping of 50%, under angle of 25 degrees counterclockwise with the horizon in the direction of flow, has the best performance in control of pier scour protection.

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Local scour around bridge pier is one of the important problem in bridge stability against water flow that is created due to hole scour around bridge pier and castrates its stability. So as, providing methods for control and scour reduction around bridge pier have very importance. Yet different methods have been proposed for preventing and reducing the local scouring around the bridge pier. Use of Submerged Vanes is one of the methods that researchers are interested in. Submerged plates are thin rectangular structures that because of having angle with the flow direction, is created high pressure and low pressure region on both sides. These structures create a secondary vortex and change the flow pattern in the river bed and as a result, change the sediment and scour transmission. Submerged vanes performance to reduce the bridge pier scouring the sediment movement around the vanes due to the downward flow in front of them, are affected by the layout of the plates. These vanes are designed in cross section of the channel and fixed with a little angle relative to flow direction perpendicularly on bed. In this research, submerged vanes were used to reduce the local scour around the single bridged pier located in bend head. Effective variables in this study were vanes overlapping length, space of submerged vanes from bridge pier center and space of submerged vanes from each other perpendicular state on flow direction. For this purpose, a cylindrical bridge pier to diameter 5 cm in the laboratory was performed with a sharp bend 180 degree with central radius to channel width ratio equal 2, a width 1 meter and height 90 cm with straight direction length of bend upstream 6.5m and straight direction length of bend downstream 5m in clear water conditions( u)⁄u_c =0/98 with water discharge of 70 liters per second and depth 18cm. The submerged vanes were Plexi Glass with width 1.5 equal pier diagonal (7.5cm), thickness equal 20% pier diagonal and located in 25 angle relative to horizon with height of out of bed 4.5cm (submergence percent 0.75) with sitting vanes center in the middle of channel (50% channel width from inner shore, with overlapping length (Lcv) 80 and 100% and intervals of submerged vanes from each other perpendicularly on flow direction 5 and 10cm (Lvv/D)=1.2 in position 83 and 79.5 degree from beginning of the bend (interval equal 5 and 7.5 pier diameter toward upstream from located pier site) (Lvp/D=5, 7.5). According to the results of this study, the 20 percent reduction in the overlapping length of the submerged vanes decreases the depth of the scour hole around the bridge pier about 30 percent. Also use of submerged vanes, is transferred location of maximum scour depth to a place near than pier and limited width of scour hole around pier. Furthermore, submerged vanes limit sedimentation region to 0-12% channel width from inner shore and in 70-127 degree from the beginning of the bend. Minimum and maximum scour in hole around pier with submerged vanes is created 0.53 and 0.65 equal flow depth in the beginning of the bend in V80-5-2 and V100-7.5-1 Tests, respectively. The discussion about the results of this research is from the other parts of this article.

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Study of different scouring areas relative to flow velocity in Downstream Base in pairs of bases and Impact of cable protection method on these areas Abstract Bridge failure is a common phenomenon all around the world. Bridges are one of the most important structures which are under attention from many years ago. Bridge is a structure to cross over obstacles such as rivers or valleys. Investigation of scouring in water structures especially in bridges is absolutely important in river engineering. Failure of several structures in all over the world are usually due to structural consideration and giant scales on piers. Created procedure of scouring by group of piers are more complicated than one single pier. Increasing the resistance of bed materials and decreasing the power of erosion factors are the ways to stand against local scouring. To decrease the power of erosion factors (horseshoe and wake vortex), equipment such as collars, submerged vanes and etc. are being used. This study was conducted with freshwater on cylindrical piers. The experiments were with a constant discharge during 6 hours in hydraulic laboratory of Ferdowsi University of Mashhad using a flume of 10 m length, 0.30 m width and 0.50 m depth. Sands with median diameter of 0.72, special gravity of 2.65 grams per cubic centimeters and geometric standard deviation of 1.12 are used in the experiments. Range of flow rate was from 8 to 18 l.s-1. An adjustable weir in the downstream regulates the water depth in the channel. The area for conducting the experiments in the channel has 1 m length and 10 cm bed height, which is 6 meters away from the beginning of the channel. Scouring procedure of downstream pier was investigated base on flow velocity. Results show that depth of local scouring of downstream pier can be categorized in 4 zone based on flow velocity: 1- No scouring occurrence zone, 2- Synchronized scouring zone, 3- Transitional zone, and 4- Deviance zone. Following previous investigations, effects of application of rolled cable over piers on reduction of scouring around two piers and zones of downstream pier (zones related to velocity) were examined. In this study, the efficiency of using rolled cable around the piers to decrease scouring is investigated. Results show that rolled cable, scouring will decrease. In fact, rolled cable around the piers will decrease the power of down flow, horseshoe and wake vortexes. Results show that scouring was reduced around piers due to application of rolled cable. So that cable at its best state reduces the maximum scour depth by 50 percent for downstream pier in the situation distance 3D and 54 percent for downstream pier in the situation distance 5D. Reduction of scouring depth of downstream pier was less than upstream piers. Scouring depth of downstream pier with rolled cable was 7 and 26 percent reduced in comparison with piers (No rolling cable was used) located at 3D and 5D from it. Because of scouring reduction as consequences of rolled cable, downstream zones were significantly changed that finally caused synchronized zone removal. Keywords: Local Scouring, Base group, Protective method, Downstream Base, Scouring zones

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Improvement of the river route is one of the goals that considered in using a spur dike to control the flood, prevent bed erosion, stabilize and protect the walls, and set river width. Spur dikes are structures that with adjustment hydraulic conditions and make smooth flow cause to reduce flow erosion power and the ability to carry sediments. And also makes good situations for sedimentation and sides consolidation. Spur dikes are permeable and impermeable. Impermeable spur dikes have different shapes which according to erosion amount and condition can be used. Common spur dikes have simple, L and T-shaped geometric shapes. This research has been conducted to optimize the various combinations of spur dikes to reduce scouring. All of the scour and flow measurements were collected in a flume with 14 m long, 1.5 m wide, and 0.6 m deep located at the Soil Conservation and Watershed Management Research Institute. Impermeable spur dike with different geometric shapes were tested in a series with 3 spur dikes for different compositions in U/Ucr≈1 conditions. Due to threshold flow condition by using Shields parameters in all tests, the calculated discharge at the mentioned conditions is 28.5 Lit/s. So according to discharge and flume dimensions in all the experiments, thereby concentrating on clear-water scour condition, flow depth (y) was taken as 0.06 m. For determine the equilibrium scour depth for each geometric, control test with 30 hours have been done. The first spur dike in all combinations was T-shaped. The results show that for first spur dike in combinations, in 10% of scouring equilibrium time, about 90% of scouring occurred. So with these results, 300 min (5 hours) test time was selected for do all main tests to achieve more than 85% of scouring. Also, in the results of different tests it was observed that maximum scour depth happens around first spur dike. So geometry of first spur dike is very important in reduce average scour depth in combinations. Mean scour depth in these combinations for first, second and third position respectively are about 2.44y, 1.21y and 0.75y which in that for second and third positions with 50% and 69% have fewer scour depth in comparison with first position. Combination (T L T) is the best composition for the lowest average scour depth in all three positions, which 2 times the flow depth have erosion. The best performance in the whole range of spur dikes due to the amount of erosion volume is for the composition (T I I), that’s about 70% of the massive erosion in other compositions. Mean scour depth in all positions for these 2 series are 1.39y and 1.63y. Average scour depth in (T T T) series is 1.41y which more than (T L T) combination. The reason for this results can be effect of middle L-shaped spur dike on T-shaped spur dike scour depth in third position. This effect cause to reduce scouring in about 28%. (T I I), (T L T) and (T T T) series spur dikes are the best combinations which each one has special performance, therefore, for design, the best composition should be choice for target of exploitation and optimal economic conditions.

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Nowadays, extraction of materials from river bed is one of the effective factors in the occurrence of scouring phenomena around bridge piers. The extent of scouring around the bridges depends on a number of factors, including the type of foundation, the Froude number, flow rates and bed granulation. In , in vitro evaluation of scouring around piers groups in two different grains was investigated. The effect of scouring and armoring of scours in scouring control was investigated in both natural and river conditions. In the present study, 44 experiments with identical laboratory conditions were tested in a rectangular channel with of 13 m, width of 1.2 m and depth of 0.8 m. In this study, 44 experiments were conducted in two models 1 (control or simple groups) and model 2 (modified groups), both scaling behavior. B = 0.7) and Bꞌꞌ (= 1.7 mm) were analyzed. In addition, to investigate the effect of material extraction on the scour rate of bridge pedestals, experiments were conducted for both pit-bed (pit-extraction mode) and pit-free bed (river natural state). A removable sand bed with a height of 22 cm was placed between the floorboards. Two series of pedestals were located upstream and downstream of the bed with a clear distance from the flooring. The pedestals were arranged in the same arrangement (consecutive tripods in the direction of flow and in the center of the channel width) with center to center 21 cm apart.
  The results showed that the armed (rough) pier group was less than the simple pier group (flat surface), due to the excavation of river materials, it increased the scour equilibrium time. The armed pier group also controlled the impact of extraction of materials on the scour rate. By examining the upstream and downstream materials mining, it was observed that extraction of materials of upstream of pier group decreased and extraction of materials of downstream pier group increased the scour. Therefore, it can be concluded that the scouring of pier is more sensitive to the downstream pit hole and even the mining of materials from upstream of the pier should be possible. In other words, the percentage of scour depth reduction in downstream bed due to extraction of materials and percentage of scour depth in upstream bed of extraction of materials in model with armed pier group were higher and lower than model with simple pier group, respectively. The percentage of scour reduction due to armed of the pier was also studied and it was observed that at best, the maximum scour depth in the aggregate with mean diameters of 0.78 mm and 1.7 mm by armed pier group were 55 and 66 percent, respectively. It is also observed that the extraction of materials from the bed increases the equilibrium time. It should be noted that scour is balanced when the driving force is approximately equal to the resistive force (particle saturation weight). The results show that the presence of the pit leads to an increase in the scour equilibrium time. In other words, when the sediments reach the pit site, due to the decrease in water velocity and increasing depth, the flow cannot carry the larger sediments and the sediments settle in the upper wall of the pit.