Bridges are one of the most important structures which are under attention from many years. Bridge is a structure to cross over obstacles such as rivers or valleys. In recent decades, despite using modern materials and technology, and spending lot of costs for designing and building bridges, failure of them are commonly reported due to flood and Local Scouring. Local Scouring occurs by placing obstacles such as abutments in flow direction. Different methods of reducing scour hole have been investigated by researchers. (Johnson et al. (2001) and Kayaturk et al. (2012)). The methods of scour reduction are divided to two main groups, known as direct and indirect methods. In direct methods or bed resistant methods, the resistant of bed against Scouring is increased by adding different materials to the bed and near groin. In these methods, flow patterns remain constant but resistant of bed materials increases. Morales et al. 2008 investigated these kinds of methods by using of gravels and rocks. Korkut et al. 2006 used sacks of sands (geo bag). In indirect methods which are known for changing flow pattern, changes are made to flow pattern to reduce the power of destructive vortexes or remove them from head of abutment. Examples of investigating these methods are using parallel walls in abutments by Li et al. 2006, using submerged plates by Johanson et al 2001 who investigated a short vertical abutment in flood plain of a river. They investigated effects of different cases of placement submerged plates in main channel on water Scouring. They reported that these plates eliminate vortexes from abutment and scour hole will transfer to the middle of the river; however scour depth will increase in this method...

Scouring around bridge piers causes serious damages to these structures all around the world every year. In order to control this phenomenon, riprap is placed around the piers to increase streambed resistance (direct method). However, in indirect method, some partitions such as collar slot and submerged vanes are used to reduce Scouring caused by horseshoe vortex and downstream flow. In this research, effect of two types of square and circular collar on a single cylindrical model has been investigated. The results showed that using the two kinds of collar, especially below bed level decreased the scour depth. Square collar was more effective than circular one in decreasing the scour depth. The square and circular collars showed 70% and 50% decrease in the rate of scour depth, respectively, as compared to pier without any collar.

The structure of turbulent flow over the scour hole is important for understanding the sediment particle entrainment and transport. In the present study, stochastic nature of turbulent flow around a bridge pier under a clear water regime has been investigated experimentally. Inside the scour hole, near the bed, the flow does not have enough energy to transport the particles; hence, the sedimentation occurs in this region. The particles in the scour hole near the bed are lifted up, however, they cannot move along the flow and finally they return to the bed. By comparing depth average values of the occurrence probabilities at the pier upstream, it was found that the sweep events probability is more than other events, which followed by ejection, outward and inward interaction. Since the sweep events are dominant phenomena at the pier upstream, the maximum scour depth takes place at this region and the eroded sediments are transported heading downstream. Scour is a natural event caused by the erosive action of flowing water on the bed and banks of streams, which also takes place on region near the bridge piers and abutments. The stochastic nature of turbulent flow around the bridge pier has been investigated only in handful studies; therefore, the precise effect of pier on sediment transport is yet unclear. Kline et al. (1967) have introduced the concept of bursting phenomenon as a mean to describe the momentum transfer between the turbulent and laminar region near the boundary. Lu and Willmarth (1973) introduced the quadrant analysis for studying the the bursting phenomenon structure. The quadrant analysis was employed to determine the occurrence frequency of each individual event within a bursting process, i. e. outward interactions, ejections, inward interactions, and sweeps. Jafari and Keshavarzi (2010) investigated turbulence flow and sediment entrainment over the ripples by using quadrant analysis. However, despite the importance of coherent structures of turbulence and in particular the bursting events around the bridge pier; their characteristics have not been investigated in detail. Since the quadrant analysis is a powerful technique to recognize the structure of the bursting phenomenon and consequently to find the susceptible regions for sediment entrainment and deposition, this technique is considered in the present study to investigate the coherent structure of turbulent flow in Scouring process around the bridge pier. The experiments were carried out in a smooth rectangular flume with 8 m length, 0. 4 m width and 0. 6 m height. The channel entrance was filled with sand in order to generate fully developed flows. The working section, in which piers were located, was 1. 6 m long with a 0. 15 m recess on the bed and was located 4 m downstream from the flume entrance. The recess was filled with 0. 72 mm mean particle size uniform sediment and the standard geometric particles deviation was 1. 12 mm. Uniform sand, having the same size as that used for the Scouring test, was glued over the false floor. The velocity profiles were measured around the bridge pier. In each vertical profile at least 20 points were measured within the flow depth from the bed. The ADV readings were taken when the scour hole was at the equilibrium condition. The variation of the fractional contributions, |Si, H|, as a function of the hole size H for each of the four quadrants at z/h=0. 2 (near the scour hole edge) at the up and downstream of the pier are shown in Fig. 1. At z/h=0. 2, quadrant (II) and (IV) events are dominant and quadrant (I) and (III) events appear to contribute weakly to the Reynolds shear stress production. Generally, by increasing the hole size, the contribution of each event to the Reynolds shear stress generation becomes small. As indicated in Fig. 1, at the pier upstream at z/h=0. 2, ejection (|S2, 0|≈ 0. 8) is the dominant event which is followed by sweep (|S4, 0|≈ 0. 6). The sweep contribution tothe Reynolds shear stress production becomes negligible for H>10, whereas the ejection contribution is significant even at H>20. On the other hand, the contributions of outward and inward interactions to the Reynolds shear stress are rather weak (|S1, 0|=|S3, 0|≈ 0. 2). These contributions vanish when H>6 and H>10 for quadrant (III) and (I), respectively. At the pier downstream, the contribution of each event to the Reynolds shear stress production is more significant than pier upsream. In this region, at z/h=0. 2, the contributions of ejection and sweep become comparable (|S2, 0|=|S4, 0|≈ 1. 4) and both are greater than the outward (|S1, 0|≈ 0. 9) and inward interaction (|S3, 0|≈ 1). For each of the four quadrants at z/h=0. 2 in the pier downstream the contribution of each event to the Reynolds shear stress is still significant for hole sizes as large as H>20. Therefore, at the pier downstream, although quadrant (II) and (IV) are more significant, each of the four quadrants has important effects on the Reynolds shear stress. Fig. 1-Variation of |Si, H| with H for z/h=0. 2 at upstream and downstream of the pier for each quadrant (I, II, III, IV)

Scoure is the removal of particle sediment which results variation of flow pattern. Local scour is considered as one of the reasons of instability and ultimately failure of bridges. Therefore, proposing some controlling methods to reduce this phenomenon is essential. In the study, effects of two types of squar and circular collar on a single cylindrical model have been investigated. In the next step by providing a slot through the pier and combination of collar and slot was used to investigate the Scouring reduction. The results showed that use of both collar, specically below bed level decreased the scour depth. Square collar was more effective than circular in decreasing the scour depth. Combination of slot and collar on the pier could further reduce the Scouring depth in which a square collar with W/D=2.5 in the bed with a slot near the bed reduce Scouring depth up to 80 percent consequence.

Bridges are the most important structures in river engineering. One of the most causes in bridges destruction is Local Scouring around the bridge piers. Many bridges failed in the world because of the extreme scour around piers, which have caused to disappear a lot of investments. Then, it is essential to predict the scour depth around bridge piers. In this research, the Fluent three-dimensional numerical model was used to investigate the Scouring around the group cylindrical pier in clear water and uniform sand bed conditions. In this model, sedimentary flow was considered as two-phase flow (water - sand) and Eulerian two-phase model was used. To estimate the parameters of flow turbulence in the water phase, the RNG K-e model was used. To evaluate and verify the numerical model, the computational results were compared with experimental data. The maximum scour depth in front of the first pier on a numerical model equal to 12.5 cm and in experimental model equal to 12 cm have been measured. Also scour depth at the second pier less than that at the first pier and scour depth at the third pier has been less than the values of the first and second pier. The results showed that the two phase model can simulate the scour phenomena around the pier.

Spur dikes are structures that constructed for protection of the river walls against the erosion. Spur dikes are generally built perpendicular or at an angle to the river bank or revetment, protruding into the watercourse. The effect of the geometrical characteristics of the hockey spur dikes on formation developing of scour hole has been rarely studied. Spur dikes. The current study aims to evaluate the effect of the length of the hockey spur dike on the formation and development of scour hole and comparing with that effect in L-shaped spur dike. In this direction, all experiments were done in clear water conditions using the spur dikes in length of 8 cm and 12 cm and in a laboratory flume. The results asserted that the dimensions of the scour hole and the length and thickness of the sedimentary hill were increased by raising the length of the spur dike. However, this increment was lower in hockey spur dike than the L-shaped spur dike. The maximum depth, area and the volume of the scour hole were also increased by raising the length of the spur dikes. This increment in-average was equal to 57.5 and 67.7 per cent in L-shaped spur dikes and equal to 33.3 and 42 per cent in hockey spur dikes for two different lengths of spur dikes. Furthermore, no Scouring was observed in downstream section of the hockey spur dikes near the wall. Therefore, the dimensions of the scour hole around the hockey spur dike was lower than those in the L-shaped spur dikes.

Using of spur dikes is one of the usual methods in river engineering for river bank protection against erosion and destruction due to water flow. In this research the influence of Bandal-Like spur on the erosion pattern in non-submerged conditions was investigated. Experiments were performed in clear water condition, considering 3 spaces between Bandal-Like spurs, 3 placement angels of 1- Bandal-Like spur Bandal-Like spurs and 4 discharges in 45%permeability of Bandal-Like spurs. The results indicated that maximum depth of Scouring was occurred around first Bandal-Like spur. Also in a constant Fr, the maximum depth of Scouring decreased with increasing space between Bandal-Like spurs. Finally the impact of placement angel of Bandal-Like spurs on the maximum depth of Scouring with degrees of 60, 90 and 120 degree was investigated. The results showed that the maximum depth of Scouring in degrees of 90 and 60 degree are maximum and minimum, respectively.

The construction of bridges within the river beds often makes changes to the shape and direction of the rivers. These changes take the natural actions of the river, that one of them is the Local Scouring around the bridges' piers and can cause annually damage. Therefore, many researches have been carried out to control and reduce the Scouring. One of the methods presented by researchers is using slot at piers. In present study, the effect of Pier Opening Area on Local Scouring around the pier with rectangular section is experimentally investigated. For this purpose, piers with square shape slots and different dimensions were used. The piers were tested at three levels (near the water level, on the bed and under the bed) and four Froude numbers. The result showed that the maximum Scouring depth and the volume of hole scour had a direct relationship with slot level relative to bed and Froude number and an inverse relationship with Pier Opening Area. The best performance belonged to the slot with greater dimensions which was located under the bed level in the minimum Froude number condition that reduced the depth of Scouring about 55. 4 percent.

Background and objectives: The ecosystem and equilibrium of rivers can be significantly affected by the river bank erosion which can also limit the human access to the rivers. Groyne is an important river restoration structure that prevents bank erosion through deviation of flow from the river banks to the main channel. From the permeability aspect, these structures can be classified into three types of permeable, impermeable, and bandal-like ( hybrid type which includes permeable and impermeable types ). Moreover, these structures can be categorized to straight, T-shaped, and L-shaped configurations. This research aims to investigate the Local scour around a new type T-shaped bandal like groyne.Materials and methods: The total number of 66 experiments were conducted through a straight flume ( 12 m length, 0.6 m width, and 0.6 m depth ) under non-submerged and clear water conditions. T-shaped bandal like and T-shaped impermeable groyne structures were fabricated in three web to wing length ratios of 0.5, 0.75, and 1. Also, three upstream to downstream wing ratios of 0.5, 1, and 2 and the permeabilities of 33%, 50%, and 60% were selected for the T-shaped banal like structure. The experiments were carried out at the flow discharge of 6 Ls-1, 9Ls-1, 12 Ls-1 and 15 Ls-1 in the presence of the T-shaped impermeable groynes and the T-shaped bandal-like groynes.Results: It was revealed that, increasing the structure permeability resulted in decreasing of the maximum relative scour depth. Under 33%, 50%, and 60% permeabilities of the T-shaped bandal-like groynes, the maximum scour depth was decreased by 63%, 78%, and 83%, respectively compared to the T-shaped impermeable groynes. Moreover, it was observed that the maximum relative scour depth was increased by the average of 46% as for the greater values of structure length. The maximum relative scour depth was also increased for the greater values of flow discharge. It was found that there is no relationship between the maximum scour depth and the ratio of upstream wing length to the downstream wing length of groyne. Conclusion: Based on the results, the permeability and length of the groynes and the flow discharge are among the factors affecting Local Scouring around T-shaped bandal-like groyne. The significant decrease in the relative scour depth in T-shaped bandal-like groynes compared to T-shaped impermeable groynes indicates that the T-shaped bandal-like groynes have better performance than the impermeable ones in Scouring control, structural stability and river bank protection.