One way to reduce scour around bridge piers is to install a collar on the piers. The collar is a flat plate with small thickness which is installed on the bed or with a short distance from the bed. Installation of a collar on a pier will reduce the power of the down flow and horseshoe vortex. Many studies have been done on the performance of the collar, but the performance of the netted collar has not been examined so far. Therefore, the present study intends to analyze the performance of the netted collar around the oblong bridge pier. The experiments have been done on the flume with the length of 6 m, width of 73 cm, and a depth of 60 cm with a slope of near zero. In this study, oblong-shappe pier with 22.5cm in length and 2.5 in width, was used and after some experiments, the dimensions equal to 7.5×27.5 were selected for the collar.
In this study the effects of installing simple collar and three netted collars (with opening parts equal to 30 percent, 50 percent and 70 percent) around the oblong bridge pier in four levels including on the bed, 0.1B under the bed(B: pier’s width), 0.5B and B above the bed and three Froude Number equal to 0.13, 0.16 and 0.19 in clear water conditions, one examined. By installing the collars on the pier, the scour was decreased in comparison with the experiments without using collars. The use of netted collar with an opening percentage of 50 percent showed best results in Froude Numbers equal to 0.13 and 0.16 with 63 percent and 67 percent decrease in maximum height of scouring. The levels of installation under the bed and on the bed were the best position to install the collars. On the bed, the simple collar had best result by 100% efficiency in reducing the scour. In the level of under the bed the simple collar and netted collars had the same performance and scour depth were decreased by 88%.

 Bridges are one of the most influential structures in open channel hydraulic and river morphology. One of the methods to reduce scouring around the piers of bridge is to install a collar on the pier. In the present study, the effect of the netted collar on the scouring of the bridge piers is studied using numerical methods three dimensional computational software engineering FLOW3D is emploied for this study. Three important steps in implementing a software model to simulate the hydrodynamic phenomenon include calibration, validation and prediction. In this study, for the numerical of the model the laboratory results of Jalili (2013) was used for calibration. In order to calibrate the model, the turbulence models LES, k-ε and RNG k-ε were evaluated. The results showed that the k-ε model in numerical simulation of scouring with 5% yields better than the other two turbulence models. After calibration, entrainment coefficient (Ce) and bed load coefficient (Cb) were selected to be 0.5 and 9 respectively. A bridge pier with a diameter of (D) 4 cm and a circular collar with a diameter of 3D were simulated. The simulations were performed with three Froude Numbers of 0.19, 0.21 and 0.24. Changes in scour hole were examined by placing collar at five levels equal to D, 0.5D, 0.33D, 0.25D and on the bed at Froude Number of 0.19 and level 0.25D for Froude Numbers 0.21 and 0.24. Also, the performance of four simple collar, 15% netted, 30% netted and 40% netted were evaluated in the variation of scour hole. The results show that the strength of the horse vortex was decreased by installing of collars. Therefore, decreasing of scouring was seen in total simulations rather than simulation without using collars. In Froude Number of 0.19, at a distance of 0.25D from the bed, the simple collar has the highest efficiency in reducing scouring and between the netted collars the best performance was 40% netted collar. The results also showed that the collar installed on bed surface has the best efficiency in reducing scour. In Froude Number of 0.21, 15% the netted collar and in Froude Number of 0.24 the simple collar,showed the best efficiency.

 Crossing the bridge over the river will cause a change in the river flow system and can cause serious problems for the structure. One of these changes is the formation of vortex systems around the pier and the bridge abutment which causes erosion of the bed of the channel around these obstacles and formation of scour hole. Collar is a flat plate installed on the pier to weakening the pattern of flow around the piers. In this study, the effect of netted collars on scouring of cubic and cylindrical pile groups with side length (B) or diameter (D) equal to 4 cm under clear flow condition was investigated. The collars had no opening portion (simple collar), 30, 50 and 70 percent of opening portion and the size of 3B or 3D. The cubic pile group was tested with the presence of collars in three levels on the bed, equal to 0.5B and B above the bed in the Feroud Numbers of 0.16, 0.14 and 0.12. Also, the effect of collars around the cylindrical pile group in two levels on the bed and 0.5D above the bed was investigated in the Feroud Number of 0.16. the result show that a simple collar placement on the bed of cubic pier in Feroud Number of 0.16, reduced the 95% of scour in compare to the non-collar state. In this Feroud Number, the 30 percent netted collar completely controled the scour around cylindrical pier. The 30 percent netted collar on the cylindrical pier at the 0.5D level showed the best result with 57% efficiency; while other collars at this level could not have a great effect on reducing scour depth. For the cubic pile group, the 70 percent netted collar at 0.5B level from the bed and the 30 percent netted collar installed on the bed had the greatest effect on scour reduction with a decrease of 86 and 84 percentage scour, respectively. In general, for all experiments, with the reduction of the collar level, its efficiency was increased; only the 70-percent netted collar around the cubic pile group due to the full development of the boundary layer flow around the collar showed the best result at the 0.5B level. In the Feroud Number of 0.14, all collars reduced 56 percent of the scouring, and the opening percentage did not affect on the efficiency. In the Feroud Number of 0.12, only 70 percent of the netted collar could reduce 33 percent of the scour; in other words, for high .openings portions, the collar could not have significant effect on the scour

The aim of this study was to investigate the influence of vortex caused by obstacles to the transfer of sediment in the lateral intake. To this end the cube obstacles with the confluence of the edge on, were used. Obstacles to side with the size of 25 mm, in both parallel and staggered arrangement in the main channel and on the sandy substrate with 0.65 mm diameter was used. The tests carried out in two modes with vortex impact caused by the obstacles and the vortex was being reduced. In order to reduce the effect of vortex, the pages between any two consecutive obstacles, was used. In all experiments, constant discharge of 25 liters per second was considered. Due to the effect of discharge ratio on the bed sediment transfer, testing research were made in four of discharge ratios 0.3, 0.35, 0.4 and 0.45. With reduce the vortex impact of obstacles in two parallel and staggered arrangement, the amount of sediment deposit around the entrance of intake reduced in comparison with the vortex case. The amount of sediment deposit in the main channel and intake, in both modes of vortex and reduce the impact of vortex, is more of control tests case. Vortex reduction caused by obstacles, increase the amount of sediment entering the intake compared to the control and Vortex case that Most of these deposits was occurred in parallel arrangement with the plates. The results showed that the installation of the plates between obstacles reduce the total volume of sediment accumulated compared to non-page, in the main and lateral channels. The amount of sediment accumulated in this case is over the accumulation of sediment in control case. The greatest reduction value of this volume occurred in parallel arrangement with pages installation and discharge ratio 0.4, equivalent to 16.2 percent. The staggered obstacles due to the intensification of vertices, scour around obstacles intensified and the accumulated of sediment after obstacles in this case is more than the parallel and control cases. Discharge ratio of the most important factors affecting flow separation zone at the beginning of the intake. In all three experiments the control mode, with Vortex and Vortex decreased, with increasing dewatering, length and width of the separation is reduced. Given obstacles to the staggered arrangement in the main channel, length and width of the separation zone compared to controls (without obstacles), is reduced. Placing obstacles in parallel arrangement, increases the width of the separation zone in a 0.3 and 0.35 discharge ratios and causes separation zone width reduction in 0.4 and 0.45 discharge ratios compared with controls case. Put the plates between obstacles and reduce the impact of Vortex, reduced the length and width of the separation zone in the staggered arrangement, compared to scenarios with Vortex (no pages) and control mode. Vortex effect reducing in parallel obstacles installation, reducing the length of the separation and increases its width.

Fluid density difference causes the movement of the density current in ambient water. Under-flow occurs when the fluid density is higher than the surrounding fluid. Concentrated in the area of ongoing contact with the ambient fluid, the difference between the two layers of the operating speed on the border to shear stress and the instability of the ambient fluid flow and thus the entry into concentrated stream to be the reason why the occurrence of the phenomenon of concentrated flow in the back of the reservoirs caused water pollution, clean the inside of the tanks. Immersion area is one of the areas of concentrated flow such that maximum amount of fluid on the entry into the thick flow. so far, many in the field of research, the understanding of the characteristics of this area has been done, mainly related to the understanding of the characteristics of this area is in direct routes. the research of flow behavior of concentrated salt in a Flume with three 90 ° arc with three different relative curvature radiuses: r/b=2, 4 and 6 and a direct route to the 1.8 meters, height is 70 cm and width is 20 cm in the hydraulic laboratory University of Shahid Chamran University of Ahvaz were studied. Tests on four discharges (1, 1.5, 2, 2.5 lits/s) and four concentrations (5, 7.5, 10, 12.5 g/lit) and three arc with Relative Curvature Radius 2, 4, 6 and a direct path and the slope was 33%. For measure the speed of fluid, we used the speedometer alubond acoustic Doppler (ADV) model Vectrino+. Vectrino+ water based on the phenomenon of Doppler speed measurement. It is also based on the value of the pulse intensity the playoffs the ability to measure the concentration of a fluid as well. The results show that the increase in the radius of curvature resulting in reduced centrifugal force and get high speed in the direction of the flow and this would increase the mixing coefficient can be caused. So on the third arch (the ratio of Relative Curvature Radius was 6) we had a most strongly mixing coefficient. When concentrations of density current were increasing, the height of density current was reduced. With regard to the reduction of the height of the flow and also reduce the severity of incorporation for an increase in the concentrations of it can be conclude that even if the fluid density is added on thick tend to inhabit clear water penetrate inside it is reduced and the fluid on the bed to the downstream side of the bounces. In this study we tried to check the mixing coefficient in the plunging area. It seems with effect of the pressure gradient, operating the Secondary flow corresponds to the ambient fluid near the plunge point in the clear water also plunging into the dense flow. Also in the context of the ambient fluid into the dense flow entering a relationship as well.

 

<p>Road or railway crossing over the rivers is limited to the particular reach of the rivers which is determined by the general direction of the road or railway. Moreover, the general direction of the road or railway determines the position of the bridge over the river. Selection of the bridge path angle relative to the river flow direction is very important. Sometimes, due to the geographical conditions of the region and the general direction of the road or railway, the bridge crossing directly perpendicular to the flow direction is impossible. In this case, the bridge deck diagonally crosses over the river and the bridge group piers are angled relative to the flow direction. In such case, the distance between the piers, the flow direction relative to the piers and the piers submergence are very important parameters which affect the scour depth. Therefore, in this study, the effect of the angle of the bridge group piers on the maximum scour depth at deferent angles relative to the flow direction (0, &pi;/18, &pi;/9 and &pi;/6) at the clear water condition and for the three Froud numbers (0.13, 0.15 and 0.17) were experimentally investigated. For this purpose, at the first position, the dicrection of the group piers is placed perpendicularly to the bridge deck. The result showed that with increasing the bridge deck angle relative to the position which is perpendicular to the flow (0 to &pi;/6) (increasing the angle of the bridge group piers relative to the flow direction), the maximum scour depth at the three deferent Froud numbers 0.13, 0.15 and 0.17 increases about 36.84, 28.57 and 25 percent respectivly. At the secend position, the bridge deck angle,similar to the first position, is placed perpendicularly to the bridge deck but the group pires are placed parallel with the flow direction. By comparing of the maximum scour depth at the two deferent position (for the similar angles and hydraulic conditions), it was found that the maximum scour depth at the first position is decreases relative to the secend position and the maximum amount of decreasing is equal to 30.67 percent that happens at the angle of &pi;/6 and the Froud number 0.13.</p>

 Abstract: Density current is one of the most important effective phenomena of sedimentation in reservoirs. Density currents that generated in mad made reservoirs are mostly under flow. If the reservoir ambient water is density-stratified, in this case the upstream flow at first will move as under flow and when its join to the density stratification layers the density current will separate from bed and intrudes into the ambient fluid in the form of interflow density current. Thus to understanding the interflow density current and the role of layers of dens fluid in separation point of density current from bed, the study was provided for investigate intrusion and movement state of dense flow in ambient layers, improve sediment management in reservoir and control these flow for prevent their damage.
To achieve the purposes of this research, a physical model is employed and the effects of discharge, concentration and the slope variations on the characteristics of separation point of density current Including the average height of density current at the separation point, the concentration profile body of density current before and after the separation point, the concentration of the ambient fluid at the origin of separate of density current from bed and the angle of separation of the flow body from the bed was investigated. A total of 48 experiments were carried out by 4 concentrations (5, 10, 15 and 20 grams per liter), 4 discharges (1, 1.5, 2 and 2.5 liters per second) in three slops 2.5%, 3.25% and 4% in a flume equipped to a changeable slope system, using a solution of water and salt to form a salinity stratification in the ambient fluid and mixture of water and sediment in order to form a turbidity current.
The results indicated the average height of the turbidity current body in separation point at all slope and concentration increase 35% in average, when discharge rise from 1 lit/s to 2.5 lit/s. Also increasing of concentration from 5 g/l to 20 g/l in all slopes and discharges, on average reduce 27 %. Furthermore by increasing the slope of the bed from 2.5% to 4%, for all discharges and concentration the average height of the turbidity current 29% increased.
The study also showed that the concentration profile body of turbidity current In terms of the under flow, the maximum value of the concentration profile was at the bottom of the body. But when the interflow turbidity current formed the maximum value of the concentration profile, shift to the upper layer of the current and as the interflow turbidity current move forward, the maximum point of concentration profiles will shift near to center of concentration profile. It was also found that the height of turbidity current body will increase when the discharge of current increased. However, profile of turbidity current longer and its high reduce when concentration increase. By analyzing the measured data related to the concentration of the ambient fluid in the turbidity current separating from the bed it was found that by increasing the flow rate and concentration of turbidity current, the momentum of flow increase And causing separation happens in more salinity rather than the state that discharge and concentration is less.
The measured rising angle of the turbidity current at the point of separation from the bed showed that in all experiments, the angle is always greater than the angle of flume bed. Also, the ratio of rising angle to the angle of the flume bed, with increasing discharge increases and decreases with increasing concentration.
By dimensional analysis and using measured data, two equations were developed for prediction of the average height of turbidity current at the separation point and the ratio of ambient fluid concentration to current concentration.

Sedimentation in dam reservoirs, is the most important factor reducing dam service life. Turbidity currents are sediment-laden flows, that motion under clear water of reservoirs in the form of layer. They are major and significant factor of sediment transport into the reservoirs, seas and oceans. Thus with recognition this type of flow and its influencing factors do the effective actions for management of reservoir sedimentation. Underflow turbidity currents are moving in the thalweg so they pass from meandering ways. One of the parameters in the changing of turbidity currents hydraulic is passing through this ways. Accordingly, in this study, the effects of bend curvature radius, turbidity current concentration and flow rate passing through three consecutive 90 degree bend has been investigated on thickness, velocity and concentration profiles of turbidity current body. For this purpose, the experiments were carried out using sediment dense flow with D_50=1.93 μm and 0.5 , 1.1 l⁄s flow rate in four concentrations at flume entrance (9, 14, 19, 23 g⁄l) with 20cm flume width and three radius of curvature (40, 80 and 120 cm), under subcritical condition of input flow. An Acoustic Doppler velocimeter used for velocity measurements. All the measurements were performed along the axis of the flume. According to the obtained results, upwelling of the water surface in the outer wall and height reduction in the inner wall of the bend by turbidity current passing through of 90 degree bend with the radius of curvature of 40 and 80 cm. It was also observed that with concentration increasing, thickness of turbidity current body decreases at the inner and outer wall of the bend and with flow rate increasing, mentioned thickness increases. In constant concentration and flow rate, by increasing the radius of bend curvature, the height of turbidity current body in the inner and outer walls of the bend and also the transverse tilt of the turbidity flow, are reduced. With concentration increase, transverse tilt created on the surface of turbidity current in constant flow rate in steep 90 degree bend (R⁄B=2) decreased. Average flow velocity and maximum velocity component of flow direction are increased by concentration increasing. Flow rate Increasing caused maximum velocity component of flow direction and the height of corresponding increase. In this study, it was suggested equations for velocity profiles of main flow direction of jet and wall regions. Results of transverse velocity profile showed that in the most experiments secondary circulation cells near the bed like river channels and circulation direction of this cell is from the outer wall to the inner wall at the bottom of the cell. Results related to the turbidity current body concentration showed that the profile concentration has been as a function of flow body height and with height increasing from the bottom of the flume, decreases. It was also observed that the concentration in the upper layers of the end section of steep 90 degree bend, more than the beginning of this bend.

 Prediction of rivers condition after the emission of pollutants in order to reduce damages to urban and rural areas and farms is very important. On the other side, human life destructive effects influenced different rivers of the country in various forms with different intensity. Hence, hydraulically and qualitative simulation of rivers in order to predict the damages of the pollutants emission in different conditions, river engineering projects, and river restoration studies is necessary. The aim of the present study is the qualitative simulation of Karoon river (located in khoozestan state) using MIKE11. The results show that MIKE11 model can provide an appropriate numerical values in order to hydraulically and qualitative study of the river flow and can be used to predict momentary quality condition of the rivers with high accuracy and low costs

One of the most important problems that arise after construction of a dam is the phenomenon of sedimentation in the dam reservoir and one of the causes of this sedimentation is density current. A density current is the movement of a fluid through an other one that has a different density. If there was salin stratification in the vertically downward direction in the reservoir of the static fluid (similar to what has happened in the Upper Gotvand Dam) the flow entering the reservoir will first expand as an under flow current and after moving for some distance, will enter the saline layers of the fluid with salin stratified, as this flow moves on, it separate itself from the bed at a location in the reservoir where the density of the dense flow equals that of the layered one, finds the suitable density in its environment and continues its movement in a horizontal layer. The density current in the present study was of the inter flow type and this study intended to investigate head velocity of inter flow turbidity current through a fluid with salin stratification. The experiments were conducted in a flume 8 meters long, 34 centimeters wide and with a height of 70 centimeters using a solution of water and salt to form the fluid with salin stratification and a mixture of water and sediment as the dense fluid. Experiments with 4 discharges (1, 1.5, 2, and 2.5 l/s), 3 slopes (2.5, 3.25, and 4 percent) and 4 concentrations (5, 10, 15, and 20 g/l) that is 48 experiments were carried out. The head velocity of density current was first determined at the separation point and then where the inter flow density current started to form (0.5 meter past the separation point) and compared with that at the separation point. In general, results indicated that the head velocity at the separation point increased with increases in any of the parameters of slope, discharge and concentration. Moreover, higher discharges and concentrations increased the head velocity of inter flow density current. Using the results of the present laboratory study, the Keulegan relationship coefficient was obtained 0.67 at the separation point and the value of this coefficient declined to 0.6 where the inter flow density current started to form (0.5 meter past the separation point). The current velocity at a distance of 0.5 meter from the separation point (as the base point ) was compared with the average flow velocities at 1, 2, 3 and 4 meters past the base point to study the head velocity of inter flow density current it moved through the salin stratified and this was done to find a relation for the head velocity of inter flow density current as it followed its path through the salin stratification. In the following experiment, the head movement of inter flow density current through the salin stratification was studied and it was found that the path of inter flow density current through the salin stratification changed with changes in the concentration of the incoming current and the density current moved in a layer of the ambient fluid that had a TDS level close to the concentration of the density current. Furthermore, in some of the experiments, the density current penetrated into the very saline layers of the ambient fluid past the separation point (into layers with TDS levels higher than that of the incoming current) and salin tuck happened, in fact, with the separate of the density current from the bed and formation of inter flow density current, the head of inter flow density current that passed the salin stratified ambient fluid, caused fluctuations in the form of local instability in the ambient fluid layers and penetrated into the saline layers. Over time, the extent of these fluctuations declined, the layers returned to their stable and horizontal state and the head of inter flow density current passed through layers with uniform salinity close to the concentration of the head.

In order to calculate trash rack head loss many studies have been conducted to determine the effective parameters and develop equations. The parameters that can be taken into account are bar shape, bar thickness, clear space between bars, trash rack inclination and blockage ratio. Less researches have been done on the effect of bar shape and those brief studies performed on unsubmerged trash racks. This research presents an investigation on the flow head loss coefficient of three trash rack with different bar profiles (ellipsoid, rectangular, ellipsoid-rectangular bar shape) in hydraulic model of ballarod dam outlet tunnel.
Comparison among trash rack with different bar profiles indicated that approximately in range of boundary layer Reynolds number between 4×〖10〗^2 to 〖10〗^3 because of major separation in flow the head loss of trash rack with ellipsoid bars was higher than rectangular-ellipsoid one. But with increasing of boundary layer Reynolds number between 1.4×〖10〗^3 to 2.3×〖10〗^3 and turbulence of flow due to coarseness of bars the separation point went downstream and the head loss decreased. The result shows the importance of fabrication quality and its effect on flow head loss. Investigation on trash rack with rectangular bar shapes indicated that in all Reynolds numbers except very low numbers the head loss was higher than other bar profiles. It was observed that in very low Reynolds numbers the head loss across trash rack can be negligible and flow behavior can be approximately considered as a non-Newtonian fluid.
Researches on head loss coefficient indicated that in very low Reynolds numbers the amount were fluctuated and the coefficient value were lower than higher Reynolds numbers. This result represent the importance of restriction for the domain usage of head loss coefficient.
In order to obtain bar shape coefficients of submerge trash racks the calculated head loss of many equations were compared with measured one. In Reynolds numbers greater than 4.7×〖10〗^4 meusburger (2002) equation can give approximity acceptable results to determine bar shape coefficient. Hence the bar shape coefficients for ellipsoid, rectangular, ellipsoid-rectangular bar profiles are respectively 1.57, 2.73 and 1.74. for Reynolds number lower than 4.7×〖10〗^4 measured headloss didn’t have any correspondence with calculated Values. Therefore to solve the issue charts were presented.
 

Every year large quantities of sediment caused by floods entered in lakes and reservoirs and most of this sediment will trap there because of low velocity zone. Sediment deposition caused reduction in volume of the reservoirs and therefore reduces the useful life of the reservoirs. Density current is a phenomenon that may effects reservoirs sedimentation seriously. River Bend is also known for having the helical flow pattern and always has been interested to hydraulic engineers. To evaluate the concentration and velocity profile of the body of density currents a set of experiments were conducted in an experimental flume in Shahid Chamran University. The experiments were conducted in a flume with three 90 degree bend with 80،40 and 120 cm radius, 60 cm height and 20 cm in width. In this study, the dense fluid is created by mixing water and salt with different amount to make density currents. In each experiment 6 different sections are selected for concentration sampling and 9 different sections for velocity measuring from the body of density current. In total, 144 samples of concentration profiles and 216 samples of velocity profile were collected. Four concentration (8gr/lit, 12gr/lit,16 gr/lit and 20gr/lit) and two discharge (0.5lit/s and 1.1lit/s) were tested. The results showed that the thickness of the body of the current will increase during the current passing the bend. Also, when the concentration increases the thickness of the body is reduced. The body thickness increased with increasing discharge and body thickness increased with increasing discharge. When the radius of the bend is increase the body thickness is reduced. Velocity profile increasing at the end of bend and at the end of the bend there are two spines in the jet and flow. Also the average velocity in the bends with R/B=2 is more than the bends with R / B = 4.

Transverse waves are creating when flow attacked a group of obstacles such as bridges piers, docks and etc., as vortex is created behind obstacles, and due to adapting of the vortexes frequency with natural frequency, transverse wave will produce. So this study is focused on the transverse waves, which was performed by physical model, for cubic obstacles in two cases; flow hits to the top and side of them, and cylindrical obstacles. All experiments were done on the flume with 6m in length, 0.72m wide and 0.6m height in the laboratory of "physical and hydraulic models" at Shahid Chamran University, Faculty of Engineering Sciences. In these experiments, a group of cylindrical and cubic obstacles were used with diameter and side of 2.5 cm as obstacles in the way of flow with parallel and staggered arrangements in 12 and 18 cm distance, respectively. The experiments of this research were performed in non-submerged and submerged modes. The maximum amplitude of wave type 1 is 27.3 mm of corresponding to cubic obstacles in the case of flow hits to the top of the parallel arrangement of 120*120, and the minimum amplitude of wave type 1 is 0.9 mm corresponding to cubic obstacles in the case of flow hits to the side of the staggered arrangement of 180*180. The maximum amplitude of wave type 2 is 42.3 mm corresponding to cubic obstacles in the case of flow hits to the top of the parallel arrangement of 120*120 and the minimum amplitude of wave type 2 is 2 mm corresponding to cubic obstacles in the case of flow hits to the side of the parallel arrangement of 180*180. According to the Froude number, the regime of flow in all experiments is subcritical. Due to effective parameters on the transverse waves amplitude, relationships are presented for calculating the ratio of amplitude of submerged state to amplitude non-submerged state (𝐴𝑠𝑏⁄𝐴𝑛), by using dimensional analysis and a statistical "SPSS" software. The Strouhal number, percent of submergence obstacles, row spacing from each other, and the wave type are the effective parameters in the calculation of (𝐴𝑠𝑏⁄𝐴𝑛).

 
In open channels, water flow through obstacles causes in the formation of a boundary layer upstream and separation of flow lines downstream, resulting in vortex. When the vortex happens on both sides of the obstacles, alternative periodic forces are created on the obstacles which are also transferred to the flowing water. Resonances occur whenever the frequency of vortex and natural frequency of flow become equal. The experiments were conducted using a rectangular flume (6 m long and 72.5 cm wide) containing wooden obstacles with triangular cross section, or cylindrical wooden obstacles. The side, diameter and height of the obstacles were 25 mm, 25 mm, and 30 cm, respectively. The experiments were replicated as in-line or staggered arrangements, with obstacles located at 120 or 180 mm distance, water flow striking the obstacle at the side or edge, under free or submerged conditions, and water flow oscillation of one or two. For each test, the amplitude, height and duration of ten frequencies of water at a constant discharge rate of 20 liters per second were recorded. Overall, 277 tests were done under free and 182 under submerged flow conditions. Under submerged flow condition and mode one, the highest amplitude of flow was recorded for prism obstacles with triangular cross section and staggered arrangement and with the obstacles positioned at 120-mm distances. On the other hand, under submerged flow condition and mode two, the highest amplitude of flow was recorded for cylindrical in-line obstacles located at 120- mm distances. Finally, by using the experimental data and statistical software, equations for predicting the amplitude under submerged flow and different sections were presented.

 Worldwide population growth and the need to establish the relative prosperity, change has accelerated in nature. Control of surface water by the dam and reservoir dams in the world, such as changes. The dams are constantly threatened by sediment transport of watershed. One of the factors influencing the useful life of dams, sedimentation and sediment accumulation in reservoirs them. Density current is a phenomenon that may effects reservoirs sedimentation seriously. Due to the fact that knowledge right from the start plunge point of density current at the mouth of the river during high water and small dams also rising due to fast moving stream of water that is clear, In the control and containment of turbidity currents and prevent losses and problems resulting from this process are helping us a lot of useful; In this study, Experimental study of the Relationship between depth of plunging point of density currents when the clear water is moving. The experiments were conducted in a flume with adjustable slope, 8.8 m long 0.35 m width and 0.66 m depth. In this study, the dense fluid is created by mixing water and salt with different amount to make density currents. Three channel slopes include 2%, 3% and 4% are used.
All together, 54 tests were conducted with different inflow and different concentration included 1005 and 1009 kg/m3. The results showed that the slope on the plung point effect and increase slope causes increasing the depth of plung point. The results indicate that when the entry rates of clear and current fluid are the same maximum depth of plunf point is formed. The results showed an increase in the depth of plunge point when average speed of current flow is increased . In all of the experimental the densimetric Froude numbers in plunge point were subcritical. Increase in densimetric Froude numbers caused Increase in the plunge depth. Based on experimental data, check out Relationship between depth of plunging point of density currents when the clear water is moving and an equation is proposed

The main cause of concern about the stability of bridge foundation is the occurrence of scour around the piers. Therefore, there is an interest in finding reliable ways to reduce and control local scour depth. Local scour around a solid pier results from the down flow at the upstream face of the pier and the horseshoe vortex (HSV) at the base of the pier. Separation of the flow at the sides of the pier also creates the so-called wake vortices. These vortices are unstable and shed alternatively from each side of the pier. They act as little tornadoes lifting the sediment from the bed and form a scour hole downstream of the pier.
Countermeasures for local scour at bridge piers can be grouped in two categories: armoring devices and flow-altering devices.
This study is done with the purpose of examination of the effect of bridge pier’s dimension in the scour experiment.
Therefore, the tests carried out for six cylindrical bridge piers (D) with diameter of 10, 20, 30, 40, 60 and 100 mm in condition of clear water with Froud Number of 0.16, 0.14, 0.12 and 0.11 in an laboratory flume with mean measure of bed deposit of 0.5 mm and Froud Number 0.17, 0.15, 0.14 and 0.12 for the mean measure of the bed deposit 0.7 mm.
The results show that for all piers diameters, to the maximum scour depth of increases Froud Number. That with an increase of 45.45 percent of Froud Number of flow from 0.11 to 0.16 for pier with diameter of 60 mm and with an increase of 66.6 percent. Those in the constant hydraulic conditions to the maximum scour depth of increases pier’s diameters. With an increase of 20 percent of pier’s diameter from 50 to 60 mm with Froud Number of 0.16, the depth of scour increased 10.34 percent, respectively. In addition, by analysis of the tests, the pier with diameter of 30 mm is the appropriate pier for the other similar experiments that have been proposed. Also, about the effect of the diameter bridge and adapted to desert conditions, The bridge piers Smaller than 30 mm, these relative scour depth near of the bridge piers Naderi and fifth.
 

Existence obstacles such as piers of bridge and embankments, pier and pile jetty beach, offshore barges, water plants, coastal or ponds vegetation in flow and or braided flow during a flood stream and also sudden deformation of the sidewalls can flow disruption and upset it natural form and path.
With passing the flow from these obstacles disturbances will created, called the vortex shedding in downstream and is created waves known as horseshoe in upstream. Transferring the force of vortex shedding to the wall of the channel create small transverse wave with specific wavelength and frequency equal to the vortex wave specification. When the frequency of this small wave is adapted to the channel wide then the resonance will occur and the transvers wave with heights amplitude will appear.
In the present study, experiments were performed using cylindrical obstacles with 25mm diameter and 30cm height in a laboratory flume with 6m length and 72.5 cm width. Tests were defined in four stages which their different is in the arrangement of the cylinders of the stream in parallel and staggered configuration and the other is the distance between the cylinders (60, 120 mm). At each stage, specifications of the transverse wave of flow with non-submerged obstacles in two modes, I and II, are measured. Then, in constant flow depth, submerged cylinders as percentage of the water depth are performed and the specifications of the transvers wave are measured. During the third and fourth stages of experiment the distance between the obstacles were less than the second stages of experiments. Finally, the data collected in this study are analyzed and relationships are presented for prediction of the characteristics of transverse wave in submerges conditions. Finally, was presented relationships to predict and estimate the characteristics of a transverse wave by analyzing the data collected in laboratory conditions present study.