جستجوی مقالات مرتبط با کلیدواژه « آب شستگی » در نشریات گروه « آب و خاک »

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.

Engineers in recent decades have come to the conclusion that the design of bridges should be based not only on structural considerations but also on the impact of flow on bridges due to the long-term experience of building bridges over rivers. In this study, we investigated the effects of the longitudinal development of the pier, the vertical angle of the pier, the pier thickness, and the shape of the base nose for sediment with an average diameter of 1.2 mm. Experiments were performed on piers with angles (45, 60, 75 and 95). The results showed that the angle was different from different points along with the distance between the hole and the pier, and the scour depth was above the maximum depth created. At an angle of 45 degrees without a nose, the scour depth was reduced by 51% for the base with a thickness of 30 mm, 79% for the pier with a thickness of 15 mm, and 89% for the triangular nose with a thickness of 30 mm. Among the triangular and long noses, the triangular nose in all the studied conditions was better reduced by 96.4% scours depth. In addition, as the thickness of the pier decreased, the pressure applied to the pier decreased and, as a result, scouring decreased by 8.3%.

River bed control is a critical issue that river engineers facing with it today. Block ramps are grade control structures, implementing as a countermeasure to overcome successive erosion in rivers bed, having suitable environmental conditions in terms of aquatic migration to upstream reaches, and also increasing the dissolved oxygen in the water. One of the important issues in designing and safetying these structures is to predict and reduce the magnitude of scour depth in the downstream pools. In the present study, the effect of apron installation on the reduction of scour in the downstream of the block rams under the smooth and rough surface of the structure was investigated, experimentally. The experiments were performed for slopes of 1:3 and 1:5, the ratio of the critical depth to the height of the structure 0.14-0.2, roughness elements height of 1.15-5.2 cm with different arrangements; as well as apron installation with a length of equal and half of the height of the structure at the hydraulic and physical hydraulic lab of University of Guilan in 2020 and 2021. The comparison of the results of all slopes of the structures showed that the apron installation is directly related to the reduction of the maximum scour depth, so that by installing an apron with length of equal to the structure height, the maximum scour depth for slopes 1:3 and 1:5 reduced by an average of 58 and 43%, respectively, compared to the smooth block ramp. By increasing the roughness height, the maximum scour depth over the range of minimum and maximum flow discharges and the structures slopes reduced by an average of 39 to 62 % compared to the corresponding smooth block ramp. A comparison of the results shows that for block ramp with the slope of 1:3, changing the roughness arrangement from staggered to compact in case of large roughness, had no effect on reduction of the maximum scour depth, but in the slope of 1:5, reduced the maximum scour depth in the range of 18 to 42 %.

Spur dikes are river training structures that developed from the natural river banks with proper length and angle from the flow dominant direction, cause to divert the flow attack at the riverside and the critical regions and directs the flow to the river central axis. There are several researchers focused on the effect of the spur dikes angles on the flow pattern however there is not any study on hockey spur dikes angle on scouring patterns. In present study, the effects of the hockey spur dikes angle on scouring and the bed topography was carried out experimentally while the results were compared to those provided for L-shape. The experiments were conducted on a series of hockey spur dikes also the L-shape in three various angles equal to ,  and  (towards the downstream channel lateral walls) inside a laboratory flume in 10.5m length, 0.5 width and 0.5m height under the clear water conditions. The results revealed the scour hole parameters including the length and thickness of the sediment hill are lower in hockey spur dikes than the L- shape by increasing the spur dikes angle. Furthermore, the maximum scour depth, mean area and volume of scouring are increased by 41.4, 41 and 75.5 percent in hockey and by 33.8, 39 and 73 percent in L-shape through increasing the angle from   to , respectively. Also, no scouring was taken place in the vicinity of the channel lateral walls downstream the hockey spur dikes, hence, those beter act against the destruction also in protection of river beaches against the erosion, with respect to the L-shape.

Masonry check dams are small structures that are built to reduce the slope of the canal, reduce the flow velocity as well as control bed erosion. The distinguishing feature of Masonary check dam and other similar structures is the presence of pipes in the body of check dams. This adds to the complexity of the hydraulic conditions of these structures. As the flow overflows through the Masonry check dams, only some of the kinetic energy of the flow is dissipated in the stilling basin and the excess kinetic energy is occurred downstream of the structure. This situation can cause erosion of the riverbed downstream of the structure. Various methods are designed and implemented to control this excess energy. These methods include changing the height of the bottom bed, roughening the bed and creating a protrusion at the end of the stilling basin in order to create a submerged hydraulic jump into the stilling basin. Due to the fact that the stilling basin used in the main structure is USBR type 1 and in this type of basins, no baffles or end sills are used to dissipate the flow kinetic energy, embedding a sill at the end of the stilling basin is one of the innovations of this research. Also, using a physical model of mortar stone dams has not been reported anywhere and hence, this is also one of the innovations of this research. Therefore, using the physical model of "Tol Beneh" mortar rock dam can help to better understand the impact of scour reduction methods in the main structure constructed on the Gorgan Ziarat River and similar structures

in order to identify scour in Masonary check dam and its control methods, a physical model with a scale of 1:20 was developed. The flow rate in all tests was 25 l/s At first First, experiments were performed to determine the amount of scouring at the stilling basin. The results of these experiments were used to compare with the remaining test conditions. In the second series of experiments, to create a rough bed, the 54 cm long distance (equal to the length of the stilling basin) was covered with materials with a median diameter of 2.5 cm. three heights of 3, 6 and 9cm were used to model the increase of bed elevation (third series experiments). In the fourth series of experiments, to create a sill at the end of the stilling basin, a plastic blade 3 cm high was used in four stages. In the first stage, only a 3 cm sill was installed at the end of the stilling basin. In the second stage, the height of the bed bottom increased by 3 cm along the length of 54 cm. It should be noted that the average diameter of bed particles in these two methods was 4.5 mm. In the third stage, the roughness thickness of the bed materials increased to an average diameter of 2.5 cm without increasing the bed height. In the fourth stage, in addition to increasing the roughness of the bed material, the height of the bed also increased by 3 cm along the length of 54 cm.

In the stilling basin model, the scour depth was 130 mm without any obstacles. In other words, this magnitude represents a scour of 2.60 meter in the prototype. The presence of the end edge at the end of the stilling basin as well as raising the end of the channel causes a submerged hydraulic jump and consequently reduces scouring. If it is used in combination with these two methods, the effect will be greater. The results show that the presence of the end edge at the end of the calm pool shows a greater scouring reduction than increasing the height of the bottom,

The phenomenon of scouring around bridge piers is one of the important issues in river engineering science. Scouring creates a trench around the bridge piers and ultimately destroys them. So far, many studies have been done in this regard and numerous relationships have been proposed to estimate the scour depth parameter. However, due to the influence of various parameters and uncertainty in the scouring phenomenon, existing relationships do not lead to accurate and comprehensive results. In the present study, using a series of experimental data, the efficiency of the Gaussian Process Regression (GPR) method was evaluated to estimate the scour depth of bridge piers in cohesive and grainy beds. Various models were developed and the impacts of hydraulic parameters were evaluated. The results proved the high efficiency of the applied method in the research in estimating the scour depth compared to the semi-empirical equations. It was observed that the defined models for cohesive soils are more successful in estimating the scour depth than grainy and non- cohesive soil. The best result for test series was obtained in the state of soil with clay and sand with the values of CC=0.952, DC=0.801, RMSE=0.132 and MAPE=15.23%; in clay soil state with the values of CC=0.889, DC=0.883, RMSE=0.054 and MAPE=11.82% and in non-cohesive soil state with the values of CC=0.988, DC=0.796, RMSE=0.191 and MAPE=18.21%. The results showed that soil moisture and clay soil density were effective in predicting scour depth. Based on the results of sensitivity analysis, in the state of soil with clay and sand moisture with mean absolute percentage error of 24.42%, in the state of clay soil shear stresses and the percentage of soils density with errors of 43.42% and 47.04%, respectively, and in non-cohesive soil state pier Froude number with error of 28.65% were respectively the most effective parameters in estimating the scour depth in cohesive and non-cohesive soils.

The process of scouring is removal of sediments from river bed, caused due to moving water or waves. Scour can be classified into two broad categories: General scour and local scour. Contraction scour, as a type of general scour, occurs due to a reduction in channel cross-sectional area. Local scour on the other hand occurs due to the direct effect of an obstruction on the flow field. Contraction scour is observed where the flow is constricted due to the placement of structures like bridges etc. The flow accelerates in constrictions which increase the bed shear stress and the turbulence associated with it. The development of contraction scour is noted when the critical shear stress of the bed materials is overcome by the bed shear stress. This paper provides a comprehensive discussion on scour within channel contractions. Scour within a channel contraction occurs where the waterway is restricted by the foundations or road approach embankments of a bridge. Alternately, contraction scour takes place when a bridge is located at a natural contraction in the river width. Contraction scour is an important phenomenon in rivers. To reach the aims of this work, both experimental and numerical modeling has been done. In this study, the experiments curried out in a flume with length of 20 m and width of 0.6 m, located in hydraulic laboratory of Shahrekord University. The average size of the sediments in the flume was d50 = 0.78 mm. The bed sediment layer was 16 cm thick. The experiments were run with three different discharges: 20, 30 and 40 l/s and flow depth was regulated at 30 cm. Also, the experiments were conducted with four different contractions of 20 cm, 30 cm 40 and 50 cm wide, which was resulted in three different the contraction ratio of 0.33, 0.5 and 0.67. SSIIM computer model has been used for contraction scour prediction in stream for two different conditions, including sudden (with angle of 90o) and gradual (with angle of 50o) contractions. Calibration of SSIIM model was conducted based on the results from the experimental study. SSIIM numerical model is capable of solving the Navier-Stokes equations on three-dimensional network with k-ε turbulence model. Likewise, it utilizes volume control with power upstream or second-order law for discretizing equations. This software also addresses to solve the passive pressure field using iteration technique and simple method (semi-implicit method for solving equations with pressure). After calibration of experiments to analyze the output results, Tecplot software was employed because the display of the obtained results from scouring through SSIIM was not clear. In current study, parameters such as flow pattern, scouring pattern, and water depth were simulated. Calibration of results was carried out by the experimental data. With monitoring model results, the start of scour for all models in the beginning of the narrowing part and the side walls was simulated. The greatest value of the scouring achieved at the same place as in experimental model. According to the results of the model regarding flow pattern simulation, it can be stated that flowing lines are constricted by reaching to narrowing part beginning and along the narrowing section changed to parallel lines. At the end of constriction, flow lines are being expanded and at the gradual opening, rotational currents are formed. Maximum amount of scour was calculated 12 cm in flow rate of 40 L/s and 20 cm constriction with 9.09% error that this amount was measured 11 cm in the laboratory. In addition, the least amount of scour was measured 1.8 cm in flow rate of 20 L/s and 40 cm constriction with 20% error in numerical model and 1.5 cm in the laboratory. Obtained results showed that the model was adequate for modeling of contraction scour, in parameters of scouring maximum depth, erosion pattern and circular flows. Accuracy of the model was acceptable according to the average of Nash – Sutcliffe coefficient of 0.923, average error of 10.18 and the maximum error of 20%. Based on the calibrated model, contraction scour was simulated for sudden transition and results showed that scour maximum depth was increased at a rate of 29.5%, comparing with gradual transition. This indicated that gradual transition plays a positive role to reducing contraction scour.

One of the common ways for bank protection against erosion along rivers’ bends is spur dike application. Spur dike changes the flow pattern and diverts it towards the river centerline and as aresult protect the river bank from erosion. However, a new flow pattern is formed with higher velocities and this phenomenon causes the local scour around the structure nose to be increased. The length of spur dike is one of the important parameters affecting the local scour around the structure. In order to investigate the effect of the permeable spur length (permeability was 33%) on local scour, experiments were conducted in a rectangular laboratory flume with a mild 90 degree bend (R/B=4; where R=radius and B=flume width). In this research a series of spur dikes with three different spur length including 10.5, 14.0 and 17.5 cm, corresponding to 0.15, 0.2 and 0.25 of flume width, respectively, was installed along the bend for each experiment. Four Froude number values including 0.21, 0.23, 0.26 and 0.28 with a constant flow depth of 14cm under clear water condition were applied for each spur length. The results show that the maximum scour depth increased with increasing the spur length for a constant Froude number; so that the maximum scour depth was happened for the length of 17.5cm with a Froude number of 0.28, which was 10.71% and 42.86% more than the spurs with 14.0m and 10.5cm length, respectively. The maximum local scour was observed to happen at the end part of the outer bank of the bend. It was generally found that with increasing Froude number and the spur length the scour hole dimensions increased.

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.

Flood currents are considered as a threatening factor which creating local scour along bridge piers. In studying the reasons for the destruction of many bridges, scour resulting from flood currents has been identified as the major reason for the failure. Scour is a natural phenomenon which occurs as a result of erosion in bed and drift riversides by water current. This phenomenon is created locally as a result of mutual effect of water way geometry, bed and current specifications around the pier. As a matter of fact, when a current strikes bridge pier, holes are made around the pier and complex vortex systems are created whose performance causes a hole around piers called a scour hole. The development of this hole around the pier causes under the foundations to get empty leading to their destruction and finally the destruction of the bridge. In order to prevent and decrease scour at the bridge pier, two basic methods have been presented. One of them is the direct method in which the resistance of the bed against tension increases; and the other is the indirect method in which the effect of the destructive forces is reduced by changing the current pattern around the pier. Prediction of depth and the final status of scour hole are the most important cases of hydraulic design of bridges. Geotextiles, which are produced from polypropylene and polyester fibers, form a large group of geosynthetic products. These materials can be used to strengthen river beds adjacent to bridge piers and to control the scour around them concurrently playing the role of riprap and collar. Geotextile spread around bridge piers to prevent the scouring around it. In terms of economics, determine the extent and pattern of suitable geotextile cover is essential.
In this study, coverage area with geotextile around the single pier and a group of two and three piers in the case of clear-water flow over uniform sediment were investigated. The experiments were carried out in a 20m long, 0.60m wide, and 0.60m deep, Plexiglass-sided flume. The piers of Teflon were selected with 5cm diameter and fixed parallel the streamline. The space between the piers was 3 times bigger than pier diameter. The granulated silt of bed materials was chosen so that no ripples are formed in the test area bed. The formation of ripples causes separate small protrusions in the bed; it also causes an increase in current speed compared to the critical speed in the movement threshold of sediments causing some of the upstream sediments of the pier to be washed and carried thus filling the scour hole and causing the scour depth to decrease compared to its real maximum amount. Ripples and non-sticking sediments with mean sized from 0.05 to 0.7 mm develop; hence, the mean diameter of sediments should be over 0.7mm.
The results showed that in group piers the sheltering effect of the first pier decreases 50% of coverage pattern and the reinforcing effect of the last pier increase the coverage pattern about 40%. Sheltering effect in a group of two and three piers let to decreasing scour hole about 50% and 71%, respectively, than the single pier. At the rear pier of a group of three piers, the dimensions of the scour hole were 21% less than a group of two piers because the first and second piers protect the rear pier. With experiment on coverage patterns, it was found that the oval layer in single pier and the semi oval layer in group piers is the best pattern for scour reduction. In this state, after 19 hours, the first signs of scour in downstream are observed whose longitudinal and widthwise progression were about 3cm to the end of the test and its depth, too, reached 0.5cm. Base on the obtained results, with regard to the negligible amount of scour, the semi-oval pattern with more coverage in behind the pier is suggested as the best pattern in geotextile installation. By using geotextile with an appropriate cover, apart from a delay in scouring process, the scour location is transferred to downstream and the scour depth is decreased. In other words, the geotextile layer has a dual performance in decreasing scour. As far as economy and method of application are concerned, the larger layer; and as far as the scour is concerned, the smaller layer would be problematic.

One of the common methods to dissipate energy of the flow passing over a dam is using flip bucket spillways to create free falling jet to the downstream. However, the collision of the falling jet to the downstream bed will cause topography changes due to scour threatening the stability and safety of the hydraulic structures. In case of precise analysis of the downstream topographic conditions due to the falling jet, such structures perform better than other dissipaters. Experimental results show that the dimensions of scour hole are dependent upon upstream water depth, discharge and tail water depth. Due to water and sediment flow complexities and the effect of different geometric-hydraulic parameters on bed profile variations, more studies are needed.In the present study, the effect of flip bucket tooth and upstream gate opening on downstream bed topographic changes due to falling jet was investigated using a flat flume having dimensions of 2m*0.5m*0.5m. The free falling jet was controlled using a sluice gate located upstream of the flume. Falling jet hit a downstream sedimentation basin having dimensions of 2 m long, 1.5 m wide and 0.7 m deep. Tail water depth was controlled using a gate located at the end of the sedimentation basin. Spillway and flip bucket of the Karoon III dam were modeled considering a 1.165 scale. Experiments were carried out on a normal (simple) and slotted flip buckets. Slot dimensions were selected as 2 cm according to USBR (1987) recommendations. To control the water surface level at upstream of the spillway for different discharges, a sluice gate was used at the spillway inlet. To investigate bed topographic changes, sedimentation basin was filled with non-uniform silica sediments with a mean particle diameter of d50=2.76 mm, the geometric standard deviation of σ=2.11 mm, uniformity coefficient of Cu=4.07 and a specific gravity of γs=1.52 gr/cm3 according to grading curve up to a depth of 40 centimeters. Researches show that several geometric-hydraulic parameters influence bed topography changes at downstream of the flip buckets. Most important parameters include input flow velocity to the flume (V), tail water depth (Yt), flow density (ρ_w), kinematic viscosity (μ), acceleration of gravity (g), specific or mean diameter of bed particles (d50), bed particles density (ρ_s), falling jet height from the bucket edge to sediment level (Hw), gate opening height (L), bucket tooth height (h), Manning coefficient of shoot surface (n), flip bucket radius (R), time (t), sedimentation basin width (B) and geometric standard deviation of non-uniform materials (σ). Using dimensional analysis and combining dimensionless parameters, the dimensionless densimetric Froude parameter (Frd) is achieved.In this study, after depiction of the longitudinal profile changes of the hole and mound scour due to falling jet, variations of the obtained dimensionless parameters were first investigated. Then, using statistical analysis, experimental relations to estimate the scour hole depth and downstream sediment mound height were presented. For this purpose, the effect of a tooth located at the end of a flip bucket on downstream bed topography changes was experimentally investigated considering different discharges, spillway gate opening percentages and tail water depths. After leveling bed sediment surface at the beginning of each experiment, discharge was adjusted using the electromagnetic flow meter and water depth was controlled using a spillway sluice gate. Besides, tail water depth was stabilized using a gate available at the end of the sedimentation basin and the falling jet was finally released to the basin. In order to determine experiment’s equilibrium time, several primary experiments were carried out considering different discharges in different time periods. By drawing equilibrium time curves, 360 min time duration equal to formation time of 88% of the total scour hole depth was considered as experimental time duration. Therefore, a total of 54 experiments were carried out considering the studied variables in this study. Water jet was released from 57 centimeters height of the bucket end level to the non-uniform bed sediments during 360 minutes experiments. Bed topography changes were measured at the end of each experiment using a dot sounder with 0.01 mm precision and depicted using Surfer V. 9.0. By calculating the changes of bed sediment volume, the influence of the slot on reduction of the scoured sediment volume can be evaluated in comparison to the normal condition. It was found that scour hole dimensions enlarge with discharge, but increase in tail water depth shows a descending procedure. In addition, in the case of slotted flip bucket in comparison to the normal one, by increasing gate opening by 33%, the hole volume increased by 125.64 %, and increasing gate opening by 66% and 99%, the hole volume decreased by 45.92 % and 22.85 %, respectively.

Among the methods which can be used for preventing the sediment deposition is self-cleansing in the structure. In the first of this research, a general relationship for conditions of self-cleansing in open channel and inverted siphons was developed by applying the dimensional analysis. Then experimental tests were conducted by using two experimental models and 14 non-cohesive sediment with different dimensions of 0.2 to 4.4 mm in three channel bed’s slopes of 0.5, 1 and 1.5 percent and four different bed slopes of 0.0, 8.0, 16, and 24 degrees for horizontal and outlet conduit of inverted siphon. Two graphs were drown that can be used for determining the condition of self-cleansing in open channel and horizontal and outlet conduit of inverted siphon. Then, by using these graphs and suspended load particle size distribution curves of the Karkheh River in Paypol station, the self-cleansing velocity was extracted for preventing the deposition of sediment particles with diameters less than 2 mm that is the largest particle size observed in Paypol channel and their inverted siphons.Among the methods which can be used for preventing the sediment deposition is self-cleansing in the structure. In the first of this research, a general relationship for conditions of self-cleansing in open channel and inverted siphons was developed by applying the dimensional analysis. Then experimental tests were conducted by using two experimental models and 14 non-cohesive sediment with different dimensions of 0.2 to 4.4 mm in three channel bed’s slopes of 0.5, 1 and 1.5 percent and four different bed slopes of 0.0, 8.0, 16, and 24 degrees for horizontal and outlet conduit of inverted siphon. Two graphs were drown that can be used for determining the condition of self-cleansing in open channel and horizontal and outlet conduit of inverted siphon. Then, by using these graphs and suspended load particle size distribution curves of the Karkheh River in Paypol station, the self-cleansing velocity was extracted for preventing the deposition of sediment particles with diameters less than 2 mm that is the largest particle size observed in Paypol channel and their inverted siphons.Among the methods which can be used for preventing the sediment deposition is self-cleansing in the structure. In the first of this research, a general relationship for conditions of self-cleansing in open channel and inverted siphons was developed by applying the dimensional analysis. Then experimental tests were conducted by using two experimental models and 14 non-cohesive sediment with different dimensions of 0.2 to 4.4 mm in three channel bed’s slopes of 0.5, 1 and 1.5 percent and four different bed slopes of 0.0, 8.0, 16, and 24 degrees for horizontal and outlet conduit of inverted siphon. Two graphs were drown that can be used for determining the condition of self-cleansing in open channel and horizontal and outlet conduit of inverted siphon. Then, by using these graphs and suspended load particle size distribution curves of the Karkheh River in Paypol station, the self-cleansing velocity was extracted for preventing the deposition of sediment particles with diameters less than 2 mm that is the largest particle size observed in Paypol channel and their inverted siphons.Among the methods which can be used for preventing the sediment deposition is self-cleansing in the structure. In the first of this research, a general relationship for conditions of self-cleansing in open channel and inverted siphons was developed by applying the dimensional analysis. Then experimental tests were conducted by using two experimental models and 14 non-cohesive sediment with different dimensions of 0.2 to 4.4 mm in three channel bed’s slopes of 0.5, 1 and 1.5 percent and four different bed slopes of 0.0, 8.0, 16, and 24 degrees for horizontal and outlet conduit of inverted siphon. Two graphs were drown that can be used for determining the condition of self-cleansing in open channel and horizontal and outlet conduit of inverted siphon. Then, by using these graphs and suspended load particle size distribution curves of the Karkheh River in Paypol station, the self-cleansing velocity was extracted for preventing the deposition of sediment particles with diameters less than 2 mm that is the largest particle size observed in Paypol channel and their inverted siphons.Among the methods which can be used for preventing the sediment deposition is self-cleansing in the structure. In the first of this research, a general relationship for conditions of self-cleansing in open channel and inverted siphons was developed by applying the dimensional analysis. Then experimental tests were conducted by using two experimental models and 14 non-cohesive sediment with different dimensions of 0.2 to 4.4 mm in three channel bed’s slopes of 0.5, 1 and 1.5 percent and four different bed slopes of 0.0, 8.0, 16, and 24 degrees for horizontal and outlet conduit of inverted siphon. Two graphs were drown that can be used for determining the condition of self-cleansing in open channel and horizontal and outlet conduit of inverted siphon. Then, by using these graphs and suspended load particle size distribution curves of the Karkheh River in Paypol station, the self-cleansing velocity was extracted for preventing the deposition of sediment particles with diameters less than 2 mm that is the largest particle size observed in Paypol channel and their inverted siphons.

Bridge failures due to scour at bridge abutments have clarified the importance of scour depth prediction. Most of bridge abutments are located in the floodplain. Also, one of the common cases in a floodplain is vegetation. Velocity and shear stress distribution in compound channels are not uniform and the obtained results from rectangular channels cannot be used for compound channels. In this study, based on experimental observations, dimensional analyses and multivariable non-linear regression, a dimensionless relationship for prediction of scour depth at vertical wall abutment terminating in the vegetated floodplain of a compound channel is suggested. The results indicated a good agreement between the experimental observations and predicted values by suggested relationship. For suggested relationship, coefficient of determination (R2) was 0.94 and root mean square error was obtained 0.79 centimeters.

A large number of authors have studied to find out how to control scouring around a pier along direct stream. The objective of this research is then to study a scour pattern around such piers on curves rivers due to the fact that there may be a difference between a flow pattern on a direct line and the meander. Thus, this study tries to check whether the use of cable and collar alone and in a combination of cable and collar affects scouring around bridge pier group constructed on rivers meander. In this study two thickness of cable 0.2D and 0.4D and three steps 0.2D, 0.5D and D are used. The results showed that more scouring depth is decrease as a cable diameter increases and the pitch of helix decrease. About pier groups that are in the direction of water flow, scour depth for first pier is more than single pier, that represents increase of reinforcing phenomenon, also scouring depth for middle and back piers due to sheltering phenomenon, is less than single pier. About piers perpendicular to the flow direction, the maximum scour depth is observed in middle pier, also at this case scour depth is reduced by increasing distance between piers. Using collar is more effective than cable for small distances between piers. Also it is found that using a combination of cable and collar results the most reduction in scoring depth.

Scouring around the bridge pier during the flood events threaten the bridge as important hydraulic structure. Thus, designing the economical device in reducing the local scouring needs to be investigated. Cable has been introduced as new and economical countermeasure in local scouring. In the present study, different diameters and thread angles are studied through the experiments. In addition, groove is introduced in reducing the local scouring. The results show that with increasing cable diameter and decreasing thread angles the reduction of scour depth increases. The maximum scour reduction is achieved for pier protected with cable equal to 13% and 17% in front and behind of the pier respectively. While the groove is reduced scouring equal to 17% and 25% in front and behind of the pier respectively. Comparing the efficiency of cable with groove indicated that groove has higher efficiency in reduction of local scouring.

The lip angle of submerged roller bucket as the main design parameter, has an effective role in energy dissipation and scour downstream of this structure. The purpose of this study is the investigation of bucket lip angle influence on the scour process and determining the best lip angle and presentation non-linear regression equations to estimate the scour dimensions downstream of submerged roller bucket. Therefore, 64 tests were conducted in different hydraulic conditions on four experimental models with different lip angles 30˚, 35˚, 40˚, 4 ˚. The results showed that with increasing the lip angle from 30˚ to 45˚, the maximum depth of scour hole, the lengthwise hole expanse, the height of upstream and downstream berms and the relative surge height, increased in average to 150%, 27%, 110%, 24% and 213% respectively. Based on the results of this study, 30˚ bucket is an appropriate option to reduce the maximum depth of scour, volume of scouring, height of berms and height of ripples in tailwater to the minimum possible and 40˚ bucket is also a suitable option to further the beginning and the deepest point of scour hole and the surge peak to the maximum extent possible. Both angles have advantages to reduce bed scour, bucket abrasion (Due to the trapped material in unsymmetrical spillway operation) and negative effects of turbulent rippling tailwater on outlets operation and riverbank.

Advancement of technology in construction of structure caused to design modern type of bridge piers including inclined bridge piers group. Due to importance of identifying effective mechanisms of scour around this type of bridge piers, in this research the effect of flow parameter and level of bridge foundation on the scour depth was investigated. Bridge piers group included two inclined rectangular piers of 2.5cm width and 3.5cm length which installed at the angle of 28 degree on the top of rectangular foundation of 10cm width and 16cm length. Experiments were performed for various relative velocities, depth of flow and relative top level of the foundation from the channel bed (Z/D*) -1 up to 1. The results showed that the velocity of flow has more effect on the local scour depth in comparison of the flow depth. Comparison of results for different levels of the foundation showed that level of the foundation has significant effect on the scour depth. A maximum and a minimum scour occurred for relative foundation level 1 and -0.5. Furthermore, except of relative foundation - 0.5, the scour at the inclined bridge level is more than individual pier.

Scouring is a type of local erosion that usually occurs downstream of most of hydraulic structures and around any obstacles in rivers. This phenomenon can be intensified at the river bend due to occurrence of secondary flow in comparison with straight channels، so attention to the erosion and its control and mitigation at this part of river is very important. Using riprap is one of the usual methods to protect river banks and bed against erosion. In this research، the riprap placement level at a bridge abutment site located at a 90 degree river bend was investigated. This research was carried out to observe and analyze the riprap behavior with various specific gravities and sizes and three different riprap placement levels namely، the same، upper and lower than river bed sediments level. Three different types of riprap with specific gravities of 1. 51، 2. 05 and 2. 65 and four different sizes of 4. 75، 9. 52، 12. 7 and 19. 05 millimeters were also utilized. The results show that the riprap placed at the bed level has the most stability، and the riprap placed above the bed has the lowest stability.

Local scour around bridge pier is one of the most important destruction factors of bridges. Many researchers have investigated scour around bridge pier; however, there is still not available single solution for this issue due to complexity of the problem and multiplicity of the effective factors. Different methods have been proposed to prevent or reduce scouring around bridge piers such as Riprap, collar, slot, submerge sheet and so on. According to researches, installing a collar around the base to delay the onset of scour in some cases significantly reduced the depth of scour around the base. In this study, by using the rectangular collar around the cylindrical pier, the effect of the collar thickness on scour reduction around bridge pier was investigated. The results of the experiments showed with installation of the collar not only velocity of scour is reduced but the depth of scour hole around the pier especially in downstream of the pier is also decreased. Also, with increasing collar thickness, the performance of the collar is reduced. Based on the results, the collar thickness was equal to 5 percent of the pier diameter and less than that had negligible reduction in the performance of the collar. However, the performance of the collar decreased when the collar thickness was more than 5 percent. Therefore, the appropriate thickness of the collar is proposed 5 percent of the pier diameter.

The local scour at pile is the main reason for bridges failure. Although numerous researches have been done on scouring, the appropriate equation to predict scour at bridges foundation has not been presented yet. In this research, an experimental study on clear water scour at pile groups under steady flow at threshold velocity is presented. Uniform bed material with median particles size of 0.8 mm, in a 46 m long, 1.52 m wide and 1.9 m deep flume were used. The objectives of this study are to present changes in scour at multiple piles due to the pile arrangements and present empirical relationship to estimate the scour depth at multiple piles with different arrangements. Wide ranges of pile group arrangements are studied when the diameters of piles were 60 mm and 42 mm. The number of piles in line with flow (m) and normal to flow (n) were regularly increased at each successive experiment. In total, 40 experiments were carried out used possible arrangements of pile group where maximum number of n and m were 4 and 10 respectively. It was observed that the scour at pile group is affected by pile arrangements. The collected data were used to propose a new empirical equation to compute effects of the studied variables (m and n). The outputs of this research can be used to improve the pile group arrangement procedure to