JOURNAL OF HYDRAULICS
Year:2020 | Volume:15 | Issue:1|Papers Count:11

Introduction: Submerged vanes are flow-pattern altering structures that are mounted vertically on channel-bed at a small angle of attack to the approach flow. A submerged vane generates a secondary circulation (a spiral flow), due to the vertical pressure gradients on the two sides of the vane, which originates below the top elevation of the vane and extends in the downstream of the vane. The vane-induced vortex redistributes sediment within the channel cross section and changes the alluvial bed profile. However local scour around the vanes is one of the problems in using of submerged vane technique. The extension of local scour hole is related to the shape of the vanes. Primary submerged vanes are generally flat rectangular plates. In the present research, cutting a part of the leading edge of the vanes out is studied as a countermeasure in reducing the local scour. Studied vanes include a rectangular vane (as the baseline vane), and five other modified vanes with tapered leading edges with angle of  = 30° , 45° , 60° , 70° , and 73. 3° . The present study aims to evaluate the effect of this modification on the vertical velocity components at the leading edge and strength of the secondary circulation in the downstream of the vanes. Flow-3D numerical model, version 10, is used to study the flow field around the vanes. Methodology: The commercial CFD model Flow-3D was used in this research. Experimental velocity measurements were used for calibration of the model. For this purpose, a recirculating flume (7. 30 m long by 0. 56 m wide by 0. 6 m deep) was used. A centrifugal pump discharged the water into the stilling tank at the entrance of the flume. In order to create a uniform inflow of water, a screen was placed at a distance of 1 m from the flume entrance. A tail gate was used to adjust the depth (do) of water in the flume to a constant value of 0. 25 m. The dimensions of the vanes were determined using Odgaard’ s (2008) design criteria: a vane height-to-water depth ratio of Ho/do = 0. 3 and length of L = 3Ho. A mean flow depth of do = 0. 25 m yielded Ho = 0. 075 m and L = 0. 25 m. velocity measurements carried out using vanes V0 and V3 at a flow Froude number of Fr = 0. 16. In each test, the vanes were installed on the centerline of the flume at an angle of 20° to the flow. In order to study vane-induced velocity field, 4×4 cm 2 grids across the flume were taken at the center of the vanes. At each grid point, three-dimensional components of velocity vector (u, v, w) were measured by means of an electromagnetic velocimeter (EVM). Velocity very close to the walls of the flume was not measured. Results and discussion: On the high-pressure side of the vanes, vertical velocity components were upward (positive) and on the low-pressure side were downward (negative). Therefore, a clockwise secondary circulation was generated at downstream of the vanes. Downward velocity components at leading edge of primary rectangular vane (vane V0) were obvious. By cutting parts of leading edge out of vane V0 for tapered vanes V1 and V2, the magnitude of negative w-velocity components was respectively reduced by 40% and 69%. By increasing the taper angle for vanes V3, V4 and V5, downward velocity components were diminished, effectively. Moment of momentum (MOM) quantity was used in order to evaluate strength of vaneinduced circulation. MOM values were applied for comparison of performance of the vanes. For this purpose, velocity data at two sections at the distances of 2Ho and 4Ho, i. e., 15 cm and 30 cm downstream from center of the vanes was used. In the calculation of MOM, 100 velocity components (50 v-components and 50 w-components) were used. Therefore, this quantity is a useful criterion for evaluation of the performance and efficiency of the submerged vanes. Conclusion: Velocity distribution and moment of momentum (MOM) of the vanes indicated the reduction of erosive negative velocity components at the leading edge of the tapered vanes. Based on MOM values, cutting the leading edge out of the vanes causes lower performance. In other words, this modification restricts the vane-influenced field of the tapered vanes relative to the rectangular vane (vane V0). Results showed that the performance of tapered vanes (V1 to V5), relative to the rectangular vane, (at distance of 2Ho) is respectively reduced by 5. 8%, 7. 3%, 17. 8%, 33% and 42. 6%; at distance of 4Ho the amount of reduction respectively is 7. 4%, 11. 9%, 17%, 25. 5% and 34. 3%. On the contrary, the efficiency of the tapered vanes increased. The amount of increasing at distance of 2Ho from the center of vanes V1 to V5 respectively is 3. 2%, 9%, 11%, 14% and 14. 8% and at distance of 4Ho respectively is 1. 4%, 3. 6%, 12. 1%, 26. 7% and 31. 3%. Therefore, if tapered vanes are used to reduce the local scour, big values for the distance between the vanes arrays (δ s), according to the design criteria, are not recommended.

Introduction: Meandering rivers, as prime examples of nature tendency to reach a regular form, have been the focus of many researchers. These rivers contain a series of alternating bends and curves, joined by short straight intervals across their plan and flow over gently sloping channels in which sedimentary load settles as point loads on the inner wall of the bend. River morphology studies the geometrical form of rivers in the plan, longitudinal profile (channel slope), cross section geometry and topography. Morphological analysis of meandering rivers is performed in two stages: determination of independent variables (flow and sedimentary discharge), calculation of geometrical parameters of river morphology through physical or experimental relationships. Such parameters are mostly studied using Euclidean geometry. Sinuosity, for example, has been calculated with Euclidean attitude in Cartesian coordinates. Quantifying geometrical parameters of meandering rivers morphology in a Euclidean approach arises problems such as inaccuracy or complexity in calculation. Instead, Fractal geometry is widely used in river engineering in recent literature, due to its more detailed perspective of an object and its non-Euclidean properties. In Fractal Geometry, the mathematical space classified into one-, two-, and three-dimensional spaces on the basis of Euclidean geometry, is expressed as is fractal spaces in which the irregularities of the shapes are expressed in terms of fractal dimension (a real dimension and not necessarily a natural number). Single-fractal analyses are mainly carried out using methods such as box counting, variation, scale change, and Brownian motion methods, while multi-fractal analyses include methods such as spectral or wavelet analysis. Methodology: Box counting is one of the fractal dimension calculation methods, widely used in rivers and shorelines. In this method, the set of points is meshed on a curve or a surface with squares (boxes) and the number of squares covering each part of the curve is calculated. Variation method also is one of the most accurate and popular method that can be used to calculate fractal dimension in various fields, however it is rarely used in river engineering up to now. In the present study, the fractal dimension in the Mond River was calculated over a 15-year period from 2000 to 2015. Mond River, with 685 km length is one of the most important rivers in southern Iran, originating in Fars province and flowing into the Persian Gulf through Bushehr province. Two fractal methods namely, box counting and variational methods were applied to calculate fractal dimensions in I) the whole river II) 3 longest bends III) 13 meanders. The results were then compared with those of sinusoidal coefficient. To calculate the fractal dimension by changes method, the area covered by different characteristic lengths is calculated in fixed intervals. Then, for different characteristic lengths the area covered by meander curve is calculated using code written in Matlab. The correlation coefficient values for the river coordinate data at each of the river intervals are obtained and compared in the bends. In the box counting method, different dimensions of the box and therefore different grids were considered. Then, in order to calculate the fractal dimension, the number of boxes involved was calculated for different widths using codes written in Matlab. Variations in the box width with the number of boxes in logarithmic scale are used to calculate the fractal dimension in the box counting method. Result and Discussion: The values for fractal dimension ranged between 1. 01 to 1. 09 and 1. 0027 to 1. 991 using box counting method and changes method, respectively. Additionally, the calculated fractal dimension values were compared with sinusoidal coefficients in three long meanders and fourteen bends of the river. Results indicated high correlations (R2 = 0. 940. 99) between fractal and sinusoidal coefficients in the meanders. The fractal dimension obtained in 2005 (1. 05) was larger than those in other years. The largest fractal dimension was met in the second meander, with a value of 1. 06. Highest sinusoidal coefficient was also found in the second meander indicating a direct relationship between these two parameters. There was a high correlation coefficient (close to 1) between the fractal dimension and the sinusoidal coefficient in the long meanders. Conclusion: A considerably high correlation coefficient of 0. 96 was obtained between the parameters of the sinusoidal coefficient and the central angle calculated from the morphological analysis, which indicates a direct relationship between these parameters. The correlation coefficient of 0. 85 between the fractal dimension parameters and the sinusoidal coefficient as well as the correlation coefficient of 0. 86 between the fractal dimension parameters with the central angle indicates that the fractal dimension parameter is an appropriate indicator for expressing the changes and complexity of the meandering rivers.

Introduction: The scour at the downstream of the structure may cause structural instability and finally structural damage. Therefore, it is necessary to estimate and predict the depth of scour downstream of structures before constructed. Empirical equation to predict the depth of scour is always has error and reduces the accuracy of the results. Therefore, in last decade, the method of combining models has been used to increase the accuracy of predictions in different sciences. Instead of choosing the best single model for a specific condition, which is a traditional task, it is recommended to use a single model combination method, which will result outputs of the combination model is better in all conditions. The purpose of this study is to estimate scour depth using different combination methods by combining empirical equations (single). The single equations were also compared before and after bias correction. Methodology: In this study 306 data set are used, including 264 laboratory and 42 field data. Randomly, 75% (230 data set) of the total data were choose for training and the remaining 25% (76 data) were choose for testing the combination models. Different technique including Shu and burn, EWA, GRA, BGA, AICA, BICA, KNN and LS-SVM have been used to combine single model. Bias correction has been performed to each model before using combination models. It was determined by the ordinary least squares estimator (OLS) using training data set in each model. Results and discussion: In this study bias correction was perform on single model. In general, the slope and intercept of the single equation indicate that the scour depth predicted by a single equation is greater than measured scour depth. The best estimation before bias correction is Mason and Arumugam and the National Institute of Hydraulic Laboratory Science and Technology (National Institute) equation. The National Institution's equation is chosen as the best single model before bias correction. After bias correction, the error of all single equations has been reduced and Mason and Arumugam equation with correlation coefficient of 0. 74 and error value of 0. 23 m has the highest correlation and least error among single equations. The error values of the Machado, Martins, and National Institute equations are approximately the same, with very little difference (about 0. 01) with the Mason and Arumugam equation. The results showed that after bias correction the Mason and Arumugam predicted scour depth more accurately and selected as the best single equation after bias correction. The equations of Martins, Machado, National Institute, Mason and Arumugam, D’ Agostino and Ferro were considered as inputs (independent variable) and scour depth as outputs (depended variable) of combination methods. Before bias correction, the correlation coefficient and error of the direct weighting methods showed that the GRA method has the least error in predicting scour depth (RMSE = 0. 25) and the W2 method has more error than this method (RMSE = 0. 31). Comparison of direct weighted combination methods with single equations before bias correction showed that the GRA method has much less error than the best single equation (National Institute). The AICA and BICA combination methods provided the best estimate before bias correction in indirect weighting methods and the results are similar to the best single equation before bias correction (R2 = 0. 70, RMSE = 0. 87). All three indirect weighting methods produce approximately the same results after bias correction. The error of indirect weighting methods decreased about 70% after bias correction compared to pre-correction. The results showed that artificial intelligence combination method (LS-SVM) scour depth prediction after bias correction are similar to the results before bias correction. Conclusion: Due to the scour depth uncertainty estimation by the empirical equations, the purpose of this study was to estimate scour depth downstream of structures using combination of empirical equations (combined methods). The National Institute and Mason and Arumugam equations was selected as the best single (empirical) equations before and after bias correction, respectively. The accuracy of combination methods increased because of low accuracy of single equations before bias correction, but after bias the accuracy of combination methods did not much change with single equations. Comparison of direct weighting methods showed that GRA is the best method and has much less error than the best single equation before bias correction, but after bias correction the EWA method is the best combination method and its almost similar to the best single equation after bias correction. The results of the artificial intelligence method (LS-SVM) were same as the local weighting method before and after bias correction. LS-SVM was able to greatly increase the accuracy of the estimation by combining the single equation before bias correction, but after bias correction the effect of the combination of the individual relations was reduced and the scour depth estimation as same to the single equation.

Introduction: Drop manholes are widely used in sewer and drainage systems in steep urban catchments. Those are often employed to provide energy dissipation in order to control high flow velocity and minimize structural damage. Under Regime R2 insufficient energy dissipation and excessive air entrainment could lead to hydraulic problems in the downstream system. Therefore, the plane jet-breaker device was recommended by Granata et al. (2014) to improve drop manhole performance. It would have some positive impacts on hydraulic features of the drop manhole if is properly designed. Methodology: In the present study, the effects of the jet-breaker length, width, sagitta, and angle, on drop manhole energy dissipation (as response variable) have been analysed under various inlet pipe filling ratios. Dimensional analysis and modern statistical Design of Experiment (DoE) have been brought together and experiments have been designed according to the 2 5 full factorial design with four replications at the center point. Seventeen jet-breakers have been examined and about 350 tests have been performed on a physical model of drop manhole at the Hydraulic Structures Laboratory of Shahid Bahonar University of Kerman, Kerman, Iran. Results and discussion: Energy dissipation is closely related to the flow regimes. The variation of Ed/Eo versus the impact number (I) showed that some jet-breakers effectively leveled Ed/Eo at one (1) over different flow regimes, which is the optimum condition. Moreover, reduction of the filling ratio from 80% to 40% causes obvious deviation from manhole optimum energy dissipation operation. Significant main and interaction effects were distinguished from the full model Analysis of Variance (ANOVA). This analysis revealed that inlet pipe filling ratio (factor A) effect was significant at 0. 01 significance level (α = 0. 01), whilst AD (inlet pipe filling ratio and jet-breaker sagitta ratio interaction) and AE (inlet pipe filling ratio and jet-breaker angle interaction) effects were significant at α = 0. 05. The significant effects of the full model ANOVA (i. e. A, AD, and AE), together with factors D and E, were used to perform reduced model ANOVA and fit a regression model to the response variable. The former factors were considered to maintain the model hierarchy. The result shows that all considered effects are statistically significant at α = 0. 01, apart from factor E effect which is significant at α = 0. 05. The statistical significance is determined by using pvalue, which shows the probability value and is associated with the test statistic F0 value; smaller p-value (or larger F0 value) leads to a more significant effect. The ANOVA indicates that there is no evidence of second-order curvature in the response over the region of exploration at 0. 01 significance level. Additionally, the lack of fit (LOF), which is defined as the deviation of the data from the fitted model, is not significant. It means that there is a strong indication that the regression function is linear and the model fitted to the data well. Moreover, a regression model was intudeced regarding the result of the reduced model ANOVA. Conclusion: The statistical analysis of the results revealed that the response variable was significantly improved when the inlet pipe filling ratio was 80% and jet-breaker sagitta was equal to zero, and its angle was at 70 ˚ . Jet-breaker length ratio and width ratio had neither significant main nor significant interaction effects on the response variable. Even though with reference to practical considerations and previous investigations, jet-breaker length equals manhole diameter and jet-breaker width of 140% larger than inlet pipe diameter, were suggested. Moreover, the use of DoE resulted in straightforward data analysis and unbiased concluding.

Introduction: The deposition of sediments in reservoirs seems to be one of the fundamental problems in the operation of dams. An operation known as flushing, with two free and pressurized types, is used to discharge these sediments. In the free flushing method, all the water in the reservoir is drained from the bottom outlet and large amounts of the deposited sediments are discharged; however, this method does not perform well in the case of large dams. In the pressurized flushing method, the discharge of sediments is done under constant water height at the upstream of the bottom outlet. The efficiency of the free flushing method is superior to the pressurized flushing method; but it is not much common to be applied due to causing environmental problems resulting from the sudden outflow of large volumes of water and sediments in the downstream and is specifically used only for small reservoirs. Hence, due to its low efficiency, some strategies are needed to increase the efficiency of the pressurized flushing approach. A few researches have been conducted so far on the topic of increasing efficiency. By installing a group of cylindrical piles in the upstream of the orifice, Madadi et al. (2016) increased the efficiency of pressurized flushing by 250% compared to the control test (without piles). Also by installing a semi-cylindrical structure in the upstream of the orifice, Madadi et al. (2017) managed to enhance the efficiency of pressurized flushing by 450% compared to the control test. A new method has been provided in this study to examine the effect of using a square single-pile at the upstream of the orifice on the dimensions and the volume of the flushing cone in the pressurized flushing. Materials and Methods: The experiments were performed in a rectangular flume in the hydraulic research laboratory of the Faculty of Water Sciences and Engineering, Shahid Chamran University of Ahvaz, Iran. Three flow rates (Q) of 4. 17, 6. 39 and 8. 34 l/s were considered for the experiments. In all experiments, the level of sediments (Hs) was set constant at the level of the orifice lower edge. The water level in the flume to the center of the orifice (Hw) was considered to be 52 cm in all experiments. The diameter of the outlet orifice (Do) was also set to be 7 cm. The gradation of the sediments used was also considered fixed in all experiments (d50 = 0. 5mm). We set the experiment time as150 minutes in all cases. We utilized four different sizes of the side (1. 4, 2. 1, 2. 8, and 3. 5 cm or the corresponding ratio Dp/D0 equal to 0. 2, 0. 3, 0. 4, and 0. 5, respectively) aimed at examining the effect of square pile size (Dp) on the dimensions and efficiency of the score cone. We determined the pile placement distance from the orifice (Lp) in such a way to avoid any impact on the water level at the upstream of orifice and the outlet flow rate when discharging and also to be located at the closest distance from the orifice. This distance was calculated to be 4. 9 cm by performing successive experiments. The pile was installed with the highest impact on flushing at different distances from the orifice upstream to examine the effect of pile placement distance (Lp). These distances have defined as a ratio of the orifice diameter equal to 𝐿 𝑝 𝐷 𝑜 ⁄ = 0. 7, 1. 2, 1. 7, 2. 2. Results and Discussion: The control experiments were made in a state of non-installation of the pile at the orifice upstream. Revealed by the results, by increasing the flow rate from 4. 17 l/s to 8. 34 l/s, the volume of the flushing cone has increased by approximately 287%. Also, the length, width, and depth of the flushing cone have increased by 57%, 42% and 53%, respectively. The movement of sediments in the pressurized flushing and their outflow are made due to shear stress along the bed and two clockwise and counterclockwise vortices in the orifice upstream. As the flow rate increases, more sediments removed as a result of more shear stress caused in the bed and the strength of the vortices enhances as well. This leads to the removal and exit of further sediments from the orifice, which will increase the volume and dimensions of the sediment flushing cone. The results of the pile installation experiments demonstrated that the application of the square pile has significantly increased the volume of the flushing cone so that in the case of a flow rate of 4. 17 l/s and a pile installation with a side size of 3. 5 cm at a distance of 4. 9 cm from the orifice upstream, the volume of the flushing cone increased by approximately 362% compared to the control state. Also, in the same case, the depth, length and width of the flushing cone respectively increased by 120%, 57%, and 42% in comparison to the control state. When a pile is placed in the path of the water stream with a sedimentary bed, a series of downward currents are formed known as Horseshoe Vortices due to the collision of the flow lines to the pile upstream side, which causes the hydrodynamic scour phenomenon around the pile. Installing the pile at the orifice upstream causes the erosive sediments caused by the presence of the pile to exit from the orifice in addition to the removal of sediments from the sediment flushing phenomenon, increasing the efficiency of flushing. To explain this phenomenon, we can say that more downward vortices are formed in the pile upstream by increasing the pile dimensions. Also, the separation of the flow lines in this case increases and a low-pressure area is created with a larger area at the pile downstream. Thus, more sediments are detached from the orifice upstream and exit from it. It was found that the highest effect of the square pile dimension on extension of flushing cone is related to the size of 𝐷 𝑃 𝐷 𝑜 = 0. 5 ⁄ . Therefore, in order to investigate the effect of the pile distance from the orifice on flushing cone volume and dimensions, the measured flushing volume and dimensions related to the relative distance of 𝐿 𝑃 𝐷 𝑜 = 0. 7, 1. 2, 1. 7, 2. 2 ⁄ with the abovementioned pile size were only analyzed here. As the pile placement distance from the orifice upstream increases, the volume of the sediment flushing cone decreases; for the furthest distance the effect of pile placement almost vanishes. Conclusion: The study of the effect of installing a single square pile at the upstream of the orifice on the pressurized flushing efficiency indicated that the presence of a single pile can lead to an increase in the sediment flushing efficiency. The greatest impact of the pile placement (𝐿 𝑃 𝐷 𝑜 = 0. 7 ) ⁄ belongs to the largest pile (𝐷 𝑃 𝐷 𝑜 = 0. 5 ⁄ ). In this case, the volume of the flushing cone increased by about 362% compared to the control state. In other words, with the same amount of discharge of water from the orifice in the pile-less state, we can increase the volume of sediments discharge to a considerable extent by installing the pile.

Introduction: In practical applications, at the downstream of hydraulic structures, in some cases, the width of the basin may be larger than the upstream supercritical flow (sudden expansion in the flow section). In such cases, an expanding hydraulic jump with symmetrical or asymmetrical shape will be developed at the downstream. Under the design of three parallel gates, the operation of the side or middle gate can be lead to the asymmetrical or symmetrical hydraulic jump, respectively. According to the position of the jump toe, expanding hydraulic jump can be classified into four types. The present study focuses on a T-shaped hydraulic jump, which the toe is established at the beginning of the divergence section. Most of the previous studies are related to the symmetrical expanding hydraulic jump. In this case, the downstream diverging channel is symmetric on the central axis of the channel. However, a systematic study on the effects of symmetry and asymmetry of the expanding hydraulic jump was not found in the literature. In this study, using the momentum principle, some theoretical equations to determine the ratio of the sequent depths of symmetrical and asymmetrical expanding hydraulic jump were derived. Also, some regression relations were proposed to estimate the length of expanding hydraulic jump. The new proposed equations were also extended for the presence of a sill. The equations were calibrated using available experimental data obtained in this and previous studies. This research also considered the characteristics of expanding hydraulic jump under the symmetrical and asymmetrical operation of the parallel gates. Methodology: To calibrate new proposed relations and investigate the effects of different parameters on the expanding hydraulic jump characteristics, two experimental data sets were used. In addition to the data set from Bremen (1990), the experimental data from the present study were used. The data were collected from a hydraulic model of three parallel radial gates for operating the side or middle gate, which corresponds with the asymmetrical or symmetrical expanding hydraulic jump, respectively. The experiments provided a wide range of different parameters as the approaching Froude number, hydraulic jump length, sequent depths ratio, divergence ratio, sill height, and relative length of gate separator wall. Results and discussion: Equation (4) was developed to determine the ratio of the sequent depths of expanding hydraulic jump based on the momentum equation. For the presence of a sill, a combination of Equations (4), (7) and (8) can be used to calculate the ratio of the sequent depths under the asymmetric and symmetric developments, respectively. Determining the ratio of the sequent depths requires the calculation of the adjacent water depths of the closed gates. For this purpose, in addition to regression equation development (i. e. Equation 13), Equation (12) was proposed. This equation is based on the calculation of the hydraulic jump profile. It was observed that under the calibration range, the regression equation is more accurate. However, Equation (12) is recommended for the range outside of the experimental observations. The results showed that: ❖ As the divergence ratio increases, the ratio of sequent depths approaches to the classic hydraulic jump. ❖ By decreasing the relative length of the gate separator wall and decreasing the width of the gate on the downstream channel width, the relative depth at the side gate and consequently the ratio of the sequent depths will decrease. ❖ For the lower length of the separator wall and under the operation of the middle gate, longer horizonta distance is needed to develop the jump than the side gate. However, as the length of the separator wall increases, the length and sequent depth of hydraulic jump due to the side gate increases on the middle gate. ❖ In the presence of a sill, the relative length of the hydraulic jump decreases, and the ratio of secondary depths increases. ❖ It was observed that the hydraulic jump due to the operation of the middle gate leans toward the left or right side of the channel due to oscillatory behavior. ❖ Under operating the middle gate and in the absence of a sill, an asymmetric hydraulic jump is formed in the channel face when the length of the separator wall is less than 38% of the classical hydraulic jump length. For the presence of a sill, the minimum length of the separator wall decreases to about 26%. ❖ By decreasing the initial depth of the hydraulic jump on the width of the gate and converting the output jet into a linear jet, the relative development length will be increased. ❖ As the sill height increases, the difference in the depths attached to the side gates will decrease, and the hydraulic jump will develop more symmetrically. ❖ As the relative height of the sill decreases, the minimum length of the separator wall increases and a symmetrical hydraulic jump in the flanks forms. Conclusion: This research developed a set of theoretical and regression relationships for estimating the length and sequent depth ratio of expanding hydraulic jump. Moreover, the effects of sill height, divergence ratio, and the length of the gate separator wall, were investigated. This study compares the effects of side and middle gate operations based on the variation of jump length and sequent depth ratio. The results can be used as a guide for the hydraulic structures operators to reduce the asymmetric severity of the expanding hydraulic jump and achieving the complete development under the minimum length.

Introduction: Vegetation in compound channels by increasing factors such as roughness in the floodplains rather than main channel, velocity difference and momentum exchange between the sub sections, makes the transverse velocity gradient and apparent shear stress increase of the channel interface. In natural rivers, changing the cross section makes the uniform flow convertion to non-uniform. In prismatic channels, shear stress in the interface between main channel and floodplains, influences the transfer capacity and velocity distribution pattern significantly. This effect in non-prismatic channels, due to the extra momentum exchange between the sub-sections is more intense. In such conditions, identifying the flow hydraulic is too complex. Although forming the vegetated and non-prismatic floodplains at the same time in natural rivers is highly probable, there are no specialized studies to investigate the hydraulic of flow in such the conditions. Therefore, in the present study, experimental measurements were conducted in a compound channel with nonprismatic and vegetated floodplains simultaneously and flow behavior is investigated on it. Methodology: The experiments were conducted in a 10 m long, 2 m wide compound channel located at the National Laboratory for Civil Engineering (LNEC) in Lisbon, Portugal. The channel cross-section consists of two equal rectangular fl oodplains (fl oodplain width Bfp=0. 7 m) and one trapezoidal main channel (bank full height, hb=0. 1 m, bottom width bmc = 0. 4 m, bank full width Bmc = 0. 6 m and side slope of 45° , sy= 1). The channel bed is made of polished concrete and its longitudinal slope is S0= 0. 0011 m/m. The vegetated floodplains were obtained by covering their bottoms with a 5 mm hight synthetic grass. For the polished concrete, the roughness coefficients i. e. n= 0. 0092 m-1/3s and ks=0. 15 mm are considered and for the synthetic grass, n=0. 0172 m-1/3s and ks=6. 8 mm are used. Measurements were performed for relative depths of 0. 21 and 0. 31. The experiments in the non-prismatic channel performed at two convergent angles of floodplains (θ =7. 25° and θ =11. 3° ). In this cases, the mentioned relative depths were set up in the middle sections of convergences by changing the downstream tailgate. The velocity measurements performed for Entrance, Middle and End sections of convergent angles. Results and discussion: High velocity distribution pattern gradients are observed in nonprismatic channel rather than prismatic channel for a given relative depths. Comparisons between similar sections indicates that by increasing the relative depth, the interaction intensity through the main channel and floodplain decreases. As presence of vegetation on the floodplain leads to the channel transfer capacity decrease and in high values of relative depth, this effect decreases. Except the areas close to wall and interface, the flow on floodplain is twodimensional, while in the main channel and especially in low relative depths is threedimensional. This issue has also been affected by different convergence angles. The maximum velocity generally occurs near the outer wall of the main channel. But, by increasing the relative depth, position of the maximum velocity moves to the floodplain. In the lower relative depth, in vicinity of interface, a bulge is visible in isovel lines that is already reported in previous works. Due to the mass transfer from the floodplain towards the main channel, this bulge occurred more intensively in the middle sections in both the convergent angels. In nonprismatic channel, for all the flow cases, at the interface, the intensity of the secondary flows is more apparent and in the down part main channel flow, a vortex is formed that by increasing the relative depth from 0. 21 to 0. 31 and convergent angels from 7. 25° to 11. 3° , moves from the outer wall of the main channel towards the floodplain. Also at the beginning of the floodplain, one vortex is formed that becomes more apparent by increasing the convergence angles. Due to converging floodplains, in the upper layers, a transverse current is directed from the floodplains to the main channel. This transverse current enters the main channel from both sides and, due to symmetry of flow, plunges to the channel bed and as a result, two helical secondary flows are generated in the main channel, rotating in the channel length which is very important in terms of sediment and pollutant transport. By increasing relative depth, velocity gradient between the main channel and floodplains decreases. Conclusions: In present study, using an experimental model, flow behavior in a prismatic and non-prismatic compound channel is investigated. Non-prismatic channel consists of two convergence angles; 7. 25° and 11. 3° . All the experiments are conducted at two relative depths of 0. 21 and 0. 31. In order to investigate vegetation cover effects, floodplains are covered with synthetic grass and a vecterino (ADV) is used to measure the fluctuations of instantaneous flow velocity. Variations in the streamwise velocity distribution, secondary currents and Reynolds stresses based on proportions of vegetation and non-prismaticity in the flow hydraulic are investigated. Results show for high relative depth, by increasing convergent angles, the floodplains are less involved in discharge carrying and transferring. The maximum velocity values which occur at the main channel center, by increseang the relative depth and extending secondary currents, towards to the floodplains. By increasing the convergent angle, the roughness values in the main channel and floodplains increases. Distribution of flow mean kinetic energy shows that by increasing relative depth, its values in the middle section decreases for both the convergent angles.

Introduction: Investigation of the scour in rivers and related structures are very important. Scour around bridge piers and bridge abutments are the main cause of bridge failure. The scour around the bridge piers causes instability of them, and without applying an appropriate solution, it eventually leads to the demolition of the structure. Therefore, a study on the mechanism of the scour and the effective parameters on the amount of scour are important. So, until now, various studies have been done on the mechanism of scour around hydraulic structures especially bridges piers. In this field, researches are more focused on the scour of piers, but no effective results were obtained on the scour phenomenon around the piers. Bed erosion and transport of sand material from its initial location by a flow called scour. Local scour is a special type of scouring that may occur around the bridge piers or bridge abutments. This type of scouring is the main reason for many bridge failures in the word. Because of this, using a method to control and reduce scour is important. One of the methods to reduce the scour depth around the bridge pier or abutment is installation a thin flat rigid plate (collar) on the pier or abutment. There is no comprehensive study to use perforated collar for protecting the piers against scour so far. Therefore, this topic was considered for this research. Methodology: This study was performed in the flume with a length of 6 m, a width of 0. 72 m, a height of 0. 6 m, and a constant bed slope equal to nearly zero in the Hydraulic Laboratory of Shahid Chamran University of Ahvaz. The bed materials were noncohesive sediment with an average diameter equal to 0. 73 mm and a geometric standard deviation of 1. 22. As well as Plexiglas plates with a thickness of 3 mm were used to build the collar. In this study, 27 tests were performed to measured, sediment scours and determine the two-dimensional velocity components. A series of tests were performed as a control experiment. The tests of scouring were performed in three flow rates equal to 25, 30, and 35 liters per second. In this condition, Froude Number was equal to 0. 26, 0. 32, and 0. 37 respectively. Three unsymmetrical collars with different dimensions were tested. Then series of experimental tests were conducted in a physical model using three different Zc (0, 0. 25, and 0. 5 high). For analyzing the measured data at first a general nondimensional relationship was developed. Results and discussion: Dimensionless plots were drawn regarding the effects of the dimension of collars on scour reduction around bridge pier. Different positions of installation of the collar were tested. Dimensionless plots were drawn for finding the effects of collar performance in various heights. After many testing, one of the collars that showed the best performance is selected as an optimum collar. Then, the perforated unsymmetrical collars were tested. Also, two tests were performed to determine three-dimensional components of velocity around the collars in different depths. The results show that the performance of the perforated collar in unsymmetrical shapes improves by increasing its dimensions. The performance of the collars located on the bed is better than the others located above the bed. Conclusion: The results show that the collars have an important role in the reduction of scour development. In the section of determination of three-dimensional components of velocity, the results show that the collar act as a shield against the downflow. Therefore, it can control the horseshoe scour around the pier. Literature review shows that the maximum scour depth occurs in the case of the cylindrical pier. Therefore, in this study, the cylindrical shape of the pier was selected and the effects of Froude Numbers were analyzed on scouring development. Result shows, that increasing in Froude Numbers of flow will cause an increase in scour depth. Also, as the height of mounting the collar increased, so the scour depth and the width of the scour hole increase. At the final step of the study, three-dimensional components of velocities were measured by ADV. The speedometer-ADV-was fixed at 0, 1, 3, and 5 cm above the bed channel. When the 15% collar fixed on the bed, then scour decreased to 72%. In addition, the 30% and 40% collars had the same results. Velocimeter and flow pattern was drawn around the collars. Also, the results confirm that near the piers because of the downflow usually, maximum velocity occurs near the bed. Generally, downflow and generated wake vortex behind the piers are effective parameters on bridge piers scour.

Introduction: Study of the flow pattern at the lateral intakes where separation occurs is a critical issue. The flow rate and sediment trap are highly dependent on the flow structure in this area. Flow separation occurs due to the detachment of stream lines from the channel side walls. It creates a secondary flow similar to what happens at river bends. Flow separation reduces the efficiency by decreasing the flow effective area at lateral intakes. It also creates a region with horizontal vortices where is prone to sedimentation. Hence, finding a method to reduce the separation zone dimensions is significantly important. Different techniques have been introduced in the literature such as installation of submerged vanes, deployment of different intake angles to main channel, construction of the entrance part as a part of circles with various radiuses, etc. This study examines the effects of roughness coefficient and drop implementation at the entrance of a 90-degree lateral intake on the dimensions of the separation zone. As far as the knowledge of the authors show, these two variables have not ever been studied to decrease the separation zone dimensions and enhancing the turnout efficiency. Methodology: In order to investigate the effect of roughness coefficient and drop implementation on the separation zone dimensions, four different discharges (16, 18, 21, 23 l/s) in subcritical conditions, seven manning roughness coefficients (0. 009, 0. 011, 0. 017, 0. 023, 0. 030, 0. 032) and 3 invert elevation differences between the main channel and lateral intake (0, 5 and 10 cm) at the entrance of the intake were considered. Totally, 84 tests were performed in a concrete flume with 15 m length 0. 5 m width and 0. 4 m depth. The intake structure was made at a 90-degree angle to the main channel with 0. 35 m width. The Manning roughness coefficient values were selected based on available and also feasible values similar to real condition, so that 0. 009 is equivalent to galvanized sheet roughness and selected for the baseline tests. Also, 0. 011 is for cement with neat surface, 0. 017 and 0. 023 are for unfinished and gunite concrete respectively. 0. 030 and 0. 032 values are for concrete on irregular excavated rock. (Chow, 1959). The roughness coefficients were created by gluing sediment particles on a thin galvanized sheet which was installed at the upstream side of the lateral intake. The values of roughness coefficients were calculated based on Srickler’ s formula. For this purpose, some uniformly graded sediment samples were prepared and the Manning roughness coefficient of each sample was determined with respect to D50 value pasted into the Strickler’ s relation. All the experiments were recorded and photographs were taken severally during the experiment and after steady flow conditions were established. The photos were then imported to AutoCAD to measure the separation zone dimensions. The velocity values were also recorded by a one-dimensional velocity meter at 15 cm distance from the intake entrance and in transverse direction (perpendicular to the flow direction). Results and Discussion: Negative velocity values were seen in the separation zone indicating dominant secondary currents at the intake entrance. The velocities were intensified by moving toward the intake midway showing that the effective area is scaled down. The velocity values were almost equal to zero near the side walls, as expected. Results were presented as dimensionless separation zone area (ratio of the separation zone area to intake area). Analysis shows that by increasing roughness coefficient alone, separating zone dimensions reduce up to 38%. This technique requires minimal changes in intake geometry and is definitely an inexpensive method to be applied for intakes under operation. Besides, the studied roughness coefficient was quite accessible. Implementation of a drop can decline this area respecting the roughness coefficient value differently. Naturally there is an invert elevation difference between the feeding canal and the areas to be irrigated. This idea was developed base on this issue. A minor part of this difference can be compensated at the intake entrance. This method increases the discharge ratio (ratio of intake to main channel discharge). The results are compatible with literature. Some other researchers reported that intensifying the discharge ratio can scale down the separation zone dimensions (Rumamurty et al., 2007; Keshavarzi and Karami Moghaddam, 2007). However, these scientists employed other methods to enhance the discharge ratio. Employing both techniques simultaneously can decrease the separation zone dimensions up to 41%. A comparison between the new methods introduced in this paper and traditional methods such as installation of submerged vanes, and changing the inlet geometry (angle, radius) was performed. The comparison shows that the new techniques can be highly influential and still practical. Conclusions: This study introduces practical and still easy and costly beneficial methods for enhancing intake efficiency by declining the separation zone dimensions. Increasing roughness coefficient and implementation of inlet drop were considered as remedied for reduction separations zone dimensions. Results showed that enhancing roughness coefficient can decline the separation zone dimensions up to 38% while drop implementation effect can scale down this area differently based on roughness coefficient used. Combining both methods can descend the separation zone dimensions up to 41%. It is proposed to investigate the effect of roughness and drop implementation on sedimentation pattern at lateral intakes for further researches.

Introduction: Water is the most strategic liquid in the world. The life of all humankind and animals and plants are relying on the water. The water should supply to the location of the demands. One of the most common water transmission ways is open channels. If a sudden change occurs in the channel section, it can affect the whole water flow in the channel. These changes can happen naturally, like aggregation of sediments in a section of the channel. Moreover, the changes may cause by humans, like sharp and broad-crested weirs. Thus, it is necessary to simulate open-channel flows to predict possible changes in water surface profile and velocity. Basically, researchers follow three approaches to simulate water flows: the analytic, the experimental, and the numerical approaches. Analytical approaches for solving the flow equations is not sufficient due to the complexity and nonlinearity of the equations so there are several restrictions in the modeling. On the other hand, experimental approach is time consuming and expensive. Since the high-performance computers have been developed, researchers attracted to the numerical approaches. There are different numerical solutions which are used to solve the water flow equations such as finite difference method, finite element method, finite volume method, etc. The finite volume method is one of the most applicable methods in several computational aspects of engineering, such as computational fluid dynamics and heat transfer problems. In this method, it is necessary to have a strong approximation of the numerical flux term for solving flow equations. The Riemann solver provides a reliable approximation for the numerical flux term. The Riemann problem for a set of PDEs is an initial value problem for such PDEs in which the initial condition has a special form. In order to apply numerical solutions, one can use the exact Riemann solver or approximate Riemann solver. The exact Riemann solver uses Newton-Raphson method that takes noticeable cost in time and money and the results rely on the first guess of Newton-Raphson. Therefore, researchers prefer the approximate Riemann solvers such as Harten Lax van Leer (HLL) scheme, Harten Lax van Leer Constant (HLLC) scheme and Weighted Average Flux (WAF) scheme that have acceptable results and running time. Materials and Methods: WAF scheme can be categorized as a branch of finite volume method. The scheme was first applied to the Euler equation. This scheme is one of the approximation solution (besides HLL and HLLC methods) of the Riemann problem. Then, Toro used the WAF scheme to simulate two-dimensional shallow water equations. Subsequently, WAF has been utilized to simulate flow over different kinds of open channels. Although the scheme shows reasonable results, it is noticeable that the numerical scheme is not well-balanced essentially. Thus, a well-balanced WAF scheme should be developed to simulate flow in open channels accurately without non-physical fluctuations in flow surface. The aim of this research is to use the ability of the WAF scheme to simulate shallow water and applying some consideration on the scheme to prevent non-physical fluctuations in water surfaces. Conclusion: In this paper, a well-balanced form of WAF which is combined with HLL for estimating flux has been employed to simulate one-dimensional flow open channels. MINMOD as an effective slope limiter has been used in order to prevent non-physical oscillations. Moreover, Runge-Kutta has been employed as the time integration method to renew depths and velocities. Several different cases have been used to show that the scheme has an excellent shock-capturing ability and can handle the wet and dry condition of channel bed. Importantly, the linear reconstruction for the scheme has been applied to have secondorder accuracy and to prevent the negative depth effect on computations. The scheme is shown to be well-balanced by evaluating stationary solutions at steady state conditions. Besides, the capability and accuracy of the scheme are verified by the comparison of scheme numerical results with the analytical and experimental literature results. The numerical results have shown that the scheme can satisfy the continuity equation and prevent negative depth. For real applications of the scheme, the simulations of flow over sharp changes and dam-break show that RMSEs are in acceptable ranges and there is no non-physical fluctuations on the water surface profile. Simulating dam break on the wet and dry beds, show that the scheme is capable in shock capturing as well as solving wetting-drying problems. In addition, flow with wide range of Froude number over different forms of broad crested weirs, have been employed to verify the robustness, accuracy and stability of the scheme. Hence, all of these results prove that the presented well-balanced scheme is able to simulate different cases of shallow water equation examples accurately.