مجله هیدرولیک
سال شانزدهم شماره 4 (زمستان 1400)

The industrialization of human societies is one of the factors in increasing the injection of pollution into surface waters. Contamination in the river is maintained both in the water stream and in the sediment bed of the river. The hyporheic zone is the saturation zone of the riverbed, which has a very important function in the transmission of pollution. River bed-form is one of the effective factors in creating hyporheic exchanges between surface flow and sediment bed. Transient Storage Model (TSM) is one of the suitable methods in the analysis of advection and dispersion of pollution in rivers with hyporheic zone. The efficiency of the Transient Storage Model (TSM) depends on accurate estimation of the four parameters of the model (Dx, As, A and α). Previous studies have investigated the effect of bed-form on hyporheic exchanges, but the effect of these exchanges on contamination transmission has not been investigated. On the other hand, previous studies have not investigated the effect of hyporheic exchanges caused by the formation of the bed-form on the four parameters of the transient storage model (TSM). In this study, the effect of dune bed-form on the transmission of pollution was investigated. Also, the effect of dune formation on the four parameters of the transient storage model (TSM) with a numerical model (OTIS and OTIS-P) and the temporal moment approach (TM) was discussed.

Experiments of tracer material (NaCl) were performed in a flume with a length of 12 m, a width of 0.5 m and a height of 0.7 m applying four different flow discharges (5, 7.5, 10 and 12.5 l/s). The experiments were performed in the range of average flow velocity (U) from 0.087 to 0.361 and in the range of Froude number (Fr) from 0.069 to 0.290. An ultrasonic flow-meter was used to measure the flow discharge in all experiments. Grain material with an average diameter (D50) of 11.85 mm and the porosity (n) of 0.28 were used to create a sedimentary bed. The first bed (WF1) with a thickness of 32 cm, a width of 0.5 m and a length of 10 m was created in the Flume. In order to investigate the effect of sediment bed thickness on contamination transmission, a second bed (WF2) with a thickness of 8 cm, a width of 0.5 m and a length of 10 m was also created. In this study, the effect of dune bed-form on the transmission of contamination was investigated by creating three dune bed-forms (D1, D2 and D3) with different wavelengths (λ) and different amplitudes (∆) in the second bed (WF2). The length of the flume was divided into three equal reaches. Two sensors were placed to measure the electrical conductivity (ec) of water in each reach aiming to monitor the concentration of contamination. A Pitot tube and an ultrasonic depth-gauge were used to measure the velocity (U) and depth (d) of water flow at each reach, respectively. The laboratory results were simulated by the OTIS-P numerical model and the four parameters of the Transient Storage Model (TSM) were estimated. OTIS-P numerical model estimates the four parameters of the Transient Storage Model (TSM) using the Nonlinear Least Squares (NLS) optimization algorithm and then simulates the breakthrough curves using the Crank-Nicolson implicit finite difference method. The parameters of the transient storage model (TSM) were estimated by optimizing the temporal moment approach (TM) relations using the Genetic Algorithm (GA) method and the breakthrough curves were reproduced using these parameters in OTIS software.

The results showed that increase the thickness of the sediment bed (from 8 cm (WF2) to 32 cm (WF1)) reduces the (Dx). Hyporheic exchanges decrease with increasing d_b/d, so the amount of hyporheic exchanges in WF2 bed is more than WF1 bed. Increasing hyporheic exchanges in the WF2 bed-form reduces the amount of contamination concentration in the main flow area, so the amount of (Dx) in this bed-form increases. The results showed that increasing Froude number (Fr) increases the (Dx) in both cases of bed thickness. The results showed that the storage zone exchange coefficient (α) in WF2 bed was higher than WF1 bed. Decreasing d_b/d increases the hyporheic exchanges at the time scale (t_f^*), so the residence time of contamination in the sediment bed increases. Since the storage zone exchange coefficient (α) indicates the amount of time exchanges of contamination in hyporheic zone, so reducing the bed thickness (db) increases this parameter. The results showed that the formation of the dune bed-form does not cause an absolute increase or an absolute decrease in the longitudinal dispersion coefficients (Dx). The main channel area (A) considering the D2 bed-form case was estimated more than that in the D1 bed-form case. Therefore, increasing the wavelength of the bed-form (λ) increases the share of the main flow region area (A) in the contamination transmission. On the other hand, in the case of less exchanges of contamination with the storage zone, the share of the storage zone area (As) decreases with increasing wavelength of the bed-form (λ). The results showed that the effect of dune bed-form on changes in TSM parameters was in the range of Fr

Weirs are structures to provide the passage for excess water to flow from upstream to downstream in flood conditions. Since the special geometry of ogee weir in terms of matching the flow Trajectory with the surface of the weir, increases the efficiency of this type of weirs, so the use of terminal structures to dissipate destructive energy downstream of weir is of great importance. Increasing the water level in the Ogee weirs generally increases the contact level and head loss, but specifically in gabion weirs leads to increased permeability. One of the new methods of energy dissipation is the use of gabion structures, artificial roughness, blocks and lattice plates in the flow path as alternative solutions to using the stilling basins. Based on the results of previous research in the field of artificial intelligence, in the present study, the amount of energy consumption of the Ogee weir terminal structure (gabion structure) was predicted using the support vector machine and the effect of dimensions and grain size of the gabion structure. The amount of energy dissipation was also examined.

For this purpose, the experiments were performed in a rectangular channel located in the hydraulic laboratory of Maragheh University, 13 meters long, 120 cm wide and 80 cm high, with a metal floor and a glass wall 1 cm thick, which allows accurate observation of flow behaviors. The gabion used in this experiment was made of rebar number 6 with a width of 120 cm, a length of 10 cm (in the direction of flow) and a variable height, then it was surrounded by a metal mesh with a thickness of 1 mm and a diameter of 1 cm. To predict energy dissipation in the support vector machine, we need a series of functions based on the parameters extracted in the dimensional analysis. Models with different percentages of training and testing (65-35, 70-30, 75-25 and 80-80) and using the radial basis function (RBF), with the appropriate gamma value obtained during trial and error, were checked by a support vector machine. The following criteria were used to evaluate the obtained results and evaluate the efficiency of the models. 1- Normal root mean square error (RMSE), which no matter how close the index (RMSE) is to zero, the model has high accuracy. 2. The normal root mean square error (NRMSE) where NRMSE below 10% indicates the accuracy of the model, 10-20% indicates the suitability of the model, 20-30% the average accuracy and more than 30% indicates the weakness of the model. 3. Performance coefficient (Nash and Sutcliffe) which shows the linear correlation between the measured and predicted values and the closer the value is to one, the better the data correlation.

The results are presented in three sections: Laboratory, Soft Computing and Sensitivity Analysis. To investigate the energy dissipation of the downstream gabion structure, the Ogee weir was performed according to the various variables extracted in the dimensional analysis, including the number and width of openings, grain size, and Froude number. It can be seen that in all models, energy dissipation values are directly related to the Froude number. At the same flow rate, with decreasing Froude number, the flow depth increases and most of the flow passes through the gabion structure as a weir and the energy dissipation decreases. At shallow flow where all or most of the flow passes through the structure, most of the energy dissipation is due to the collision of the flow with the particles inside the structure. However, in higher Froude numbers, the structure is submerged under the flow and both internal flow and overflow are effective in energy dissipation, with the difference that in overgrowth structures, overflow and in fine-grained structures, internal flow is predominant.

Therefore, at a constant opening, fine-grained has the highest amount of energy dissipation. In other words, with increasing the diameter of the rock grains, the volume of the pores increases and the flow passes more easily through the rock grains and the turbulence and flow of the flow in this area decreases, so the energy dissipation decreases. It can be seen that for all models, the values predicted by the support vector machine are close to the laboratory results, but in the Froude numbers the accuracy of the support vector machine is further reduced. The reason for this can be considered as turbulence and turbulence in higher Froude numbers. Finally, it can be stated that the energy dissipation of the gabion structure in the test and training phase has acceptable compliance and overlap with laboratory values. Sensitivity analysis showed that the parameter of relative water depth after gabion has the greatest effect on the correct prediction of energy consumption due to gabion structure.

Bridge scour is one of the most important challenges in river engineering. Every year, thousands of bridges around the world are destroyed due to scouring. Hence, the accurate prediction of maximum scour depth for saving financial resources and the safety of human lives is of paramount importance. One way to reduce scouring is to use slot at the pier of the bridge. Research on the effect of the slots, in reducing scour around the bridge pier, has been done bed sediments of uniform type and in most cases the depth of flow have been considered as a constant factor. The aim of the present study is to investigate the effect of sediment non-uniformity in the presence or absence of slots in the bridge pier and the relative effect of increasing the depth of flow (with increasing flow rate) on the scour depth around the cylindrical pier.

The present experiments have been conducted in hydraulic laboratory at Bu-Ali Sina University, Hamadan (Iran). The pier model with a diameter of 4 cm was put inside a rectangular flume with dimensions of 0.5 m wide, 10.5 m long and 0.5 m height. Three different types of slots were used along with the pier without slot. In order to obtain the effect of sediments on scour depth, two types of bed were used. The bed of the first and second types had uniform and non-uniform sediments, respectively. In this experiment, flow rates of 8, 10 and 12 l/s were used with corresponding flow depths of 5.7, 6.6 and 7.4 cm, respectively, Melville and Chiew (1999) chose a time as equilibrium after which scour depth changes of less than 0.5% of the pier diameter over a 24-hour period. According to this criterion, the time of all experiments was considered to be 6 hours.

The percentage of scour depth reduction varies according to the height of the slot and its location. Comparison of S1 and S2 models for two slot models in the same dimensions showed that the closer the slot is to the bed, the greater its effect in reducing scour depth. Also, increasing the height of the slot under the bed (S3 compared to S2) is more effective in reducing the scour depth. Comparison of the first and second beds showed that by converting uniform to non-uniform sediments under constant particle diameter conditions, the maximum scour depth in models S0,S1,S2 and S3 at a flow rate of 8 l/s was 76, 78, 76 and 79%, is respectively reduced. The reason for this can be the formation and expansion of a layer of coarse particles on the bed surface (armor layer). As the flow rate increases due to the increase in flow depth, the scour dimensions increases. According to the obtained results, the scour hole in the non-uniform bed reaches equilibrium with less time than the uniform bed. The formation of an armor layer in a non-uniform bed is the reason for less equilibrium time in similar conditions than in a uniform bed. With increasing the Froude number of flow in all base models, the depth and dimensions of the scour hole have increased. Increasing the Froude number makes the downflow current stronger, and as a result, horseshoe vortices are formed and act with less time. In clear water conditions, the maximum scouring depth will occur in the state u/〖 u〗_c =1 (Melville and Chiew 1999.( The results showed that with increasing the ratio u/〖 u〗_c of clear water scouring conditions, scouring depth increases in a variety of models and beds. According to Guo (2012) if the ratio of flow depth to pier diameter is less than 6. By increasing this ratio, the scour depth in uniform and non-uniform sediments increases.

The results of this research showed that the use of slots in Cylindrical bridge pier was more effective in reducing scouring than the use of bridge piers. With the conversion of uniform to non-uniform bed due to the formation of the armor layer, the scour depth has decreased by an average of 77% in different base models and also the time to reach the scour equilibrium has been reduced. Scour depth has increased with increasing flow rate, Froude number and ratio u/〖 u〗_c in different pier and bed models. In general, the closer the slot is to the bed, the more it reduces the scouring depth and the non-uniformity of sediments due to the formation of an armor layer around the pier causes a significant reduction in scouring depth.

Farmers in arid lands construct long levees along contour lines called bandsars adjacent to an ephemeral stream in floodplain areas to harvest floodwater and cultivate crops. The flood water stored in reservoirs behind the bandsars ensures soil moisture through flood harvesting. The use of bandsars contributes to the development of domestic agriculture. Thereby, seasonal and flush floods are prevented from being wasted into the desert. This method is common in the provinces of South Khorasan, Razavi Khorasan, Kerman and some other regions of Iran and as well as neighboring countries of Afghanistan and Pakistan. Bandsars can be directly constructed across the ephemeral streams or at their flood plains in a short distance. The purpose of this study is to model the flow in dry rivers and bandsars based on MODCEL algorithm to route the incoming flood and assess the amount of stored water in this traditional structure to evaluate its role in flood alleviation. Flow modeling is performed in two modes of controlled and uncontrolled inflow to bandsar and the importance of controlling the inflow is investigated. The program code is written in MATLAB software.

The structure of the cell model (MODCEL) is based on the concept of flow cells, inwhich the study area is divided into a set of different cells that the surface or channel currents between them are expressed via hydraulic laws. This arrangement forms a quasi-two-dimensional hydrologic-hydraulic model, although all relationships are written in one dimension. The cellular model is based on the laws of conservation of mass, energy and momentum. Model cell types include river/ canal, normal surface, and reservoir cells. River / canal cells are used to model flow in open channels. Superficial cells are used for natural surfaces where runoff occurs. These cells are usually larger than the river cells. The reservoir cell is used to simulate a temporary pond or reservoir and is represented by an area-volume-height curve. The hydraulic relationship for surface flows is based on the St. Venant dynamic equations. The output flow from the reservoirs is calculated from the classical formula of wide-crested weirs. Cells are storage elements where the principle of mass conservation is applied to them. Therefore, at any time increment, the amount of water stored in a cell is related to the inflow-outflow rates from the adjacent cells plus the shares of rainfall and penetration. The volume of water inside each cell is a function of the water level in the cell center and the discharge between two adjacent cells at any given time.

The performance of bandsars in Akbarieh village (33°41′N, 59°06′E), in Qaen County of South Khorasan are studied in this research. An ephemeral stream is bifurcated into two channels at the apex of an alluvial fan in the region. The bandsars are constructed over the floodplains of the ephemeral stream, in alignment with the contours of the alluvial fan. The maximum height of bandsars are 0.95 m above the bed with a 3. m wide spillway at 0.5m height. A five-year flood hydrograph was developed from the available climatological data using HEC-HMS and GIS tools and was given to the model as an upstream boundary condition. The inflow hydrograph was routed for the system of stream-bandsar using MODCEL model and the time history of water elevation was obtained for each bandsar, separately. The effects of infiltration and evaporation were added to the model as well. Computational results indicated that the volume of floods at stations R1 and R2 located at the downstream of each bifurcation decreased by 91 and 94 percents, respectively, when the bandsars were active. The peak discharge of hydrographs at the same stations were reduced by 81 and 89 percents as well. The bandsars were able to control a total of 92% of the volume of the incoming flood. This amount of flood penetrated into the soil surface layer, making the land suitable for cultivation. The high efficiency of bandsars in the region reduced the volume of floods in the village downstream of the bandsar complex. On the other hand, if the inflow to the earthen bandsars are not controlled, water level in some of the upstream dikes overflow the levees and breaking them, successively. Moreover, the downstream bandsars will not be able to drew water from the stream.

Inflow, outflow and the amount of water storage in traditional levees or bandsars were modeled using the MODCEL algorithm. These structures were able to control 92% of the total volume of an incoming 5-year flood. The bandsars had an effective role in reducing the peak and volume of flood flow and delay its lag time.

Hydraulic phenomena are generally studied in the laboratory, so it seems necessary to use a method that reduces the number of experiments and saves time and time with good accuracy, and Taguchi method is one of these methods. In this regard (Dalir et al., 2021), Taguchi method and response level in the laboratory model of the pond were used to evaluate the efficiency of trapping and sedimentation and introduced the effective parameters. (Ranjbar-Zahedi et al., 2021) To reduce local scouring around bridge piers and to minimize the number of experiments, they used the 27 proposed Taguchi experiments to determine the optimal size and location of the structure (Atarodi et al., 2020) for Design of decomposition geometric parameters using Taguchi and Taguchi-GRA methods. In this study, in addition to the Taguchi property in reducing the number of studies in the study of the stable size of the riprap around the bridge piers (in the experimental part the number of experiments and in the neural network the number of responses), the optimization and prediction of Taguchi (a property that is less studied Taken.) Be used. Then, for validation, the results of Taguchi prediction were compared with the results of artificial neural network.

Taguchi method was studied as one of the experimental design methods based on reducing the number of experiments and proposing different but limited compounds for studies. Also, the analysis of the results has been examined using the mean mean graph and the signal to noise ratio (S/N) and the best combination of parameters has been introduced. Also, using the ANOVA table, the effect of the levels of each parameter and finally the effective parameters have been determined. In order to evaluate the results, the results of Taguchi method with the results of ANN artificial neural network were evaluated using the predictive property. It should be noted that Taguchi method has been used to adjust the adjustable parameters of the neural network for the phenomenon of stone crushing failure. In designing the stable size of the riprap around the bridge piers to protect against scour, 145 research laboratory data (Karimaei Tabarestani and Zarrati., 2013) have been used and according to these data, four parameters including flow rate in six levels, rock size, ratio The length to the width of the bridge pier and the angle of the pitch relative to the flow direction were examined at three levels. Also, the adjustable components of the neural network, including the four components of the number of neurons in the first and second hidden layers, the training function and the transmission function in each layer were examined at three levels. Finally, the results of the neural network were compared with the results of the Taguchi prediction.

In designing a stable size of riprap around bridge piers to protect against scouring, the Taguchi method with a reduction of 87 and 89%, respectively, compared to the results (Karimaei Tabarestani and Zarrati., 2013) and the complete factorial method, reduces the number of tests and saves time and money. have been. In the analysis of the results using Taguchi, it was found that the maximum flow depth for crimping stability will occur when the flow rate is 0.06 m3 / s, d50 is 0.00205 m, L is 35 m and θ = 20 is 20 Degree and in this regard the most effective parameter Q was introduced. Also, the best ANN artificial neural network based on the optimal combination introduced by Taguchi based on S/N diagram analysis, with three layers and correlation coefficient (R) equal to 0.971, will occur when the first and second hidden layers each contain 7 The neuron is a training function of trainlm and the transmission function of each layer is tansig. Also, according to ANOVA analysis, the most effective factor with a high rate of 95.07% participation is the transfer function. Finally, the Taguchi-assisted neural network with a detection coefficient of 0.94 performed better than the Taguchi method with a detection coefficient of 0.79 in predicting the results of designing a stable size of riprap around bridge piers to protect against scouring.

The results of the present study show that by using the Taguchi orthogonal array table and analyzing its results in the experimental section, the optimal combination of parameters can be determined with only a small number of experiments and the optimal solution can be predicted. Also, Taguchi method is a more suitable alternative to trial and error method for adjusting neural network parameters, and the results obtained from designing neural network parameters with Taguchi method are of good accuracy.

One of the most important problems in hydraulic structures is the kinetic energy of the flow. If this destructive energy is not controlled, the structures downstream will be damaged and cause significant damage. One of the functions of energy dissipator structures is to change the flow regime, reduce the flow velocity and eliminate excess flow energy. One of the methods that can deplete the flow is to create a narrowing along with the roughness in the flow path. By creating a constriction in the flow path and using roughness in the constriction wall and forming a hydraulic jump, a significant part of the destructive energy of the flow can be dissipated. Hydraulic jump is a common phenomenon downstream of hydraulic structures that increases the flow depth by rapidly converting the flow from supercritical to subcritical and plays an important role in influencing hydraulic parameters. Examining previous studies on stenosis with natural wall roughness, what is certain is that no laboratory and numerical studies have been observed so far.

A laboratory flume with a rectangular cross-section 5 meters long, 0.3 meters wide, 0.5 meters high, and with Plexiglas floors and walls was used to perform the experiments. Two pumps each with a capacity of 450 liters per minute enter the flow into the flume and the flow inlet flow is read by two rotameters with an error of ± 2%. A point gauge with an accuracy of one millimeter was used to measure the water depth, and a construction meter with an accuracy of one millimeter was used to measure the length of the jump length. To create narrowing in the cross section of the channel from glass boxes with a fixed height of 0.5 m, widths of 2.5, 5, 7.5 cm on each side and to create supercritical current upstream of the section Narrowing A valve with a width of 0.3 m, a thickness of 3 mm with an opening of 2 cm, which is located at a distance of 1.5 m from the narrowing, has been used.Figure 1, schematic of the canal and the equipment installed on it and Figure 2, an example of stiffening placement, hydraulic jump formed in the flow path and rough placement method with three average diameters of 2.08, 1.28, 0.8 Shows centimeters on the wall.

In order to achieve the objectives of the present study, flow path constrictions have been provided using glass boxes and sand materials have been used to roughen the constriction walls. In total, 270 experiments were performed in the range of Froude number 2.5 to 7.5 and relative contraction range of 8.9 to 12.42. By adjusting the laboratory model and opening the pump, the flow enters the channel supercritically after passing through the vertical valve and moves towards the narrowing section.As the downstream Froude number increases, the relative energy dissipation increases and this amount is greater than the energy dissipation in the constriction of 15 cm. The reason for this is that due to the collision of supercritical flow with the constriction section, the backwater profile at the point of water collision with the sides of the constriction elements and also the formation of hydraulic jump upstream of the constriction section increase turbulence and climate interference and consequently it increases the relative energy dissipation.Changing the diameter of the rough particles has little effect on the amount of flow energy dissipation. But it can be seen that the effect of roughness with an average diameter of 1.28 cm is slightly more than other roughnesses. The reason for this is that the roughness of 1.28 cm has more contact surface with the flow and also the empty space between the grains increases the surface tension and shear stress. Therefore, some of the energy is wasted by hydraulic jumping and some of it is consumed by the backflow of the flow.

Comparison of the models with each other as a control showed that with increasing the amount of narrowing of the channel width, the relative energy consumption increases. According to laboratory results, the use of roughness significantly increases the relative energy consumption relative to the upstream. Energy dissipation in 15 cm constriction is 25.48%, 20.88% and 23.83% less than 0.8, 1.28 and 2.08 cm roughnesses in control mode, respectively. Energy dissipation in 10 cm constriction is less than 44.34, 43.68, and 40.63% in roughness compared to 0.8, 1.28, and 2.08 cm roughnesses, respectively. Energy dissipation at 5 cm constriction is 50.75, 51.19, and 40% less than 0.8, 1.28, and 2.08 cm roughnesses in control mode, respectively.

Over recent decades, utilizing desalination plants with reverse osmose technology has been expanded all around the world whereas discharging their brine has become a serious environmental concern since this phenomenon can have catastrophic environmental consequences. Consequently, numerical models have grown which enable engineers to simulate and predict brine discharge before erecting marine outfalls. CORMIX is a functional and useful model which is able not only predicts discharge effluent behavior but also applies environmental limitation in its simulation. Therefore a plethora of researchers have used the CORMIX to design marine outfall and recognize jet's behavior in waterbodies. However, evaluating the reliability and accuracy of the CORMIX is crucial.

After conducting approximately 180 simulations, the CORMIX outcome for dilution at the impact point (Si), the horizontal location of the impact point (Xi), the horizontal location of the centerline peak (Xm), and the vertical location of the centerline peak (Zm) were normalized in dimensionless form.3.1. Validation of dense jet discharge into stagnant ambientAs for Si and Xi parameters, the more port diameter and discharge velocity decline, the more dilution rate at the impact point increase until the relation Fr>15 applied on CORMIX Results. After that, the outcome followed the experimental data trend with 0.2 and 0.025 differences for Si and Xi, respectively, meanwhile, they were underestimated which is so vital to be considered when the brine is discharged in a water body with a sensitive ecosystem. In addition, the Si parameter was more sensitive to discharge velocity fluctuation whereas Xi was not so reliant on port diameter and discharge velocity. However, Zm, which is an effective parameter for brine discharge in shallow water, was sensitive to both port diameter and discharge velocity also its results were accurate and reliable only if Fr>30. About Xm, the outcome of CORMIX for Fr>25 with grate turbulence followed experimental data while they were underestimated with 0.14 error.3.2. Validation of dense jet discharge into dynamic ambientIn dynamic ambient, due to lack of studies in terms of jet geometric features for θ =60° and σ =0, the study limited to dilution at the impact point. For Si, overall, decreasing port diameter and discharge velocity had a positive effect on the dilution rate increase. Although their changes were negligible when ur.Fr <0.2. Also, CORMIX results were overestimated with 0.77 compared to experimental data.

According to this study, in a stagnant ambient, port diameter and discharge velocity were capsulated in densimetric Froude number. Therefore, the results of CORMIX will be reliable only if the values of Fr has located in the specified domain (for Si and Xi, Fr>15 and for Xm and Zm, Fr >30). In dynamic ambient, besides port diameter and discharge velocity, the ambient velocity has an effective impact on dilution rate and jet geometric properties. Consequently, the design should be done based on relation ur.Fr >0.2 for Si parameter. Nevertheless, since CORMIX results were underestimated compared to experimental studies, calculated errors must be considered.

The main purpose of the Labyrinth Spillway is to increase the length of the Spillway crest by nonlinearzing its shape in the plan so that is increase the efficiency and discharge coefficient. In Spillways, the overlap of the falling flows and the resulting compression of the flow during the Spillway reduces the efficiency and discharge coefficient of the Spillway. In this study, in order to reduce the interference of falling flows, the congressional Spillways with the length of unequal congresses have been studied and compared.

In this study, the congressional Spillways with the length of unequal congresses in two cases A and B in laboratory and in 5 cycles with effective length and same height which are 336 and 10 cm, respectively in the channel of the hydraulic laboratory of Bu Ali Sina University with a length of 14 meters and a width and height of 60 centimeters have been studied and compared. To conduct this research, 10 laboratory models of Labyrinth weirs with different congress lengths and one laboratory model of Labyrinth weir with the equal length of congresses have been constructed for comparison with other models. In each case, the flow rate and water depth on the Labyrinth crest were carefully monitored. This operation was repeated 3 times for each case to minimize the errors caused by the test. From the average data of each case was used for analysis and conclusion.

The results of this study show that in all congressional Spillways with unequal congress lengths, the changes of C vs. Ht / P are decreasing and with increasing the Ht / P ratio, the value of C decreases. According to the results of this study, in general, the efficiency and discharge coefficient of the Spillways of congresses of type A is better than type B.

The results show that the reduction of the impact length of falling flows up to 25% compared to the Spillways with the same length of congresses, increases the efficiency and improves the discharge coefficient and reduces the impact length of falling flows by more than 25% changes Spillway performance from the concave state and reduces the efficiency and discharge coefficient of the Spillway. Also, the best sample made in this research improved the discharge coefficient of congressional Spillways with the same length of congresses by 40.7%.