جستجوی مقالات مرتبط با کلیدواژه « سرریز کنگره ای » در نشریات گروه « آب و خاک »

Labyrinth weirs have always received special attention compared to linear weirs due to the increase in flow capacity through the increase in width. The number of 23 models was simulated using Flow-3D software to investigate the effect of various factors such as changing in the height of the dam body, changing the height of the weir apexes (weir height), the discharge passing over the weir, and the effects of different angles of the weir apex in the plan on the amount of bed erosion in the downstream of Labyrinth weir was studied. Validation of the numerical simulation results with the experimental model indicated a very good agreement between the numerical simulation and the experimental values. This reduction in the weir with an apex angle of 60 degrees is more than other models and the scour depth is reduced from 31 to about 90%. Also, the amount of flow traversability in this type of weir is more than other models, which made the weir with an angle of 60 degrees to be introduced as the most optimal weir in investigating the efficiency of the weir and the reduction of scouring compared to linear models, 45 and 90.

Weirs of the labyrinth have some advantages including the high coefficient of the irrigation of weir and the low fluctuation of water when the flow passes over the crest of the weir. In this research, the flow rate coefficient has been investigated by changing the weir geometry in terms of wall slope, arc cycle angle, and nose length change in the upstream and downstream of each cycle of the trapezoidal arc labyrinth weir. A total of 240 tests have been performed on 16 different physical models in a channel with a width of 120 cm and a narrowing of 20 cm from each wall. All models have been compared with the control model (normal labyrinth weir) (80A). The results showed that the 80B weir with an arc cycle angle of 20 degrees and without wall slope has a better performance than other weirs. Also, the weir with an arc cycle angle and a wall slope of 20 degrees in a divergent form (D20B) in the area (Ht/P) <0.31 has a better performance than other weirs with an arc cycle angle of 20 degrees, and after this area, the weir with a wall slope of 10 degrees has performed better in divergent form (D10B). In weirs with different cycles at an arc cycle angle of 20 degrees, the labyrinth weir with 5 cycles (N5) has performed better up to the point (Ht/P)=0.36. Also, at the maximum point, the difference is 13 and 17%, respectively, compared to the 4-cycle and 3-cycle weirs.

Piano key weir is a form of nonlinear weir designed to improve the discharge capacity of spillway structures. Due to the increase in effective length, they can be used in dam spillways or water regulation structures. It is modified form of labyrinth weir which easy to place on the existing spillway or newly constructed dam with less base area. There is no standard method available for PK weir design, and the amount of published information is insufficient for the design of PK weir. A large number of geometric and hydraulic parameters affect the discharge capacity of PK weir, and their effect on the hydraulic performance of the weir can be investigated with a numerical model or laboratory data. Simulation of flow over PKW using FLOW-3D software and the effect of the turbulence model on the accuracy of the numerical model is one of the goals of this study. Also, in this research, the effect of the ratio of the inlet key width to the outlet key width (Wi/Wo) and the effect of the energy head on the discharge capacity are investigated.

Laboratory data from Anderson (2011) were used to validate the numerical model. The total length and height of the weir are 4.848 and 0.197 m respectively, the floor slope in inlet and outlet key are 1:1.8, and number of keys is 4. The inlet and outlet key width are 0.116 and 0.925 m respectively, and the Wi/Wo ratio is 1.25. Selection of boundary conditions for the numerical model is one of the most basic stages of simulation. In order to define the boundary conditions, in the inflow point (Xmin) volume flow rate, in the sides of the weir (Ymin, Ymax) and bed (Zmin) wall condition, on the upper border (Zmax) symmetry condition and in the outflow section of the weir, outflow condition was used.

The numerical model results were compared with the laboratory data. The results showed that if the second order scheme and RNG k-ε turbulence model are used in the numerical model, the simulation accuracy of the flow over PKW increases. Also, the results show that increasing the He/P decreases the discharge coefficient. So that the discharge coefficient for He/P=0.92 decreases by about 50% compared to He/P=0.24. With the increase of the water depth on the weir, the interference of the flow takes place at the breaking point of the weir cycles, and as a result, the discharge coefficient decreases. Another factor affecting the flow coefficient of the piano key is the ratio of the inlet key width to the outlet key width. By increasing the Wi/Wo, the flow coefficient has increased, and then it becomes maximum at Wi/Wo=1.5.

In this research, the simulation of the flow over piano key and labyrinth weir was done using a numerical model. The results showed that for a fixed depth, the piano key weir passes more discharge than the labyrinth weir, and the ratio of flow through the piano key weir to the labyrinth weir is about 1.08. In other words, at a constant depth, the piano key weir passes 8% more flow. In this research, the effect of head energy on the discharge coefficient of the piano key weir was also investigated. The results show that increasing the He/P decreases the discharge coefficient. The results showed that if the Wi/Wo equal to 1.5, the highest discharge coefficient occurs for the piano key weir.

The cost of implementing spillways includes a large part of the dam construction budget. Optimizing these structures can significantly reduce the cost of building dams. So far, many studies have been done on optimizing the dimensions of spillways in order to reduce the amount of materials used. Among the used optimization methods, the methods based on meta-heuristic algorithms have had stunning results. The review of the studies conducted in the field of stepped and labyrinth spillways shows that the goals of all studies in stepped spillways have been to provide an acceptable plan for energy dissipation and in labyrinth spillways to reach a the largest amount of water passing. The purpose of this study is to combine stepped spillways with labyrinth spillways and optimization in order to increase the water passage coefficient and energy consumption at the same time. For this purpose, the multi-objective optimization approach has been used.

In the present study, the redesign of the spillway of the Sarouk rockfill dam located in West Azarbaijan province has been studied. In the case of labyrinth-stepped spillway, the decision variables, constraints and objective functions of the two spillways are combined and analyzed as a multi-objective optimization problem. In this study, a dynamic coefficient is used to improve the performance of the dragonfly algorithm in the search and exploitation stage. After determining the optimal values of the regulatory parameters of the MODA, NSGA-II, MOPSO and MOIDA algorithms, four benchmark examples were solved with each of them 20 times with an initial population of 50 and a maximum number of iterations equal to 100.

After validating the improved dragonfly algorithm on benchmark functions and evaluating its performance in solving multi-objective problems, this algorithm was used to design a combined spillway on the introduced dam. In multi-objective problems, there is a set of optimal solutions rather than a single optimal solution, which appear as a Pareto front. The implementation of the improved dragonfly algorithm with 200 initial population and 500 repetitions has resulted in providing 200 optimal answers on the Pareto chart. After performing the calculations related to the fuzzy decision-making method, a design with the values of the objective functions of concreting volume: 59795.54 cubic meters, dissipated energy: 75.18%, flow rate: 1255.19 cubic meters per second was selected as the optimal answer. In addition, the design with the highest and lowest cost of concrete consumption was selected as two other answers. The flow rate passing over the spillway has increased by 120% in plans A and B, and by 25% in plan C compared to the initial design flow rate. The amount of energy dissipation of plans A and B is about 76 and 75%, respectively. In plan C, where the flow rate has not increased significantly (25%), energy dissipation has reached about 81%, which is more than the other two cases.

Among the available answers, according to the priority of the cost, the plans with the lowest (C) and the highest (A) implementation cost based on the volume of concrete were selected. Also, by using the fuzzy decision-making approach, an optimal plan (B) that has a suitable balance between the three objectives was selected. Based on the results, it was found that each of the plans A, B and C can be used based on the needs of the employer. From the economic point of view, according to the project conditions and the needs of the employer, all the proposed plans are suitable options for replacing the actual spillway and reduce the implementation costs. Also, the comparison of plan C with the stepped spillway plan presented by previous researchers showed that with almost the same volume of concrete, using a multi-objective approach in comparison with a single-objective optimization approach, in addition to increasing flow energy consumption, also led to an increase in flow through the spillway.

For the first time, in the current study, the discharge coefficient of labyrinth weirs was simulated using the Self-Adaptive Extreme Learning Machine (SAELM) artificial intelligence model in both cases including normal orientation labyrinth weirs (NLWs) and inverted orientation labyrinth weirs (ILWs). The Monte Carlo simulations were also implemented to evaluate the accuracy of the artificial intelligence model. In addition, the validation of the numerical model results was carried out by means of the k-fold cross validation approach. In this study, k was considered equal to 5. First, the most optimized neuron of the hidden layer was computed. The number of the hidden layer neurons was calculated 30. Also, by analyzing the results of different activation functions, it was concluded that the sigmoid activation function has higher accuracy than others. After that, the superior model was identified by conducting a sensitivity analysis. The superior model estimated the discharge coefficient values in terms of all input parameters. This model approximated discharge coefficient values of labyrinth weirs with reasonable accuracy. For example, the values of R2, the Scatter Index and the Nash–Sutcliffe efficiency coefficient for the superior model were calculated 0.966, 0.034 and 0.964, respectively. In addition, the ratio of the total head above the weir to the height of the weir crest (HT/P) and the ratio of length of apex geometry to width of a single cycle (A/w) were identified as the most effective parameters. Finally, a partial derivative sensitivity analysis (PDSA) was conducted for the input parameters.

In this research, an evolutionary based Neuro-fuzzy technique was utilized to estimate the discharge coefficient of labyrinth weirs. In order to optimize the parameters of the adaptive Neuro-fuzzy inference system (ANFIS), the Firefly Algorithm (FFA) was implemented. In modeling the ANFIS-FFA and ANFIS methods, the Monte Carlo simulation was used to evaluate uncertainty of the model. Furthermore, several models with significant flexibility and generalizability were provided using the k-fold cross validation method. First, the input dimensionless parameters including the Froude number (Fr), ratio of the head above the weir to the weir height (HT/p < /em>), cycle sidewall angle (α), ratio of length of the weir crest to the channel width (Lc/W), ratio of length of the apex geometry to the width of a single cycle (A/w) and the ratio of width of a single cycle to weir height (w/p < /em>) were defined. After that, seven different models were introduced for ANFIS and ANFIS-FFA. Then, using a sensitivity analysis, the superior models (ANFIS-FFA 5 and ANFIS 5) and the most effective input parameter (Froude number) were identified. In addition, the error distribution results showed that about 70% of the superior model (ANFIS-FFA 5) results had an error less than 5%. In other words, the superior model had a high statistical significance. Ultimately, the uncertainty analysis for the superior models was carried out.

The use of labyrinth weirs is one of the most effective and economical ways to increase weir efficiency by enhancing weir crown length, so that at a specified width and hydraulic height compared to other weirs, more discharge passes. In this study, the hybrid method of the Whale optimization algorithm and the fuzzy neural- inference system to estimate the optimal discharge coefficient of labyrinth weirs with the curved plan is introduced. In the proposed method, the efficiency and convergence of the Whale algorithm have been measured. The experimental data were used to validate the proposed method. The performance of the proposed method was evaluated with four statistics, including the correlation coefficient (R2), the root means square error (RMSE), the mean absolute error (MAE) and the efficiency criterion (NSE). The results indicate a good match between the observed and estimated values. The results of the WOA-ANFIS method with (H /P) and (θ), showed that the discharge coefficient of labyrinth weirs with the curved plan (Cd=0.786) in compared to labyrinth weirs with a triangular plan (Cd=0.682), it increases by 10%. Also, statistical analyzes performed on the obtained results showed that the WOA-ANFIS method with high values of RMSE = 0.021, R2 = 0.981, MAE = 0.010 and NSE = 0.976 has high efficiency in estimating the discharge coefficient of this type of weirs.

Labyrinth weirs are structures for transferring large flows at low heads, in which the effective length of crest for a given channel width is increased. In this study trapezoidal arced labyrinth weirs with different arc radius and cycle length were investigated. Several experiments were conducted using physical models to evaluate the effect of R/w1 (ratio of arc radius to middle cycle width) and B/w1 (ratio of weir length in flow direction to middle cycle width) on weir discharge coefficient. The experiments were carried out using a 6 m long test flume with cross section of 0.6 m width and 0.6 m height. Using Buckingham method of dimensional analysis, it was found that the discharge coefficient is a function of three variables; hydraulic head, arc radius of weir and weir length ratio. In general, the results of this study showed by increasing arc radius ratio, discharge coefficient of trapezoidal arced labyrinth weir increases up to 27.3%. Besides, by decreasing the weir length ratio from 1.5 to 1, discharge coefficient increased up to 29.7%.

 One of the important parameters of water quality is the high level of dissolved oxygen (DO) content that is essential for the survival of all aquatic organisms and water quality improvement. Aeration refers to the physical process of oxygen absorption from the atmosphere and enhancement of the dissolved oxygen of water. Some hydraulic structures enhance the oxygen transfer by creating a great deal of turbulence and entering air bubbles. Stepped spillways are efficient in terms of air bubble entrainment. Advantages of stepped spillways include strong turbulent mixing, a large residence time and a substantial air bubble entrainment. Moreover, based on the laboratory data, some researchers have studied the aeration performance of labyrinth weirs in order to develop regression models for the prediction of aeration efficiency. The experimental results showed that the labyrinth weirs aerated significantly better than the normal weirs, especially at the lower drop heights. One of the methods to increase the content of dissolved oxygen is installation of structures that help increasing turbulence and entering small bubbles of air into water body. A falling jet of weirs is a specific case of creating turbulence in the water and increasing DO.  

Experimental measurements were conducted in the hydraulics modeling laboratory of University of Guilan, Iran in a flume with rectangular cross section having a 1.5 width, 1 m depth and 15 m length the experimental models consisted of five steps made of PVC panels. In this study three different slopes of spillway (1:1, 1:2 and 1:3 V: H) and one step height (h=0.10 m) were examined. In order to clarify the influence of labyrinth geometries on dissolved oxygen efficiency, intermediate blocks with different configurations were set in a zigzag pattern on every two steps. The height of labyrinths (H) was chosen 0.05 and 0.075 m, and the installed spacing between the labyrinths (L) along the width of channel were 0.1 and 0.2 m. In this study, the flow characteristics over the stepped weirs with intermediate labyrinths were compared with the pooled stepped ones which made by sill with height and thickness of 0.032 and 0.025 m, respectively. In order to investigate the aeration efficiency of stepped-labyrinth weirs, and in particular, to determine the effects of hydraulic and geometrical parameters, 572 tests were Experimental measurements were conducted in the hydraulics modeling laboratory of University of Guilan, Iran, in a flume with rectangular cross section having 1.5m width, 1m depth and 15m length the experimental models consisted of five steps made of PVC panels. In this study, three different slopes of spillway (1:1, 1:2 and 1:3 V:H) and one step height (h=0.10 m) were examined. In order to clarify the influences of labyrinth geometries on dissolved oxygen efficiency, intermediate blocks with different configurations were set in a zigzag pattern on every two steps. Two heights of labyrinths (H) were 0.05 and 0.075 m, and the installed spacing between the labyrinths (L) along the width of channel were 0.1 and 0.2 m. In this study, the flow characteristics over the stepped weirs with intermediate labyrinths were compared with that of pooled stepped ones which made by sill with height and thickness of 0.032 and 0.025 m, respectively. In order to investigate the aeration efficiency of stepped-labyrinth weirs, and in particular, to determine the effects of hydraulic and geometrical parameters, 572 tests were carried out. Moreover, the variation of DO concentration in water flowing over the weirs can be affected by a proportion of the upstream DO deficit. Therefore, in order to make the comparison as fair as possible, four different upstream DO concentrations (Cu) 2, 3, 4 and 5 (mg/l) were chosen to illustrate the effects of Cu value on the dissolved oxygen efficiency. The upstream DO concentrations were based on a range between minimum DO concentrations (2 mg/l) and dissolved oxygen saturation concentration (8-10 mg/l). 

Comparison of results of DO concentrations (Cu) on aeration efficiency of the flat and stepped-labyrinth weirs with 1:1 slope under two tailwater conditions (dp=h and dp=2h) indicated that the S1H4L4b1 configuration had the highest DO efficiency. Thus, for upstream oxygen transfer efficiency (Eu) of 1.28, the concentration of dissolved oxygen associated with the stepped-labyrinth weirs was almost 48% higher than that for flat stepped weirs. For flat stepped weirs, since the upstream concentration of DObecame larger (Cu = 2, 3 and 4 mg/l), there was a decreasing tendency of Eu to 0.56, 0.42 and 0.27, respectively. However, corresponding Eu values for stepped-labyrinth weirs were 0.65, 0.45 and 0.33. As a consequence, for a given geometry and hydraulic condition, decreasing the upstream dissolved oxygen concentration increased the average DO efficiency of stepped weirs. For Cu=2 (mg/l), the S1H3L3b1 was the most efficient configuration due to providing the strong turbulent mixing and substantial air bubble entrainment which the average value of Eu in flat stepped weirs with S1 configuration, corresponding to the upstream dissolved oxygen concentration of 3, 4 and 5 (mg/l), was 0.55, 0.35 and 0.25, respectively (Fig. 12). However, intermediate labyrinths on the steps led to increase the air entrainment and the average value of Eu increased to 0.66, 0.42 and 0.33. for slope of 1:2, the S2H3L3b2configuration had the best performance in this slope. Hence, for Cu=2 (mg/l), this configuration increased the E20 and Eu up to 47% and 71%, respectively, compared to the flat stepped weirs. By reduction of stepped weir slope to 1:3, Cd of tested labyrinth weirs with the average E20 =0.44 and Eu =1.25 increased by 50%. The DO efficiency in the S3H3L3b2, S3H4L4b2, S3H6L6b1 and S3H7L7b1 configurations, which labyrinths were installed at the same edge as the steps, had better performance, compared with that of other tested geometries.  

The air bubbles transfer and dispersion into water are governed by overflowing the jet, hydraulic jump and interaction of flow jet with receiving pool. The stepped-labyrinth weirs were shown to have an overall aeration advantage over the flat stepped weirs, largely because of the high turbulence and the high air bubble entrainment.The aeration advantages of the labyrinth-stepped weir become greater at smaller weir slopes. Conclusions revealed that for the slopes of 1:1, 1:2, 1:3 and tailwater of h, a labyrinth stepped weir with labyrinth height of 0.75h and labyrinth interspace of h, had 48%, 71% and 15% higher aeration efficiency than that of flat stepped weirs. However, with doubling of the tailwater depth, the dissolved oxygen efficiency increased by 77%, 51% and 15%, compared with the similar flat stepped weirs.

In this research, optimal design of trapezoidal labyrinth spillway has been investigated using Gray Wolf Optimization (GWO) algorithm with respect to hydraulic conditions. By choosing the assumed volume of spillway concrete as the objective function, after several running the model and trial & error, parameters of the algorithm such as iteration, number of wolves and the penalty coefficient were determined to be 1000, 30 and 〖10〗^11, respectively and by five times of testing, at the 996th iteration, the optimal response of objective function was achieved. The obtained value from the proposed algorithm was compared to the real value and also the results of the Cuckoo Search (CS) algorithm, Genetic Algorithm (GA) and Differential Evolution (DE) in previous studies. Using GWO algorithm for designing the considered dam's spillway, made reduction of 40.928% in amount of assumed concrete volume and increase the rate of discharge to 10.71% than to real value, which showed a better performance compared to above algorithms. Significant reduction of the consumed concrete volume in the proposed spillway by using GWO algorithm indicates ability and necessity of using this algorithm to solve optimization problems in the field of spillways.

Flow water passing through spillways of dams has a high level of kinetic energy, which can lead to extensive damage to downstream facilities and bring about severe erosion of river beds. Energy dissipation would usually be accomplished by creating structures such as still basins at downstream of weirs, flip buckets, or steps in weirs. Stepped spillways are one of the common structures for energy dissipation, as well as reduction of the dimensions of still basins. The effects of labyrinths on total energy dissipation at downstream of the stepped spillways with slopes of 1:1, 1:2 and 1:3 was investigated; the height of labyrinths was 0.5 and 0.75 of the height of steps (h), working interspaces were equal to two times of the height of steps, and three roughness heights on the step face were 0.002, 0.004 and 0.006 m. The results showed that in first case, 1:1 slope of the stepped spillway, a labyrinth with height of 0.5h, working interspaces of 2h and equal length of the steps caused an increase of 12.7 percent in dissipation of relative energy. The comparison of results showed that for slope of stepped weir of 1:2, installation of a labyrinth with a height of 0.75h, interspaces of 2h and equal length to the height of the steps, the relative energy dissipation increased by 8.4 percent. When stepped weirs with slopes equal to1:3 were used, results indicated that installation sill with a length h, a height of 0.5h instead of labyrinths on steps, caused an increase of 4.7 percent in relative energy dissipation. Result showed that increase surface roughness of studied weirs reduced the relative energy dissipation by 3.6 percent.

The amount of dissolved oxygen (DO) in water is an important parameter of rivers water quality. Installation of weirs in channels is one of the methods entering air babbles into the falling water and increase DO. In this research, the performance of trapezoidal labyrinth weirs was investigated as compared with the linear weirs under various geometries and hydraulic conditions in terms of DO Experimental observations and result analysis showed that the length of cycle in the flow direction, thickness of weirs and nappe patterns are three effective parameters on DO amount in trapezoidal labyrinth weirs. The results of this study indicated that the three cycles-labyrinth weirs had better performance compared to two cycles-labyrinth weirs. Also, the results showed that the three cycles-trapezoidal labyrinth weirs with the lower length in the flow direction at low relative head and with the longer length in the flow direction at high relative head had the best performance in terms of DO that increased 58 and 44 percent, respectively. The results of this study indicated that, by increasing the ratio of falling height to weir height from 0.4 to 0.8, the DO efficiency increases (13%) by labyrinth weirs.

One effective method of increasing the length of the weir for a given weir width is the use of weirs featuring nonlinear plans, namely triangular, trapezoidal and parabolic, that are generally termed labyrinth or zigzag weirs. These are made in one and/or several cycles and as a consequence to the construction of these weirs, the volume of flow passing through them increases and lower free height of the current will be needed in the upstream section in respect to the linear weirs. The issue becomes more important when the weir is served to discharge the floodwater and leads to the facilitation of the flow of the flood current. The present study investigated 4 discharge rates (5l/s, 10 l/s, 15 l/s and 20 l/s) for a channel width and height of, respectively, 30cm and 40cm in trapezoidal, square, triangular and piano key labyrinth weirs in laboratory using Flow 3D software which was in diffusion model K-ε in type RNG was investigated and the results were compared. From among all the models, triangular labyrinth weir accounted for the highest discharge coefficient. It was found out that the Ht/P ratio increases for all of the models results in the decrease in the discharge coefficient. However, it can be concluded that there is a relatively good match between the numerically acquired and laboratory values.The best range for proportion Ht/P for design is between 0.14-0.42 that the maximum discharge coefficient equivalent to Cd=1.24 would be placed in this range.

The piano key weirs (PKWѕ) are type of nonlinear weirs which can increase the discharge for a given width without the increase in head water .In piano key the length of weir crest in both upstream and downstream can be incresead and therefore can be considered to be a suitable substitution for the labyrinth weirs, with a relatively small footprint In this study, in order to evaluate the Hydraulic performance of PKWs of free & submerged flow, totally 554 experiments are conducted on 11 physical models. Results showed that in the free flow the PK₁.₄ (inlet over outlet key width; wi /w₀=1.4) in the head water ratio of 0.5≤H₀/P≤1 and the PK1.25 in H₀/P≥0.1 as compared with other weirs, has higher Hydraulic performance. In the case of constant values for the wi/w₀ ratio and changing of the floor slope from 1:1.5 to the curve (a quarter of the circle; PKC) the discharge coefficient of these weirs increased about 3 percent. In the condition of submerged flow the value of the submerged upstream head over the free flow of upstream head (H*/H₀) increased by decreasing the submerged upstream head ratio (H₀/P). For the PK1 weir and in the submergence values lower than 0.48, the downstream depth had no effect on upstream depth of weir, and H*=H₀. The modifying of PK₁ causes a decrease the modular submergence range in this weir and occurrence of the full submergence with a little delay. Modifying of PKC₁, lead to an increase in the modular submergence range and no change in the full submergence.

Labyrinth weir is one of the nonlinear hydraulic structures that its geometrical shape increases the discharge coefficient of flow over the weir. In this study, a labyrinth weir, located in a 14.6 m long channel, was simulated and verified using an experimental model with 6 different discharges (15

Grade control structures are commonly used to prevent degradation, increase bank and bed of rivers stability and prevent cross structures failure in rivers. In order to design a safe grade control structures, estimation of local scour depth downstream of these structures is crucial. In this study effect of different parameters on local scour at the downstream of grade control structures with labyrinth planform was experimentally investigated. Different types of rectangular and trapezoidal labyrinth planform weirs were studied. Experimental results showed that labyrinth planform has a high effect on reducing scour depth. It was found that decreasing the length of cycles in trapezoidal weirs decreases the depth of scour while, decreasing the width of cycles in rectangular weirs increases the depth of scour. It was found that by increasing parameter and drop height, depth of scour increases, while increasing tailwater depth decreases the depth of scour and it varied from 2 to 8 percent for labyrinth weirs. Results showed that the scour depth follows an exponential law, dimensional equation for prediction of scour depth is presented. The accuracy of developed equation was examined with the available prototype data.

Labyrinth weirs are often a favorable design option to regulate water surface elevation in upstream canal and increase flow capacity. Due to their hydraulic performance and geometric versatility, labyrinth weirs have been used extensively in canals, rivers, ponds, and reservoirs as energy dissipaters, flow aerators, and spillways. Nevertheless, it can be difficult for engineer to optimally design, labyrinth weirs due to the complexities of nappe behavior and many geometric and hydraulic variables. A level of sedimentation in upstream and submergence in downstream of the weirs are effective parameters which affects the discharge coefficient, and the performance of these structures. In this investigation effects of 408 tests of different levels of tail water (increase of downstream canal bed level to one third and two third of weir height) and upstream sedimentation level (non-sedimentation and sedimentation level of 90 percent of weir height) on the discharge coefficient of different geometers of trapezoidal labyrinth weirs was investigated experimentally. The analysis of results indicated that increase of tail water level to one third of weir height didn’t affect on the discharge coefficient of weirs. By increasing tail water depth to two third of weir height, air cavity volume under nappe decreased. Therefore, the flow pattern of the nappe changed from leaping to clinging condition and upstream head decreased. As a result, the labyrinth weirs discharge coefficient in non-sedimentation and sedimentation level of 90 percent of weir height increased about 3.3 to 12.2 and 2.1 to 9.2 in comparison with non-submergence tail water for maximum discharge respectively. Finally, the statistical equation for estimation of the discharge coefficient of trapezoidal labyrinth weirs for upstream sedimentation and submerged conditions was developed.

Weirs are common structure to regulate water surface and flow control in water conveyance channel and hydraulic structure. One of effective and economical method to increase the efficiency of weirs is utilization of labyrinth weirs which length of weirs increase with modification of plan form and therefore flow discharge will be increase. In this research، the discharge coefficient and the unit length discharge of labyrinth weir with liner-semi circular and semi circular with radius of 11، 16 and 20 cm and cycle of 2 to 6 was experimentally investigated. Comparison of results showed that in all labyrinth flow discharge coefficient had increasing trend with increase of relative effective head () then decrease for due to collision of nape and with increasing، weir coefficient tend to broad crest weir because of local submergence. Comparison of results showed that the labyrinth weirs with circular plan have a better performance in comparison with liner-circular plans.