جستجوی مقالات مرتبط با کلیدواژه "ogee spillway" در نشریات گروه "آب و خاک"

One of the most important hydraulic structures in a dam is the spillway. The design of the ogee spillway crest is based on the lower profile of the free-flow jet passing through the sharp-crested weir. When the downstream ogee spillway profile for the design discharge conforms to the lower profile of the free-jet passing through the sharp-crested weir, the pressure on that surface of the spillway becomes zero. In this study, the design of the ogee spillway was performed initially based on both two- and three-dimensional numerical modeling and then compared to the USBR standard method. The comparison of the final numerical and analytical results showed that although the vertical two-dimensional outputs were completely in agreement with the USBR standard profile, the three-dimensional profiles were different because in this model, guide walls were not considered. According to the analysis, if the flow entering the spillway is parallel to its axis, the lower profile of the sharp-edge spillway will be in complete agreement with the standard profile. Since, the design of guide wall geometry for ogee spillways is carried out using physical modeling which iteratively revises during a high-cost trial and error procedure, this research based on the case study of the spillway of Karun-3 dam has been tried using numerical modeling. The closest geometry to the geometry of the overflow guide wall was obtained which creates the least difference in transverse velocities. In this way, the design of guide walls can be done with more accuracy and low cost in comparison to physical modeling.

In the last decade, the use of gabion structures in hydraulic engineering for stabilizing the structure due to its high density and weight has become widespread. Also, the material's roughness and porosity cause it to be used in energy dissipation and drainage projects. This study evaluates the relative energy dissipation of gabion structures downstream of the ogee spillway in the conditions of a submerged hydraulic jump. The evaluated parameters in this study were Froude number, gabion height, gabion thickness, and material diameter. The experiments were performed with three average diameters of 1.5, 2.2, and 3 cm for rock material, three gabion heights of 10 and 20 cm, and Max. The end sill heights were 10, 20, and 30 cm. The operated discharges were regulated from 20 to 40 l/s. The results showed that by decreasing the average diameter of gabion aggregates, the amount of relative energy dissipation increases in all tested models, so that in gabion with a 1.5 cm average diameter of aggregates, the amount of energy dissipation increased by 3.6% in comparison with using the diameter of 3cm for the average diameter of the material. Increasing the height of the gabion to the extent that the flow is entirely inward can have up to 33% more relative energy dissipation than the gabion with a height of 10 cm. Also, by increasing the diameter of the gabion from 10 cm to 30 cm, relative energy dissipation increases up to 15%.

Cavitation is one of the most important problems that may occur due to high flow velocity in dam spillways. In order to predict of dam spillway structure during operation, Azad dam spillway hydraulic model has been modeled in Tehran Water Research Institute.

In this study, using computational fluid dynamics in the form of a finite volume method used in ANSYS FLUENT software, flow modeling in these channels, and a fluid volume model (VOF) in a three-dimensional state, including two-phase flow of water and air, used for Considering current turbulence, k-ε model has been used. In order to confirm the results of the model, a comparison was made with the results of a hydraulic model implemented without the aero-damping system of Azad spillway.

Then, in order to confirm the location and number of aeration systems, two scenarios (two and three aeration systems) including step ramp (RAMP) on the floor and the wall of the duct with a suitable slope and the installation of the aeration slot in the wall have been used, which sends air near the floor And the walls will be.

Then, by checking flow parameters such as speed, pressure and cavitation index, overflow with two aeration systems was confirmed as the best option.

The purpose of this study is to generate the relationships to directly calculate waterfall height at the downstream of the spillway to form a jump at the toe of the spillway and to prevent erosion and destruction of the downstream river bed or body of the spillway in a submerged and free hydraulic jump.

The purpose of this study is to provide a relationship to directly calculate the waterfall height (h) without the need for a trial and error procedure. For this purpose, the application of the momentum relationship between two sections (1and 2) yields the waterfall height (h) according to Eq. (1).   h=y1 .....   (1) Since in Eq. (1), Fr1 and y1 are themselves a function of the waterfall height (h), so this equation must be solved by trial and error or by using design charts provided by other researchers. To calculate the waterfall height in oscillating jump conditions (2.5<Fr1<4.5) and also for steady and strong jump conditions (4.5<Fr1<15.5), by assuming different values ​​for p, y0, yt and C (where C is the discharge coefficient), 300 and 1146 series of numbers have been generated by trial and error, respectively. Then, the parameters in Eq. 1 (y1, Fr1) were also calculated. The final waterfall height (h) was obtained for each series of numbers. Using the existing variables, dimensionless parameters ( ) and Fr1 were extracted. Then, multiple linear and nonlinear multiple regression relationships were tested for direct calculation of . Finally, the best relationships with the least error were selected. The results of multiple regression (MR) relationships are also compared with the results of ANN and SVM methods.

The proposed non-linear multiple regression relationship (MR-3) shows higher accuracy in estimating the waterfall height, compared to MR-1 and MR-2 regression models based on three statistical indices (RE%, RMSE, R2) for 2.5<Fr1<4.5 and 4.5<Fr1<15.5. Therefore with having the Froude number related to the initial hydraulic jump depth (Fr1), tail water depth (yt), weir height (P) and initial jump depth (y1), the calculation of waterfall height (h) will be possible using MR-3 model without any trial and error procedures. Moreover, the results show that among the intelligent models, the ANN model has very close results to the proposed nonlinear regression relation (MR-3) based on the statistical indices.

A new method for calculating the height of a waterfall at the toe of the ogee spillway was presented to control hydraulic jump. To calculate the height of the waterfall directly, multiple nonlinear regression (MR) relationships were presented for two ranges of different Froude numbers. The MR, ANN, and SVM models showed good performance in predicting the height of the waterfall downstream of spillways, but the ability of the two MR and ANN models were better than the SVM.

Flow over spillways has a great amount of potential energy, which is converted into kinetic energy downstream control structures. This energy should be dissipated to prevent the possibility of excessive scouring of the downstream waterway bed, minimize erosion and undermining of structures, which endanger the structure safety. Local scour downstream is usually one of the most important issues in designing process of hydraulic structures, which is mainly some applications have been proposed to reduce this occurrence. Present study has been carried out on the effects of V-shaped baffle piers in order to reduce the local scour downstream of the ogee spillway.

Experiments were carried out in a flume which is 6 m long, 0.5 m wide and 0.6 m deep with horizontal bed slope. A pump with a maximum discharge capacity of 14 lit/s circulated water from sump. A movable weir located at downstream of flume controlled water level. The hydraulic and geometric characteristics of these baffle piers were investigated with three different discharges (20, 24 and 28 Lit/s.m). The positions and height of these blokes were presented to decrease the amount of scour downstream. The position and height parameters were defined based on the length of stilling basins as follows respectively, Lb/Lf=(0.22, 0.44, 0.66, 0.88) and Hb/D=(0.66, 1, 1.33, 2). The test area in the channel was 2 m long and 12 cm in height, 2.5 m from the beginning of the channel. The experiments were carried out using non cohesive sediments with median diameter of 0.72 mm, specified gravity of 2.65 and geometric standard deviation of 1.12.

The presence of the block decreases the final depth of scour and the length of the scour which shows the role of the blocks and their role in this case. According to laboratory observations, the existence of the block distinguishes three types of flow around it. The first is a flow that jumps above the block. The second is the convergence flow between the blocks and the third the eddy flow that forms in front and inside the blocks. The presence of the block and the three types of flows resulted in greater turbulence and reduced jump energy, resulting in a shorter jump length and an earlier secondary depth. Taken together, these factors reduce the flow strength at the bottom of the plate and also cause less sediment transport downstream. The more the Froude number increases, the more stable the jump is due to the category of jump types. (Depending on the group of jumps created in this study) The amount of scour depth decreases due to the presence of blocks. Also, the result indicates that by decreasing the distance of baffle from weir toe, the length and the depth of scour have been remarkably diminished. Meanwhile the raise of baffle height decreases the scour depth across a longitudinal section. In addition, in different block positioning, as the height of the blocks increases, the length of the scour decreases. So that block with height (Hb/D=2) has a significant decrease during scouring compared to block with height (Hb/D=0.66).

Overall, the suitable geometrical condition proposed in order to reduce this sediment deposition which is propose based on length of stilling basins and Froude number as, Hb/D=2, Lb/Lf=0.22 It assumes that the scour depth is decreased between 30 to 76 percent and the scour length is decreased between 57 to 71 percent. The present study demonstrates the importance of positioning the blocks and their height at different Froude numbers. Therefore, pre-execution modeling is suggested for better conclusions to achieve the best position and height of the block.

The ogee spillway with a curve axis has a longer crest length than the spillway with linear crest. Therefore, in a specific reservoir water level, it can discharge higher flow rate compared to a straight one and due to this reason is preferred in applicable plans. In this study, physical model of Germi-Chai spillway which include an ogee crest with a curve axis and converging training walls was constructed in scale of 1:50. The SCWMRI Soil Conservation and Watershed Management Research Institute, has led a research effort on it. For each of the convergence angles, including 60 and 90 ̊ in both symmetrical and asymmetrical situations, flow characteristics such as discharge, water surfaces, depths and distributions of pressure were investigated in the downstream channel of the spillway. Experiments conducted in varying flow discharge from 30% to 177% of  design discharge. Based on visual observation, at the toe and the end of straight portions of the spillway face, due to converging training walls, interference streamlines occurred which led to generate a rooster tail phenomenon. It was observed that in the convergence angle of 90°, rooster tail had been witnessed up to slightly more than 118% Qd. However, it saw nearly 147% Qd in 60° convergences. Moreover, it should be emphasized that due to asymmetric angles, closest wall to the rooster tail had more static pressure.

One of the ancient hydraulic structure that mankind make it’s in the past until now is spillway. This structure use for regulator and change the water direction in the rivers. So that this structure must be a stable structure and have good hydraulic performance. The aim of research was simulation Molasadra spillway dam with laboratory scale 1:40 height and its performance analyzed using different discharge. The result shown that discharge coefficient have average value 2.1. Meanwhile result of cavitation index indicated have degradation trend and in the large than 1000 (m3/s) discharge, cavitation index reached to critical value with additive trend. Cavitation index in the range of discharge that used in this investigation permanently is more than critical value but with increase discharge the cavitation phenomena is occurred in the end way of the spill way. Minimize and maximize pressure take placed for large discharge respectively in section 4, 9 and 10.

The spillway is one of the most important elements of dam building. So studying and designing of the spillway hydraulic should be considered in dams and other similar projects. The ogee spillway, because of its superb hydraulic characteristics, has been widely studied. Its ability to pass flow efficiently and safely, when has been properly designed, with relatively good flow measuring capabilities, has enabled engineers to use it in a wide variety of situations. In the last two decades, there has been an increasing interest in the stepped spillways in various laboratory experiments around the world. This is partly because of technical advances in the construction of Roller Compacted Concrete (RCC) dams and considerable amount of energy dissipation along the chute, leading to reduction in the size of the stilling basin. Flow analysis using laboratory experiments usually involves considerable time and cost requirements .Nowadays, availability of computational fluid dynamic (CFD) programs and powerful computers has resulted in increasing usage of numerical methods of flow analysis. Free surface flows are encountered in hydraulic engineering problems including water jets, weirs and around gates. For the numerical modelling of a steady flow, the area of calculation and therefore the position of the free surface have to be known. The main object of this study is numerical analysis of free surface profiles on ogee and stepped spillways by finite volume and finite element methods and comparison of the two methods. The physical laws governing a fluid flow problem are represented by a system of partial differential equations regrouping the continuity equation, the Navier-Stokes equations and any additional conservation equations. The numerical analysis resolves these equations by accurate and complex numerical schemes. A program or code, where the numerical algorithm is implemented, is then solved on a computer. In recent study experimental results offered by Tabara and CHatila (2005) have been used to investigate stepped spillway physics models of Tabara and Chatara (2004) for studying ogee spillway. FLUENT and ADINA software have been used to simulate flow field of types of stepped and ogee spillways. It should be noted that k-£ model has been applied in order to modeling turbulence. Gambit preprocessor software is a tool for networking flow field. In recent study we have used PRESTO scheme for discretization of pressure, quick plan for discretization of terms of displacement of momentum equations, turbulence formulas and PISO algorithm for coupling velocity and pressure. In finite element method, Galerkin relation has the second order accuracy. SUPG method is used in momentum equations and turbulence for discretization of term advection which is effective in problem convergence. Meshing type has been selected as triangle form in ADINA code, but quadrilateral in FLUENT code regarding the spillway geometry. In some area structured mesh and in some other ones non-structured mesh have been chosen. Due to existence of rotatory flows over the steps, more fine meshes have been used in both codes near to body of stepped spillway as well as ogee spillway, because of the velocity gradient nearby wall, where flow enters spillway channel from reservoir. In recent study, water surface profile has been simulated in four types of stepped spillways and 3 types of ogee spillways on the basis of finite element method using FLUENT code and finite volume method using ADINA code. Relatively close consistency has been observed between water surface profiles in both codes by comparing experimental results. Note that free surface profile simulated over the ogee spillway was closer to water surface profile evaluated in laboratory than the profile by finite element method. There were observed better consistency in results from free surface profile over stepped spillway with finite volume method. Maximum differences between results of water surface profile in numerical model of FLUENT and ADINA were nearly 1.2 cm and 1.6 cm, comparing with laboratory results respectively. This value in numerical simulation is acceptable regarding to different meshing in model networking. On this basis, numerical methods of FLUENT and ADINA are proper in order to simulate similar structures for saving costs due to construction of physical model. Flow surface can be determined considering the lower error of FLUENT model in measuring free surface flow; thereby, designing lateral walls of spillway is realized with more precise.

A stilling basin is one of the energy dissipaters downstream of a spillway. The place of maximum pressure caused by jet impact and the effect of various factors on the amount and location of pressure are important factors in designing of stilling basin. Extensive experimentally and few numerically researches have been carried out in this regard. In this research, dynamic pressure fluctuations on the basin floor are studied using two phase flow finite volume numerical method considering different geometries of ogee spillway and sharp crested weir, height of spillways, different flow velocity, Froude number and type of stilling basin. Firstly, numerical results were compared with the experimental ones and relative errors of 8% to 12% have been achieved in this comparison. The results of numerical analysis of spillways with height of 5,7,9,11 and 15 meters and Froude numbers between 3.7 to 6.2 for ogee spillways and between 4 to 6.8 for sharp crested weirs showed that, hydraulic jump happens in 1/3 of the beginning of the stilling basin in all spillways. Maximum pressure fluctuations increase from 62000 to 144000 Pa for ogee spillways and 54000 to 156000 for sharp crested weirs with the height of spillways. The influence of types of stilling basin on maximum pressure fluctuations is also evaluated.

One of the most effective strategies for energy dissipation of hydraulic structures is hydraulic jump .The position of hydraulic jump play an important role in design of stilling basin. In this study, hydraulic jump in ogee spillways were simulated by using fluent software. The governing equations were solved through finite volume method and the standard model was applied for estimating the turbulence flow. The equations were discretized in structured mesh accommodate the well-defined boundaries and the volume of fluid (VOF) method was introduced to solve the complex free-surface problem. The study examined the effect of increasing the discharge and the slope on the hydraulic jump position and lentgh. the results suggest that increasing the slope and discharge caused the spatial delay in hydraulic jump. It was found that in ogee spillway with a constant slope, the hydraulic jump length increases up to 120% when the discharge increases. Additionally, for a certain discharge and a constant length of spillway, increasing the slope of spillway decreases the hydraulic jump length up to 43%.

Ogee crested spillways having superb hydraulic properties including simplicity in design and flow passing efficacy. So far, limited research in the area of prediction and the extraction of discharge coefficient relationship is conducted. In current study two different methods for modeling the discharge coefficient of the converging ogee spillway with a curve axis by was developed and results were compared with the observed experimental values through the Genetic Expression Programming (GEP) and artificial networks (ANNs) approaches. For this purpose, the experimental data of the Germi chay ogee spillway model with varying training wall convergence angles (), was used. Based on the obtained results, applied Artificial Intelligence (AI) models have reliable performance in predicting the discharge coefficient of converging ogee spillways. Moreover, the performance of GEP model is a bit better than ANN technique with relatively low error and high correlation values. To recognize the most effective variables on the discharge coefficient, sensitivity analysis of GEP for the best model was carried out. Results showed that ratio of the design head to the critical depth (Hd/yc) and ratio of the crest length to the downstream channel width (L/Lch) are the most and least important parameters in predicting the discharge coefficient of the converging ogee spillway respectively. The best evaluation of test series were observed in GEP approach with the values of DC=0.818 and RMSE=0.089 and in ANNs approach with the values of DC=0.77 and RMSE=0.099 which demonstrates the high accuracy of predictions.

Three-dimensional pattern of flow on ogee spillway and unlimited geometric parameters changing like a change in crest shape, or modification of the approach channel owing to positional geometric qualities may change the flow characteristics on the one hand and the limited information available about hydraulic ogee spillway with curve axis on the other hand, as a major challenge, has led to the use of meta-model systems and data oriented used by researchers. In current study Artificial Intelligence Techniques (Adaptive Neuro-Fuzzy Inference System (ANFIS) and Support Vector Machine (SVM)) were applied to predict the discharge coefficient of the ogee spillway with curve axis and compared to experimental data. For this purpose, the experimental data of the ogee spillway model with varying training wall convergence angles, 0

The hydraulic jump or water jump, is one of the fast variable flow types and if the water have a supercritical condition in a part of direction, and in special situation the channel wants to change to the subcritical condition, it’s necessary in a very short path the flow’s depth increase significantly and as a result will face a significant energy depreciation. So far many studies were carried out for investigation of hydraulic jump characteristics on rough beds with different forms. Including: Ghazali et al. (2010) analyses the effect of stilling basin floor’s triangle shaped roughness on hydraulic jump characteristics. The results shows that the tailwater depth and jump length on the triangular rippled beds in compare of smooth bed are smaller 25 and 54.7 percent respectively and the sheer stress factor in a rough bed is 8.5 percent more than smooth bed situation in average. One of the solutions which can replace with the bed blocks, is the creation of roughness in flow’s bed. Also Samadi Borujeni (2013) studied the hydraulic jump parameters for six rippled bed. Results showed that the rippled bed in compare with the smooth bed shows a decrease of 25 percent in conjugate depth and a decrease of 54.7 percent in jump length and the factor of sheer stress of the rippled bed was 8.5 times bigger than smooth bed. In this research the characteristics of hydraulic jump has been studied in rough bed condition with the use of physical model. The purposes of this research includes assessing the average diameters of particles at natural roughness condition of bed on the secondary to primary depth ratio, hydraulic jump relative energy dissipation, sheer force coefficient, Comparing the experimental results with the results of other similar research on a variety of rough beds and eventually representing relationships for each of the above terms.
In this research the characteristics of hydraulic jump on natural rough beds with aggregated particles carried out with an average diameter of 4.75, 3.55, 2.18, 1.59, 0.74 millimeters and a Froude number of 3.5 to 4.5 in a rectangular horizontal flume with the length of 5 meters and width of 0.075 meters and the heights of 0.175 meters. For creating a hydraulic jump, ogee spillway with the height of 0.12 meters has been used in a condition which places the rough beds in downstream. For dimensional analysis, after identification of effective parameters on hydraulic jump, dimensionless numbers, has been extracted using the Buckingham π-theorem.
Relative depth, the dissipation of jump relative energy, sheer force coefficient, was obtained as a function of Froude number. The results show’s that between all of studied roughness with different values of roughness relative depth, has no significant differences in terms of influence on decreasing relative depth, increase relative energy dissipation and increase sheer modulus, but the effect of this rough values can be seen in compare with smooth bed.
Results show that the rough bed in compare with smooth bed, will decrease the jump relative depth in an average of 56.7 percent, and the relative energy dissipation increases 69 percent and the sheer modulus increases 2.6 percent. On the other hand, comparing of this experimental results with the other similar researches on different types of rough beds show that the graph of the fitted Curve ∆E /E_1 to Froude number, is matches the fitted graph on triangular substrates which Samadi Broujeni (2013) was studied, and changes in shear force coefficient and jump relative depth in the range of above Froude number will be increased which expresses match results.

In this study, the effect of flip bucket at the end of ogee spillway on the energy dissipation rate and jet length has been investigated experimentally. Experiments on standard ogee spillway for buckets with take off angles of 32 and 52 and for no bucket condition were conducted. The rate of energy dissipation in this type of spillway was investigated with conducting 21 tests with discharge range between 330 to 864 L min-1 .The results showed that at the spillway with flip buckets and take off angles of 32 and 52 , the rate of energy dissipation was increased from 10 to 20 percent compared to the spillway having no bucket. The highest energy dissipation was occurred in the flip bucket with take off angle of 52 . Also the relative energy dissipation was decreased in all three modes with increasing discharge. The length of jet for flip buckets with angles of 32 and 52 was measured and it was releaved that the length of jet for bucket of 32 was greater than that for bucket of 52 . By increasing the discharge, the difference between the jet lengths of the two buckets was decreased and at the discharge rate of 864 L min-1, the length of jet was equal for the two buckets.

The water surface profiles on spillway are important for design of free board and spillway training wall height. The engineers have used physical modeling to design these kinds of structures, Considering that the scale effect in the spillway modeling, leads to the different measured data between model and prototype, in this study, an experimental model based on Garmi-Chay Mianeh dam spillway was designed in three 1:100, 1:75, and 1:50 scales. Next, the water surface profile on spillway crest measured in seven discharges and compared with basic scale of (1:50), the percentage of water level difference on the crest calculated in two physical models with 1:100 and 1:75 scales. Results and observations revealed that in due to the effect of viscosity and surface tension the difference of water level in the scale of 1:100 and 1:75 was 18.4% and 15.6% respectively, relative to the base scale. The larger discharge, water level on spillway increases, leads to decrease viscosity and surface tension effects. For the difference in water level in the scale of 1:100 and 1:75 was 5.8% and 4.8% respectively relative to the base scale. In this study, viscosity and surface tension effects is stated with correction equation (K'), that was functions of Reynolds and Weber numbers. With the ogee spillway modeling the effect of viscosity in Reynolds numbers larger than 3.1*104 and the effect of tension surface in Weber numbers larger than 270 can be neglected and by extrapolation prototype results from model studies can be obtained.

Weirs are one of the common structures for discharge and flow measurement. Therefore,these types of hydraulic structures depending on the purposeofuse havedifferent shapes. In some cases, due to practical constraints, spillways with curvature in plan are designed. In such situations study of flow distribution over the spillway and other related parameters, will be important. In this study, a physical model of dam spillway, which is type of ogee-crested weir with curvature in plan, were tested. Also in order to investigate the effects of curvature on the performance of the flow, the second model of spillway in normal shape, with similar geometric and hydraulic conditions, were compared.

First physical model of prototype is built at the scale of 1:75 and the second model was constructed in straight form (without curvature in plan) with similar geometric conditions to the first model. Spillways have been designed according to USBR standard for design head at value of 4 cm in model and vertical upstream face. Experiments were performed in Soil Conservation and Watershed Management Research Institute at reservoir with dimensions 1.2 m length, 0.70 m width and 0.5 m height walls of Plexiglas. To measure the flow discharge, a sharp triangular weir with apex angle of 90˚ in the output of channle was used. Measurements in first model were conducted with five discharges and five values of h/Hd (0.53, 0.74, 0.90, 1.08 and 1.44) and for six sectors on spillway body. To evaluate the effect of curvature, flow performance and discharge coefficient changes were compared for five early discharges (ratio of critical depth to design head at value of 0.28, 0.44, 0.58, 0.72 and 0.81) and six other discharge (mentioned ratio at value of 0.36, 0.51, 0.66, 0.76 and 0.83) in both models.

The results related to the first model showed that by increasing the ratio of head to design head (h/Hd), rate of spillway discharge coefficient increases to the value of 1.72 and decreases to 1.23, when the weir was submerged. It also observed that with increase in flow rate of each discharge and reducing the pressure along the spillway, possibility of vacuum-creation and corrosion of structure increased and the corrosion rate witch introduced by Cavitation Index decreased. The minimum value for Cavitation Index that has been calculated was 1.45 that is greater than the critical value of it. The results of the pressure distribution and changes of Cavitation Index in first model showed, the minimum height of the pressure for each discharge occurred at the end of ogee profile and the minimum value of the Cavitation Index occurred at the last section of spillway in downstream for the value of h/Hd=0.53.As well as for all test cases in this study, the maximum velocity and minimum of Cavitation Index were calculated at the same section of spillway where hydraulic jump was observed. On the other hand, it was observed that with increasing flow rate, the critical section moves upward on the spillway body. The results related to the spillway efficiency generally indicated that by increasing the ratio of critical depth to design head (yc/Hd) discharge coefficient increases. In fact, by increasing the ratio of h/Hd and increase the discharge rate up to design discharge, the amount of evacuation and efficiency of both models goes up. For larger discharges, the flow is blocked by the spillway forehead and model efficiency will decrease due to submersion and flow rejection. Results obtained from comparison of two models indicated for the spillway in normal shape submergence of the weir occurred faster and discharge coefficient of each test achieved in lesser value per test, So that the discharge coefficient increasing in curved spillway continued until the value of 0.81 yc/Hd (at 10.3 lit/s of discharge) and in normal shape until the value of 0.72 yc/Hd (at 9.2 lit/s of discharge). Therefore it seems that the upward central arch factor will increase the discharge coefficient and efficiency of spillway.

In the present research the hydraulic performance of ogee spillway with curved plan to investigate the pressure distribution and the vacuum-creation and in particular to compare the results related to flow performance and the effect of spillway curvature on its performance were studied using two experimental models. The impact of increasing the discharge coefficient for the weir with upward central arch compared to weir with straight crest, in terms of similar geometric and hydraulic conditions, was calculated to the value of 21 percent, in this study.

One of the usual ways to dissipate excess energy in the dam's downstream is hydraulic jump. Hydraulic jump is a rapidly varied flow, in which the flow conditions change from supercritical to sub-critical with a large amount of energy loss. In this research, a combination of two water jets in the form of overflow dam and underflow through a slot on the body of an ogee dam with the USBR standard was established in order to decrease the length and sequent depth in a hydraulic jump. In these experiments, the underflow from the slot was designed with three out passages of 0, 45, and 90 degrees in respect horizontal line. Six different discharge ratios were used for each slot and the effect of each experiment conditions on decreasing of the length and sequent depth of hydraulic jump was investigated. The results showed that the confluence of two jets with 45 degrees from the slot had the maximum effect on the reducing of the length of hydraulic jump and sequent depth, and when 26 percent of the total discharge passed through the slot as underflow, it caused the length of hydraulic jump to be reduced by 50 percent in comparison with the classic jump. This slot not only decreases the length and sequent depth of hydraulic jump but also the sediment behind the dam can be evacuated through it. Moreover, it increases the discharge coefficient.

In this study, the effect of sedimentation behind Ogee Spillway on the characteristics of flow including upstream head and velocity, discharge coefficient, water surface profile, critical depth position and flow conditions downstream of a spillway, are investigated experimentally. The experiments were carried out by using an Ogee spillway with height of 25 cm and different upstream side slopes as 1H: 3V, 2H: 3V and 3H: 3V. The used sediment had a diameter of 0.4 mm and sedimentation heights in the range of 0-24 cm were considered. The results showed that the upstream flow depth and upstream flow velocity are increased by increase of sediment level upstream of spillway. As a result, the design head (He) will be increased. A change in He decreases the discharge coefficient of spillway. It was also found that the discharge coefficient changes from 2.25 for no sediment deposition (first stage of operation) to 1.69 for full sediment deposition in upstream reservoir. Thus, these results showed that the design of diversion weirs based on initial conditions is not accurate and causes major problems during operation of diversion weir.

Constructing stilling basins usually are expensive، so reduction of stilling dasins length is economically important. The dimensions of the stilling basin depend on the length and sequent depth of hydraulic jump. Therefore، increasing the energy loss in dam structure decreases the length and sequent depth of hydraulic jump and as a result reduces the stilling basin cost. Also in designing of diversion dam، in order to prevent the agricultural land flooding during the flood season، a smaller height of diversion dam is designed and this may produce many difficulties for upstream intake structures. In this research study a combination of two jets in ogee dam was used، in order to increase the energy loss along the dam structure and to reduce the hydraulic jump length and sequent depth. The laboratory models of ogee dams were designed and built based on the USBR standards with a designed slot near to the toe of the dam. In these experiments the directions of the flow out of the slot were 0، 45 and 90 degrees in respect to the horizontal line. The effect of six discharge ratios (discharge from the slot to the total discharge) for each angle was investigated on the hydraulic jump length and sequent depth. The Froude Number was measured 1. 5 to 4. 5. The results showed that the angle 45 degrees has the maximum effect on reducing the hydraulic jump length and sequent depth، with an average discharge ratio of 26% the hydraulic jump length being reduced about 50% in comparison with the classic jump. This structure is also able to increase the total discharge coefficient.