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.

Introduction: Due to the height of the dams, water behind dams have a high energy and the amount of velocity on the spillway is high. Downstream of the spillway as a result of high energy and velocity of water on the spillway, is at the risk of cavitation and damage. The study of cavitation is crucial in this respect, and indicates the amount of flow degradation in the structure. Agreat number of research has been conducted on how to eliminate cavitation. Given the nature of cavitation, caused by high speed and pressure reduction, the use of roughness in parts of the spillway can help reduce or eliminate this phenomenon. The aim of this study was to investigate the effect of roughness under different conditions on changes in cavitation index in the downstream peak body. Methodology: To achieve a better understanding of how the roughness works, this research was carried out by changing its arrangement, number and different heights on the cavitation index using a laboratory model. In order to achieve a more realistic simulation, a spillway was installed at a distance of 5. 5 m from the beginning of the canal to ensure the turbulence of incoming current is minimized. Ogee spillway was considered in the study, designed and constructed according to USBR standards. Eight holes were installed on the spillway which were connected to 8 piezometers located in the channel body through flexible pipes to read the amount of pressure static. Effective parameters were identified with dimensional analysis, and three parameters (roughness arrangement, number of roughnesses, effective height of roughness) were tested. The roughness used in this research is made of PVC. After installing the spillway in the channel, the roughness was installed on the spillway. The piezometers were ventilated before each experiment and the channel slope was adjusted. Then, the pump was turned on, and after adjusting the flow rate, the test began. The depth gauge was calibrated for each aperture to measure and correct the height on the apertures. The equivalent pressure height inside the piezometer tubes was read and adjusted for the piezometer base and channel slope. Finally, according to the data, the roughness performance was evaluated using the cavitation index. Results and Discussion: The experiments of the present study were performed with different Froude numbers and slopes. After the control experiments, the experiments were evaluated in three modes: the effect of arrangement, number and effective height. Evaluation of cavitation index changes in control experiments: Observations show that cavitation index decreases as water falls on the spillway. The minimum cavitation index in the control experiment occurs at point 8. Moreover, the average cavitation index increases compared to the control mode by placing the roughness. • Investigation of roughness arrangement on the cavitation index: Observations show that the placement of roughness with convergent, divergent and row arrangement increase the cavitation index compared to the witness experiments. In the Froude number of 1. 08, the changes in the cavitation index range from 1 to 8, 3. 7, 4, 4. 2, 4. 4, 4, 3. 7, 3. 8 and 3. 5%, respectively, compared to the case. • The number of roughnesses on the cavitation index: By placing 9, 12, 15 and 18 roughnesses in the row arrangement, the observations showed that in all graphs, the cavitation index increased compared to the witness experiment. Moreover, with the number of roughness, the cavitation index has a slight increasing trend. With 18 roughnesses in the flow rate of 1. 08, the increase in the percentage of cavitation index (compared to the witness experiments) was piezometric points 1 to 8, 11. 1, 4. 03, 12. 3, 17. 6, 4. 4, 4, 3. 7 and 7. 1. • Investigation of effective roughness height on the cavitation index: Considering the three effective heights of roughness, the observations showed that in all three cases, there is an increase in the cavitation index compared to the witness experiments, and the most evident change in the effective height has occurred at 0. 017. With 1. 08% increase in the flow rate of cavitation index compared to the control condition, 1 to 8, 7. 5, 4, 12. 7, 26. 9, 4. 1, 3. 8, 7. 3 and 6, respectively were obtained. Conclusion: In general, it can be concluded that the installation of roughness on the spillway, the effective height of roughness, the number of roughnesses and its various arrangements, increase the cavitation index compared to the witness experiments. The presence of roughness reduces the flow velocity and increases the pressure on the spillway. This issue has a key role to play in eliminating or mitigating the cavitation phenomenon on the spillway. Compared to the witness experiments, the average cavitation index increased by 15. 17% in the convergent arrangement, 11. 8% in the divergent arrangement and 16. 11% in the row arrangement. The results show that the greatest change in row arrangement and effective height occurs at 0. 017 and n = 18.

Dam's weir is one of the most important dam structures that play a significant role in flood routing in the dam reservoir. Since the dam's level significantly affects the storage, changing the level and increasing its height can increase storage volume and flood control in some situations. Shahid Abbaspour Dam (Karoon 1), due to the reduction of the dam volume, affected by the accumulation of sediments and the construction of upstream reservoir dams, it is necessary to increase the dam's weir height. This research used a numerical simulation of the weir with Flow3D software. Moreover finally, after the model verification, its height was increased. All model outputs were compared with the physical model results and the dam's data, and the simulation fit well with both systems. According to the model results, in exchange for changing the level of the dam from 510 to 513.5 and the fully opening of the Gates, no negative pressure is created on the weir surface, and the cavitation index is within the allowable range.

The role of dams in the human well-being, especially in countries like Iran is known as one of the underlying bases of sustainable developments nowadays. The spillway is one of the important structures of any dam.[that enables the bypass of flood flows or flows that exceed the capacity. [In other words, controlling the height and the volume of the reservoir is another important function of the spillways. Among the different types of the spillways, Ogee spillways are mostly used, regarding their high hydraulic efficiency. According to the fact that testing is proposed to be the most precise method in studying the problems of such structures, this has made the researchers and designers to investigate the hidden aspects of the subject by means of making physical models and modeling real flows. In order to investigate the flow regime on a part of Sivand dam Ogee spillway, the physical model of the spillway was built to a 1:100 scale] in the flume of the hydraulic laboratory of Marvdasht Islamic Azad University. [Data were in 14 steps with different discharges. Analyzing the collected data, it was found that the Frude number had the maximum values on the chute structure according to the high velocity. And in the sections between the main and the control spillways the least values for the Frude numbers were observed resulted from submergence of the flow]. The C coefficient of the Ogee spillway was computed to be 1/796. In addition, the flow was modeled up to a discharge of about 2000 m3/s in the prototype, Regarding the critical cavitation number in a number of the tests, the dam structure is threatened to damage. Hence, construction of air vents at the outlet section of the spillway is strongly recommended.

This study aimed to analyse the design of spillway in curved plan and downward angle of convergence. In this plan the effective length of the spillway is reduced from the crest to the toe for several times. Tests were carried out in two stages. In the first stage, a physical model of the real sample was prepared for a specific site in the scale of 1: 50. In this stage, experiments were performed for eight different discharges making up to 25 to 150% of the design discharge of the real sample. The spillway demonstrated a satisfactory performance up to the discharge of 1. 13Qd (Design Discharge). Gradually an increase in the discharge led to a decrease in the performance of the spillway so that with a discharge of 1. 26 Qd the spillway was fully submerged and the downstream channel took control of the discharge. Observations and experiments indicated that one of the factors contributing to the swamp of the spillway was a severe variant of the guide wall (120 degrees) as well as the considerable decrease in the ratio of channel length (Lch) to crest length (L), i. e. . In the second stage, the effect of variation of convergence angle of the guide walls of the spillway was studied. To this end, a physical model with three convergence angle of the guide walls, including a 0-degree angle and ratio of; a 60-degree angle with ratio of; and a 90-degree angle with ratio of was tested. The effect of variations of angles in discharge coefficient was reported to be negligible before the swap. At the 0-degree angle with ratio of, the highest discharge was 1. 99 because the model was not submerged in a discharge equal to the PMF discharge of the real sample. In all angles, the static pressure on the crest was reduced while it was increased in the shoot and toe. So that, in the crest a ratio of was recorded for a discharge of 1. 13 Qd. At the angles of 90 and 120 degree, higher discharges led to swamp of the spillway and a change of the current flowing on the spillway from supercritical to subcritical. The high pressure was reported to be of the 120-degree angle for a discharge of 1. 5Qd. Since at the 60-degree angle ( ), the length of the crest was smaller (45% less than the 120-degree angle with ), it was selected as the proper angle.

Now a day, the role of dams in the human life especially in countries like Iran is known as one of the underlying bases of sustainable development. The spillway is one of the important structures of any dams, that enables the bypass of flood flows or flows that exceed the capacity of the dam. Among the different types of the spillways, Ogee spillways are mostly used, regarding their high hydraulic efficiency. The most precise method in studying the problems of this structure, is making physical models and modeling real flows. In order to investigate the flow regime on a part of Mollasadra dam Ogee spillway, the physical model of the spillway was built to a 1:30 scale in the flume of the hydraulic laboratory of Marvdasht Islamic Azad University. Data was gathered with different discharges. Analyzing the gathered data by means of hydraulic regimes, it was found that the energy dissipater structures are working properly, due to tested discharges. The C coefficient of the Ogee spillway was computed to be 2.86. In addition the regime of the flow was modeled up to the discharge of about 1680 m3/s in the prototype, but we did not see any special hydraulic problem.

In this study, the roughness at downstream of Ogee spillway has been simulated numerically for different flows, and the effects of roughness on the transformation of flow regime, the water surface profiles, and the energy losses also have been investigated. Hence, after solution domain generation, meshing, and specification of boundary conditions, the numerical simulation has been run by using k- standard turbulence model, and in order to validation of the numerical results of the investigated Ogee spillway, the experimental model of Ogee spillway proposed by Chatila and Tabara (2004) has been used. Also, the effects of three types of roughness at downstream of this spillway were evaluated. The results indicated that by increasing the heigh of roughness, the energy loss increases up to 80 percent. The roughness types of 3 and 4, imposed the regime transformation and caused 70 to 50 percent, in average, energy losses respectively. Also, we found that increase in flow discharge affected directly the water surface profiles. Results showed that if the design of stilling basin was considered, the roughness with a height of 0. 6Hd had the ability of flow regime transformation and was evaluated as the most successful design.

The Crest of an Ogee spillway with a curved plan is longer than that of one with a straight crest, therefore, its capacity for the overflow at any reservoir level is higher than that of the straight-crested spillway. Thus it is a preferred design in most water ponding projects. The objective of this study was to investigate the degree of its curvature on its hydraulics. This was a achieved on a 1:25 experimental model of the Germ chai Ogee spillway at the Hydraulics Laboratory of the Soil Conservation and Water Management Research Institute of the Ministry of Jihadi Agriculture. The results revealed that the cavitation number at any discharge rate was higher than the critical value compared with that of the straight- crested weirs Moreover, the discharge coefficient was lower than that of the other type with an equal crest length.

Abstract spillways are structures used for releasing the surplus floodwater in necessary conditions from storage dams. Ogee spillway is one of the most common and simplest structures. . In this research, a three dimensional flow field over the spillway was simulated with Flow-3D, using two turbulence models, namely RNG and. First, for precise prediction of hydraulic specifications of over spillway flow, the mentioned turbulence models were validated using data gathered from a laboratory flume (Sivakumaran et al., 1983). Data collected from software validation showed that the RNG turbulence model produced better results than. In the next stage, this model was used for simulating the physical prototype of the Nimrod Reservoir Dam. The measurement factors included pressure and water surface profile. The obtained values were compared to the existing laboratory measurements. Results from the simulation were well consistent with experimental measurements. Keywords: Flow Pattern, Nimrod Reservoir Dam, spillway, Flow-3D, Turbulence Model.

Introduction: The cost of dam construction is very high. A lot of dams are broken due to the water passing through dam crest. The most important factor which causes this is, insufficient spillway capacity. The aim of present study was investigating optimal height and length for Ogee-Crested spillway because such height and length minimizes the cost of spillway construction. In order to determine objective function, the spillway length variations were considered in the range of 10 to 30 m and the flood return period was estimated in the range of 1000 to 10, 000 years. Optimization was done with using genetic algorithm in MATLAB software environment. In fact, the aim of this study was investigating the effect of height and length of spillway on the cost of spillway construction, therefore, Analytical relationships presented with using regression model. The main function of Ogee-Crested spillway is providing ideal conditions for passing designed flood from upstream to downstream. Bagatur & Onen in 2016, used gene expression planning (GEP) models as an alternative approach to predicting appearance features and spillway design coefficients and therefore, proposed new relationship, for Ogee-Crested spillway. It was found that GEP is much better than regression model for predicting Ogee-Crested spillway characteristics. Haghbin in 2015 proposed that using multi-objective genetic algorithm can optimize spillway geometrical dimensions...