Irrigation and Drainage Structures Engineering Research
Year:2019 | Volume:19 | Issue:73|Papers Count:10

In this study, a non-structural and eco-friendly solution has been used to reduce scouring at downstream of screens. The upstream of screen which are known as stilling basin, are protected against scouring but the downstream of screens always are subjected to the flow scouring. Since clay and nanostructured-clay has suitable compatibility with river system and ecology as a view of the environment, the bed sediment at the downstream of the screen have been admixed with clay and nanostructured-clay, after grouting its effect on scour reduction have been evaluated in the three different flow. The experimental results indicate the positive effect of clay and nanoclay on scour depth reduction at the downstream of screens. The best performance has been occurred for clay and nano-montmorillonite clay mixture. The positive effect of clay and nano-montmorillonite clay mixture for scour length reduction is observable, and by utilizing this mixture, the length of scouring has been decreased 33 percent. Furthermore by addition of clay and nano-montmorillonite clay mixture, the scour depth reduced up to 39 and 46 percent. According to the result, utilizing clay and nano-montmorillonite clay mixture has a positive effect on scouring control, and as a practical view, it could be very useful for some cases such as rivers which bed protection by some materials such as concrete is not possible.

Most of the previous studies related to radial gates are focused on the estimation of discharge from the gates as a flow measurement structure. However, determination of the gate opening for passing a certain value of the discharge is rarely considered in previous studies as a regulator structure. The present work presents some theoretical equations for explicit estimation of the outflow from the gate (first problem), and gate opening (second problem) for free and submerged flow conditions by combination of Energy and Momentum principles. For any problems, it was developed some criteria to identify flow conditions These equations were calibrated and validated by means of 2657 experimental records retrieved from research conducted on three types of radial gates. The paper would present an analytical approach to illustrate the reliability of proposed equations for estimation of discharge and the opening of the gate by taking benefits from the mean absolute relative errors which observed to be 1. 94% and 2. 67, respectively. It was noted that the used criteria conform with 99. 6% and 98. 8% of all observations at first and second problems, respectively. The results show that the tailwater depth under distinguishing limiting decreases by increasing in the gate lip angle and the ratio of turnnion pin height to the gate arm radius. Also, the hard rubber bar gate tends to operate under free flow condition in a wider range in comparison with two other gates.

In the present research, height and velocity of shock waves in contractions of open-channel with trapezoidal and rectangular sections was investigated using experimental models. For this purpose, length of transition (0. 5m), convergence ratio (1/2, 1/3 and 1/4) and side slope angle (45º , 60º , 70º and 90º ) were considered as geometric variables of the experiments. Also 4 Froude number was assumed as a hydraulic variable of the experiments in the range of 3. 25-9. 23. Analysis of free surface and velocity profiles of shock waves showed that in general, the increasing of side slope angle of the transition wall, reduction of convergence ratio, and increasing of Froude number have a direct relationship with the increasing height and velocity of shock waves. The results showed that in the contraction with trapezoidal section with the convergence ratio (1/2) and side slope angle (45º , 60º and 70º ) compared with rectangular cross-section, on average maximum height of shock waves respectively decreased to: 59. 34, 44. 27 and 24. 04. In the same condition, the maximum velocity of shock waves respectively decreased to: 37. 51, 25. 23 and 14. 67. As Executive channels mainly with a trapezoidal cross-section are building and operating, so the findings of this study can be very useful for design engineers.

Controlling seepage from earth dams foundation and calculation of its valve is so important for monitoring and stability control of earth dam. Doroodzan is an earth-rock dam which is located on North-west of Kor River. In this study simulating, calibrating and validation of numerical model of Doroodzan dam were conducted in Seep/W software using result of monitoring report. Then changes of foundation seepage flow of Doroodzan calibrated earth dam model were studied changing Foundation seepage control method (consisted in using clayey blanket and cut off wall) and parameters of each method (such as blanket length and cut off height and location) and changing the geometry and hydraulic parameters (such as foundation permeability and reservoir water level). Results showed that increase in blanket length and using cut off wall at the first and middle of dam, decreases foundation seepage flow. In addition simulate using blanket and cut off wall had the most effect on decrease in foundation seepage flow. Finally a regression equation due to determine earth dam foundation seepage was developed using Spss software. Comparison of the accuracy of the proposed equation results with previously presented equations showed that estimated foundation seepage discharge using proposed equation has higher accuracy.

Agricultural water pumping stations has an important role in water conveyance and distribution, increasing energy and the agricultural water productivity due to its high application in most of irrigation and drainage networks. So incidence of any problem for these installations will cause operation problems and water resources losses. In this study, lack of supplying the proper elevation in the suction part of pumps, was identified as one of the important operational problems, which have harmful consequences such as disability of pumps, reducing the pumping capacity, economic losses and water users’ dissatisfaction. Reducing the water elevation in the pumping station occurs because of lack of attention to the hydraulic conditions, improper location of pumping stations and changes in the normal condition of river. Some problems in many cases, could be solved and be modified by the proper hydraulic methods which are complying with the geometric conditions of region. In this study for Veis pumping station, after simulation of priming hydraulic from river by SOBEK model, appropriate curative methods were proposed by change in the topography of the river and they were compared with in-situ corrective method. Then, influence of some effective hydraulic parameters on increasing of water level in pumping suction such as intake canal slope, distance between pumping station and intake port, water level curve changes in the pumping phase and changes in river flow regime were investigated. Thus the problem of pumping stations’ priming on the design and operation phases were evaluated and effective parameters and appropriate criteria are presented for the proposed corrective method.

Labyrinth weirs are considered as appropriate option for correction of weirs facing problems with maximum conveyance flow rate. In this research, 5 rectangular labyrinth weirs with 4 different slopes in downstream and upstream ramps were investigated in laboratory condition. The experiments were carried out for 4 different ramp slopes, including: no slope, 15, 30 and 45 degrees. Our findings showed that, for rectangular labyrinth weir with upstream and downstream ramps slope, discharge coefficient decreased when Ht/P increased. It was also indicated that, in case of creation of slope in downstream and upstream ramps, the discharge coefficient of rectangular labyrinth weir increased and decreased, respectively compared to no slope condition. Furthermore, it was found that in rectangular labyrinth weir model, increase in weir's effective length resulted reduction in discharge coefficient, and that increase in weir's height caused increase in discharge coefficient. Finally, we presented equations of discharge coefficients based on effective dimensionless parameters.

Stilling basin is one of the energy dissipater structures that are used frequently in downstream of hydraulic structures, such as spillways, sluice gates and chutes. The energy dissipation, due to macro-scale turbulence, makes intensive pressure fluctuations so it must be carefully considered when structures are designed. The experiments were carried out in a rectangular flume, 0. 3m by 0. 4m; and Froude numbers from 3 to 12. The pressure variations data at flume bed and the water level data were recorded by electronic pressure transducer and by piezometers, respectively. The results showed that the intensity of pressure fluctuations in hydraulic jump was related to the Froude number and relative situation from the jump toe. The maximum pressure fluctuation intensity coefficient C'pmax varied from 0. 08 to 0. 28 at the distance of 17 to 33 percent of the jump length. The maximum value of C+P was equal to 2 and maximum absolute of coefficient C-P was equal to 1. 2 occurred at X/Lj≤ 0. 4. Longitude distribution of pressure and its fluctuation and critical values in the length of hydraulic jump also were obtained.

Secondary currents and flow separation at the intake lead to sedimentation and erosion at the lateral and main channels, resulting changes in bed topography. In the separation zone, circular flow with low velocity causes sediment’ s accumulation happens in this area, the consequences of which would be reduction of intake efficiency. Hence, determining the optimum conditions of the impoundment has been one of the concerns for the researchers. In this study, the effects of bed topography on the flow separation dimensions in the 55-degree water intake with the sharp and rounded edge entrances were assessed. Four different discharge ratios: 0. 2, 0. 4, 0. 6 and 0. 8 were tested in this experimental study and the results were compared with those issued in previous papers. Additionally, the effects of bed roughness and submerged vanes on shear stress within water intake were tested in sharp edge and rounded edge entrances. The results showed that in high diversion flow ratio and in round edge entrance, comparing to sharped edge entrance, about 97% of separation dimensions were reduced. In sharp edge entrances, increasing the diverted flow ratio, caused the length of the separation zone increased about 20% and its width reduced about 70%. Furthermore, the bed topography and roughness reduced the width of the separation zone. Also, the shear stress in rounded edge entrance was less than that in sharp edge entrance. The shear stress, in case of absence of submerged vanes, was more than that when submerged vanes were installed. By installation of submerged vanes with parallel and zigzag arrangements and with angles equal to 10 and 30 degrees, shear stress in transverse happened to be uniform, indicating that vanes have helped rotational flow being reduced and velocity being changed.

In practice, U-shaped channels are used in urban sewer networks. Also, most of aqueducts in Iran are made of U-shaped channels. In this study the flow field turbulence and free surface variations within the U-shaped channels along a side weir are simulated using the FLOW-3D and RNG k-ε turbulence models and the volume of fluid (VOF) scheme, respectively. Comparison between the experimental and numerical results shows that the numerical model predicts the flow field characteristic with reasonable accuracy. Then, the effects of the side weir length change on the free surface and the flow pattern in U-shaped channels are investigated. According to the simulation results, the free surface variations are not significant at the side weir upstream and, so the side weir effects could be ignored. For the L/D=3 case, before the side weir, the free surface flow is affected by the weir and a height difference is observed in all longitudinal profiles. Also, a surface jump occurs for both L/D=2 and L/D=3 cases in the downstream end of the side weir. According to the simulation results, a secondary flow is created after the side weir so that the cell of this secondary flow develops by proceeding to the main channel downstream. The specific energy variation in the upstream and the downstream of the side weir for L/D=2 case is computed to be about 1. 18% in average.

Despite the importance of determining and measuring the indices of irrigation water management in the agricultural sector for application in macroeconomic planning, these indices have not yet been done in modern and conventional irrigation networks. Therefore, the present study was conducted to compare the indices of irrigation water management (water consumed, water productivity and water application efficiency) in modern and conventional irrigation networks producing silage maize in Iran. The data were obtained by direct measurements from fields in the provinces of Alborz, Tehran, Fars, Khuzestan, Khorasan Razavi, Ardebil, Isfahan and Qazvin, which covered about 70% of areas under cultivation of silage maize in Iran, in more than 100 farms in modern and conventional irrigation networks. Results showed that the differences in water consumption and water productivity indices of modern and conventional irrigation networks were statistically significant to produce silage maize. Consequently, the yield of silage maize measured 50. 54 and 54. 32 ton ha-1, water consumption measured 6983 and 9085 m3 ha-1, water productivity measured 7. 46 and 6. 26 kg m-3, and water application efficiency measured 73% and 68% under the modern and conventional networks, respectively. These findings indicate that development of modern irrigation networks can promote water productivity and are valuable to be applied in the five-year national development plan and economic programs.