نشریه تحقیقات مهندسی سازه های آبیاری و زهکشی
سال هجدهم شماره 68 (بهار و تابستان 1396)

Modeling of flow through the compound open channel is one of the main problems in the field of hydraulic engineering. One of the main parameter related to the flow properties in the compound open channel is Shear Stress. The shear stress is because of difference of velocities between the main channel and floodplains. The Shear Stress causes of turbulence and vortex creation on the border of main channel and floodplains. The difference between the roughness of main channel and floodplains intensities the shear stress in the border zone. In this investigation using the physical and numerical modeling the flow properties in the heterogeneous roughness prismatic compound open channel was studied. The study was carried out in the hydraulic laboratory of Tehran University and numerical modeling was conducted using the Flow 3D as famous computational fluid dynamic (CFD) tool. The results indicated that the Flow 3D software has high ability for modeling the flow characteristics in heterogeneous roughness prismatic compound open channel and the RNG turbulence mode is suitable for modeling the vortex on the border of both sections.

About two-thirds of rivers, lakes and groundwater are applied for agricultural production in the world. Same as other countries, a significant fraction of surface and groundwater resources are used in agricultural sector in Iran. Water balance at country scale is the origin of estimation of applied water as agricultural consumption. The variability of annual precipitation is as the origin of the components of water balance in hydrological cycle, caused changeability in the water consumption of agricultural sector which are important reasons for estimating and re-estimating consumptive water in agricultural sector. Therefore, in this study, consumptive water of agricultural sector was analyzed based on long term (50 years) and short term (current 7 years) measured data for precipitation with the method of water balance in hydrological cycle in the country. Results revealed that average annual precipitation were 249±53 and 206±33 mm for two long and short studied periods, and the consumption water in agricultural sector were 67 ±18 and 83±6 km3 for long (50 years) and short (7 years) periods for non-modified conditions. The modified consumption water for the short period was 75±6 MCM.Results revealed that for the long period, the water consumption in agricultural sector was 0.50 of renewable water in the country. The outstanding of this study was up to date estimating of the water consumption in agricultural sector and its analysis. But applying water balance method for this purpose has some substantial limitations and non-reliable simplifications. Therefore suitable experiments are needed to reliably the results.

Improving management of existing irrigation canals is indispensable in order to save more water. In this study, a set of four nonstructural solutions introduced in order to improve the operational performance of a main irrigation canals suffering from fluctuations of inflow water. To this end the existing operation of the Roodasht main irrigation canal was simulated applying a mathematical model and assessed by the operational performance evolution indices. Then the abovementioned solutions were investigated. The four solutions consist of operation with known disturbances; unknown disturbances; rotational water delivery out of the intakes alongside of the main canal and increasing discharge inflow. The results indicated that operational level were improved by the solutions, for example by employing the third and the forth operational solution, average value of the maximum error in water delivery was decreased by 25% and adequacy of water delivery activity was improved by18% respectively. Also, the results showed that under severe decrease of inflow to the canal, the mentioned solutions improved water delivery and distribution between upstream and downstream 17 percent.

An important tool in current multi-purpose erosion control, stream restoration, and habitat improvement projects is the bendway weir. A series of upstream-angled low-elevation stone sills (bendway weirs) are designed to control and redirect currents and velocities throughout a bend of a river or stream. Consideration of scour and sedimentation pattern at a 90 degree bend (with relative radius of curvature equal to 3.3) in the presence of weirs and without weirs is the aim of this study. To reach the purpose of this study, series of bendway weirs (7 weirs) with height of 30, 50 and 70 percent of flow depth were constructed in multiple flow conditions at the outer bank side. The inclination angle, length and distance of weirs were kept fixed in all tests, and set equal to 60 degree, 30 percent of canal width and three times of weir length, respectively. The results showed that the channel talweg moved as effective length of weir from outer bank to the center and along the weirs tips at the result of bendway weirs installation. Owing to installation of bendway weirs with 0.5D and 0.7D height the scour volume accessed 53% and 120% higher than no-weir state, respectively. While for weirs with 0.3D height, it was equal to no-weir condition. Also, the maximum relative scour depth at the tip of weirs with height of 0.5D and 0.7D were two times of weirs with 0.3D height.

The determination of consolidation properties of the clayey soils is one of the most important steps in designing and constructing the civil engineering projects; especially, irrigation and drainage projects. It is mainly important due to the fact that the settlement of these soils may cause a significant damage to the structures. Generally, the consolidation behavior of the soils is being evaluated by Oedometer in the form of one-dimensional consolidation. However, some modified gradation techniques should be employed in order to prepare samples of coarse grained clayey soils due to the smaller size of the test mold, which causes an alteration in the soil gradation. The hydraulic consolidation cell provides controlling drainage pathways and recording the pore pressure of the specimens during the test. The main objective of this study is to investigate the alterations made on coarse grained soils due to modified gradation. In this regard, the coarse grained clayey soils were grade modified by using scalped and replacement methods. Then, the consolidation behavior of the graded and modified specimens was tested by oedometer test. Moreover, the base soil specimens were tested by using hydraulic consolidation test. The results showed that by performing modified gradation techniques, the values of compression index and coefficient of consolidation, respectively, increases 1.5 to 2.5 time and decreases 30% to 80%. These alterations are more intense in grade modified specimens with sculpted method. Thus, the replacement method is a better approach for evaluating the consolidation behavior of coarse grained clayey soils, by providing closer values.

In this study performance of evolutionary optimization methods for designing of cross section of heterogeneous earth dams is investigated. The methods applied were Artifical Fish Swarm (AFSA), Shuffled Complex Evolution (SCE) and Simulated Annealing (SA) algorithms. The model consisted of a nonlinear optimization function by applying different constraints such as slope stability constraints and geometrical dimensions. Design variables in optimization process were the geometrical parameters in cross section of earthen dam and stability safety factors constraints were determined as explicit functions according to design variables by using analyses results such as seepage and slopes stability analysis for a set of sample designs by using linear regression models. Efficiency of the optimization methods in identifying the global optimum point was compared according to mean performance and mean time required for calculations. After optimization of dimensions in Barzok dam by using SCE, AFSA and SA methods, dam volume was reduced 38, 37 and 30 percent respectively as compared to the primary design volume. Results showed that SCE method is more efficient than the SA and AFSA methods in achieving the optimal dimensions in cross section of earth dam.

The statistics of bridge failures by US Federal Highway Administration show that the local scour around the bridge abutment is main reason compared to the local scour of piers. Various methods have been suggested for the control and reduction of local scour around the bridge piers and abutment. Using submerged vanes is one of these methods. In this study, the effect of submerged vanes to reduce the local scour around the bridge abutments with rounded nose was studied. Experiments conducted in a compound channel with non-cohesive sediments with diameter (d50) of 1 mm. Experiments carried out in two stages: in first stage without using submerged vanes and at the second stage with the presence of submerged vanes. Two rows of submerged vanes with length of 10 cm, height of 3.33 cm (L/H =3) and with angle of 20° was used. The results showed that the geometric properties of the scour hole in the nose of abutment was similar to the results obtained by other researchers. Results also showed that at all flow conditions submerged vanes reduced the scour hole around the bridge abutment and they moved the scour hole from the near of the abutment to the center of channel. Also the results showed that using submerged vanes averagely reduced 60.1% of the maximum scour depth. Finally the best layout of submerge vanes which had a distance of 5 and 15 cm between first and second rows with abutment, reduced the maximum scour depth by 71.74 percent.

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.

Variable water requirement in growing season, altitude difference in hydrant points, incompatibility in irrigation hours, cropping pattern alternation as well as other environmental factors are conducive to dynamical factors to influence the operation of pumping stations. Thus, pumping stations have dynamic or time-dependent operation. In this study, we examined operation of variable speed pumps in an olive plantation of 85 ha in Ashrafiyeh agro-industry complex located in Qazvin province, considering various utilizing condition. In this regard, the dynamic model of the pumping station is developed and presented using MATLAB/SIMULINK software. The results inferred from five operation scenario's simulations represent 18 percent reduction in energy consumption of controlled pumping station with variable speed mode compared to constant speed mode operation. Moreover, the analysis of the results from hydraulic sensitivity index in variable speed pumps indicated that the highest amount of model sensitivity to pressure difference occurs during utilization time.