Irrigation and Drainage Structures Engineering Research
Year:2019 | Volume:20 | Issue:76|Papers Count:8

In order to decrease the amount of sediment entering intakes, skimming wall could be used as control structure. Skimming wall changes the flow pattern and consequently changes the volume of sediment. In intakes, the average of the flow lines angles that enter the intake increases from the floor to the surface. The main propose of this research was to evaluate the effects of skimming wall and spur dike in controlling the sediment entrance and to find out the changes in velocity. The velocity components were determined in two dimensions-in the direction of the channel's length and perpendicular to flow in front of the span of the intake-and the angle of entry of the flow along the span of the intake. The velocity distribution and the method of entering and transporting of sediment to the intakes in different layers were investigated by using velocity angle of the entrance of flow to the intake and the longitudinal and transverse components of the velocity, Changes of velocity in front of the intake were compared in three layers. The results showed that the velocity angle of the surface layer was higher than that of other layers, due to directing of flow through the spur, the existence of a separator wall structure and the effects on the middle and floor layers, . The spur dike caused longitudinal velocity near the bed layer increased 2. 25 times, and the transverse velocity in the surface layer increased 1. 33 times comparing to when there is no spur dike.

Sluice gates are designed and used in ogee spillways with high height (regulator dams) or low height (as sill) for better controlling the flow. In latter case, according to different combinations of weir geometry, gate opening, upstream and downstream flow depths, four different flow conditions are recognizable: (a) free uncontrolled flow, (b) submerged uncontrolled flow, (c) free controlled flow, and (d) submerged controlled flow. Determination of change threshold of these flow condition is useful for choosing the proposed discharge equations in any situation. In current research, using the experimental data gathered from two ogee spillways with different height in this program and using the data gathered from typical spillway structures in central and southern Florida water-control project, different equations for determining the change threshold and flow discharge in four different flow conditions are developed. In free uncontrolled flow condition, the proposed discharge equation has an average relative error of 1. 95% while in free and submerged controlled flow condition, the proposed discharge equations have the average relative errors of 2% and 5%, respectively. Results showed that the change threshold of uncontrolled flow into controlled flow occurs when upstream flow depth increases about 1. 46 times the gate opening. Furthermore, the relative submergence threshold and flow discharge increase by increasing the downstream flow depth and decreasing the upstream flow depth.

Different studies show that the performances of many irrigation and drainage networks are less than what expected due to design and implementation defects and lack of proper management. On the other hand, the existence of several effective factors in the performances of these networks has made their evaluation as a complicated issue. Data Envelopment Analysis (DEA) is one of the most effective methods to evaluate efficiency. Of course, the precise and accuracy assumption of the data has restricted the use of this model. Therefore, in this study, Data Envelopment Analysis with conservative control parameters (RDEA) were used to determine the technical, scale, and pure technical efficiency of 4 irrigation and drainage networks of Great Karun with considering the uncertainty problem in the data. The results showed that at the level of 50% probability of deviation, Gotvand and Northwest Ahwaz irrigation and drainage network with the mean score of 1 and 0. 52 have the highest and lowest efficiency, respectively. Investigating the causes of inefficiencies in the networks showed that personnel costs and maintenance cost had the highest impact on this way, so that the difference between actual use and the optimal level of these two inputs are 48% and 41% respectively. Finally, to validate decision makers in using the results, validation of the method was performed by Monte Carlo simulation. The results of this simulation indicated the ability of the RDEA model against uncertain data.

Rivers during floods carry branches, leaves and trunks of trees that their accumulation in front of bridges, change the flow pattern and accelerate the scouring process around bridge piers by blocking the entire or part of the bridge span. In this case, intensification in scour depth and development of scour hole beneath lead collapsing the bridges with shallow foundation. In this paper, the effects of debris dimensions, pile cape thickness and installation levels, array and diameter piles on the maximum scour depth around inclined bridge pier groups were investigated experimentally. The bridge pier, consisting of two rectangular piers were used with 2. 5 and 3. 5 cm dimensions mounting at an angle of 28 degrees on a pile cap with 10 cm width, 16 cm length, 3 and 5cm thickness which placed on an array of 2×2 and 2×3 piles with different diameters. The experiments were performed for relative flow depth (y/D) 6. 42, 7. 85, relative pile cap levels (Z/Tpc) 0, 1, 1. 5, relative debris width and 2. 85 and length 2, the relative thickness 0. 85 and 1. 42, in clear water condition. Comparison of results proved that the increasing flow depth had no significant effect on maximum scour depth. Results also showed that in presence of the debris for pile cap relative level Z/Tpc=0, the maximum scour depth increased about 8. 5%, comparing with no debris. For pile cap relative level Z/Tpc=1, presence of the debris increased the maximum scour depth up to 4. 5% compared to no debris. By increasing the pile cap relative level to 1. 5, presence of the debris caused an increase in the maximum scour depth about 4%, comparing with no debris.

The precise prediction of shear stress in open channel is important in many engineering issues such as designing of sustainable channels, calculation of energy losses, and sedimentation in channels. In flood duration, due to difference in depth of flow between the main channel and the flood plains surrounding the flow, the flow velocity is also different, and subsequently the stress and distribution of stress significantly changes. In this paper, it has been shown the performance of the Ansys Fluent three-dimensional numerical model in simulating various hydraulic parameters for a rectangular compound channel with smooth and rough bed and wall. Comparison of shear stress values showed that with decreasing depth in flood plains, the amount and percentage of shear stress in flood walls, and in main channel increased and decreased respectively, and also it was shown that with increasing roughness, shear stress increased. Results also indicated that with increasing flow rate, the power flow increased and velocity and vortices were formed at the intersection of flood plains and main channels. The results of this research can play a role in designing of sustainable channels, especially at the intersection of the main channel and flood walls.

Water after passing over weirs or through gates often has a lot of energy. If the water enters to the river with the same energy, it will damage downstream structures. Creation hydraulic jump is one of the approaches to reduce this energy. Therefore, it is important to study hydraulic jump. In this study, the characteristics of hydraulic jump on bed with vertical trapezoidal roughness with heights of 0. 5, 1 and 2 cm and bed slope of 0,-1. 5 and-3% were investigated. Based on the results, sequent depth ratio, in Froude number range of 4-9, was decreased by 18. 8% more than the classic jump. The energy loss was increased by 9. 6% compared to the classic jump. The maximum decrease in sequence depth was related to roughness with 2 cm height and bed slope of-3%. Moreover, the rough bed with adverse slope affected the jump length and caused to decrease it compared to the classic jump.

Estimating water surface profile would be important if it happens simultaneously with surface recharging (eg. precipitation). Surface recharging can fluctuate the subsurface water profile, so that designers cannot predict the water profile. This condition will be worsened when the media consists of coarse alluvial and highly permeable texture and the flow regime is Non-Darcy. For this reasons, it is necessary to determine accurate seepage profile through the media and consider the technical problems to avoid financial and human risks. In this regard, subsurface profiles through coarse porous media was investigated by presenting analytical solution considering recharge and Non-Darcy assumption and full-developed turbulent flow. In this study, we used the data resulted from a laboratory model (5*0. 6*1 m with 0. 0135 slope) and different upstream and downstream level affected by surface recharge for modelling. Results showed acceptable accuracy when analytical results were compared with available analytical solutions of other researcher.

This study was carried out in 2012 to determine the total irrigation efficiency and real hydro module of Nazlouchai plain in Urmia, using water balance method. In addition to field experiments, we used data gathered from previous documents and related analytical conclusions. Field experiments conducted in 14 farmer’ s fields. The result showed that water application efficiency varied from 55. 4 to 78. 8%. Water distribution efficiency varied from 75 to 94% and water conveyance efficiency was 66 to 92%. Total efficiency of traditional network estimated 44% and net water requirement of cropping pattern of the plain based on Penman-Monteith method calculated about 4930 m^3/ha, thus gross water requirement of cropping pattern was 11204 m^3/ha. The traditional irrigation network of Nazlouchai plain, with 29050 hectares of land, is located in the lower part of Nazlouchai basin. Annual water withdrawal from Nazlouchai river estimated about 128 Mm^3 and differential of input – output of the plain groundwater estimated about 13 Mm^3 annually. Water balance of Nazlouchai plain was negative with 29 Mm^3/year shortage. Estimation reveald that water consumption of Nazlouchai plain was 170 Mm^3 and irrigation actual hydro module of the plain 5838 m^3/yr/ha. The results showed that water efficiency of Nazlouchai plain in agricultural activities was about 85%. The results of this study showed that the actual rate of agricultural water consumption was lower than what was declared, based on national efficiency; the figures announced for water productivity in agricultural production should be reviewed too.