Irrigation and Drainage Structures Engineering Research
Year:2018 | Volume:19 | Issue:72|Papers Count:10

Analysis of flow passing through earth dam as an important problem is included in analysis and design of earth dams. In this research by using a numerical method based on finite difference; called extended pressure, location of the first seepage stream in earth dam as well as developed pore pressure in the dam body was investigated. In order to assess the accuracy of the applied method, results with analytical solution in one dimensional condition and in case of two dimensional conditions. The numerical results were compared with results obtained from earlier experimental data and other methods. Furthermore, the results obtained were compared with results of SEEP/W as popular software in seepage analysis. The results of this investigation confirmed that the presented method estimates the location of phreatic line and pore pressure distribution very well in earthen dam. Finally, a dimensionless parameter was presented for determination of exact height of water table.

In this research the effect of floating debris accumulation in the debris flow at the weir entrance on hydraulic coefficients of crown wheel weir is discussed. For this purpose, an effort was made to create different amount of blocking at the opening of crown wheel weir, by using experimental setups and by use of woods with various slenderness coefficients. In order to study the effect of weir opening shape on the Hydraulic Profile, several conditions were created by changing the gradient keys (z) and number of cycles (n) of crown wheel. Regardless of the shape of inlet to intake, results showed that increasing the slenderness coefficient decreases the possibility of blocking in overflow openings and consequently, reduces the upstream head water and increases the coefficient of dischargespill flow. In oter words by changing the slenderness coefficient from 15 to 20 and 25 respectively, the discharge flow on an average increased from 8. 02 to 14. 44 percent. . Moreover, the key slope (z) and cycle numbers (n) of crown wheel weir, affected the amount of blocking and consequently characteristics of hydraulic flow such that the best performance belonged to key slope of equivalent to1. 5 which was observed in weirs with 8, 6, 4 and 2 number of cycles, respectively.

The river is an active natural phenomenon, which continuously changes its sides and its bed. This has caused the river course to undergo major changes over time. There are different ways to reduce erosion, one of the ways is using spur dike in sides. In this experimental study, the effect of simple L and T shapes series spur dike on time variation of scour depth around spur dike was analyzed and compared under straight channel condition. The results showed that T shape spur dike within 10% of elapsed time reaches to more than 90% of equilibrium scouring, whereas for simple and L shape spur dike within 15% of elapsed time reaches to more than 80% of equilibrium scouring or erosion. Simple and L shape spur dike had the maximum scouring depth which was found to be equivalent to 3times of the flow depth, which was created a bit behind the spur dike's nose. The scouring of T shaped spur dike was 0. 3y (y is flow depth) less than other shapes in first position. The results of scour depth comparison in different section around the spur dikes showed that the average of scouring value for T-shaped spur dike was 0. 4y and 0. 25y less than simple and L-shaped spur dike, respectively. Finally, an equation for calculation of time variation of scour depth due to the shape of the spur dike is proposed. Further, the experimental results of scouring depth as a result of present study was compared with results obtained by other researchers. Also maximum side erosion on the opposite shore was found to belong to L-shaped spur dike.

In river conservation practices, maintenance of a river bed level especially at under situations where the slopes of bed increases due to different reasons such as sand mining is very important. The inclined grade control structure is one of eco-friendly structures that is applied in order to stabilize rivers beds and banks. One of the important parameters for design of such structures, is estimation of a local scour depth around downstream of the structures. In present study, the effect of different hydraulic and geometric parameters on the maximum scour depth at the downstream of inclined grade control structure was experimentally investigated. Experiments were conducted for slopes of 14 to 33%, unit discharges of 28. 4-45. 5, tail water depths of 3. 5-6 yc and roughness sizes of 4 to 10 mm. Comparison of results of the maximum scour depth for the grade control structure with slope of 33% showed that the tail water depth had direct effect on the scour depth increased from 4. 5 to 6 yc, and the maximum scour depth increased by 13 percent. By decreasing the installation bed level to 20 and 14, increasing the tail water had inverse effect on the maximum scour depth in such a way that by increase of the tail water depth from 3. 5 to 4. 5 yc, average reduction of the maximum scour depth was found to be 9 and 25 percent for slopes of 20 and 14 percent, respectively. Comparison of the results indicated that increasing the roughness of bed caused decrease in the maximum scour depth from 5 to 21 percent within the range of the minimum and maximum roughness.

In recent decades, Meta-heuristic algorithms has played an effective role in solving different engineering problems such as optimal operation of reservoirs. Owing to the complexity of water resources management problems, as well as, the daily growing need for the development and expansion of these methods, in this research, a model based on Symbiotic Organisms Search (SOS) algorithm was developed for modeling the optimal operation of complex multi-reservoirs systems. In the first step, the performance of the method was successfully assessed through several benchmark functions. Then it was used for the monthly operation of Tangemashure, Sazbon and Karkheh reservoirs located in Karkheh basin. The optimal allocation were considered for meeting the irrigation demands of 4 agricultural regions, and priority was with allocation of water for the environmental demands., for a 5 year period (from 1980-81 to 1984-85). The results of SOS algorithm were compared with other developed evolutionary algorithms including Genetic Algorithm (GA) and Particle Swarm Optimization (PSO). The results indicated that, optimized operation policy through SOS algorithm with the sustainability index of 99. 99, 99. 11, 82. 92 and 79. 47 percent for Sazbon, Tangemashure, upstream and downstream of Karkheh reservoirs was more appropriate performance as compared to GA and PSO algorithms in optimal operation of multi-reservoirs systems.

In this research, distribution of flow in irrigation networks with the aim of optimizing the covered distance to open and close the gates for irrigation, as well as the regulation number of control gates inside distributor channel was investigated. In order to simulate the flow distribution, flow function model was used because it simulates the flow distribution by considering the existing restrictions in irrigation networks such as canal flow capacity and the operation time, there is possibility to provide optimized irrigation planning. The optimization was carried out using Genetic Algorithm and in order to verify the performance of the provided model, the flow distribution in AMX canal of Varamin Irrigation Network was simulated and the optimized value of the relevant parameters was determined. According to the results obtained from the model, it was found that to achieve optimized irrigation planning, the number of regulation gates in distributer canal could be reduced to 7, while the covered distance for opening and closing the gates, the discharge of main canal, and the operation time of the canal should be 37526 m, 1244 litre per second, and 216 respectively. Comparing the results with those provided from previous researches showed that the model presented in this research can be used as a powerful tool for modelling some functions of the flow distribution in irrigation networks.

By entery of pollutants into the canals and rivers along a certain distance (Mixing length), the pollution due to factors such as the molecular motion, turbulence and vertical distribution of flow velocity are distributed throughout all the cross sections. There are several techniques to achieve this goals including increasing cross-mixing. In this study, the application of submerged vanes mounted on the bed of the channel at a certain angle for the purpose of increasing the transverse mixing in a straight rectangular flume was investigated. The experiments are conducted for four different flow conditions including with and without structure. Salt solution as a tracer, was entered to the center of the flume with constant flow rate. The concentration of tracer in four stations downstream of tracker, were measured with EC meter. The results showed that the mounted submerged vanes caused an increase in transverse mixing coefficient of about 1. 5 to 1. 7 times as compared with the case of no vane. Also, it was found that increasing the rate of flow discharge in case of no vane caused an increase in the transverse mixing coefficient of about 2. 4 times. Similarly, an increase in the rate of flow discharge with structure caused the increase in the transverse mixing coefficients of about 2. 5 times. Generally, the results showed that submerged vanes were very effective on Transverse mixing coefficients.

Hydraulic sensitivity analysis is considered as a new approach for flow behavior investigation in irrigation networks during the last decade. Operation methods along irrigation canals can be investigated using sensitivity indicators. In this study, operation methods along BLMC canal which irrigated the B3 and B4 development regions of Bilavar irrigation network in Kermanshah province was studied. According to the water irrigation scheduling in the previous years, the maximum and minimum discharge of the canal were 1. 18 and 2. 11 cubic meter/sec respectively. In this research, two scenarios were considered for operation of Bilavar irrigation network. In the first scenario, the delivered flow to the fieldswas controlled by neyrpic orifice module, and in the second scenario, control of the flow was done through valve on the pumps. In the first scenario, most off take’ s sensitivity index for the maximum discharge operation condition at the beginning and end of the canal were negative and positive, respectively. Hence, once the flow of the BLMC channel increased, the discharge delivered to off takes at the beginning of the cannal decreased due to the negative sensitivity indicators. In the second scenario, the discharge sensitivity indicator base on pressure for pumping stations was developed, and the amount of acceptable pressure variations was calculated considering the permissible variations in discharge for each station. In this study, considering a variation of 20% in flow rate entering the B4 region as hydraulic perturbation, the sensitivity indicator for conveyance was calculated and results were compared with the results of HEC-RAS model. The average percentage error for calculating conveyance of perturbation based on sensitivity analysis method was found to be 3. 42%.

Piano key weir has a higher effective length in comparison with other weir types. Piano key weir Lateral weirs can be employed in irrigation and drainage networks, flood control systems and water & waste-water systems instead of common side weirs. Keeping in view that discharge coefficient evaluation of the weirs is mandatory in channels having longitudinal curvatures, in this investigation; discharge coefficient of a Type-C piano key weir was studied in 30-degree sector of a channel having longitudinal curvature. During course of investigating 12 piano key weirs were investigated by performing 133 experiments on discharge flow. Influential parameters were defined using dimensional analysis and then their impact was analyzed. An experimental equation was developed for discharge coefficient calculation in the conditions under consideration. The accuracy of the equation was acceptable by having a correlation coefficient of 0. 916 and mean absolute error of 0. 089. Therefore, it can be suggested that the equation can be used for discharge coefficient estimation in design of piano key side weir.

Irrigation canals, as one of the most important structures of irrigation networks, have a significant role in reducing seepage losses and increasing the water conveyance efficiency. This research was conducted from 2016 to 2018 in irrigation networks of Khuzestan province. In this research, in order to determine the distribution efficiency, the input-output flow method was used with the use of a propeller velocity meter. To have a rational comparison between canals with different dimensions and capacities, the ratio of losses to inlet discharge per kilometer of canal reach has been considered as an evaluating parameter. In total, 26 concrete trapezoidal canal reaches and 17 semi-elliptical prefabricated channel reaches have been studied. The studied canal reaches were located in Omidieh, Andimeshk, Gotvand, Behbahan, Hamidieh, Dezful, Shoosh, Shooshtar, Ramshir, Ahvaz, Bavi and Shadegan, counties of Khuzestan province. Results showed that distribution network efficiency changes from 38. 9% to 99. 7% for both canals and semi-elliptical channels. The seepage losses per kilometer of canal length varied from 20. 92 to 12454. 10 m3/day. Maximum and minimum values of seepage losses relative to inlet discharge for concrete trapezoidal reaches were 0. 35% and 61. 76%, respectively. In prefabricated channels, the average length of studied reaches, conveyance efficiency and seepage losses per kilometer of channel were 978 m, 84. 3%, 2133. 11 m3/day and 17. 18%, respectively. Using t-test method for concrete trapezoidal canals and semi-elliptical channels showed that the amount of seepage losses per kilometer of canal length in a trapezoidal concrete channel with a value of 1920. 05 m3/day has no significant differences compared to prefabricated channel with a value of 2133. 11 m3/day. The calculation of Pearson correlation coefficients showed that any increase or decrease in the parameters of the discharge and velocity, as well as the amount of time interval, does not lead to significant changes in the process of conveyance efficiency.