Irrigation and Drainage Structures Engineering Research
Year:2017 | Volume:17 | Issue:67|Papers Count:10

Proper operation of irrigation networks because of population growth and limited water resources is essential. The poor operational performance of irrigation systems is partly as a result of improper distribution of water to the tertiary units and branches. In this study, the genetic algorithm has used in order to determine the optimal schedule of water distribution in BLMC channel of Bilavar network, located in Kermanshah Province. The optimal schedule of water distribution was presented in the form of single purpose, including minimizing the difference between the delivery and required amount of water for each farm. Initially, the genetic algorithm parameters and operators impact on the objective function were studied using sensitivity analysis.Suitable values for number of generations, population size, crossover and mutation probability for optimizing water distribution was determined to be 250, 200, 90% and 1%, respectively. In case of every 24 hours on and off water pump, differences between delivered and needed volume of water for all farms in Bilavar network, during first 10 days of April and first week of May, were 28910 and 14130 cubic meters, respectively. In this study, some hydraulic performance indices for irrigation programs presented by operator and program prepared by genetic algorithm were calculated. Adequacy, efficiency and Equity Index in the entire network for irrigation programs offered by the operator company were 0.97, 0.76 and 0.076 and for program prepared by the genetic algorithm, 0.985, 0.99 and 0.01 respectively. Result indicate that the program prepared by the genetic algorithm has better hydraulic performance parameters.

One of the main reasons of destruction of the coastal slopes and riverbanks is failure of side slopes under the rising water table or sliding of the side slopes under the drawdown of channel water. In this research, effect of variations of water table and channel water level (peak and drawdown conditions of flood, respectively) on the piping of coastal slopes was studied and effect of cutoff wall on the phenomenon was investigated. Experiments were conducted in a seepage tank having a trapezoidal cross-section with the side slope of 1.5% and 0.58 mm mean diameter of the particles. Cutoff wall was fixed in the relative depths Z/d=0.5, 0.67, 0.83 and 1 (Z is the depth of cutoff wall and d is the depth of channel). Results of peak conditions of flood (rising the water table), under controled experiment showed the relative channel water level was equal to y/d=0.7. In the experiment with cutoff wall Z/d=1 and without occurrance of piping, exit flow gradient was decreased approximately 41 present with respect to the control experiment. Piping was occurred only in the relative channel water level equal to y/d=0.167. Results of drawdown conditions of flood showed, piping phenomenon occured in the all channel water level. In the experiments with cutoff wall, in the cases with high water table, despite of existence of cutoff wall, increasing the exit flow gradient caused piping phenomenon in the all of the experiments because of increasing hydraulic head. Other wise, in the experiment with the relative water table equal to h/d=0.933, piping was occurred in the all depths of cutoff.

Sharp crested weirs and sluice gates, because of their ease of making, water surface control potential and flow rate capabilities measuring have been broadly studied. Since the nature of flow on the weirs is highly complicated, mostly the driven equations are taken in to account a series of simplified hypothesis that are bases of empirical experiments. On the other hand most of the weirs cause a relatively calm zone of water on their upstream, which is a place of waste material and sediments to precipitate that is the disadvantage of the device. With gradual storage of sediments, the condition of flow changed and driven equations will lose their precision. In this case composition of weir and gate can be a useful solution for passage of floating materials over the weir and transmission of sediment materials from the lower part of the gate. In this study, hydraulic characteristics of the 18 combined model of trapezoidal weir-gate in the tree groups with three different opening gates at the end of an open channel with a circular cross section were studied. Using dimensional analysis, analytical solutions and statistical analysis, an equation for combined discharge by combined model of weir-gate was introduced and was evaluated by experimental data. The Results showed that the obtained discharge coefficient have a good agreement with experimental data.

The energy dissipation through hydraulic structure is an important issue in hydraulic engineering.The performance of hydraulic structure with regard to energy dissipation can provide stability of structure and river bed. In this study the laboratory investigation on screen performance as the energy dissipator of supercritical flow is evaluated. The investigated parameters include: Froude number; screen porosity and location of screens. The Froude number of supercritical flow could vary within the range of 2.5 to 8.5, and the screen openings were 40 and 50%. Also the location of screens was considered as 62.5, 125 and 250 cm after supercritical flow generator gate. The results indicate that screen openings, location of screens from supercritical flow generator gate and also Froude number of supercritical flow have a significant effect on screen performance.The energy dissipation of system through screens was more than free hydraulic jump in the entire evaluated cases. The results also showed that the increasing Froude number results in screen performance (relative energy dissipation) increase, but screen efficiency (difference between the relative energy dissipation of system from free hydraulic jump) decrease. Also the screen with 50 openings which was been located at 125 cm from gate had the best performance.

Labyrinth weirs are often a favorable design option to regulate water surface elevation in upstream canal and increase flow capacity. Due to their hydraulic performance and geometric versatility, labyrinth weirs have been used extensively in canals, rivers, ponds, and reservoirs as energy dissipaters, flow aerators, and spillways. Nevertheless, it can be difficult for engineer to optimally design, labyrinth weirs due to the complexities of nappe behavior and many geometric and hydraulic variables. A level of sedimentation in upstream and submergence in downstream of the weirs are effective parameters which affects the discharge coefficient, and the performance of these structures. In this investigation effects of 408 tests of different levels of tail water (increase of downstream canal bed level to one third and two third of weir height) and upstream sedimentation level (non-sedimentation and sedimentation level of 90 percent of weir height) on the discharge coefficient of different geometers of trapezoidal labyrinth weirs was investigated experimentally. The analysis of results indicated that increase of tail water level to one third of weir height didn’taffect on the discharge coefficient of weirs. By increasing tail water depth to two third of weir height, air cavity volume under nappe decreased. Therefore, the flow pattern of the nappe changed from leaping to clinging condition and upstream head decreased. As a result, the labyrinth weirs discharge coefficient in non-sedimentation and sedimentation level of 90 percent of weir height increased about 3.3 to 12.2 and 2.1 to 9.2 in comparison with non submergence tail water for maximum discharge respectively. Finally, the statistical equation for estimation of the discharge coefficient of trapezoidal labyrinth weirs for upstream sedimentation and submerged conditions was developed.

Consolidation and stability of soil is influenced by the presence of minerals in the soil and it is especially related to its moisture which is prevalent difficulty in the construction of irrigation and drainage networks. In this research, the effect of natural gypsum on the physical properties of silty soil and its settlement was studied. In order to achieve answers which comply with the conditions of operation, samples were collected from the construction site, containing natural gypsum in soil. Samples were selected, based on a weighted combination of soil and natural gypsum, with percentages of 1%, 4%, 10% and 15% and by conducting standard chemical tests to determine the percentage of gypsum and some general properties of soil were determined. In order to assess the rate of dissolution, consolidation test was also conducted and in this process EC was measured for a month in outlet water samples extracting from the process of replacing distilled water, in a one-day period and under the stresses of 0.25, 0.5, 1, 2, 4 and 8 kg/cm2 in the consolidation device. The results showed that by increasing the amount of gypsum, plasticity index and dry density of soil samples have decreased, but permeability and settlement rates was increased. Since in the calculation of settlement of gypsum-containing soils, parameters such as volumetric compression ratio and stress are also effective, an emperical formula was developed for predicting relationship between consolidation pressure, percentage gypsum and consolidation coefficient.

Flood routing is one of the most complex problems that is encountered in open channel hydraulics and river engineering. Among the different flood routing methods, the Muskingum model, as the most applied hydrologic method of flood routing, has been widely used with high accuracy in river flood studies. The parameters estimation of the nonlinear Muskingum flood routing model has been considered by different researchers. In this paper, the wolf search algorithm (WSA) was used to this for assessing the optimum values of Muskingum parameters, the objective function was defined as the minimizing of the sum of square residuals between the observed and routed outflows. To investigate the suitability of research findings, the results of the WSA were compared with other heuristic algorithms including genetic algorithm (GA), particle swarm optimization (PSO), harmony search (HS), and imperialist competitive algorithm (ICA).Six benchmark functions with different dimensions were used to evaluate the capability of algorithms. The results showed that the WSA is capable of providing satisfactory estimates of nonlinear Muskingum parameters. The obtained values of R2 and RMSE were 0.99261 and 2.419886 for Kardeh river and 0.778425 and 0.712358 for Wilson river, respectively.

Due to specific climate conditions in Iran and impossibility of increasing new resources of water for agricultural sector, agricultural water management is essential for improving water productivity. Assessment of low irrigation efficiency in the Country and providing appropriate solutions to improve irrigation efficiency and water productivity at the national level can be a great help for modifying irrigation efficiency. For this purpose, available data on irrigation efficiencies in different irrigation systems and differnet irrigation networks (traditional and modern) were analyzed. Analysis was based on results obtained from about 200 field scale studies including 1900 measured irrigation events across Iran from 1991 to 2015. The finding showed that application irrigation efficiency (Ea) ranged between 22.5 and 85.5% having meant of 56%. The averages of Ea in the basin, border and furrow irrigation systems were 55.3, 52.9 and 52.5%, respectively. Although, Ea in sprinkler irrigation systems for example wheelmove and solid set systems were 66.9 and 52.1%, respectively. Average of Ea in pressurized and surface irrigation systems were 66.6 and 53.6%, respectively. As well as, Ea in sprinkler and drip irrigation systems were 62.1 and 71.1%, in order. Results also indicated that Ea over three decades (1992-2001, 2002-2011, and 2012-2015) were 52, 58.4, and 58.8%, respectively.However, network irrigation efficiency for three decades was in order of 67, 68.5 and 74.2%. As a result, total irrigation efficincey (Ep) was 34.8, 40 and 43.6% in these decaceds, respectively.This means that, Ep had annully increased about 1% from 1996 to 2013. An important reason for increase of irrigation efficiency over these decades are improvment of knowledge of users and beneficiars with regards to water and soil issues, improvment of new irrigation systems and extension of research findings to operators and beneficiars.

Density currents are formed when gravity acts upon a density difference between two different fluids. These currents are the most important transport mechanisms and deposition of noncohesive sediments in narrow and deep reservoirs. In this research, 63 experiments were performed to investigate the effects of two shapes and three heights of artificial roughness on sediment-laden density currents. Velocity and concentration profiles were measured in the body of current. Results showed that presence of roughness causes 47% increasing in the density current body thickness, 29% decreasing in the maximum value of velocity and 163% increasing in the distance of peak value of velocity point from the bed in the normal velocity profile. Also for different roughness and with special hydraulic conditions, Lifting phenomenon has been observed, which is affected by densimetric Froude number, relative roughness and blockage factors. This phenomenon effects on the velocity and causes 5-25% increasing in the maximum value of velocity the stream line of current. Sedimentation rate in the current over rough bed is approximately 223% more than smooth bed if lifting phenomenon has not be occurred.

A major problem with which most of the lateral intakes, is accumulation and sediments entering the intake entrance and as a result diversion efficiency is reduced. Sediment control is one of the most important issues in river engineering. To reduce sediment entering the intake entrance several methods of controlling the sediment entering to the intake entrance and the exit of sediments from sediment out let is used. In this study effect of the location, and angle of the spur dike by using skimming wall on the amount of delivered sediment into the lateral intake and intake ratio were tested. Effects of angle variations (30, 45, 60, 90) of spur dike and spur dike location (b, 2b, 2.5b, 3b) on intake ratio and delivered sediment into the intake were investigated (b is the intake width). Results showed that discharge of 60 lit/s, and spur dike with 60 degree angle and 2b distance from the center intake entrance in combination with the skimming wall compared to an angle of 30, 45 and 90 degrees, respectively caused 27, 14 and 12 percent less sediment and 53, 45 and 16 percent superior discharge into the intake divertions. Also by increasing the value of parameter of the ratio of distance of spur dike, to the width of intake, the ratio of flow deviation to the intake for angle of 30°, 45°, 60° and 90°, and u/uc=1.05 was 5, 13, 2 and 23% respectively, and for ratio of u/uc=1.08 was 2, 3, 3 and 2% respectively, and for u/uc=1.11 was 17, 24, 2 and 10 percent increase respectively.