maryam mohammadi; farzad hassanpour; Majid azizpour pirsaraie
Abstract
Introduction: Poor performance of irrigation and drainage networks causes to reduce the transfer and distribution throughputs and in result comes useless water and makes too much consumption in forming. A significant portion of water losses in irrigation and drainage networksis related to transmission ...
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Introduction: Poor performance of irrigation and drainage networks causes to reduce the transfer and distribution throughputs and in result comes useless water and makes too much consumption in forming. A significant portion of water losses in irrigation and drainage networksis related to transmission and distribution. Therefor more consideration in thrirrigation network management, improve irrigation efficiency and also the exploitation of water resources, especially in the agricultural sector is necessary. Controlling and adjusting structures of water level in the direction of drainage and irrigation canals can influence on increasing of throughput and decrease the use of water. So, right choosing and recognition of the deficiencies of these structures helps carry up the throughput of the networks and prevents to waste water. It is hard to solve equations of water flow in canals and related institutions by using analytic methods. For this reason, this research was done with HEC-RAS hydraulical model in the main channelof irrigation and drainage network of Sistan plain.
Materials and Methods: Sistan plain is located in southeastern of Iran with good potential for agricultural production because of the alluvial sediments from Hirmand River. 23820 ha of the Sistan plain is covered by 5 blocksof the Shibab irrigation and drainage network. While Sistan’sShibab irrigation network efficiency is low, HEC-RAS Hydraulics model in unsteady condition was performed to control and adjust this network’s main canal in approximately 19 Km length. In this research, the evaluation model in the canal was performed for more suitable intakingwater in the quadruple order 2 canals . So, the existing structure’s operation was analyzed on controlling structures in management and lack of management situations.This research was assessed during a 15-day impounding period using hydraulic model of HEC-RAS with the aim of performance and operation evaluation of existing structures on the Shibab main canal. HEC-RAS model was prepared by United States army corps of engineers which is developed by the hydrologicengineering center.HEC-RAS analyzes river system and runs under the Windows operating system. This software package is of hydraulic analysis program series, where the user communicates with the system via a graphical user interface (GUI). The system is capable of performing steady and unsteady flow water surfaceprofile calculations. HEC-RAS software is designed to perform one dimensional hydraulic calculation for a full network of natural and synthetic channels. Visits were made before and after the beginning of irrigation, and during the Operation, in order to record the data of the flow and observe the way of utilization of canal, and existing structures. Then, the model was calibrated on the basis of depth and discharge measurement and simulation data in real condition of operation for 10 days impoundment during 21 to 30 April, and the Statistical parameter values:RMSE, EF, MBEand R2 were calculated. Then the objective functionwas evaluatedusingoperational performance indexes of adequacy, efficiency, equity and reliability of Molden and Gates regarding to HEC-RAS simulation results in unsteady condition.
Results and Discussion: According to the simulation results in existing condition,theerror of delivery dischargeis equal to 0.54 while applying the management onthe adjustment structure of irrigation networkdeclined theerror to 0.42. By the canal routstructuremanagement in HEC-RAS model, on the basis of proposed operation option, according to existing operation condition, delivery discharge loss in comparison to the total discharge of the network 0.12 value decreases.Based on the simulation results, the mean percentage of improvementin performance indexes of adequacy,efficiency, equity and reliability, as well as objective functionofdelivery discharge are equal to 19.7, 20.90, 66.07, 65.24and54.81. Therefore based on simulation results of different scenarios and investigation of the effective factors onto the flow, onthe forms of charts and tables show that without management on controlling structures, it isn`t possible to appropriate of flow rate onto second class canals and traditional streams branched out main canal and also streams branched out second class canals, properly.
Conclusion: The results show that the model of HEC-RAS is proper for hydraulic simulation of main canal in the irrigation and drainage network of Sistan plain. Based on the simulation results of different scenarios of this research, the mostimprovements intheobjective functionare allocated toequity and reliability indexes in the Shibab main canal with the proposed management method.
M.M. Heidari; S. Kouchakzadeh
Abstract
Introduction: Unsteady flow in irrigation systems is the result of operations in response to changes in water demand that affect the hydraulic performance networks. The increased hydraulic performance needed to recognize unsteady flow and quantify the factors affecting it. Unsteady flow in open channels ...
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Introduction: Unsteady flow in irrigation systems is the result of operations in response to changes in water demand that affect the hydraulic performance networks. The increased hydraulic performance needed to recognize unsteady flow and quantify the factors affecting it. Unsteady flow in open channels is governed by the fully dynamic Saint Venant equation, which express the principles of conservation of mass and momentum. Unsteady flow in open channels can be classified into two types: routing and operation-type problems. In the routing problems, The Saint Venant equations are solved to get the discharge and water level in the time series. Also, they are used in the operation problem to compute the inflow at the upstream section of the channel according to the prescribed downstream flow hydrographs. The Saint Venant equation has no analytical solution and in the majority cases of such methods use numerical integration of continuity and momentum equations, and are characterized by complicated numerical procedures that are not always convenient for carrying out practical engineering calculations. Therefore, approximate methods deserve attention since they would allow the solution of dynamic problems in analytical form with enough exactness. There are effective methods for automatic controller synthesis in control theory that provide the required performance optimization. It is therefore important to get simplified models of irrigation canals for control design. It would be even more interesting to have linear models that explicitly depend on physical parameters. Such models would allow one to, handle the dynamics of the system with fewer parameters, understand the impact of physical parameters on the dynamics, and facilitate the development a systematic design method. Many analytical models have been proposed in the literature, Most of them have been obtained in the frequency domain by applying Laplace transform to linearized Saint-Venant equations. The got transcendental function can then be simplified using various methods to get a model expressed as a rational function of s (the Laplace variable), possibly including a time delay. It is therefore important to develop simple analytical models able to accurately reproduce the dynamic behavior of the system in realistic conditions.
Materials and Methods: Changes in water demand can create transient flow in irrigation networks. The Saint Venant equations are the equations governing open channel flow when unsteady flow propagates. In this research, the finite volume method using the time splitting scheme was employed to develop a computer code for solving the one dimensional unsteady flow equations. Considering stationary regime and small variations around it, the Saint-Venant equations around initial condition was linearized.
The Laplace transform is applied to the linearized saint venant equations, leading to an ordinary differential equation in the space variable x and parameterized by the Laplace variable s. The integration of this equation lead to a transfer matrix, and gives the discharge Q*(x, s) at any location with respect for the upstream discharge. This matrix is coupled with the downstream boundary condition and developed an equation that solved using Simpson integration algorithm. It should be noted numerical solution of developed equation is easier than solving fully dynamic saint venant and is less sensitive to the spatial step and the researcher simply writing code.
Results and Discussion: Froud Number (F), variation of inflow discharge (ΔQ/Q), and dimensionless parameter of KF2 in which K is the kinematic flow number, are effective factors on accuracy of developed equation. In order to determine the effect of the factors on accuracy of presenting formula, several simulations were performed using numerical model. The presented formula and numerical model were compared for 10, 20 and 30 percent discharge variation and error calculated, the maximum error increases with increasing ΔQ/Q.
To assess the importance of Froud Number and KF2, also several simulations were carried out, the results showed that the maximum error in the development equation for various Froud Number and KF2>1, is less than 3.8 percent.
Conclusion: Using Laplace transform to the saint venant equations and with respect to upstream and downstream boundary a formula for routing discharge presented. Investigation of the applicability range of presenting formula and cognitive effective factors on accuracy is necessary. So, the finite volume method using the time splitting scheme was employed to develop a computer code for solving the one dimensional unsteady flow equation. Then some tests of unsteady flow were simulated and verified the equations. The results showed that the maximum error increases with decreasing KF2 and increasing the rate of sudden changes of discharge. The maximum error in the presented formula for all tests with KF2>1, less than 3.8 percent.
Ashkan Alebouyeh; Saeed Reza Khodshenas
Abstract
Flash flood is due to rapid precipitation in arid and semi-arid areas. This flood is example of unsteady flow which has hydrograph with little time duration and high discharge. Investigation behavior of these floods is very important on sediment transport and characteristics streams. In this research ...
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Flash flood is due to rapid precipitation in arid and semi-arid areas. This flood is example of unsteady flow which has hydrograph with little time duration and high discharge. Investigation behavior of these floods is very important on sediment transport and characteristics streams. In this research evaluated the effect of flash floods on bed load transported to downstream. The input hydrographs are symmetric and Asymmetric triangles. Time duration of hydrograph was selected 90 second and constant and the maximum discharge were changed 6.58 to 16.18 l/s. The median size of particles is 2.5 mm; three bed slopes 0.005, 0.01 and 0.02 were select in these experiments. The results show that a temporal lag was found between the flow hydrographs peak and the sediment hydrograph peak. The temporal lag was found to be about equal to 5 - 11% of flow hydrograph duration. Also bed slope and maximum discharge of hydrograph are effect on upstream erosion and transportation of sediment to downstream. Since increases the bed slope from 0.005 to 0.01 increased 50% bed load transported and with two times the slope it show increase 400% in bed load transported. Bed load transported to downstream with symmetric triangle hydrographs more than symmetric triangle hydrograph.
