Performance assessment of main canal of Kosar irrigation network using upstream and downstream automatic control

Poor operation and management of irrigation networks result in inadequate water delivery and distribution in canal and branch of networks. Irrigated agriculture comprehensively uses large volumes of water compared with municipalities and the other sectors, and competition for pure quality water is at any time high in many areas around the world. Thus, it is recognized that amended water management practices in agriculture can result in significant benefits in terms of water availability for expanded agricultural activities and for other usages, and can directly address many environmental problems. Sagacious management of open-canal conduction and delivery systems is necessary to arrive higher water savings in irrigated agriculture. Use of control systems in irrigation network for improving performance in water distribution and delivery to farmers is more suitable. The main objective of a flow canal control system is to optimize the water delivery based on special operational purposes related to water levels or discharges, which are subject to external disturbances. Providing adequate amounts of water is not possible for irrigation areas in arid regions because of the water scarcity. Therefore under this condition, the upstream and the downstream operational systems are not able to meet an equitable water delivery to downstream parts of irrigation networks, as well as to upstream ones. New operational scenarios should be implemented to reclaim water deliveries.
This study carried out with the aim of performance evaluation of water distribution for different water operational scenarios in the main canal of Kosar irrigation network of Khuzestan Province. The total length of the proposed canal is 20km. The canal has a design discharge capacity of 16.5 m3/s at its head. There are 8 ‘in-line’ check and 15 offtake structures, and 7 cross-structures along the length of the canal. The proposed model was calibrated and validated based on the real data for three conditions consist of the actual condition of operational network, upstream control system and downstream control system. Simulations were carried out for two operational scenarios consist of the increased and decreased demand periods. In order to control the local water level, PI-feedback controller was applied at upstream and downstream of this canal. To reduce the impacts, the pools were coupled in the upstream and downstream direction. The effects were considered by adding decouplers to the controller structure. The control actions, as output, were calculated based on the magnitude of the water level deviation which was taken as input to the controller. The calculated value was added to the upstream gate directly to make a centralized controller. In case of distant downstream feedback control, the water level at the downstream side of a pool was controlled by adjusting the gate at the upstream end of the reach, in reaction to the deviation from the setpoint. The model of the proposed canal was formulated in the SOBEK simulation package. The control system was also programmed in MATLAB. To evaluate the control system potential, simulations were done for one month of the real offtakes schedule. Also, this study presented the evaluation objectives of an irrigation system, its impact on water delivery performance by control systems to improve water management in Khuzestan province by using the performance indicators proposed by Molden and Gates. For these two periods, the mean value of delivery efficiency, adequacy, equity, and reliability performance indicators was estimated.
The results showed that, for actual condition, the equity index is greater than 0.2 and consequently, it is in poor condition. Also, adequacy and reliability indicators have had poor performance during operation period. Moreover, it is found that the control systems had better performance than operational actual condition. Also, downstream control has bather performance than upstream control. The results indicated that all indicators had better performance in increased demand period than in decreased demand period. For downstream control, distribution and delivery of water happened in shorter time and more uniform over all offtakes which was located in the main canal. For the system after improved, the using control operation for water delivery among irrigation networks was improved water delivery efficiency by improved equitable contribution among irrigation areas through irrigation periods and performed in a constant way could be considered reliable. Based on the evaluation of indicators in this study, it can be concluded that for this main irrigation network, continuous monitoring of the water management and distribution system is difficult by using manual delivery system because there are not any control points to distribute water among them.