ارزیابی عملکرد سناریوهای مختلف مدیریت توزیع آب در شبکه های‌ آبیاری و زهکشی

Background and Objectives
Population growth, increasing competition in various sectors of water consumption (industry, drinking, and agriculture), and limited water resources require the need for proper management and optimal use of water resources. Irrigation and drainage networks play an important role in the economic development of the region and the main factors of their structure change during the operation period. So that a single management program over time, can not meet the needs of the operation and this issue, reduces the efficiency of networks compared to the expected performance at the time of design. Poor performance of irrigation networks and their effect on reducing water productivity in the agricultural sector has necessitated the need to provide effective methods for the proper operation of irrigation networks. What has not regained its proper importance and status is the operation of networks in a scientific manner and under the principles of the original plan and to increase the productivity of the water consumption unit. Low irrigation efficiency reducing the useful life of irrigation facilities, increasing the costs of managing the operation and maintenance of irrigation networks, and increasing the government's financial losses are among the common problems of irrigation networks in Iran. Conventional design and operation of irrigation networks due to the lack of tools to comply with the rules of operation with the changing needs of water time, causes significant losses in the networks.
For this reason, the present study was conducted to examine and determine appropriate options for managing the delivery and distribution of water in terms of space in the network.
Methodology
In this regard, part of the irrigation and drainage network of Gavoshan, in the south of Kurdistan province was considered. The main channel of the network covers 2854 ha of downstream lands, which includes 9 rural cooperatives. A total of 14 intakes ranges were considered along the route, including 2 inverted siphons at the beginning of the network, 13 duckbill weir, and 23 intakes (18 farm intakes and 5 main and grade 2 intakes). 4 different operation periods were considered. 4 operation scenarios were studied based on the evaluation indices of distribution adequacy, efficiency, and reliability. To perform simulations and evaluate the performance of the main network from the perspective of operation in this study, the hydrodynamic model SOBEK, Ver. 2.12.002 was used.
Findings
According to the results obtained from the studied indicators for the S1 operation scenario (designed based on discharge at peak consumption), the average values of the adequacy, efficiency, and reliability indices were obtained 0.80, 0.96, and 0.24, respectively. in the second scenario, the average adequacy, efficiency, and reliability indicators were 0.71, 0.84, and 0.34, respectively. Accordingly, it can be concluded that for the S2 operation scenario, the distribution efficiency index for the main network was moderate and the distribution of water throughout the network based on the above index was relatively acceptable. However, the performance of the main network in water distribution based on adequacy and reliability indicators has been very poor and unfavorable, so that most of the cooperatives in the main network, have received water unequally and unfairly. According to the obtained results for the S3 operation scenario, the average values of the total indicators of adequacy, efficiency, and reliability were estimated to be 0.62, 0.71, and 0.46, respectively. Unauthorized withdrawals along the main channel were also one of the factors aggravating the decrease in evaluation indicators in different scenarios.
Conclusion
The results showed that the technical specifications and design of the channel are closely related to the design discharge of the channel as well as the pattern of channel operation. So that during the design, the channel should be designed based on the design discharge of the entrance to the channel, as well as the operating pattern appropriate to it. In this case, the evaluation indicators used were favorable. However, in the current conditions of the network, the technical specifications of which have not been completed and the pattern of operation and discharge of the channel do not comply with it, the lowest values were obtained for the evaluation indicators. Therefore, to improve the quality of water distribution in the network and increase the operation indicators, the technical specifications of the network should be completed and water intake should not be taken in its current form.
In the current operation of the network, in addition to the problem of how to draw water from the canal and also the inflow of much less than the discharge of the channel design, unauthorized withdrawals from the canal have caused several problems of operation. In such a way that it has a direct effect on each operation indicators and minimizes them. Therefore, stopping unauthorized withdrawals from the channel in order to improve the quality of water distribution in the network is essential. It is also very important and necessary to create a mechanism to control the discharge of cooperatives located in the upstream part of the network in order to increase the indicators of adequacy and justice in the whole network.