Design of Automatic Control System to Equitable Water Distribution under Water Shortages and Inflow Fluctuation Operational Conditions, Case study of Roodasht Irrigation district

Unconventional operational conditions within main irrigation canals, due to intensifying following drought conditions, has resulted to poor performances of the irrigation districts in water distribution between the water holders from the equity perspectives. Accordingly have convinced the managers to employ the modern operational strategies. However, hiring these smart operational strategy need automatic control systems and getting the advantages of the approach is quite impossible by using the conventional operational methods. An automatic control system, using Model Predictive Control, is designed and tested in the present study. Also, simulation of the hydraulic conditions of the irrigation canal is accomplished by a simplified mathematical model of Integrator-Delay (ID) model in Matlab. Moreover, the operational strategy of different error gets employed by the MPC controller by defining a new state variable of the “Difference Error”. The Roodasht main irrigation canal is selected as the case study of the research, due to special hydraulic conditions of this canal, including consequent water shortages periods as well as inflow fluctuation at the canal head-gate. Accordingly, a wide range of operational scenarios is chosen based on the practical operational information. Then, the performance of the designed MPC controller with and without employing the operational strategy is evaluated by the equity indicator within the operational conditions. The obtained results indicate that execution of the MPC controller is reasonable enough to handle both of the regular and severe inflow fluctuations. The equity performance indicator shows that MPC controller distributes irrigation water almost equitably under the frequent and severe inflow fluctuations so that the corresponding values obtained 1.21 and 4.33 percent respectively. However, the results reveal that equitable water distribution has not achieved when water shortages scenario has appeared. During the water shortages, MPC could not be able to meet the equity objective. So, the water level difference operational strategy is required to be employed by the MPC controller. According to the results, significant improvement equal to 13 and 17 percent has been achieved in equity index after upgrading the MPC controller with the strategy. This study reveals the necessity of employing the operational strategy to improve the performance of the controller within the severe operational conditions. The main advantages upon upgrading the control systems with the operational policy, including the procedure used in this study, has not imposed and extra charges to the control system. Therefore, getting the advantages of the strategies is highly suggested to implement reasonable performances of the system. The developed plan for this study is recommended for the operation of those irrigation districts suffering from water scarcity. The strategy is capable of reasonably water distribution in a systematic manner between the off-takes locating along the canal.