Design of optimal environmental flow regime at downstream of multireservoir systems by a coupled SWAT-reservoir operation optimization method

The present study proposes an integrated framework to optimize environmental flow of the multireservoir systems in which a rainfall-runoff model and a novel form of the reservoir operation optimization are linked. Soil and water assessment tool was utilized as the rainfall-runoff model to forecast inflow of the reservoir. Then, outputs of the rainfall-runoff model were used in the optimization model. Ideal environmental flow regime was considered as the target of the environmental flow in the optimization model based on the outputs of the instream flow incremental methodology proposed by the previous studies in the case study. Moreover, minimum environmental flow regime in the optimization model was defined using penalty function method. Evolutionary algorithms were utilized to optimize the reservoir operation. Then, the performance of the algorithms was assessed by different measurement indices. Finally, the fuzzy technique of order preference similarity to the ideal solution was applied to select the best algorithm. Based on the results in the case study, the proposed framework is properly able to optimize environmental flow regime in the multireservoir system. Measuring the performance of the optimization system indicated that average reliability index is 70% for supplying environmental flow. Moreover, the optimization system is able to minimize storage loss and water supply loss simultaneously. The particle swarm optimization is the best algorithm to optimize environmental flow regime in the case study. Using the proposed method is recommendable to minimize negotiations between stakeholders and environmental managers that might provide a fair balance between environmental requirements and water demand.