Optimal allocation of water resources in critical conditions under the uncertainty of parameters with emphasis on maintaining the stability of water resources by the Goal Attainment method (Case study: Mashhad)

Iran's water situation has reached a critical level due to frequent droughts and over-abstraction of water resources. Therefore, dealing with the optimal allocation of water resources in these conditions is an important and vital issue. In the present study, the model of water resources allocation in critical conditions has been developed and the proposed model has been implemented in Mashhad. The innovation of the proposed model of the present study is to consider the sustainability of water resources and simultaneously pay attention to the quantity and quality of water resources. In this study, considering the stochastic value of available water parameter, two-stage stochastic allocation model is presented and solved by the method of Goal Attainment, and implemented in MATLAB software. This model has been developed with the aim of maximizing the profits of different users, minimizing the allocation of saline water from the underground source and minimizing the shortage of water. The results of the study indicate that even in the wet scenario, available water resources cannot meet the demand of different sectors. If the stability index is maintained at 75%, the amount of water shortage in the drought scenario is equivalent to 501.75 MCM, in the normal scenario is equal to 358.75 MCM, and the in the wet scenario is equal to 78.75 MCM. In addition, the sensitivity analysis of the model with different data indicates that if in the drought scenario, the amount of available water from both surface and treated water sources is equivalent to 300 and 200 MCM, respectively, then the optimal allocation pattern has changed and the amount of water shortage that can lead to overdraft is 103.75 MCM.