Development of Water Allocation Policies Considering the Demand Variations: A System Dynamics Approach

Abstract

The water demand and the utility functions of the decision makers and the stakeholders of a river basin are different. Due to changing environmental, social and development conditions, the utility functions of the decision makers/agencies could also vary from time to time. To study the dynamics of water resources system and the relevant policy making issues, the effects of allocated water on the growth rates are not usually considered. A comprehensive water allocation model should consider the conflicting issues facing water users as well as the changing water demands. In this paper, a system dynamics based model is presented for developing the optimal water allocation policies in Karkheh river-reservoir system in southern part of Iran considering the interactions between the conflicting utility functions, values of water demands and the allocated water. In this model, the water demand is a function of population, land use, crop pattern and the economic conditions of the region which can be affected by the allocated water. The proposed methodology includes a GAbased optimization model and a system dynamics simulation model. The objective function of the optimization model is based on the Nash compromising theory that can incorporate the utility functions of the decision makers as well as their relative authorities in the conflict resolution process. The system dynamics simulation model is used to simulate the dynamics of different sectors' water demand due to causal loops affected on demand variation during reservoir operation. The results of this study show that the population, the area of agricultural lands, and the industrial water demand have an S-shaped growth. Furthermore, this model can be used effectively in conflict resolution and optimal water allocation in river–reservoir systems. According to results of this study, considering the dynamic growth of water demands is more reliable than allocating water based on a constant growth rate for all sectors, because the demand variation due to allocated water to each sector is considered and demands growth due to each sector asymptote. This kind of planning is more useful for developing regions that the regional growth is directly related to the potential and available resources such as water.