Multi-objective decision making for basin water allocation

Abstract

Due to the significant role of water use in socio-economic development, competition for a larger share in water allocation is intense among stakeholders in watersheds. In this paper, three optimization models are developed to explore the optimal allocation of water among users, thus to resolve water conflicts in watersheds. The first model is a linear programming model. The objective function of this model maximizes the basins' revenue. The second model is a multi-objective optimization model. The objective functions of this model maximize the marginal value of water for stakeholders when environmental water supply is a constraint in the model. The third model is also a multi-objective programming model. Three objective functions; maximizing a basin revenue, minimizing the environmental water shortages, and minimizing water transfer from upstream area to downstream region are considered. These models are applied to the Sefidrud Basin, a watershed with eight administrative provinces, each considered as a stakeholder for the modelling. The formulations of three water allocation models are presented and the results of their implementation are compared. The results from the third model show that it would be able to supply more water to agriculture than other models if water authorities would not want the full satisfaction of environmental demand. In other words, if environment is taken into account as a stakeholder, for whom water shortages are acceptable, the third model is recommended. The comparison of the first and the second models reveals that the second model allocates water to stakeholders more equitably than the first model. In the case of the second model, the percentage of maximum and minimum water shortages for the Sefidrud Basin's stakeholders are 71 and 20, respectively, in comparison with 81 and 8 provided by the first model. Hence, we recommend using the second model for resolving water conflicts in watersheds when the satisfaction of environmental water requirements is crucial for water authorities. The policy of water authorities on environmental water satisfaction is a key factor determining the water allocation pattern of the Basin. Therefore, the issue of whether any shortages in environmental water supply are tolerable should be resolved before any decision related to water allocation is made.