Multiobjective water resources planning under demand, supply and quality uncertainties

Abstract

This research aims at formulating a water resources planning model for optimum allocation of water resources supplies (groundwater, surface water, desalinated water, and treated wastewater) to the various demands (domestic, agricultural, industrial and landscaping demands). Since by design the study included more than one objective and constraint (multi-objective decision making), the methodology employed for the formulation and solution of the model was goal programming. Uncertainty is associated with three parameters, i.e. demand, supply and quality of ground water. The model is applied to Saudi Arabia. Historical data for all the parameters were collected and, using the moment average method the data were forecasted. Uncertainty of demand is mainly due to unexpected behavior of the population; this was assumed to follow a normal distribution. Uncertainty due to supply (chiefly groundwater) is because of the gaps among the proven, probable, and possible reserves. There are three parameters here; Reserves are assumed to follow triangular distribution, and the quality in terms of TDS was also assumed to follow triangular distribution. Random numbers were generated and used in order to simulate the process and the basic concept of reliability analysis was applied to the results of the model, which was run upto the year 2020. The multi-objective model was run for two cases, one in which there is no restriction on the use of desalinated water and the second case in which the desalinated water is restricted to the current total capacity of the desalination plants all over the Kingdom. The results of the model showed that there is severe deterioration of the quality of the industrial and agricultural water with reliability of achieving the prescribed quality equal to 1.62% and 1.2% respectively in the year 2020. The effect on the groundwater reserves was minimal with plenty of reserve available in the year 2020. In the second case, the quality of the domestic water is severely affected (the reliability of achieving the prescribed quality in terms of TDS, less than or equal to 1000 mg/l, is as low as 2.4% in the year 2020), this shows the inevitability of needing to increase the production of desalinated water.