Conjunctive use of Inter-Basin Transferred and Desalinated Water in a Multi-Source Water Supply System Based on Cost-Benefit Analysis

Water shortage has forced coastal cities to seek multi-source water supply with a focus on inter-basin water and desalinated seawater. The differences of water supply costs pose a challenge in the optimal use of multiple water resources. This paper aims to understand the impact of desalinated seawater's variable costs on multi-source water supply through a cost-benefit analysis method based on a multi-objective optimization model, considering different combination scenarios of desalination yield, streamflow condition, seawater desalting plant (SDP) scheme, water shortage index and utilization ratio of the SDP. The application in the coastal city Tianjin, China shows that the desalination yield has an impact on the tradeoff between the water shortage index and the total water supply cost and an optimal desalination yield can be determined at a turning point. And where the turning point appears is influenced by the utilization ratio of the SDP and streamflow conditions of inter-basin water. Moreover, a single centralized SDP is found to have an overall lower water supply cost than several decentralized small-sized SDPs. Lower water shortage index leads to higher cost, and the unit decrease of shortage index will need more added cost when the shortage index is very low. This method is proven to be effective in identifying the best conjunctive use of inter-basin water and desalinated seawater, which can contribute to relieve urban water shortage.