Multiperiod planning of water supply infrastructure based on scenario analysis

Long-range infrastructure planning is fraught with uncertainties. Population growth may occur faster or slower than expected, regulations may change, and public sentiment can shift. In the face of these uncertainties, water system managers must plan for large infrastructure investments and the questions about when it is desirable to invest in infrastructure and what is the appropriate infrastructure component size to meet growing demands. One of the most powerful and intuitive ways to incorporate uncertainties is to use scenarios that represent plausible futures. Scenario-based planning is gaining acceptance in the water resources community. Preparing for a range of possible futures provides flexibility and adds robustness to the system so it can respond to uncertain events at reasonable costs while maintaining community confidence in their utilities. In this paper, novel scenario-based planning and optimization approaches are presented for the optimal design of regional-scale water supply infrastructure in a multiperiod planning framework. For demonstration, water demand projections are considered as uncertain and multiperiod construction projects are selected to minimize the economic costs. The solution approaches are applied to a decentralized water reclamation planning project in a green-field development area in southeast Tucson, Arizona, where water reclamation is viewed as a potential component for a sustainable water supply.