Accelerating urban demand growth coupled with changing hydro-climatic conditions are stressing water supply systems in many large urban areas of the United States. In response, urban water utilities must formulate sustainable infrastructure investment strategies that maintain supply reliability while balancing their debt burden. The timing of new infrastructure investment plays a critical role in the success of a sustainable water supply management strategy. If decision makers wait too long before investing in new infrastructure, they risk loss of supply reliability; if they invest too early, they may make large and inefficient expenditures. Recent work has highlighted the use of adaptive infrastructure pathways that provide decision makers with flexible tools to tailor infrastructure investment decisions to observed future states of the world. A core component of such frameworks is the use of decision triggers, measures of system state that are used to time infrastructure investment. 

This work introduces a new methodology for designing responsive decision triggers that aid in timing infrastructure investment. We begin with two classic measures of system reliability and vulnerability and examine their efficacy for triggering infrastructure. Our methodology is demonstrated on a regional water supply planning system in the Tampa Bay region of Florida. Our analysis highlights the benefits and challenges associated with the proposed infrastructure investment triggers and their influence on the timing of infrastructure investments. Our results provide a roadmap that allows decision makers to time investment decisions based on their risk tolerance. These findings are broadly applicable to water resources infrastructure investment problems worldwide.

If Not Now, When? Designing State Aware Decision Triggers to Inform the Timing of Infrastructure Investments

Created in 1999, the Environmental & Water Resources Institute (EWRI) is the recognized leader within ASCE for the integration of technical expertise and public policy in the planning, design, construction, and operation of environmentally sound and sustainable infrastructure impacting air, land and water resources.

[Paper Proceedings](https://doi.org/10.1061/9780784483466)