Development and Application of a Decision Support System for Municipal Water Infrastructure Planning: Challenges and Successes

Many water utilities across the country continue to face the challenge of intelligent planning for cost effective, efficient operation, larger demands, stricter government regulations, and potentially shrinking water supplies. Continued evolution in computer hardware and software products has provided the planners and the decision-makers the benefit of utilizing faster and more user-friendly computer models to facilitate and support long-term planning decisions. However, investment in any number of off-the shelf and proprietary models still requires a significant amount of time and financial resources. The risk for utilities is great because even after these resources have been invested, questions are often raised about how the results will be used, who will operate the model, and how long will be the model's useful life. These issues, among others, faced the City of Portland, Oregon Bureau of Water Works during the development of a long-term Infrastructure Master Plan (IMP). Forecasted peak season water demand may increase as much as 24% by 2050 due to population growth alone. Additional water will be required to promote healthy fish habitat for endangered and threatened species. Global warming may also result in higher demands as well as impact streamflow timing and volume. Coupled with these factors is an existing water supply infrastructure that may not be capable of meeting current service area demands beyond 2010. The need to plan for these future contingencies prompted Portland to develop the IMP. The IMP identified over 40 planning scenarios that included service area expansions, three levels of conservation, varying groundwater blending ratios, and a suite of infrastructure improvements. Those improvements included groundwater expansion, dam raises, water treatment plant construction, and a third dam construction. The computational requirements needed to evaluate multiple scenarios in Portland's complex system were beyond any tools available in the organization at the time. Therefore, the need for a sophisticated water infrastructure planning tool became apparent. The purpose of this paper is to discuss the development and application of the Supply and Transmission Model (STM). Successes and challenges will be presented from the perspective of Portland's planners and decision-makers.