No abstract

Effective, sustainable management of urban water systems, including drinking water, stormwater, wastewater, and natural water systems, is critical to the health and well-being of people in urban areas and the ecosystems that encompass them. The demands of human population growth, aging infrastructure, and changing climate will increase pressure on these systems and require future innovations in water management. Planning for urban water systems will increasingly require collaborations between water professionals and researchers to imagine, design and model the response of novel urban water systems to future conditions. We highlight benefits and challenges of transdisciplinary projects for integrated urban water management; organized broadly into: (1) engagement of water managers and planners; (2) transdisciplinary design of innovative systems, and once designed; (3) modeling and evaluation of urban water system response to various innovations. We describe the development of a multi-scale approach to design and evaluation of innovative urban water systems, and illustrate its application using examples from the Willamette River Basin and Portland, Oregon. The scenario-based approach described here offers several key contributions to the design and modeling of innovation. First, this process provides the opportunity to convene professionals and researchers, who do not typically collaborate, as participants in a collaborative process. Second, it engages participants in thinking together across land and water management sectors to develop plausible futures at multiple spatial extents and multidecadal time horizons. Third, it helps to identify critical gaps in extant water modeling capabilities, and thus helps define the near-term research agenda for modelers.

We used the EPA SWMM-5. 1 model to evaluate the relative impact of neighborhood design and constructed Low Impact Development (LID) features on infiltration, evaporation, and runoff for three future scenarios. In the Current Course (CC) future, current regulations and policies remain in place under lower rates of climate change and population growth. In the Stressed Resources (SR) future, rapid rates of population growth and climate change stress water systems, and conventional development patterns and management actions fail to keep pace with a changing environment. In the Integrated Water (IW) future, with the same rapid rates of climate change and population growth as the SR future, informed water management anticipates and adapts to expected changes. The IW scenario retains public open space, extensive use of constructed LID features, and has the lowest proportion of impervious surface. Neighborhood designs varied in the number of dwelling units, density of development, and spatial extent of nature-based solutions and constructed LID features used for stormwater management. We compared the scenarios using SWMM-5.1 for a set of NRCS Type 1a design storms (2-yr, 25-yr, 20% increase over 25-yr, 30% increase over 25-yr) with precipitation input at 6-min time steps as well as a set of 10-year continuous runs. Results illustrate the importance of neighborhood design in urban hydrology. The design with the highest proportion of impervious surface (SR future) produced runoff of up to 45–50% of precipitation for all variations of the 25-year storm, compared to 34–44 and 23–39% for the CC and IW futures, respectively. Evaporation accounted for only 2–3% of precipitation in the 25-year design storm simulations for any scenario. Results of continuous 10-year simulations were similar to the results of design storms. The proportion of precipitation that became runoff was highest in the SR future (33%), intermediate in the CC (16%), and lowest in the IW future (9%). Evaporation accounted for 6, 11, and 14 of precipitation in the SR, CC, and IW futures with LID, respectively. Infiltration was higher in scenarios with LID than for the same scenario without LID, and varied with the extent of LID employed, accounting for 59, 71, and 74% of precipitation in the SR, CC, and IW scenarios with LID. In addition to differences in performance for stormwater management, the alternative scenarios also provide different sets of co-benefits. The IW and SR future designs both provide more housing than the CC, and the IW future has the lowest cost of development per dwelling unit.