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Urban stormwater management is a growing challenge in many cities across the United States. Continued population growth and urbanization, coupled with inadequate investment in old and undersized storm and wastewater infrastructure, have left many cities exposed to stormwater flooding, sewer overflows, and reduced water quality.
Climate change is expected to add to this challenge by increasing the intensity or volume of rainfall from storms. In addition, there is a growing acknowledgement that these vulnerabilities are also environmental justice and equity challenges, as stormwater flooding and other negative outcomes can disproportionately affect low-income or majority-minority neighborhoods.
In recent years, there has been a substantial push towards investing in green stormwater infrastructure or other innovations that could improve water quality and/or reduce flooding while also providing new green space or other community amenities. However, most cities lack the necessary tools or research capacity to rigorously evaluate or compare these new design approaches across multiple objectives or in different plausible future scenarios, such as wetter or drier futures.
A railway viaduct in the Negley Run watershed in Pittsburgh's East End.
Photo by Jordan Fischbach
The City of Pittsburgh is a prime example of these challenges. The Pittsburgh region’s combined sewer system is inadequately sized to capture and treat most “wet weather” events, which occur frequently throughout the year. As a result, nearly every time it rains, a sewer overflow occurs in at least one of the approximately 450 outfalls in the system, draining a mix of untreated wastewater and stormwater into streams and rivers.
Furthermore, high precipitation events combined with hilly topography and poor drainage can lead to flooding in many low-lying areas. Some neighborhoods regularly face rainfall flooding, which can damage homes, businesses, and municipal infrastructure, as well as block transportation routes. In particular, the Negley Run watershed is an exemplar for these challenges and provides an ideal test bed for innovative systems design and policy evaluation.
Negley Run drains a diverse area of Pittsburgh’s East End, including several neighborhoods (Larimer, Homewood) that have suffered heavily from underinvestment in recent decades. It also represents one of the most urgent flood risk challenges in the city, as heavy rainfall in the area leads to regular flooding of a key road corridor (Washington Boulevard).
A Pittsburgh area map showing the Negley Run watershed.
RAND’s work in this watershed builds on a prior pilot project supported by the MacArthur Foundation that used a series of linked simulation models of Pittsburgh’s combined sewer system to simulate the frequency and volume of regional sewer overflows under a wide range of current and future scenarios and proposed infrastructure strategies.
