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Additional investment is needed to mitigate present and future risks

• Sewer overflow from Negley Run is higher in a range of recent historical rainfall patterns compared with a single typical year.
• Sewer overflow increases further in plausible future scenarios.
• Negley Run already faces notable flood risk from heavy rainfall events.

GSI strategies could reduce sewer overflow and flood risk

• Flood risk increases with heavier rainfall from plausible future climate change.
• A new centralized daylighted system and subsequent upstream investments could substantially reduce, but not eliminate, sewer overflows in Negley Run.
• A centralized daylighted system reduces flood depths along Washington Boulevard but does not eliminate flooding even in more-frequent, lower-intensity events.

The benefits of proposed GSI strategies outweigh their costs

• Strategies that build on a daylighted surface collection system could yield highly cost-effective sewer-overflow reduction across a range of assumptions.
• Scenarios with higher average annual rainfall generally lead to greater sewer-overflow cost-effectiveness.
• GSI cobenefits from the strategies evaluated could contribute substantial value to residents when accounting for uncertainty and using conservative assumptions.
• The net economic value of the strategies considered — taking into account life-cycle strategy costs, water-quality benefits, and cobenefits — is nearly always positive across a wide range of assumptions.
• A midranged strategy could provide positive economic benefit across a wide range of assumptions.

Urban stormwater management is a growing challenge in many U.S. cities. Continued population growth, urbanization, and inadequate investment in storm- and wastewater infrastructure have left many cities exposed to sewer overflows, stormwater flooding, and reduced water quality. Climate change is expected to add to this challenge by increasing the intensity or volume of rainfall from storms in many regions. There is also a growing acknowledgment that these vulnerabilities are environmental justice and equity challenges, as flooding and other negative outcomes disproportionately affect low-income or majority-minority neighborhoods.

Pittsburgh's Negley Run watershed is a prime example of these stormwater management challenges, draining a diverse area of Pittsburgh's East End, including neighborhoods that have suffered heavily from underinvestment. It also represents an urgent flood-risk challenge in the city, as heavy rainfall in the area leads to regular flooding of a key road corridor. In this project, RAND researchers use simulation modeling to evaluate present and future risks in Negley Run from sewer overflows and flooding given future rainfall uncertainty. The authors then evaluate proposals for a phased series of green stormwater infrastructure (GSI) investments.

In addition to estimating stormwater benefits and implementation costs, the authors provide economic estimates of recreational, amenity, and other cobenefits to local residents; compare total benefits to costs; and explore potential trade-offs. Results show that a centralized system of stormwater management in Negley Run could yield cost-effective sewer-overflow reduction, reduce street flooding, and provide positive net economic benefits across a range of assumptions about future rainfall and implementation costs.

• Chapter One

  Introduction

• Chapter Two

  Simulation Modeling and Economic Valuation Methods

• Chapter Three

  Sewer Overflows and Flooding in a Future Without Action

• Chapter Four

  Strategies to Manage Stormwater in Negley Run

• Chapter Five

  Green Stormwater Infrastructure Strategy Simulation Results

• Chapter Six

  Green Stormwater Infrastructure Economic Benefits and Costs

• Chapter Seven

  Key Findings and Recommendations