Urban stormwater management is a growing challenge in many U.S. cities, and climate change is expected to add to this challenge. RAND researchers apply simulation modeling and economic valuation to estimate the potential benefits and costs of a green stormwater infrastructure (GSI) system in Pittsburgh's Negley Run watershed. The authors evaluate a series of GSI investments and make recommendations for how local actors should proceed.

Managing Heavy Rainfall with Green Infrastructure

An Evaluation in Pittsburgh's Negley Run Watershed

Jordan R. Fischbach, Michael T. Wilson, Craig A. Bond, Ajay K. Kochhar, David Catt, Devin Tierney

ResearchPublished Oct 26, 2020

Cover: Managing Heavy Rainfall with Green Infrastructure
Download PDF

Does not include Appendixes.

Additional Downloads

Includes Appendix A; Appendixes B-F

Order a print copy

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.

Key Findings

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.

Recommendations

  • Invest in design and engineering efforts for the Central Daylighting strategy (Strategy 4) as a solution with few, if any, downsides.
  • Employ an adaptive planning approach to support assessment and decisionmaking for further increments of connected GSI.
  • Expand the range of options to address street and basement flooding through agency and stakeholder collaboration.
  • Continue to invest in distributed local GSI projects in Negley Run neighborhoods in order to take advantage of benefits for residents, irrespective of flood-risk reduction.
  • Further refine the detailed simulation model developed for this study and integrate it into regional system models to support additional sewer-overflow and flood-risk evaluation.
  • Gather additional data to inform flood-risk assessment for Negley Run, including combined system descriptions and flow monitoring.
  • Explore the use of two-dimensional surface-flow modeling to support flood-risk assessment and site-specific GSI design.
  • Consider adopting an integrated, watershed-based approach for other areas of focus across the region.

Order a Print Copy

Format
Paperback
Page count
136 pages
List Price
$45.00
Buy link
Add to Cart

Topics

Document Details

  • Copyright: RAND Corporation
  • Availability: Available
  • Year: 2020
  • Print Format: Paperback
  • Paperback Pages: 136
  • Paperback Price: $45.00
  • Paperback ISBN/EAN: 978-1-9774-0610-1
  • DOI: https://doi.org/10.7249/RRA564-1
  • Document Number: RR-A564-1

Citation

RAND Style Manual
Fischbach, Jordan R., Michael T. Wilson, Craig A. Bond, Ajay K. Kochhar, David Catt, and Devin Tierney, Managing Heavy Rainfall with Green Infrastructure: An Evaluation in Pittsburgh's Negley Run Watershed, RAND Corporation, RR-A564-1, 2020. As of October 6, 2024: https://www.rand.org/pubs/research_reports/RRA564-1.html
Chicago Manual of Style
Fischbach, Jordan R., Michael T. Wilson, Craig A. Bond, Ajay K. Kochhar, David Catt, and Devin Tierney, Managing Heavy Rainfall with Green Infrastructure: An Evaluation in Pittsburgh's Negley Run Watershed. Santa Monica, CA: RAND Corporation, 2020. https://www.rand.org/pubs/research_reports/RRA564-1.html. Also available in print form.
BibTeX RIS

Research conducted by

This research was funded by the Henry L. Hillman Foundation, the Heinz Endowments, and 3 Rivers Wet Weather and conducted by the Community Health and Environmental Policy Program within RAND Social and Economic Well-Being.

This publication is part of the RAND research report series. Research reports present research findings and objective analysis that address the challenges facing the public and private sectors. All RAND research reports undergo rigorous peer review to ensure high standards for research quality and objectivity.

This document and trademark(s) contained herein are protected by law. This representation of RAND intellectual property is provided for noncommercial use only. Unauthorized posting of this publication online is prohibited; linking directly to this product page is encouraged. Permission is required from RAND to reproduce, or reuse in another form, any of its research documents for commercial purposes. For information on reprint and reuse permissions, please visit www.rand.org/pubs/permissions.

RAND is a nonprofit institution that helps improve policy and decisionmaking through research and analysis. RAND's publications do not necessarily reflect the opinions of its research clients and sponsors.