Project Title

Performance and Effectiveness of Urban Green Infrastructure: Maximizing Benefits at the Subwatershed Scale through Measurement, Modeling, and Community-Based Implementation

Project Overview

This broadly interdisciplinary research program included multi-year monitoring of three Green Infrastructure (GI) sites that control stormwater runoff in Philadelphia's Wingohocking Sewershed, which is the largest of the city's Combined Sewer Overflow (CSO) areas. The data obtained was used to calibrate an advanced 3-D subsurface flow model to evaluate the effectiveness of these and future GI installations.

We have also calculated the potential for widespread adoption of GI technologies throughout the city to substantially reduce CSO flows of sewage into the city's rivers and creeks, while also taking into account costs and community co-benefits. Our research team has engaged community partners at each stage of the project to assure that our results and conclusions will be useful to Philadelphia's neighborhoods and city government during the city's GI adoption process. We have developed a geographical method for calculating an "equity index" to examine to what extent GI benefits are helping to improve measures of social equity across the city.

We have developed new decision support tools that evaluate placement of GI technologies on landscapes at the subwatershed level. We have developed and tested the application of methods for extending these tools to include modeling adaptive management strategies for reducing future uncertainties related to the city's long-term CSO reduction goals. These tools are being applied in two case studies in the Wingohocking and Mill Creek (Overbrook Neighborhood) sewersheds to inform polices that guide green stormwater infrastructure investments in Philadelphia, with potential for application in other urban areas. We expect our research findings, and the tools we have developed, to help improve the nation's ability to protect its urban watersheds and ecosystems through better understanding of the costs, benefits, and performance of GI technologies.

Project Results


  1. Refined methodologies, developed with data and models from our field sites, for accurate lifecycle performance assessment of GI practices at the site level.
  2. A publically available database containing field observations from our monitored sites.
  3. Refined methodologies for evaluation of cost effective, adaptive GI implementation strategies at the subwatershed scale employing a realistic cost model and multiple benefit metrics including runoff and CSO load reductions as well as ancillary benefits affecting community livability and equity in the distribution of those benefits.
  4. Case study applications of methodologies developed through our research to specific neighborhoods in Philadelphia
  5. A web app to enable stakeholders to access our case studies in the Wingohocking and Mill Creek (Overbrook) Neighborhoods
  6. Reports, peer reviewed papers in journals, and transferrable tools. STEM education at the K-12, undergraduate, and graduate levels.


  1. Increased national capabilities for assessing and implementing cost-effective and adaptive GI practices for urban stormwater management at the subwatershed level, especially in cities with combined sewers.
  2. Community input at all stages of our research that enhances prospects for our research to assist in efforts to bring about widespread, successful implementation of green infrastructure.
  3. Successful engagement with Philadelphia's nationally visible Green City, Clean Waters program that will help to promote transferability of our results, thereby improving the capabilities of other urban centers to evaluate and implement effective strategies for applying GI to the solution of national urban water quality problems.

Peer Reviewed Publications


  • Heckert, Megan and Christina D. Rosan. 2018. "Creating GIS-Based Planning Tools to Promote Equity Through Green Infrastructure." Frontiers in Built Environment, DOI:
  • Lim. T.C. and C. Welty. 2017. “Effects of Spatial Configuration of Imperviousness and Green Infrastructure Networks on Hydrologic Response in a Residential Sewershed.” Water Resources Research, DOI:
  • Heckert, Megan and Christina D. Rosan. 2016. “Developing a Green Infrastructure Equity Index to Promote Equity Planning.” Journal of Urban Forestry and Urban Greening,19, 263-270. DOI:
  • Barnes, M.L. and C. Welty. “Quantification of Water Balance Components at a Permeable Pavement Green Infrastructure Site using a Coupled Groundwater-surface Water Model.” In review, ASCE J. Hydrologic Engineering, 24, 7, DOI:
  • Hung, Fengwei and B. Hobbs. “How can learning-by-doing improve decisions in stormwater management? A Bayesian-based optimization model for planning urban Green infrastructure investments.” Environmental Modeling and Software, 113, March 2019, 59-72, DOI:
  • Lim, T.C. and C. Welty. "Assessing Variability and Uncertainty in Green Infrastructure Planning using a High-resolution Surface-subsurface Hydrological Model and Site-monitored Flow Data." Frontiers in the Built Environment December, 2018, DOI:

In Review

  • Hung, Fengwei, C., Harman and B. Hobbs. “Hydrological framework for stormwater management with green infrastructure: When does location matter?” Draft, Water Resource Research.
  • Hung, Fengwei, B. Hobbs, A. McGarity, X. Chen. "Is it worthwhile to invest in learning? A stormwater management case study with green infrastructure using Bayesian-based optimization," Submitting to Water Resource Research.

In Preparation

  • McGarity, A., S. Szalay, and J. Cohen. “StormWISE Model using Green Infrastructure to Achieve Philadelphia’s CSO Volume Reductions at Minimum Cost.” Draft, ASCE Journal of Sustainable Water in the Built Environment.
  • McGarity, A. “Nonlinearities in Optimal Siting of Green Infrastructure to Reduce Combined Sewer Overflows in Urban Watersheds.” Draft, Water Resources Research.


Peer Reviewed Conference Proceedings Papers

  • McGarity, Arthur, S. Szalay, and J. Cohen. 2017. StormWISE model using green infrastructure to achieve Philadelphia’s CSO volume reductions at minimum cost. American Society of Civil Engineers World Environmental and Water Resources Congress, Sacramento, CA, May. DOI: Download PDF
  • McGarity, Arthur, S. Szalay, and J. Cohen. 2016. Green stormwater infrastructure investment model for Philadelphia’s Wingohocking sewershed. American Society of Civil Engineers World Environmental and Water Resources Congress, West Palm Beach, FL., May, DOI: Download PDF
  • Hung, F., Hobbs, B., Rosan, C., McGarity, A., Szalay, S., and Heckert, M. 2016. “Exploring Win-Win Strategies for Urban Stormwater Management: A Case Study in Philadelphia’s Combined Sewer Area.” World Environmental and Water Resources Congress, May 2016: pp. 67-76. DOI: Download PDF
  • McGarity, Arthur, F. Hung, C. Rosan, B. Hobbs, M. Heckert, and S. Szalay. 2015. "Quantifying benefits of green stormwater infrastructure in Philadelphia." Proceedings of the American Society of Civil Engineers World Environmental and Water Resources Congress, Austin, TX., May, DOI: Download PDF

Dissertations and Undergraduate Theses

Ph.D. Dissertation

  • Hung, Fengwei. Green Infrastructure Evaluation and Planning for Adaptive Stormwater Management Ph.D. Dissertation, Johns Hopkins University, October, 2018.

Undergraduate Theses

  • Chen, M. Experimental Treatment of Nonpoint Pollution in a Constructed Wetland. Senior Engineering Design Thesis, Swarthmore College, May, 2017.
  • Cohen, J. Green Solutions for Combined Sewer Overflow Control in West Philadelphia. Senior Engineering Design Thesis, Swarthmore College, May, 2017.
  • Monaghan, U. Natural Systems for Stormwater Treatment: Swarthmore Borough Swim Club and Artificial Wetlands. Senior Engineering Design Thesis, Swarthmore College, May, 2017.
  • Philyaw, A. Modeling and Visualizing Community Benefits of Green Stormwater Infrastructure in West Philadelphia. Senior Engineering Design Thesis, Swarthmore College, May, 2017.
  • Sigman-Lowery, A. Water Monitoring and Watershed Modeling for Green Stormwater Management at Swarthmore College. Senior Engineering Design Thesis, Swarthmore College, May, 2017.