Exciting New Library of GSI Case Studies

Emilie Wetzel
Jan 31, 2017

Vernon Park
TTF’s rain garden at Vernon Park

Here at TTF, we understand the value of creating rain gardens and stream-side buffers to slow down and capture rainwater. Installing these types of Green Stormwater Infrastructure (GSI) has a variety of benefits including filtering water, providing beauty, and reducing the occurrence of flooding in our neighborhoods. To learn more about the many GSI projects that TTF has created, click here.

The GSI Partners, Delaware Valley Green Building Council, and Sustainable Business Network of Greater Philadelphia have collaborated on an incredible “Precedent Library” documenting a variety of exceptional Green Stormwater Infrastructure case studies. Their hope is that this document will be used as an tool to advocate for the creation of future GSI projects. We think it’s a phenomenal resource! Keep reading to get an overview of the report or click here to see the entire report!


Green stormwater infrastructure (GSI) occupies the nexus of environmental sustainability, adaptability, resilience, social equity, and a vibrant economy.

GSI, for the purposes of this library, is defined as soil-water-plant systems that intercept stormwater, infiltrate a portion of it into the ground, evaporate a portion of it into the air, and/ or in some cases release a portion of it slowly back into the sewer system.

In addition to stormwater management and improved water quality, GSI provides benefits such as beautified communities, improved public health, creation of ecological habitat, and enhanced local economic vitality.

These environmental, social, and economic benefits (the triple bottom line) are what makes GSI the preferred approach over centralized and decentralized gray infrastructure, and why cities and municipalities like Philadelphia have incorporated GSI into their portfolios to meet Clean Water Act goals and regulations. Philadelphia is leading the nation with its comprehensive stormwater management plan, Green City, Clean Waters, which focuses heavily on GSI, and includes regulations and incentives for developers, stormwater fees for property owners, and a defined target and timeline for achieving GSI “greened acre” goals. Because of increasing investment, especially in Philadelphia, GSI is a strong emerging industry.

In order to continue to increase public and private investment in GSI and ensure that it is incentivized and facilitated as much as possible, additional information is needed on the degree to which GSI performs – environmentally, socially, and economically.

Engineering and design professionals, developers and property owners, and regulators agree that there is a significant need for more data on the performance of GSI projects, and for that data to be publicly available. With broader understanding on the performance of best management practices (BMPs) such as rain gardens, stormwater tree trenches, porous pavement, and green roofs, industry professionals can continue to improve the design and performance of these tools; developers and property owners can increase their knowledge-base on the value of investing in GSI; and regulatory agencies can expand the performance metrics used to approve and credit GSI projects.

To address this need, the Sustainable Business Network of Greater Philadelphia’s (SBN) GSI Partners and the Delaware Valley Green Building Council (DVGBC), with team of leading industry professionals, have developed the following precedent library of exemplary GSI designs, systems, and approaches to inform the approval of more green and innovative stormwater management projects in Philadelphia. With greater understanding of how GSI performs, performance metrics and calculation methods can be updated, designs can continue to improve, and there can be more comfort and confidence from the development community that GSI is an effective and affordable way to meet city regulations.

The precedent library is a collection of highly effective GSI projects from urban areas across the country that have been selected for their ability to demonstrate the dynamic performance capacity of different types and classes of GSI practices, and their application at a range of project types and scales. Case studies discuss the degree to which these projects are exceeding their intents – environmentally, economically, and/or socially. This collection of case studies is complimented by peer-reviewed research that further defends the degree to which GSI performs.

This library will be used to support the successful implementation of Green City, Clean Waters, and to increase the industry’s collective knowledge on the performance of GSI.

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