Over the past decade, climate change has accelerated the frequency and severity of precipitation events in Philadelphia. As a densely populated urban area, Philadelphia has many buildings and paved surfaces that allow heavy rainfall to either flood properties or streets or send stormwater rushing into the city’s sewer systems. The City must adapt to its changing climate to manage stormwater in a way that both minimizes property damage and prevents sewer overflows and discharges from polluting its waterways, even if its infrastructure was not designed to handle it.
Through an innovative approach called green stormwater infrastructure (GSI), Philadelphia is managing stormwater in a sustainable and cost-effective way.
The Situation
In Philadelphia, GSI has helped the city adapt to the continual changes in precipitation. Since 2011, when city officials entered an agreement with the U.S. Environmental Protection Agency to institute the Green City, Clean Waters plan, GSI has become a common practice. Philadelphia chose this path as opposed to the alternative option to manage increasing amounts of stormwater runoff by investing billions of dollars into building a traditional subsurface system of pipes and tunnels.
GSI Basics
GSI is an effective management solution that intercepts stormwater, infiltrates a portion of it into the ground, evaporates a portion of it into the air, and/or in some cases, releases a portion of it slowly back into the sewer system. GSI largely manages rain and snowfall in place, instead of relying on a gray infrastructure system of pipes and tunnels to divert the runoff to a sewer system. This method prevents overwhelming wastewater treatment plants with more volume that they can managers, resulting in untreated water overflowing or discharging directly into waterways.
Examples of GSI in Action
One of the best-known examples of GSI are green roofs, which are extensions of the existing roof that include plants and drainage systems. Pervious pavement, made of special permeable materials (asphalt, concrete, rubber) that help capture rainwater have proven to be successful as well. Soil storage is also a means to manage rainwater in place. Other well-known GSI practices include tree trenches, in which a special basin collects runoff, as well as bio retention areas, where a grass buffer strip, sand bed, ponding area, or mulch layer surrounds a tree and collects water. GSI also has the additional potential benefits of creating amenities such as parks and gardens and providing a habitat for wildlife.
How Green Building United Promotes GSI
Through Green Building United’s partnership with the Sustainable Business Network, we have created the GSI Precedent Library – a collection of high-performing urban GSI projects. Projects were selected for the library based on how effectively they managed stormwater while also providing superior environmental, social, and/or economic benefits. The goal of the library is to share best practices as well as lessons learned to help scale GSI projects in favor of traditional gray stormwater management solutions.
Green Building United Partners
Partners who have helped worked with Green Building United to scale GSI in the region include the Sustainable Business Network, PennFuture, and the Pennsylvania Environmental Council. The Sustainable Business Network coordinates and convenes designers, architects, construction companies, and regulatory partners to deepen knowledge and facilitate communication about GSI. PennFuture works in the legal realm to protect and improve water quality. The Pennsylvania Environmental Council works with municipal governments to train staff and set goals for GSI to grow within their jurisdictions.
The Future of GSI
GSI is critical to effective stormwater management and adapting to climate change, and Philadelphia has been a trailblazer in this space. Green City, Clean Waters is a long-term stormwater management plan that is being replicated throughout the country, making Philadelphia a leader in GSI and a model for other cities. To learn more or to see examples of high-performing GSI projects, please visit .