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Eco-Explainer: What is Green Stormwater Infrastructure (GSI)?
Water

Eco-Explainer: What is Green Stormwater Infrastructure (GSI)?

You may have heard the catchphrase “GSI”, but what does it ACTUALLY mean?

We have a water dilemma.

Philadelphia already experiences a hotter and wetter city, with an increased 4 inches of annual rainfall thanks to the climate crisis. So how will Philly streets manage all of that excess water from more precipitation?

With the combination of climate change and the city’s combined sewer system, this excess of water could become increasingly problematic.

Green City, Clean Waters is Philadelphia’s $2.4 billion, 25-year plan, using green stormwater infrastructure as a solution.

What is Green Stormwater Infrastructure (GSI)?

Green stormwater infrastructure (GSI) is a nature-based solution to managing wet weather and stormwater runoff. GSI is soil-water-plant systems that capture stormwater, segmenting it back into the ground, evaporate a portion of it into the air, or release slowly back into the sewer system.

GSI varieties include rain gardens, tree plantings and trenches, green roofs, porous pavement and stormwater planters. GSI is not always obvious from the surface when you’re walking around the city. “They often blend in with their surroundings, though they have a substantial underground infrastructure.

green stormwater infrastructure south philly
GSI project alongside of Columbus Square Park, South Philly

Why use Green Stormwater Infrastructure?

It cleans our water. Green stormwater infrastructure cleans and filters stormwater, which usually causes water quality issues. GSI slows the flow of rainwater into sewers, and natural features such as soil and plants remove pollutants,” according to Philadelphia Water.

It saves (and makes) money. Green stormwater infrastructure is an economic (and sexy) alternative to grey infrastructure (i.e., pipes.) It’s estimated that Green Cities, Clean Waters will produce $4 billion in total economic impact.

It creates jobs. The city’s GSI plan is estimated to support an average of 1160 jobs annually.

GSI aids Philly socially. “In 2018, GCCW reduced crime by nearly nine percent (8.7%) and saved the city $50 million annually in avoided health-related costs attributed to access to open space,” according to the Sustainable Business Network’s GSI Partners report.

Green Stormwater Infrastructure Types

Downspout Disconnection & Rain Barrels

This is a simple process of running pipes from your roof to rain barrels, cisterns, or permeable areas.

Rain barrels hold the stormwater for later use, so you can water plants or gardens. Philadelphia Water provides residents with FREE rain barrels, too.

Stormwater Tree Trenches

A stormwater tree trench is a series of trees connected by an underground, engineered system to manage the runoff. It includes a trench along the sidewalk, permeable fabric, filled with stones or gravel, and topped off with soil and the tree.

stormwater tree trench
Photo: Philadelphia Water

See one of these systems at the intersection of Ogden and Ramsey Streets in West Philadelphia.

Stormwater Wetlands

Stormwater wetlands imitate natural wetlands, providing habitats for wildlife and beauty for the local community.

Porous Pavement

Asphalt doesn’t absorb rain water. So special options like  porous asphalt/porous play surface slow down stormwater, redirecting and filtering water through the soil.


Want to see Green Stormwater Infrastructure (GSI) in action in your neighborhood? Find it on this map.

Philadelphia Water tracks projects on this interactive map so you can search for your neighborhood’s GSI projects:

GSI map

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Jamie McClelland
Jamie is a junior at Villanova University double majoring in English and Communications with a specialization in Media Production. She is currently an Editorial Intern at Green Philly. In her spare time she enjoys writing poetry and short stories, along with watching movies and exploring Philly. View all posts by Jamie McClelland

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