Climate Change is overwhelming Philly’s sewers. Here’s what GSI can do for stormwater.

Why heavier rain means more sewage in Philly’s rivers

As climate change brings more frequent and intense rainstorms to Pennsylvania, stormwater management is becoming not only an environmental issue but a public safety concern.

Philadelphia discharged 12.7 billion gallons of raw sewage mixed with polluted stormwater each year, according to a recent report by PennEnvironment. Local waterways had 65 or more combined sewer overflows each year, which make it unsafe to recreate up to 195 days per year.

Climate change is making Philadelphia wetter; the city receives 10% more precipitation each year, by 3.8 inches. Heavier downpours overwhelm older sewer systems, increase flooding in neighborhoods, and place more pressure on treatment plants that were not designed for today’s rainfall patterns. Many cities, including Philadelphia, rely on combined sewer systems that collect both stormwater and wastewater, which means heavy rains can trigger combined sewer overflows that release untreated sewage directly into waterways.

Understanding stormwater helps us see why cities are shifting to more resilient approaches that work with nature rather than against it.

What is stormwater, and how does it affect us?

To understand stormwater, let’s go back to school.

The water cycle explains how water moves through the atmosphere. Stormwater, which is part of the precipitation phase of the water cycle (including rain and melted snow), refers to the runoff from water that does not soak into the ground. Hard surfaces such as building roofs, parking lots, roads, and other industrial materials direct stormwater into large storm drains. These drains collect pollutants, which are then carried into larger bodies of water.

But it’s not just water flowing over these hard, impervious surfaces – it can pick up contaminants, including fertilizers and pesticides residue, animal waste, motor oil, and other debris. This ca cause  unsafe drinking water, flooding after major storms, degrading infrastructure and the natural habitats destruction. Pennsylvania has nearly 5,200 miles of rivers and streams that are categorized as impaired due to stormwater runoff, according to the Chesapeake Bay Foundation. 

There are greener, more cost-effective solutions that have been shown to improve overall quality of life. 

Green Solutions: How nature supports stormwater relief

The Philadelphia Water Department (PWD) manages stormwater by two methods: 1) traditional or “gray” infrastructure and 2) green stormwater infrastructure (GSI). 

Gray infrastructure management relies on conventional water filtration systems, such as gutters and drainpipes, to direct stormwater into treatment plants or nearby bodies of water. In contrast,

Green Stormwater Infrastructure (GSI) uses natural materials including plants, soil, and stones. GSI allows stormwater to be released more slowly into traditional infrastructure systems, managing the flow at a more manageable rate.

The PWD’s Green City, Clean Water initiative promotes the reduction of stormwater pollution through city-wide projects that use “green tools” to mitigate stormwater overflow. By using nature’s tools, communities can transform their infrastructure and waterways to create a safer environment and a healthier ecosystem. 

GSI is intentionally designed to mimic natural hydrology: filtering water through soil, slowing it with vegetation, and allowing it to soak into the ground rather than overwhelming drains. These systems help recharge groundwater, reduce heat in urban areas, improve wildlife habitat, and support pollinators.

Examples of GSI include:

• Bioswales: Shallow, landscaped channels that move water slowly while filtering pollutants.
• Tree trenches: Specially engineered tree pits that store and absorb large amounts of runoff.
• Permeable pavement: Sidewalks and parking lots that allow water to pass through instead of pooling.
• Green roofs: Vegetated rooftops that absorb rainfall and insulate buildings.
• Curb bump-outs: Planted areas that extend into the street to absorb water and slow traffic.
• Stormwater planters: Raised containers with deep soil and native plants to capture runoff.

These tools together create a “green network” throughout neighborhoods, especially in areas that have historically experienced flooding or infrastructure strain.

Which native plants in Pennsylvania support stormwater reduction?

In the region once known as “Penn’s Woods,” native plants can again play a vital role in protecting our land and water. Various natural stormwater reduction methods utilize plants as effective agents for absorbing excess water.

Here are a few examples of native plants and projects that you can implement at home gardens and lawns, as suggested by The Penn State Extension program:  

• Groundcovers:
  • Grasses: River Oats, Bluestem Grass, and Muhly Grass
  • Perennials: Prickly Pear, Wild Violet, Creeping Phlox
  • Conifers: Common Junipers
• Rain gardens: Swamp Milkweed, Marsh Blazing Star, and Goldenrod
• Downspout Planters: Pickerelweed, Blue Flag Iris, and Soft Rush

Thinking of other ways to beautify your home and help reduce stormwater runoff? Check out the “Rain Check” program to find the project that’s best for you. 

Cover photo: GSI display at Philadelphia Flower Show, 2020

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