Stormwater runoff is rainwater or snowmelt that flows over the land. Runoff can carry sediment and contaminants from streets, rooftops, and lawns to surface water bodies or can infiltrate through the soil to ground water.

Urban runoff is one of the largest sources of pollution to PA’s rivers and streams, and can contain bacteria, trash, and chemical toxins–all of which are harmful to people and animals. The good news is that alot of urban runoff is preventable–and the movement to green infrastructure for stormwater management is having all sorts of beneficial effects!

The Importance of Managing Stormwater Runoff

Impervious surfaces in built-up environments prevent the natural infiltration of rainfall into the soil. This reduces ground water recharge and the pollutant removal that occurs when runoff moves through the soil. With less infiltration occurring, both the volume and flow rate of surface runoff increase. Development also reduces the amount of land available for vegetation, which would normally slow the flow of water and help filter contaminants. These changes have deleterious effects on water bodies. Studies have shown that degradation of water quality may begin with as little as 10 percent impervious cover.

There are three main concerns associated with uncontrolled runoff: increased peak discharge and velocity during storm events; localized reduction in ground water recharge; and pollutant mobilization and transport. The increased runoff rate and volume caused by impervious cover contribute to erosion (especially in areas without vegetative cover), increased flooding in low lying areas, and sedimentation in surface water bodies. The excess sediment transported by streams can increase turbidity, provide a transport medium for pathogenic bacteria and viruses, and decrease reservoir capacity. Sediment can also smother aquatic species, leading to habitat loss and a decrease in biodiversity.

Contaminants commonly found in stormwater runoff include heavy metals, organic compounds, pesticides and herbicides, pathogens, nutrients, sediments, and salts and other deicing compounds. Some of these substances are carcinogenic; others lead to reproductive, developmental, or other health problems following long-term exposure. Pathogens can cause illness, even from short-term exposure.

In urban settings, runoff is collected in storm sewers and transported to treatment facilities–but it can be discharged directly into waterways untreated during heavy rains and storms. In other words, surface water bodies that are used as sources of drinking water routinely receive contaminants carried in runoff. In certain conditions, contaminants may even reach ground water through infiltration.

The video below summarizes some of the problems with stormwater, and a suite of solutions that are being employed to manage runoff where it falls.

Managing Runoff in Paxton Creek: A Practical Approach from GreenTreks Network on Vimeo.

More information can be found at StormwaterPA >>

Stormwater Planning

On October 4, 1978, the Pennsylvania General Assembly approved the Stormwater Management Act, P.L. 864, No. 167. Act 167 was adopted based on the Statewide recognition of the adverse effects of inadequate management of excessive rates and volumes of stormwater resulting from development. Act 167 requires all of Pennsylvania’s 67 counties to prepare and adopt stormwater management plans for each watershed located in the county. The plans are to provide for uniform standards and criteria throughout a watershed for the management of stormwater volumes and flow rates from development sites through implementation of local municipal ordinances.

The video below offers a good example of how zoning can protect local water quality, AND how cooperation between developers and municipalities can result in development that’s done in a profitable and responsible way:

Cherry Creek: A Conservation Design from GreenTreks Network on Vimeo.

More information can be found at StormwaterPA >>

Green Versus Gray

“Green infrastructure” is an approach that many communities are choosing as an alternative to traditional “gray” infrastructure for managing stormwater runoff. Unlike single-purpose gray infrastructure–which uses pipes and tunnels to convey and store runoff–green infrastructure relies on “natural systems” like vegetation and soil to manage rainwater where it falls. By weaving natural processes into the built environment, green infrastructure offers many benefits beyond stormwater management, including flood mitigation, air quality improvement, and better quality of life.

The following video takes a look at the Philadelphia Water Department’s ambitious 25-year plan to protect and enhance its watersheds by managing stormwater with an innovative green infrastructure approach. All eyes are on PWD’s Green City, Clean Waters program as it unfolds, for the plan envisions transforming the city into an oasis of rain gardens, green roofs, treescapes, and porous pavements which advocates say is cheaper than tunnels and makes for a more liveable, prettier city with higher property values and better community health.

Green City, Clean Waters 9 minute Overview from GreenTreks Network on Vimeo.

More information can be found at StormwaterPA >> and at >>

On a different scale, the City of Lancaster has also embarked on a comprehensive Green Infrastructure strategy to reduce stormwater overflows, reduce pollutant load to area waterways, and ensure a healthy, vibrant community in the process. In this video, Mayor Rick Gray and Director of Public Works Charlotte Katzenmoyer share their approach to keeping 750 million gallons of runoff out of the City’s sewer system every year.

More information is available at

We have a lot more about Green Infrastructure as a Source Water Protection Strategy here >>
More Information

EPA Source Water Protection Practice Bulletin: Managing Stormwater Runoff to Prevent Contamination of Drinking Water

PHRC Webinar Handout: The International Stormwater BMP database for PA. The Water Environment Research Foundation (WERF) International Stormwater Best Management Practices Database is a centralized repository of data collected from over 500 Best Management Practices (BMPs) around the country. It is designed to allow researchers and designers access to continually updated data on the performance of stormwater BMPs. The PHRC has conducted a study of this Database to summarize data applicable to residential projects in Pennsylvania. The study resulted in two Land Development Briefs available on the PHRC website



Resources for Homeowners (.pdfs)

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