Stormwater Runoff

Pennsylvania abounds in natural beauty, its landscape entwined with 83,161 miles of streams and more than 3,900 lakes, reservoirs, and ponds. Water is the lifeblood of the Commonwealth, supporting vast forests, abundant fish and wildlife, and a wide array of human uses that draw more than four billion gallons of ground and surface water per day. This wealth of water is a blessing, but population growth has radically altered the natural systems that manage rainfall through transpiration, infiltration, and gradual runoff into surface waters-leading to everything from poor water quality to flooding, severe erosion, and droughts.

When the amount of rain falling exceeds the land's ability to absorb it, the result is stormwater runoff. The volume of runoff and rate at which it flows varies with the intensity and duration of the rainfall-and with the type of land surface upon which it falls. A short, light rain falling on permeable soils might produce little to no runoff, while heavy rain landing on an impervious parking lot can produce a substantial amount.

Local governments are adopting stormwater ordinances that comply with state and federal laws, reduce damage from flooding, erosion, and combined sewer overflows, and improve the quality of residents' lives.


The stormwater requirements of the federal Clean Water Act are administered under the Pennsylvania Department of Environmental Protection's Municipal Separate Storm Sewer (MS4) Program. Attached is information on stormwater in an urban environment.