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What is Stormwater?

Stormwater is the water that runs off the land during and after a rainstorm. It can also be called rainwater or surface flow. This water goes through inlets, pipes and channels directly to our local streams. Stormwater does not go to the wastewater treatment plant.

What is Impervious Area?

Impervious area is any land cover that prevents water from infiltrating. Examples of impervious areas are rooftops, roads, parking lots and sidewalks.

Pervious area allows water to infiltrate. Examples of pervious areas are forest, lawns, and agricultural fields.

How Does Impervious Area Impact Hydrology?

As land becomes more densely developed, rainfall leaves the site in different ways.

What is Stormwater Pollution?

Stormwater sweeps away debris, soil, and chemicals on land surfaces as flows to stormwater inlets and carries these pollutants into downstream streams and lakes. With increases in impervious surfaces and stormwater runoff, the amount of stormwater pollution increases.

Learn about how you can prevent pollution at work, home, and school.

Impervious cover relationship to surface runoff
For natural ground cover, only 10% of rainfall runs off. The runoff percentage increases as imperviousness increases. For land that is 75-100% impervious, 55% of rainfall runs off.

How Does UNC-Chapel Hill Address the Impacts of Impervious Area?

UNC-Chapel Hill stormwater provides maintenance, enforcement, and engineered solutions to reduce the impacts of impervious areas. These practices include:

  • sweeping of streets and parking lots
  • sediment removal from stormwater infrastructure
  • erosion and sediment control measures on construction sites,
  • detection and prevention of pollutant discharges to stormwater,
  • installation of stormwater control measures (SCMs) to reduce stormwater runoff from impervious areas and remove pollutants from stormwater.

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