Sources of Pollution: Urban Runoff


Urban runoff occurs when water moves off of “developed” land into waterbodies. “Developed” means that vegetation has been scraped away and replaced with some sort of impermeable surface. An impermeable surface is one through which water cannot penetrate (as it could through natural vegetation, like a forest or meadow floor). The water just runs off until it gets to a water body or a permeable surface like a forest or meadow. Impermeable surfaces include rooftops, parking lots, roadways, airports, and malls. All of these surfaces are part of the Urban Development that occurs in cities, where there are a lot of people and concrete.

What does Urban Development look like in the Satellite Image of the Barataria & Terrebonne Watersheds?

What does Urban Development look like in the Aerial Photographs of each smaller watershed where it is present within the Barataria & Terrebonne Watersheds?


How does this land use cause Non-Point Source Pollution?

Urban runoff can contribute several different types of pollutants including organic matter/low dissolved oxygen, nutrients, sediment, oil and grease, metals, heat, and disease-causing organisms. Any time these pollutants end up on concrete or rooftops, rain can easily carry them into bayous, lakes, and bays, and cause pollution.

  • · Organic matter comes from the clearing the land of plants related to development, lawn clippings, and pet manure.
  • · Nutrients come from lawn fertilizers and pet manure.
  • · Sediment comes from the clearing the land of plants related to development or canal digging.
  • · Oil and grease comes from machinery and equipment. Sometimes people change the oil in their cars or trucks and dump it in storm drains. Storm drains don’t carry water to treatment plants. They carry water straight to rivers, bayous, lakes and estuaries. Storm drains are only for rain water, NOT leaves, grass clippings, oil, or grease!
  • · Metals come from machinery, equipment, industrial businesses, and cars and trucks.
  • · Heat is a pollutant! Some cities have a lot of pavement. Pavement reflects some heat and stores some heat. When it rains and the water runs off of the pavement, the pavement can make the water hot. Hot water holds very little dissolved oxygen.
  • · Disease-causing organisms comes from pets in the cities. Some people leave their pets’ waste on sidewalks and streets. When it rains, the pet waste gets washed into storm drains and out to the local bayou, lake, or bay.


What can you do to prevent this pollution?

  • Best Management Practices for Urban Runoff
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