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Urban Run-Off After Rain Event

Urban run-off is the trash run off that occurs after each major rain or wind storm, and in Iowa results in millions of pounds of trash being washed into Iowa waterways. Shown is the trash washed out by just one rain event that took place over two days at the Missouri River Wastewater Treatment Plant. The reason this plant is able to capture so much trash is because the sewers that are feeding it are not separated yet; stormwater and sanitary are connected. Most cities have their sewer lines separated. Stormwater sewers typically go to the closest river and sanitary sewers go to the treatment plant. This is just a small representation of the trash that is coming from Iowa cities to Iowa waterways through stormwater sewers. Almost every small town and city in Iowa has stormwater sewer drains where urban run-off goes. The water that goes down these sewers carries: trash, animal waste, leaves, grass clippings, and much more, taking it to the closest river or stream. Once these pollutants enter the water source they begin to cause problems. Animal waste and biological molecules can lead to increases in nutrients and dead zones. Trash can be eaten by animals and block sunlight for plants and algae, disrupting food webs, and eventually make it into the ocean.

Missouri River Wastewater Treatment Plant (Council Bluffs, Iowa/Omaha, Nebraska).

Driving Question

How does urban run-off affect Iowa’s freshwater?

Probing Questions

  • What could this trash do to animals in rivers?
  • What could this trash do to humans who use rivers?
  • What could this trash do to plants in rivers?
  • Why do humans damage the environment even though we know that it will negatively affect us?
  • How did you feel after seeing the picture of trash after one run-off event?

Classroom Suggestions

Students could:

  • Do a cost/benefit analysis of having a separated or combined sanitary and stormwater sewers. Most cities do not have a combined system, so urban run-off goes straight into local water systems with minimal screening. Having a combined system allows you to screen a tremendous amount of trash, but requires an astronomical amount of storage or treatment. This method would fit better at the end of a storyline when you are wrapping up a unit.
  • Use a “Notice and Wonder” chart to use this as a unit anchoring phenomenon. Students could then begin to understand what urban run-off is, why it happens, what it does to ecosystems, and how we can prevent it. A final project for this could be having the students design a better sewer system or bar screen.
  • Research the negatives of this human impact: what does it cost to clean up, who are the major contributors, where does it end up, when did it start, and how does it affect local flora and fauna? If used this way, it would be a final research project. After a class has learned about food webs, trophic cascades, and changes in ecosystems they could be shown this picture and then begin to research human impacts on ecosystems or as an anchoring phenomenon to help cover each of these topics.
  • Discuss issues related to agricultural run-off and how Iowa’s water sources are affected by this form of run-off.

Relevant Related Resources

Iowa Core Alignment


Design, evaluate, and refine a solution for reducing the impacts of human activities on the environment and biodiversity

Credit Info

Submitted by Devin Yeoman as part of the Iowa STEM Teacher Externship program.

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