Troubled Waters: Wonderful Watershed
IDEAS FOR THE INFORMAL SETTING
- As an alternative, this activity can be done on a smaller scale with students creating individual watersheds using paper bags and water-soluble markers.
to search by zip code for information on local water pollution problems.
Transform a tarp into a model watershed to explore how different pollutants affect water quality.
- Define the concept of watershed.
- Describe how factors upstream can affect water quality downstream.
fertilizer, groundwater, nonpoint source pollution, point source pollution, watershed
- Topographic map of local watershed
- 1 large plastic tarp
- Stools, chairs, and/or boxes for creating a watershed
- 5 to 7 large spray bottles filled with water
- Several colors of food coloring
- 1 cup of dirt
- 1 cup of sand
- Sponges or nylon mesh scrubber
NATIONAL SCIENCE EDUCATION STANDARDS
This activity supports the following National Academy of Sciences Science Education Standards (Grades 5-8):
- Unifying Concepts and Processes—Systems, order and organization
- Unifying Concepts and Processes—Evidence, models, and explanation
- Standard D: Earth and Space Science—Structure of the earth system
- Standard F: Science in Personal and Social Perspectives—Personal health
- Standard F: Science in Personal and Social Perspectives—Natural hazards
- Standard F: Science in Personal and Social Perspectives—Populations, resources, and environments
- Standard F: Science in Personal and Social Perspectives—Risks and benefits
Streams, rivers, lakes, and wetlands flow in networks that, with the lands surrounding them, form watersheds. Watersheds collect water on Earth’s surface and help to slow the drainage of that water to underground storage and the oceans. They also help to control flooding. Watersheds have a vital role in making freshwater available to all living things, including people.
Paving, building, and removing vegetation inhibit the ability of watersheds to replenish the fresh water supply and prevent floods. Human activities within watersheds also contribute to pollution of water supplies. Pollutants can be damaging to ecosystem stability and to human health. The sources of water pollution can be divided into two categories: point sources and nonpoint sources.
Point sources include facilities like sewage treatment plants and factory discharges. They can be identified readily and can be managed. Since the passage of the Clean Water Act in 1972, significant improvements have been made in reducing point source pollution.
Nonpoint source pollution is harder to pinpoint and harder to control. Nonpoint pollution comes from many different places and includes excess fertilizers from lawns and farms, sediments from construction sites and forestry operations, leaks from landfills, hazardous dump sites, septic tanks, underground storage tanks, oil from roads, ash from burning fuels, overflows from city sewers, and animal wastes.
This activity is designed to demonstrate how watersheds are affected by point and nonpoint source pollutants and to motivate students to explore ways to prevent water pollution.
BEFORE YOU BEGIN
Select a location outside. Create a large model of a watershed by draping the tarp across stools, chairs, and other objects. Try to create several valleys, ridges, and coves. If possible, determine where your selected region of interest will be located on the model (its relative position at the top, in the middle, or towards the bottom of the watershed). Place a white bowl at the bottom of the watershed so students will be able to see the collected water, with its mix of food coloring, sand, and soil.
WHAT TO DO
1. Introduce the concept of watershed. Look at your local watershed map and find your location within the watershed.
2. Explain that the tarp broadly represents a watershed. Point out where your region will be located within your watershed. Ask students to predict what will happen if it were to rain on your model watershed.
3. Have the students use the spray bottles to spray the tarp, creating “rain” on the model. Remind them to spray over the top of the tarp, not directly on it. Compare results to students’ predictions; ask them to note where the water collects and travels down the model. Compare this to such geographic features as streams, rivers, and lakes. Point out any ridges that divide the tarp landscape into different watersheds.
4. Review what happens to precipitation that falls on land. Look at how much water has been collected in the white bowl and discuss how water may flow over land to streams, rivers, and ultimately to lakes and oceans. It may also seep into the soil, where it is stored as groundwater. Be sure to include mention of how vegetation and wetlands slow the flow and allow water to be absorbed into the ground.
5. Introduce the fact that water flowing over land might also pick up pollutants from different sources. Ask for a few examples. Discuss risks associated with water pollution.
6. Explain the terms point source and nonpoint source pollution. Have the students brainstorm examples of point source pollution. (Answers might include factories and sewage treatment plants.) Choose one color of food coloring to be “point source pollution” and have a student carefully place several drops of food coloring on one spot of the tarp. This color represents a chemical pollutant that can be traced back to its original source.
7. Have the students brainstorm examples of nonpoint source pollution. (Answers might include fertilizer runoff, street runoff, and animal waste products.) Be sure that students understand that most water flowing over streets and into storm drains is not treated before it reenters the watershed system. Choose a different color to represent nonpoint source pollution and have students place drops of their color on many different locations across the tarp. These spots represent pollutants that cannot be traced readily back to a particular spot.
8. Explain that another source of pollution is sediment. Have the students brainstorm sources of sediment pollution. (Answers might include construction sites and agricultural fields.) Have the students add some sediment sources to the watershed model by sprinkling dirt and sand on different locations across the model.
9. Have the students spray the tarp again, remembering to simulate rainfall by spraying above the tarp, and watch where the pollutants go. Ask them to think about what is happening to the water in the lower part of the watershed. How would water pollution impact where you live?
10. Explain that wetlands and other vegetation slow the flow of water and help prevent erosion as well as reduce the amount of pollutants. Simulate wetlands by placing sponges at two or three key points on the tarp.
11. With the added wetlands, set up the same scenario with food coloring, sand, and soil and re-spray the tarp. Is there a difference in the quality of water that travels downstream? How do wetlands affect water flow and quality?
12. Discuss other control methods for managing water pollution, such as sewage treatment and point source regulations.
13. Brainstorm ways to help prevent water pollution.
Have students write a descriptive story of the movement of a drop of water in their watershed. It should include examples of point source pollution, nonpoint source pollution, and sedimentation.
Needs improvement—Story is vague or incomplete or does not include examples of point source pollution, nonpoint source pollution, and sedimentation.
Satisfactory—Story generally describes the movement of water through a watershed and cites at least one example each of point source pollution, nonpoint source pollution, and sedimentation.
Excellent—Story describes the movement of water through a watershed, includes references to cities and locations upstream and downstream in the watershed, and cites at least one example each of point source pollution, nonpoint source pollution, and sedimentation.
- Participate in a storm drain marking project that alerts your community about runoff pathways into watersheds, oceans, etc.
For an excellent resource on the importance of watersheds visit The Center for Global Environmental Education Waters to the Sea Web site and award-winning CD: www.cgee.hamline.edu/waters2thesea/Chattahoochee/
For additional exercises on watersheds visit the Academy of Natural Sciences in Philadelphia’s Web site: www.acnatsci.org/education/skytosea/watershed2.html
Revised by the North Carolina Museum of Natural Sciences.
PHOTO CREDITS: Liz Baird and Tierney Thys.