What's a Watershed?
Part A: Make a Watershed ModelThis activity is adapted from similar lessons by Windows to the Universe and California's Project WILD.
Gather these Materials
Each group of 2 to 4 students needs these materials:
- Large aluminum roasting pan or paint tray
- 6 to 10 pages of newspaper
- Masking Tape
- Sheet of white plastic, slightly larger than the pan (a trash compactor bag cut into single sheet works well)
- Spray bottle
- Blue food coloring
- Absorbent cloth or paper towels
- 2 different colors of permanent markers
- Blocks of wood or a notebook to lift one end of the tray
Make your Models
In this portion of the activity, you'll use these materials to make a very simple model of a portion of Earth's surface. You'll spray model rain on your landscape and watch how it flows so you can identify watersheds and drainage divides that separate them.
- Crumble several pieces of newspaper into balls and rolls of different sizes and shapes. Place them into your roasting pan or paint tray. Use tape to keep them in place.
- Lay your plastic bag out flat on a table top or the floor and smooth out the wrinkles.
- Place one end of the pan on wood blocks or a notebook, then cover the entire pan and its contents with the plastic. Gently press the plastic down around the crumpled paper balls. Leave the excess plastic around the outside of the box to protect the area from getting wet.
- The plastic cover represents Earth's surface. The lumps represent mountains and hills, and the areas between them represent valleys. Use your imagination to visualize your model as a portion of Earth's surface.
- Fill your spray bottle with water and add a few drops of blue food coloring to make the water easy to see. Spray just enough rain over your model to see how the water interacts with your model landscape.
- Look for these features in your model. (see image, right, for a sample of how the model will look)
- linear flows of water running downhill;
- Ponds or Lakesareas where water pools up in low areas; and
- Drainage dividesimaginary lines along which the "rain" goes to one side or another.
- Use your cloth or paper towels to absorb the water from your model. Adjust the paper balls and plastic to make your landscape as realistic as you can, then spray it with model rain again.
- When you think you can predict the locations of streams and drainage divides on a model landscape, wipe your plastic dry and set up the model again. Use markers to draw your predictions for the locations of streams and divides directly on the plastic.
- Pair up with another lab group and test each groups' predictions about the location of their streams and divides. Discuss the results and your ideas for improving the model.
- Use an Internet search engine to find diagrams or images that show dendritic, trellis, radial, rectangular, and/or parallel drainage patterns.
- Use newspaper or other materials to produce model landscapes with one or more of these types of watersheds.
- Consider what type of geologic structures would result in each type of drainage. Follow up your model-building by finding examples and information on different drainage patterns.
Stop and Think1. Briefly discuss how well the model represented reality for the concept of watersheds and drainage divides.
2. Write your own description or definitions for the following terms.
- Drainage divide