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Build a Model Watershed

Summary:
Students construct a model land surface and use the model to explore basic concepts of watersheds including that (1) water flows downhill, (2) ridges of higher land can divide watersheds, (3) lower-lying areas can create pools, and (4) water quality is affected by what is upstream. Materials:
  • Aluminum tray (A turkey roasting pan works well.)
  • White plastic garbage bag (large enough to enclose the tray)
  • Newspaper or other assorted 'building materials' (such as styrofoam pieces)
  • Spray bottle filled with blue colored water
  • Two permanent markers (different colors)
  • Paper
  • Pencil

For the class:

  • Red food coloring (one large bottle)
  • Cotton balls (one for each group)
  • One pair of rubber gloves
  • A cup or bowl

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Source:
Adapted from the Water Resources Education Initiative at the United States Geological Survey, the GLOBE Programís Model a Catchment Basin, and River of Words, Teacherís Guide, International Rivers Network (1996).
Grade level:
Grades 4-8.
Time:
10 minutes prep time, 30-40 minutes class time
Student Learning Outcomes:
  • Students will be able to define the concept of a watershed
  • Students will be able to identify watersheds in a model landscape
  • Students will be able to explain that water quality is affected by what is upstream
  • Students will be able to explain the usefulness and the limitations of their models
Lesson format:
Hands on activity with discussion

National Standards Addressed:

DIRECTIONS:

Preparation

  1. Saturate cotton balls with red food coloring and place in cup or bowl until needed. Wear gloves to avoid coloring your hands.
  2. Gather images that illustrate the paths of rivers and the shape of watersheds. If possible, find examples from your region. Aerial photographs work well, and so do topographic maps (if students are familiar with those). It is also nice to have an example of a hydrological map of your area (with all the waterways and water bodies marked) and a map of a large area (your country, for example) to examine watersheds at different scales.

Teacher Directions

  1. To introduce students to the idea of watersheds, show images of landscapes (photographs and/or maps). Discuss how the shape of the land affects how water travels through it. Illustrate how rivers and streams are connected within a watershed and how highlands separate watersheds. Consider having students work in pairs or small groups to come up with a common definition of watershed.
  2. Students work in pairs or small groups to make their model watershed following the instructions in the section below.
  3. After they have made their models and sprayed them with water to understand where the rivers and lakes form, visit each group and place a cotton ball saturated with red dye into the landscape explaining that it represents something that releases pollution into the environment. (This is the last step of the student directions below.) Instruct students to make it rain again and see where the pollution travels.
  4. Because of the simplicity of the materials, student groups might devise improbable landscapes - things that might not happen in nature. At the conclusion of the activity, you may choose to facilitate a brainstorm about how these models, are, and are not, like the real world. (The other major difference is that the surface of these model landscapes is impermeable so there is no possibility of groundwater.)

Student Activity Directions

  1. Map the rivers, lakes, and stream: As a group, make a map that shows the locations of rivers in one or more watersheds. You will make a three-dimensional model that matches this map.
  2. Make a model of the shape of the land: Arrange crumpled newspaper in the aluminum tray to represent the shape of the landscape in the location of your map. This is a model of a landscape with hills, valleys, and connections between them.
  3. Add the surface of the land to your model: Place the tray and newspaper inside the plastic bag. In this model, the plastic represents the surface of the land. Adjust the shape of the bag to match the shape of the land surface that you need so that rivers flow as they do on your map.
  4. Draw the waterways on your model: Think about rain falling in your model watershed. Where would the rainwater go? Where would rivers and streams form? Would there be any waterfalls? Where will the water form lakes or ponds? Draw the locations where you think rivers and lakes would form with a permanent marker.
  5. Draw the boundary of a watershed on your model: Using a different color of permanent marker, draw the boundary of the largest watershed in your model. Also draw the boundary of a smaller watershed within the larger watershed. Mark a spot where you would like to live. Mark a spot for your school.
  6. It's time for some rain! Use the spray bottle to 'rain' on the top of your highest 'mountain.' Continue raining until the water forms streams, rivers, and lakes.
  7. Your instructor will introduce a land use change to your model. How did this land use change impact the lakes, streams, and rivers? How do you feel about the location of your house?

Summary
Consider leading a 'field trip' to view the various model watersheds that groups have made. It is interesting for all to see how different the models can look and how the change in land uses affected the waterways differently depending on the shape of the land in the model. (Note: If the class is small, you can simply guide students to each model watershed. If the class is larger, you may want to have the students place their model watersheds in a central area and form a circle around the models.)

At the conclusion of the 'field trip', lead a class discussion about the models. Ask students to consider the usefulness of this model. How is this model like a real landscape? Discuss the limitations of this model. How is this model different from a real landscape? Ask student to brainstorm what changes they would make to improve the model.

EXTENSIONS:

  • Research your own watershed.
  • Take a field trip through a local watershed.
  • Measure water quality in a local stream, pond, or lake. Be sure to consider all the factors upstream that may influence the water quality.

BACKGROUND INFORMATION:

A watershed refers to the area of land where all of the water that is under it (e.g. ground water and aquifers) or on it (e.g. surface water like streams and rivers) flows into the same place. A watershed is like a funnel in that it collects all the water within an area (the wide part of the funnel) and moves it towards the same place (the narrow part of the funnel). Watersheds are not defined by political boundaries as they can cross city, state, and national boundaries. Watersheds are separated by topographically higher areas (highlands). Watersheds come in many sizes from very small watersheds encompassing a few acres to very large watersheds that cover tens of thousands of square miles. Small watersheds are part of a network of larger watersheds. Ultimately, the water gets to the ocean. In many areas, the term watershed is synonymous with the terms drainage basin and catchment basin.

Streams and lakes reflect the characteristics of the watersheds they drain. Thus, when investigating the water quality of a stream or lake it is important to consider the characteristics of the watershed it is within. A water sample taken from a river, for example, is a synthesis of everything that has happened to the water before it reaches the point where the measurement is taken. Characteristics of a watershed that should be considered include topography, vegetation, soils, and land use. It can be challenging for students to understand the water that flows past them at a single point along a stream or river is greatly impacted by the watershed upstream.

Models are important and useful tools in geoscience education. It is important to understand the limitation of models. Before using a model, talk to your students about the usefulness of models, but also the limitation of models. Encourage them to come up with examples. "Models can easily be misused. In fact, a frequent cause of students' science misconceptions is confusion between characteristics of a model and the characteristics of the real thing it represents. Four questions, used routinely during instruction, can help prevent these misconceptions:

  • How does this model work the same as what it represents?
  • How does this model work differently from what it represents?
  • What are the strengths of this model? The weaknesses?
  • How does this model compare and contrast with what it represents?"*
(*From Understanding Models in the Earth and Space Science Ė Steven W. Gilbert and Shirley Watt Ireton - 2003 NSTA Press)

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Last modified February 12, 2008 by Lisa Gardiner.

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