After this activity, students should be able to:

• Define and describe a catchment basin.
• Define and describe a watershed.
• Relate their model basin to real-world water flow patterns.
• Explain engineers' involvement with watersheds and catchment basins.

(Hand out blank note cards, one per student.) On your note card, write down everything you can think of that would affect a stream or a river of water, and everything that you know about streams or rivers. I'll give you three minutes.

(Three minutes later, bring the class back together.) Raise your hands if you wrote on your note card any of the following items or things that fit into these categories (write them on the board as they are discussed):

• Water quality (dirt, pollution, contamination, industrial waste, spills, etc.)
• Precipitation (climate, weather, rain, snow, dry, etc.)
• Location (landforms, mountains, plains, valleys, hills, etc.)
• Life (animal life, plant life, human activities, soil, etc.)
• Human-made (dams, diversions, buildings, factories, water collection, canals, levees etc.)

What else did you write on your cards that we have not talked about yet? (Write these items on the board, also.)

All of the things we just listed and discussed affect our water sources. These are factors that can determine whether a source of water is clean enough for us to use for bathing or drinking. Have you ever looked carefully at the water in a stream or river? Did it look clean or muddy? There are many things that can affect the water you see in a river or stream. Sometimes the water looks really clean, but it really is not because of invisible pollutants or tiny bugs that live in the water. How can we tell if the water is clean?

Well, first we should figure out from where this water comes and how it gets to a specific stream or river. The whole area from where stream or river water begins to where it finally reaches you is called a catchment basin (also called a river basin or water basin; see Figure 1). The boundary between your catchment basin and the one next to it is called a watershed. A watershed is also the area of land that drains all the small streams and rainfall to a common place such as the mouth of a bay or any point along a large stream or river. Water moves between basins, watersheds, the atmosphere and back again through what we call the water cycle. Sometimes the term watershed and catchment basin are used interchangeably.

Figure 1. A catchment basin. click for copyright

What directs the flow of water though a watershed or catchment basin? Why does it go one way and not the other? How do different catchment basins and watersheds develop? Well, a lot of water flow is directed through rivers and streams by gravity. Today, we are going to figure out why different catchment basins and watersheds happen and how much of that depends on gravity.

Engineers often create models of something when they are trying to learn about how it works. To help communities get usable water for their citizens, engineers often create a model of a watershed or catchment basin to help them experiment and figure out how to move the water to a new area without hurting the land. Then, engineers develop technologies to help us clean up the water so we can use it for drinking and all sorts of other uses. Today, we are going to model our own catchment basins so we can figure out what happens to water when it falls onto different types of landforms, where it goes, and what factors might affect it. This will help us understand how engineers can move water from one watershed to the next.

Before the Activity

With the Students: Part 1: Building

1. Divide the class into teams of two students each. Provide each team with a work area and materials, including worksheets.
2. Inform the teams that they will first design their own model of an area of land using the provided materials. The land can look any way that they want.
3. Have students position their objects (cups, bowls, jars, rocks, paper towels) anywhere on the space; the tallest objects represent mountains, the other objects represent hills, lakes or plains (see Figure 2). Suggest that they arrange objects to create valleys and low spots.

Figure 2. Example arrangement of objects to represent landforms. click for copyright

1. Next, have students lay the plastic sheet over the top of their entire area (land), including all of the landform objects. Have them loosely mold the plastic around the covered objects (see Figure 3). Use masking tape to secure the position of the objects, and the plastic, as needed.

Figure 3. Example catchment basin created by plastic draped over landforms. click for copyright

1. On their worksheets, have students write down their predictions about what will happen if it rains on their model. Where will the water go? Will it go faster in some places? Why?

With the Students: Part 2: Raining and Modeling

Make sure students set up their objects in a way that allows for a good flow of water.

Adding pollutants and heavy rain could cause excessive drainage to the area outside of the model basin. Make sure to have enough measures in place to keep the area relatively clean or to mop up the excess water. To keep it really neat, have student groups create their "land" in large flat plastic tubs or cardboard boxes so water is contained as it rolls off the plastic sheets.

Introduce the concepts of topographic mapping in a hands-on way by having students follow the steps below, using their catchment basin model. This activity requires a ruler, marker, tape (optional), paper and pencil for each team:

1. Use a permanent marker (or tape) to mark points on the model that are 10 cm above the surface of the ground/floor/table where the model is placed.
2. Using a marker, connect all of these points to make a ring around the model. The resulting ring represents a 10 cm contour line.
3. Measure points 20 cm above the surface, and use a marker to connect these points. This ring represents a 20 cm contour line.
4. Continue this for 30, 40 and 50 cm, up to the tallest point on the model.
5. Looking at the model and rings from above, what do you notice? Are the rings concentric — meaning are the higher rings inside the lower rings (Answer: Yes)
6. Draw the rings from the model on a piece of paper as if you were seeing them from above. This creates a topographic map of your catchment basin / watershed.

Dictionary.com. Lexico Publishing Group, LLC. Accessed March 15, 2006. (Source of some vocabulary definitions, with some adaptation) http://www.dictionary.com

Model a Catchment Basin Learning Activity 3. 2005. Hydrology, The Globe Program (http://www.globe.gov), University Corporation for Atmospheric Research, Colorado State University. Accessed March 15, 2006. (Source of activity, modified) http://www.globe.gov/tctg/hydro_la_modelcatchment.pdf?sectionId=160

Watershed Information Network. Last updated February 22, 2006. U.S. Environmental Protection Agency. Accessed March 15, 2006. http://www.epa.gov/owow/watershed/