The Island Watershed Activity

Background
In order to understand many of the important water-related issues that society faces, students need to understand the existence and dynamics of watersheds (a.k.a. drainage basins). This will help them realize how an abandoned mine can cause the presence of dissolved metals in a stream many miles from the mine site, and how farming practices in the Midwest can contribute to a "dead zone" in the Gulf of Mexico. This activity will help students learn about the watersheds, giving them the foundation needed to understand these issues.

Materials
Modeling clay (60-75 cubic cm), Eye dropper with water, Wax paper ~35 x 35 cm, Metric ruler, Graph paper (.5 cm x.5 cm squares or similar), Blue thread (~30 cm), Scissors, Red thread (~50 cm), Colored pencils

Learner Outcomes
1. Understand the relationship between topography and drainage.
2. Recognize that runoff from a certain area as the primary source for water in a stream.
3. Apply principles and terms associated with surface water systems, including watershed, drainage basin, upper, lower, divide and tributary.

Procedures: To see student worksheet, click on HOTLINK below
1. Lay the wax paper on your table and then use the clay to build an island. Design the island so that the maximum height is less than 4 cm. The island should have at least 4 distinct drainage basins. The area of one of these basins should be at least twice as large as any of the others. It is best for students to avoid creating lakes, craters, cone-shaped peaks, and unrealistic landforms. Also, encourage them to avoid islands that look like starfish. Suggest that they consider putting the highest land somewhere away from the center of the island.

2. Use an eyedropper containing water to determine the approximate location of 4 (or more) of the island's largest rivers. Do this by gently dropping water from 3-6 cm above different locations on the island. Watch the path of the drops as they run off the island. If a drop gets "stuck", simply add more water to the drop. Eventually it should flow off the island. You may reshape the island to get the rivers where you want them to be.

3. Once you are satisfied with the drainage of the island, use pieces of blue thread to mark the location of the island's 4 (or more) major rivers. Press the thread gently into the clay to keep it in place. You will need scissors to cut the thread.

4. Next, use pieces of red thread to mark the boundaries of the watersheds of each river that you have identified (at least 4).

Here are some common mistakes:

Above: The image on the left shows three common mistakes. For one, rivers do not typically originate at the highest point in a watershed. Usually, the headwaters are some distance below that point as shown on the right.

Secondly, the divides are drawn incorrectly. They include more land (near the coast) than they should. The image on the right shows more realistic watershed boundaries.

Finally, in the image on the right, there is a gap between boundaries of the two basins. In reality, water at the top of that ridge will drain into one basin or the other, so a single line (divide) like that shown on the right would be correct.

5. Have your instructor check your island before going to the next step.

6. Lightly scratch the clay with the tip of a pen or pencil to show the possible locations of 2-5 tributaries for each stream that you have identified with blue thread.

7. Next, make a map of your island. First, peel or cut the island away from the wax paper. Place the model onto a piece of graph paper, and then trace the edge of the island onto the paper. Set the model aside and then draw each of the following onto the map: major rivers (blue), tributaries (blue), boundaries of drainage basins (red).

8. Do each of the following to your map:

a. Identify which direction will be "north".
b. Give your island a name. Place it at the top of the map.
c. Put arrows on all of the rivers (including tributaries) to show flow direction.
d. Name each of the major rivers (blue thread). Write these names along rivers.
e. Put a green UP in the upper part of each drainage basin.
f. Put a green LO in the lower part of each basin.
g. Put a green M at the mouth of your longest river.
h. Put a green D on one of the divides located on your map.
i. Put a green C at one of the confluences sown on your map.
j. Put a green H at the headwaters of your longest river.
k. Include a scale on your map. Have each side of the cubes on the graph paper be equal to 10 km of distance.

Here are some possible extension activities.

A. Imagine that there is a city near the mouth of the river that has the largest watershed that depends on this water for its people. Create a problem in the upper part of this basin that threatens this water supply. On a separate sheet of paper, write a newspaper article (complete with title) describing the problem and explaining how it will impact the water supply for the city. (3-5 good paragraphs should do)

B. Obtain a piece of 12" x 18" construction paper. Draw and color a scene that shows a portion of one of the watersheds on your island. The scene should include the river and vegetation, as well as whatever else you envision present in the area.

C. Check out the "Watershed Project" (see Hot links below).

TEACHERS: If you would like for me to email you a copy (attached file) of the student handout, contact me at the email address shown below.