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Watersheds — Watershed island
Grade Level: 6–8
Duration: 1½ hours
- Students will create a clay model of a watershed and will identify geographic features on the model.
- Students will create a watershed map representative of the clay model.
- Students will discuss the differences between each representation of the watershed, and potential human threats to the watershed.
- Yellow modeling clay
- Blue thread
- Red thread
- Wax paper
- Medicine dropper
- Measuring cup
- Metric ruler
- Graph paper
- Colored pencils
- Pen or pencil
Rather than looking at land and water resources as separate, unrelated parts, it is more appropriate to consider the connections within a watershed and see that the water and land have a dynamic relationship with each other. Every part of the Earth’s land surface is within a watershed. Divides such as ridges, peaks or areas of high ground separate watersheds. Because water flows downhill, rain falling on these divides may flow in opposite directions, becoming part of different watersheds. A watershed is the land area that contributes runoff, or surface water flow, to a water body.
The water resources within a watershed are affected primarily by what happens on the land within that watershed. Anything on the land within the watershed, however far from the water body, can eventually reach and impact that water resource. That is why it is important to think of the connectivity of water in a watershed.
The shape of the land defines a watershed. Water will flow from a higher elevation to a lower one because of gravity. Rainfall that is not absorbed by the soil but flows to a body of water is known as run off; runoff collects in channels such as streams, rivers and canals. The small channels flow into larger ones and eventually flow into the sea. The channels or streams are also known as tributaries.
Florida’s flat topography sometimes makes determining watershed boundaries difficult. Doing this activity will help students to see that the differences in topography — however slight or distinct — have an impact on which watershed the channels or streams belong to.
Part One — Growing your watershed
Begin by writing the following statement on the board or a flip chart:
“Water always flows _________________.”
Have participants write their responses on scrap paper. Share your responses.
Briefly, discuss the correct answer of “downhill.” Look at topographic maps to confirm the answer. Next, have students or participants write down term that are associated with a watershed, including watershed, drainage basin, tributary, divide, mouth, headwaters, confluence, runoff, upper basin, middle basin, and lower basin. Discuss these terms and provide definitions for each.
Give each participant a bar of modeling clay and piece of wax paper. Ask each person to create a model of an island on the wax paper using the following criteria:
- Maximum height of island less than 3 cm
- A minimum of 4 distinct drainage basins
- The shape and size of at least one basin to be much different than the others.
- No lakes or craters
- No cone-shaped peaks or unrealistic features
Use a medicine dropper and water to determine the drainage patterns of your watersheds. Gently drop water onto the island from a height of no more than 3–6 cm. Watch the path of the drops as they drain off the island. If a drop gets stuck, add more water until it flows off the island. If it won’t move, you have a wetland area. You can reshape the slope to make it steeper and allow the water to flow. Use the dropper to suck up the water once it reaches the wax paper.
Viewing the flow of water off of your island will help locate the probable locations of major rivers or wetlands and divides between watersheds. You will use blue thread to mark the location of the island’s four or more major rivers. Press the thread gently into the clay to secure it and cut the ends with scissors.
Next, use red thread to mark the boundaries and the divides between watersheds. There should be at least four watersheds. The watershed should include all the land that drains into a particular river.
Then examine each watershed and identify any tributaries that flow into the major rivers. Lightly mark or scratch the clay with your pen or pencil to show the possible location of at least two tributaries for each river you identified with thread.
Part Two — Mapping your island
Carefully remove your island from the wax paper and place onto a piece of graph paper. Trace the outline of the island onto the graph paper. Remove the clay model. Then draw each of the following onto the map: major rivers (blue), tributaries, wetlands, and boundaries of drainage basins (red).
Show the following on your map:
- Indicate which direction will be north
- Put arrows on all the rivers to show direction of flow
- Name each river
- Put a green U in the upper portion of the drainage or river basin
- Put a green L in the lower portion of the drainage or river basin
- Put a green M at the mouth of your longest river
- Put a green H at the headwaters of your longest river
- Put a green C at one of the confluences shown on your map
- Include some sort of scale on your map to show distance (km)
Discuss the differences between your watersheds and water flows.
- What are the differences between models?
- If these models did represent a real watershed, what are some potential problems that could arise from human use(s)?
- From what you have learned by testing your model, what are some implications that could be made about the watershed you live in?
watershed — land area that contributes runoff to a water body; also known as a drainage basin
divide — a ridge of land that separates two adjacent river systems
runoff — rainfall that is not absorbed by the soil but flows to a larger body of water
tributary — small stream or river that flows into a larger stream or river
drainage basin — land area that contributes runoff to a water body; also known as a watershed
confluence — a place where two rivers merge or flow together
headwaters — the source or upper part of a stream or river
mouth — the point at which a river flows into the ocean