2.6. RAINDROPS
(Level: 2 : 3 :: Watersheds)

Purpose: To observe where and why rain settles during a simulated rainfall.

What You Need: natural hill or hill display :: 6 marbles

What You Do:

1. Before this activity select an existing landform or slope or create the hill display in one of three ways:
   • if possible, use a sandbox to create a model of two hills, or
   • form hills from scrap cloth or towels and then cover with a sheet (stretch and pull tight), or
   • use two half inflated beach balls with a sheet overtop
   Test your human-made hill to make sure it works. It may be necessary to make a depression so marbles collect at the hill base.
2. Discuss the difference between absorbing water and water runoff. Explain this by comparing a sponge and a rock, or jeans and a raincoat. Both the sponge and jeans absorb water, while water runs off the rock and raincoat. Explain that this occurs every time it rains. Some things absorb water and other things do not, and thus the water runs off them.
3. Discuss where water goes after it rains. Make a list of places where water may go. For each place that is listed, decide whether or not the rain will be absorbed or if it runs off.
4. Ask students to guess where the water that falls on hills will go. Will it: stay on top of the hill, or flow to the bottom?
5. Do the run-off activity with the students observing. Pretend the marbles are raindrops, and allow each one to roll down the hill and leave it where it stops. They should accumulate in one area.

Questions:

1. Why did all the marbles go to the same spot?
2. When rain falls on a slope, what is the end result?
3. Compare what would happen to the rain falling on a parking lot, and rain falling on a forest.
4. How are temporary ponds and puddles beneficial to amphibians?

Click here to see the answers to these questions.
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Extension:

1. Visit the schoolyard prior to a rainfall. Examine the area for low depression areas where water would accumulate to form puddles. Also, examine different areas in the schoolyard to determine if water would be absorbed or forced to run off. After a rainfall, return to these areas to see if your predictions were right.