In this lesson students will use their knowledge of rainfall, vegetation, and the slope angles of hillsides to make decisions, predict outcomes, and analyze the effects of certain events or practices (e.g., overgrazing, forest fires, and clear-cutting woodlands resulting in deforestation).

This lesson will help students appreciate the complex relationships between various physical processes and the features they help create. It is essential that students understand the physical processes affecting the Earth's surface and, using that knowledge, make intelligent predictions and decisions.

Geography, environmental studies, science

Standard 7: "The physical processes that shape the patterns of Earth's surface"

Two hours

• A stream table (a long table down which you will pour water to observe erosion in action)
• Soil to cover the stream table
• Water to pour down the stream table
• Watering can to simulate rain
• Buckets to catch the water
• Small plastic toy house
• Photographs of houses in various areas (steep hillsides, flat land, heavily vegetated and denuded areas)
• Writing materials for drawing and taking notes

Students will

• predict the consequences of heavy rainfall on hillsides; and
• perform experiments to test their predictions.

Show the students several photographs of homes in different settings and climates. Have the students discuss which homes they would like to live in and why. Would they be concerned about living on or below a steep slope?

Explain to the students that they are to draw "before" and "after" pictures of the experiments you are about to perform. In addition to drawing what they observe, they should also describe it in words.

Take the class outside to where the stream table is set up. Have the students draw and describe the stream table. They should note the amount of soil, its placement and thickness, and the angle of the table.

Slowly and consistently, pour water down the table. Continue to pour until a fairly large pile of soil has washed to the bottom of the table.

Have the students draw and describe the "after" picture.

Place a toy house at the far end of the stream table (but not where the water collects). Repeat the procedure several times, varying

• the angle of the table;
• the force with which you pour the water; and
• the amount of water poured.

At each stage ask questions such as the following:

• What processes are going on (e.g., gravity, erosion, or resistance)? Gravity pulls water down a hill. Erosion is the deterioration of the soil as water carries it away.
• What happens when the angle of the table is increased? (The steeper the angle, the faster the water will flow and the more it will erode soil.)
• Note that, in nature, vegetation provides resistance and slows water. Less erosion takes place, as leaves diminish the force of falling water and roots hold the soil. What would occur if all the vegetation were destroyed in a forest fire?

Return to the classroom to discuss areas around the school, neighborhood, or town that have been eroded. Some examples:

• A local stream, gully, or creek
• Steep roadcuts
• A popular mountain bike trail
• A backyard where a dog has worn a path

Ask the students to look again at the photos shown at the beginning of this activity. Lead them in a discussion of how their new knowledge would affect their choice of homes. Include such factors as amount of rainfall, angle of hillside, and lack or abundance of vegetation.

Show students pictures of various areas (e.g., a mountainous area with a lot of vegetation, a steep hill with very little vegetation, and a flat area relatively void of vegetation). Students should be able to confidently discuss the images, answering questions such as the following:

• What physical processes are acting on this area?
• What could be the effect of a heavy rainfall in this area?
• What could be the effect if we added more vegetation to this area?
• What could be the effects after a forest fire or heavy logging?
• What could be the effects if cattle or goats overgrazed this area or if there were a grass fire?

• Watch the news; record, discuss, and analyze physical events such as mudslides. Analyze which regions of the world are most likely to experience the type of physical event in question.
  
  
• Using topographic, vegetation, and precipitation maps, decide on the location for a dream house.
  
  
• Pretend your students are real estate agents. Have them put together a portfolio of houses. Beneath each picture, write the pros and cons of buying that house, based on the safety of its location.

Nicole Sweet of East Valley Middle School in Spokane, Washington, contributed classroom ideas for Standard 7.

About.com: Water and Hydrology
EPA: Watershed Information Network
Environmental Literacy Council
National Geographic: Eye in the Sky—Deforestation