Ground Surfaces and Infiltration

Goals for the Lesson

• Students will understand and demonstrate the concept of permeability.
• Students will apply the concept of permeability to different types of ground materials.
• Students will apply concept of permeability to local ground materials.

Materials Needed

For classroom:

• blackboard or large pad of paper
• sponge
• impermeable rock
• water

For each lab group

• paper and writing utensil
• samples of surface materials
• dropper
• 50 ml graduate
• clear-sided beaker or long tube for each sample
• source of water
• stopwatch
• table for results

State Standards Addressed: Pennsylvania Department of Education Academic Standards for Science and Technology: Inquiry and Design (3.2); Earth Sciences (3.5); Pennsylvania Department of Education Academic Standards for Environment and Ecology: Watersheds and Wetlands (4.1); Ecosystems and their Interactions (4.6); Humans and the Environment (4.8)

Subjects Covered: earth science, environmental science

Topics Covered: water infiltration, permeability of different materials

Introduction

• We've looked at the hydrologic cycle and the hydrologic equation. When precipitation falls on the ground, some of it infiltrates into the groundwater system, some of it sits at the surface, and some of it runs over the surface of the land. What are some of the factors that are important in determining which of these paths precipitation follows? (steepness of the land, intensity of precipitation, surface materials)
• List ideas on board.
• The topic we'll be discussing next is permeability, which is the ability of rock or other material to transmit water.
• Demonstrate by pouring water onto the sponge and onto the rock, and asking students to describe what happens. (water soaks into sponge, not into the rock)

Observation

• Take students outside, around the school grounds. Have students list all the types of surface material they encounter (parking lot, school, grass, bushes with mulch, concrete), and predict whether the material is permeable.
• Back in the classroom, list the different materials on the board, and the consensus prediction of whether it is permeable.
• Ask if students can think of any surfaces that are not represented. (sand, solid rock, gravel)
• Ask students to suggest ways of duplicating the local surfaces and any others on a small scale in the classroom, so that they can experiment with the permeability.

Experimentation

Students work in pairs or small groups.

Activity 1: What Is Permeable and What Is Impermeable

• Have as many samples available as possible. Sand, gravel, clay or other loose materials can be put into a beaker.
• Prepare a chart, with four columns, labeled sample, impermeable, permeable, and time.
• Put a set amount of water, such as ten drops to a few milliliters, onto each sample with the dropper. Allow three minutes for the water to disappear from the surface into the material. If the water disappears, label that material permeable. If the water does not disappear, label it impermeable.
• Record the information on the table.
• Alternative plan: Pour water onto the actual surfaces outside, to see if the water infiltrates into the ground. Assign a maximum time, such as three minutes, after which the material is designated impermeable.

Activity 2: Additional Experimentation on Permeable Materials

• Have samples prepared of the permeable materials, with equal volumes of material (at least 50 cubic cm) in identical containers of transparent material. The containers might be large beakers, or long narrow density tubes. Gently pour 10 ml of water into each container, onto the material.
• Time how long it takes the water to travel through the material to the bottom of the container.
• Record the time on the table.

Analysis

Have students answer the following questions on the handout:

1. Is there a pattern to whether materials are permeable or impermeable? (The material is permeable if it has open space, and the open spaces are large enough for the water to move through the material)
2. Is there a pattern within the permeable materials as to how quickly the water moves through the material? (The larger the openings, the more quickly the water moves through the material)
3. Is there a pattern to whether human-made materials around the school are permeable or impermeable? (Many of the human-made materials are impermeable, and therefore change the hydrologic equation)
4. Describe what will happen if a slightly permeable surface is slanted. (The water will be more likely to runoff rather than infiltrate)
5. When this school was built, how did that affect the infiltration of precipitation in the area, and therefore the local water cycle and water equation? (less infiltration, more runoff)

After reading the chapter in the text, determine if any of the samples did not behave as the text predicts they would.

Assignment

1. Read section in your text on water cycle, in particular, on infiltration versus runoff.
2. Finish analysis questions.

Extensions

1. Estimate, such as by pacing, the area of each surface material on the school grounds.
2. Calculate the percentage of ground that is permeable.
3. Determine where the water travels that lands on the school.
4. Investigate historical records of lowering of local wells after development.

Evaluation

Collect initial lists, charts, and analysis questions, and check for reasonable work and answers.

References

Any earth science or environmental science textbooks, such as:

Anderson, Stanley H., Ronald E. Beiswenger, and P. Walton Purdom (1987). Environmental Science. 3rd edition. Ohio: Merrill Publishing Company.

Spaulding, Nancy, and Samuel N. Namowitz (1994). Earth Science. Massachusetts: D.C. Heath and Company.

Author

Colleen M. Serencsits