Small Communities Stormwater Project
Impervious Surface Activity
For 4th, 5th, and 6th Graders
The purpose of this 15-minute activity is to illustrate the difference between what happens to rain falling on an impervious surface compared to on a ‘natural’ surface.
Materials Needed:
-Paint trays (with stands) – about two trays for every 10 students
-8.5 x 11 pieces of green felt (the thicker, the better) – 1 piece for every 10 students
-Spray bottle full of water – one for every 10 students
Setting Up:
Make one pair of paint trays for (roughly) every 10 students. One paint tray should represent a fully-impervious urban setting. With a permanent marker draw streets, houses with driveways, grocery stores, schools, etc. on the paint tray. About ¾ of the way up, draw an X. The other paint tray should represent a fully-vegetated, permeable landscape. Tape a piece of green felt to the tray (you might want to attach smaller pieces of felt up the sides of the tray so splashing doesn’t ruin your results). With a permanent marker, draw a forest on the felt. Again, about ¾ of the way up, draw an X. At the low end of each tray, draw a river with a blue permanent marker.
Introducing the Activity:
Before you start the activity, talk about the difference between natural surfaces and paved surfaces. Ask them what they think would happen if they were to pour a glass of water on a street compared to a prairie. Ask them to think about impervious surfaces in their city – rooftops, driveways, streets, parking lots, etc. – and pervious surfaces in nature. NOTE: turf grass does not count as a pervious surface!
The Activity:
Have the students come up to a table where the trays and water bottles are set up. Hold up the impervious surface tray and explain that it represents a city. Hold up the permeable tray and explain that it represents a forest. Ask them how many sprays they think it will take until the first drop of water reaches the river in the city. Have a volunteer spray (aiming at the X about 1 foot away from the tray) while the rest of the students count aloud. Now repeat the process with the forest tray. If you notice the volunteer getting tired, have them switch sprayers.
Wrapping Up:
When you are done with the activity, ask the students if they are surprised with the difference in the number of sprays it took for the first drop of water to reach the river. If you have time, explain how planting rain gardens, trees, and other vegetationin a city would be like placing small pieces of felt on the city tray. These things help absorb stormwater in the city.
Language to Use:
-Impervious
-Permeable
-Stormwater/runoff
-Vegetation
*NOTE: Dry off the trays and replace the wet felt with dry felt at the beginning of each new trial.