Journey of a Raindrop – Session 3
Conduct this session in the schoolyard.
- Ask students what might happen to a raindrop that falls in the schoolyard. Discuss various possibilities, and explain that the focus of this session is runoff (i.e., water that flows away).
- Ask for a volunteer to look up the word topography in the dictionary. Discuss the definition, and explain that students will be looking at the topography of the schoolyard to determine which direction rainwater flows.
- Divide the class again into their map groups, and make sure each group has a tennis ball and a clipboard (if available) with paper and pencil.
- Tell students that they will have 5 minutes to walk around the schoolyard within your view. Groups should place their tennis ball in various locations around the schoolyard to observe how the ball is affected by gravity. Students then will use this information to determine which direction water will flow. Groups may record their data by drawing a map of the schoolyard and marking with arrows the direction the ball rolls and, thus, water will flow. (See Mapping the Schoolyard in the Project Action Guide.) Tell students to include details about the surfaces over which rainwater will flow (e.g., grass, bare soil, pavement).
- When the groups have completed their experiments, give them a few more minutes to analyze their data and extrapolate the likely route most of the rainwater will take to leave the schoolyard.
- Call on a spokesperson for each group to share their findings. Discuss and decide as a class where the rainwater will go. If the area has storm drains, you may need to do additional research by contacting your city or county to find into which stream or river the storm drains empty.
- Discuss the various surfaces rainwater flows over in the schoolyard and what effects the surfaces will have on the quality of the water that runs off. The chart below lists some possibilities.
Various Surfaces Rainwater Flows Over in the Schoolyard Surface What happens when water runs over Effects on water quality Large area of pavement Water flows rapidly, causing increased erosion after leaving the pavement. Negative: Erosion causes increased sediment pollution. Parking lot Water flows rapidly, causing increased erosion after leaving the pavement. Also water picks up oil and engine fluid deposited in the lot. Negative: Erosion causes increased sediment pollution; automotive products contribute to toxic pollution. Bare soil Water erodes and carries away soil. Negative: Erosion causes increased sediment pollution. Mulch Water travels slowly over bumpy mulch and soaks into the ground without carrying away soil. Positive: Slower and reduced runoff decreases erosion and, therefore, decreases sediment pollution. Grass Water travels slowly over uneven surface and soaks into the ground, then roots take in water and hold soil in place. Grass can filter out harmful toxins. Positive: Erosion and sediment pollution are further decreased; filtering decreases toxic pollution. Forest Water travels the most slowly in a forest. As it drips down through branches and leaves, much is taken in by trees and other forest plants' roots, which also hold soil. The forest has the most plants so it can filter out the most toxic pollution. Positive: The slowest and cleanest runoff comes from forests. It has the least sediment pollution and the least toxic pollution when compared to other surfaces.
- After discussing the effects of surfaces on runoff, have students add drawings and notes to their schoolyard maps to explain the effects of the different surfaces on the quality of water that leaves the schoolyard.