Grades 1 - 3

Objectives:

Show how flowing water erodes the landscape

Background

Students often know that rivers and streams can be muddy, especially newly formed ones. But they may not know that some of the clay, sand, and sediment that makes the river muddy comes from the riverbed itself, and is a result of the river eroding or cutting through the riverbed. This activity will help students understand the erosion process and its part in the formation of rivers and streams

Materials

You will need:

A 1. 9-L milk carton
A 2-L bottle
An outdoor source of soil (sandy is best)
A graduated cylinder or metric beaker
A metric ruler
Scissors
A water supply
A garden trowel

Vocabulary

Erosion
Deposition
River bed
Water flow

Method

Simulation, demonstration and discovery

Procedure

1. Discuss rivers and streams, erosion and deposition.

2. Provide student with an empty half-gallon milk carton. Use scissors to cut out the side panel of the carton under the spout, leaving the spout intact. For younger students, you may prefer to do this cutting ahead of time. (If water is not available near the outdoor site for the activity, you will have to provide containers to carry water from the classroom sink. )

3. Go outside. Lay the milk carton on its side with the cut out panel facing up, and then dig enough soil to fill the container at least half full. Gently pat the soil to smooth the surface.

4. To simulate a flowing river, set one end of the milk carton approximately 1-cm higher than the other end, maybe using a small rock or piece of wood to prop up the carton. The lower end of the carton should be the end with the open spout so when water is poured in at the top end, it will flow over the surface of the soil and out the other end without forming a "lake".

5. Place the mouth of the bottle on the edge of the higher end of the carton, and slowly pour 2 L of water on the soil, maintaining an even, constant flow of water (see the picture). The goal is to provide a small stream of water, not a sudden flood. Observe what happens to the water and the characteristics of the resulting river, including the path cut and the depth of the riverbed.

6. If the soil is dry, much of the water will simply be absorbed into the soil, but do not use more than 2 L of water. Runoff of the water in a surface stream will not begin until the soil is soaked with water.

7. Now repeat steps 3-5 with a fresh soil sample, but raise the end of the carton to 3 cm.

8. Be sure to use the same amount of water as in the first trial. Observe the difference in flow of the water and the resulting river compared to the previous trial.

9. Repeat the procedure for a third time, raising the carton to a height of 5 cm. Compare the flow of water and the river cut to those of the other two trials.

10. Compare results. Discuss how the stream beds changed as the incline increased and what happened to the soil that was carved by the water. Ask them to think about the rivers and streams they have seen and the rock formations that were eroded by them.

Extension

Students might draw pictures of rivers and plains with features carved by rivers.
Teacher might take student on a walk-about to see examples of erosion.
In a local stream bed or flood plain, note rocks that do not occur in the local area that must have been "robbed" from the land further upstream.
The lesson might begin a longer lesson on the environment in which the question of how plants slow erosion is considered.