Objective: Students will observe the effect of erosion on soil samples, demonstrate the effect of water diversion features on runoff as a way to control erosion and as a way to collect and retain soil, and simulate agricultural dry-farming techniques.
|Materials: For this activity, you will need |
- a large plastic tray (such as a kitty litter box);
- soil and gravel;
- a wooden block to support the tray;
- pebbles, small stones, or popsicle sticks;
- a 500-ml beaker;
- and a plastic drop cloth.
Procedure: Take the plastic tray and fill it with soil to within one centimeter of the top. Lightly pack the soil.
Pour about 500 ml water into the beaker, then place the tray on top of the plastic drop cloth. Tilt the tray about 20 degrees, supporting it on the wooden block. Gently pour the water from the beaker onto the middle area of the soil. Do not let the water flow too rapidly. Observe the pattern that the water makes as it runs down through the soil.
Now, repack the soil and refill the beaker with water. Place a thin layer of gravel over the top of the soil. Repeat the procedure. Observe and record. Take the small stones or popsicle sticks and place them across the path of the channel that was cut into the soil by the water. Make sure that the stones or sticks are securely in place. Again, pour the water onto the soil, observe, and describe.
Try doing this experiment while tilting the tray at various angles. You might also use a gardener's watering can with a sieve-style head rather than a beaker. This more closely simulates a rainfall and spreads the water over a greater area. The gravel mulch will significantly slow down the visible surface erosion, and the rock alignments, or check dams, will further slow erosion and serve as a means of soil catchment.
Ask students to draw or describe the erosion patterns witnessed in each step of the activity. How might the practices of rock alignments and gravel mulching have affected the people of Hupobi? (At the village of Hupobi, the ancient inhabitants used check dams and gravel mulches to control runoff, protecting the soil from erosion and slowing evaporation. These techniques increased the amount of land that could be planted and resulted in a greater abundance of crops.)
This lesson was developed by Terrill L. Nickerson, the Santa Fe Indian School.
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