Hold a Hill

Investigate the relationship between erosion and slope.

Group Size: Any size

Suggested Age: 10 and up

Time: 50-60 minutes

• Site: a site near a source of water that has a variety of slopes from gentle to steep. A site with bare patches of soil is best.

• Safety: No special considerations

• Prep: Construct a slope-measuring device (see the “Measuring Slope” equipment card), prepare a One-liter Water Source and a Tin-can Erosion Collector (or have the youngsters do this themselves as part of the activity)

• Materials:
  For each team of two: Water Source container, Erosion Collector, meter tape, trowel or digging tool, 2-4 small plastic bags or cups, marker
  For the group: 2 Slope measuring devices, a water supply, data board, short pencil to poke holes, scissors, can opener, hammer and 2 nails, wedge-shaped can opener

Focus question:
How steep can a trail be and still prevent excessive erosion?

• Soil erosion is the wearing away of soil by wind or water.
• Steeper slopes produce more erosion.
• Other factors besides slope also influence the amount of erosion.

Summary:
Using the equipment and techniques described in the folio, the students compare two slopes to determine how the amount of erosion is related to slope. They then decide as a group how much erosion is acceptable for a trail on the site and then determine the maximum slope that should be allowed for the trail.

More Background
Different soil types will vary widely in the amount of erosion even if the slope is the same. Sandy soil and sand loam soils will erode much more easily than soils containing more clay particles. Also the shape of the soil particles will influence the erosion potential of the soil. Some calcareous loess soils (wind deposited dust) which are composed of fine-grained silt and clay are very stable even on steep slopes. Ground cover that protects the soil particles from being jarred loose from the direct bombardment of rain drops also reduces erosion. Plant roots hold the soil in place, allow more infiltration of water as opposed to run-off, and keep the soil from eroding.