Soil erosion happens when moving water, wind, or gravity carries soil particles away from the land. In a school erosion prevention project, students can model this process using a tilted tray, soil, water, and different surface covers. The goal is to compare how bare soil, mulch, grass, and terracing change the amount of soil washed downhill.
This matters because erosion removes fertile topsoil, muddies waterways, and can damage farms, gardens, roads, and habitats.
A fair test uses tray lanes with the same soil depth, same slope, same water amount, and same sprinkling time, while changing only the erosion-prevention method. Water falling on bare soil can detach particles and form runoff, but mulch and grass reduce the impact of drops and slow the water. Terracing changes the shape of the slope by creating flat steps that reduce water speed and give soil more time to settle.
Students can collect runoff in cups, filter or dry the sediment, and graph soil loss to decide which method worked best.
Key Facts
- Erosion rate = soil lost ÷ time
- Percent reduction = ((bare soil loss - treated soil loss) ÷ bare soil loss) x 100%
- Runoff increases when rainfall rate is greater than the soil infiltration rate.
- Steeper slopes usually increase erosion because gravity helps water move faster downhill.
- Plant roots hold soil in place, and leaves reduce the force of raindrop impact.
- Terraces reduce erosion by shortening the slope length and slowing runoff.
Vocabulary
- Soil erosion
- Soil erosion is the movement of soil particles from one place to another by water, wind, ice, or gravity.
- Runoff
- Runoff is water that flows over the land surface instead of soaking into the ground.
- Infiltration
- Infiltration is the process of water soaking into soil through spaces between particles.
- Mulch
- Mulch is a protective layer of organic or inorganic material placed on soil to reduce water impact and slow evaporation.
- Terracing
- Terracing is a method of shaping a slope into flat steps to slow water flow and reduce soil loss.
Common Mistakes to Avoid
- Changing more than one variable at a time, such as using different slopes and different covers in the same comparison, makes it impossible to know which factor caused the result.
- Pouring water in a stream instead of sprinkling it evenly changes the test from rainfall erosion to channel flow, which can exaggerate soil loss.
- Measuring only the muddy water volume and not the sediment can be misleading because a cup can contain lots of water but very little soil.
- Forgetting to repeat trials makes the conclusion weak because one result could be affected by uneven soil packing, water placement, or measurement error.
Practice Questions
- 1 A bare soil lane loses 24 g of soil in 3 minutes. What is its erosion rate in grams per minute?
- 2 A mulch lane loses 6 g of soil while the bare soil lane loses 30 g. What is the percent reduction in soil loss compared with bare soil?
- 3 In a tray experiment, the grass lane and terrace lane both lose little soil, but the terrace lane produces more collected runoff. Explain how both results can happen and what they suggest about erosion prevention.