Soil and water are two of the Earth's most important natural resources.
Erosion is the name given to the movement of small rocks, sand and soil from one place to another either by water or wind.
Water erosion is caused by ‘runoff’ water that flows over the surface of the ground when the soil is saturated (unable to absorb any more). Soil carried off in rain water can lead to sedimentation of rivers, lakes and coastal areas.
Have you ever seen soil washed away by rain or rivers? Pesticides and fertilisers get washed off agricultural land or gardens and eventually into our rivers and streams. The chemicals cause pollution that can damage and destroy local wildlife and plants.
Plants have an extensive root system that keeps soil clumped together. Plant roots can also absorb some water from the soil and this makes it harder for water to wash it away.
How can you use this knowledge to design an investigation?
Set the challenge of finding out if different land conditions affect how much soil is washed away by rain. You could use the idea in the photo, or come up with your own method.
Here are some example conditions to test:
Grass growing in soil
Leaves covering soil
Stones covering soil
World-wide problems of soil erosion:
Areas of the Amazon rainforest, in South America, are cleared to grow crops. This is called deforestation. With frequent rain vital nutrients are washed away and the once rich soil soon becomes infertile and no good for growing plants. Without the tree roots to hold the soil together flooding moves this precious growing resource off the land and causes flooding.
Find out more:
Water a piece of turf and then squeeze it. What happens? What does this show and what further investigations could you do from this?
Find out about tea plantations in India and rice growing in China, where they use a farming method called 'terracing'.