Some soil erosion is natural, but accelerated erosion is not. A canopy of trees and shrubs, a thick leaf layer, or dense stand of grass protects soil in its natural state when raindrops fall or winds blow. We speed up erosion by removing this protective blanket when we use poor management during tillage, grazing, timber harvest, or construction. Wind and water erosion create sterile soils, fill the air with dust, plug road ditches, carry pollutants, and clog fish habitat. It pays economically and environmentally to keep soil in place.
A raindrop is like a miniature water bomb; it hits the ground at 20 miles per hour. When raindrops hit bare soil, water can splash soil up to 6 feet away, carry particles off the field, and drop sediment into drainage ways. Wind also dislodges, moves, and transports soil particles, especially in dry, windy climates.
Most Oregon soils begin to lose their ability to support plants when they erode more than 5 tons of soil per acre each year. This usually occurs through a process called sheet erosion, the gradual loss of a thin layer or “sheet” of soil. Since 10 tons of soil lost per acre equals the thickness of a dime, sheet erosion can be very hard to see!
Look for these clues of sheet, gully, and streambank erosion:
- Small rills or gullies begin to show.
- Dust clouds appear.
- Soil collects along fences.
- Cloudy or muddy water flows down the field, road, or driveway.
- Pebbles and plant pieces are supported on “pedestals” of soil because the surrounding soil has been eroded away.
- Soil splashes on windows, walls, and plants.
- Sediment builds up at low spots in the field.
- Streams and rivers run cloudy after a rain.
- Streambanks crumble and fall into stream.
Based on Fact Sheet number 13 in the Tips for Small Acreages in Oregon series.
Stream bank erosion is a natural process. All river systems have erosion, but the rate of natural erosion is generally much slower and of a smaller scale. Too much erosion can pollute water supplies, cover fish habitat, and threaten property. When a stream is healthy, it balances water flow, the sediment it can carry, and its shape and energy (the same energy used in hydroelectric dams). Flowing water tends to move from side to side as seen in meandering streams. Stream meanders and plants growing along the banks reduce the erosive energy of a stream and trap sediment.