Soil Conservation - How Soil Erodes

Soil erosion is caused mainly by the actions of water and wind. There are several different types of water-caused erosion: sheet, rill, gully, and stream channel. In sheet erosion, the flow of water over the surface of the soil detaches and transports particles in thin layers. Concentrated flows of water form small channels or grooves (rills), and eventually develop larger gullies that carry away large amounts of soil. Sometimes, underground tunnels are formed by erosion of the subsoil. Eventually, the tunnel roof falls in to form deeper gullies. Stream channels erode when soil is removed from the fringing banks, or from within the channel of the stream itself.

Soil erosion is influenced by several variables, especially climate, soil type, density and types of plants and animals, and topography. Climatic factors include precipitation, evaporation, temperature, wind, humidity, and solar radiation. Frequent and extreme changes in these conditions, such as freezes and thaws and severe rainstorms, often increase the rate of erosion.

Soil conditions that affect erosion include detachability and transportability. Detachability is the tendency of soil particles to separate from each other. Detachability increases as the size of soil particles increases. Transportability is the ease with which soil is carried from one location to another. Transportability increases as the size of soil particles decreases.

Vegetation helps to reduce erosion by intercepting rainfall, decreasing the surface velocity of runoff, physically restraining soil movement, improving the porosity of the soil so that percolation is rapid, and by decreasing the amount of runoff, by evaporating water to the atmosphere through plant transpiration.

Soil topography features that influence soil erosion include the degree, shape, and length of the slope, and the size and shape of the watershed. Erosion increases rapidly with increasing steepness and length of slope.