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Water erosion

Mechanics | Wind erosion | Risk management

Back to Soil erosion

The soil conditions that lead to water erosion are low vegetative cover (bare soil surface), low water infiltration rates, and poor aggregate stability.

The impact of a single raindrop on a bare soil surface breaks up soil aggregates. Bigger drops mean high energy and greater intensity of the storm the greater the erosive power. For example, a 25 mm storm of 1 hour duration and with a drop size of 4 mm will deliver some 8 million Joules of power to 1 hectare of soil, and the total amount of water delivered is 250 tonnes!

When rain falls faster than the surface of soil (change to soil surface) can absorb it, runoff is generated. If the land slopes the power of the water is increased. Even if only 10 % of the storm detailed above is not absorbed, 25000 litres of water will be moving across the soil surface.

Types of water erosion
Water erosion can occur as sheet, rill, gully or tunnel erosion.

Sheet erosion

Sheet erosion is the removal of a fairly uniform layer of soil from the land surface by raindrop splash and/or runoff.

Rill erosion

Rill erosion is numerous small channels of less than 300 mm depth. Rill erosion primarily caused by soil detachment from concentrated runoff. Rills can be readily removed by cultivation.

Gully erosion

Gully erosion is the removal of soil by running water, resulting in the formation of channels sufficiently large that they disrupt normal farming operations and that are too large to be filled by cultivation. For more technical details on gully erosion in Victoria
click here.

Tunnel erosion
Tunnel erosion can be considered a special type of gully erosion and is sometimes known as piping. Tunnel erosion is the removal of subsoil when the surface soil remains intact producing long cavities beneath the surface. These cavities enlarge until they collapse forming circular holes from the cavity to the soil surface. Further collapse can covert the cavity into a gully. For more technical details on tunnel erosion in Victoria click here.
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