The Five (5) Types of Water Erosion
A raindrop strikes the soil surface forcefully. The impact shatters soil aggregates and throws soil grains into the air. On a slope, water begins to flow downhill, carrying detached soil grains with it.
This water joins other flowing water, increasing in speed, volume, and soil-carrying capacity. This order of events leads to five types of erosion. All five types can occur at the same time on any given slope.
Splash Erosion is the direct movement of soil by splashing. A soil grain can be thrown as far as five feet by raindrop splash.
These splashed particles fill the voids between other aggregates and seal the soil surface.
Sheet Erosion is the removal of a thin layer of soil in a sheet. On gentle slopes, or near the tops of steeper slopes, water moves in tiny streams too small to be noticed.
This gives the impression of losing soil in a thin sheet. Sheet erosion may go unnoticed until the subsoil appears.
Rill Erosion is visible as a series of many small channels on a slope. Water tends to collect in channels, picking up energy as it runs down the slope.
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As a result, running water carves out small but visible channels called rills. A rill is small enough to be filled in by tillage.
Ephemeral Gullies are large rills. The channel is small enough that tillage equipment can cross it and largely, but not completely, fill it in by tillage.
During another heavy rainfall, water will collect in the old channel, and erosion will begin here.
Gully Erosion is the most highly visible erosion. Gullies are so large that equipment cannot cross them.
Gullies usually begin to form near the bottom of a slope or on steep slopes, where running water has enough force to carve a deep channel.
Gully heads may back up the hill as water running into the gully collapses the sides.
Each type of erosion is important to understand for different reasons. Sheet erosion is a hidden soil loss, since there are no visible signs until the subsoil appear.
Rill erosion can also be hidden, because each tillage causes the rills to disappear. The amount of the hidden erosion can be easily underestimated by a grower.
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