Rill

Sub-grooves erosion (English rill erosion, gully erosion and, in South America also Voçorocas ) is understood in the geosciences straight water erosion forms of smaller dimensions. The term is used mainly in the damage assessment of slopes, graded areas, and unpaved roads and trails.

The German Association for Water, Wastewater and Waste recommends in its Schadenskartieranleitung following definitions:

• Grooves, linear forms <10 cm depth
• Gutters, linear forms > 10 cm to <40 cm
• Ditches, linear forms of > 40 cm
• Flood channels, linear forms > 40 cm depth of greater width than depth

The grooves erosion can usually be divided into two groups:

• Extensive erosion with grooves and subordinate to channel formation and
• Individually occurring gutters, ditches and flood channels

Unpaved, slightly inclined surfaces create acceleration distances for surface runoff and thus manage large amounts of water in low-lying areas. So flood channels can arise from considerable depth. This process can become self-reinforcing if the channel cuts through a water table. In urban areas this can lead to undermining the building structure and erosion damage to roads.