rill

A rill is a small, shallow channel formed by running water that concentrates on the surface of soil. Rills are typically narrow and shallow, ranging from a few centimeters to several decimeters in width, and they may be dry for part of the year or flow only during rainfall events.

Formation occurs on sloped terrain where rainfall runoff is not spread evenly over the surface. Water concentrates in microdepressions and grooves, eroding and removing soil along the flow path. With repeated runoff, these grooves deepen and widen, and connected channels can form a network that may eventually develop into larger gullies. Erosion rates depend on soil cohesion, vegetation cover, rainfall intensity, and land use.

Rills are one step in the progression from sheet erosion to gully formation. They can appear rapidly after heavy rain on exposed soils or agricultural fields and may transport significant amounts of sediment during flow events. Rills often dry up between rains but can reappear with subsequent rainfall.

Implications and management for rill erosion include reduced soil infiltration, increased surface runoff, and potential crop loss. Control methods emphasize maintaining vegetative cover, mulching, contour farming, terracing, and conservation tillage to minimize surface disturbance and intercept runoff. In some cases, mechanical or structural interventions may be used to stabilize channels and reduce further erosion.

Rills are related to, but distinct from, rivulets (small streams), gullies (larger channels), and broader concepts of soil erosion and watershed management.