rills

Rills are narrow channels formed by the erosion of soil due to surface runoff. They are typically less than about 0.3 meters wide and can be a few centimeters to several tens of centimeters deep. Rills are often temporary, appearing during or after rainfall and sometimes remaining only for a short period, though they can persist on slopes with ongoing runoff or limited vegetation.

Rill formation occurs when rainfall impacts detach soil particles and runoff becomes concentrated along small surface pathways. Factors controlling their development include slope gradient, soil texture and structure, organic matter content, crust formation, vegetation cover, and rainfall intensity and duration. As erosion progresses, shallow rills can deepen and widen, and if rainfall and runoff continue, rills may coalesce into larger channels known as gullies.

Rills differ from other channel forms. They are smaller and more transient than gullies, and they typically form from surface runoff rather than from established streams. In agricultural and disturbed lands, rill erosion is a common early stage of soil degradation and can significantly reduce infiltration, increase runoff, and transport sediments downslope.

Management and restoration focus on reducing surface water concentration and stabilizing the soil. Practices include maintaining vegetation cover, implementing contour farming or terracing, using cover crops and mulches, reducing soil disturbance, and, where appropriate, constructing micro-detention features to slow runoff and promote infiltration. Soil scientists sometimes map rill density to assess erosion risk and guide conservation plans.