What initiates rill erosion from sheet flow?

The initiation of rill erosion from sheet flow is primarily triggered by the concentration of shallow sheet flow in low spots. When water flows over a surface as sheet flow, it is initially distributed evenly across the slope. However, as it moves, this flow tends to gather and concentrate in depressions or low-lying areas on the surface. This concentration increases the velocity and force of the water, enabling it to begin cutting into the soil and forming small channels known as rills.

As the flow becomes more concentrated, it can dislodge soil particles and create a defined channel, which is the hallmark of rill erosion. In contrast, while factors such as intense rainfall, ground cover removal, and heavy machinery usage can influence erosion processes, rill erosion specifically arises from that concentration effect of sheet flow in low areas, which drives the formation of these channels in the soil.