As spring moves forward steadily and summer approaches, I think it is important to dedicate the next few “WWotW” to erosion features. This week we will look at rills. Rills often form as the initial sign of erosion. By definition, a rill is a narrow and shallow incision into topsoil layers, resulting from erosion by overland flow.
Rills often form on steep slopes with little to no vegetation. The overland flow of water is generally not severe on steep slopes as rills are fairly shallow features. A rule of thumb is that if you can only fit your hand in it, it is a rill. If you can step in it, it is a gully.
The image above illustrates how sheet erosion (discussed next week) concentrates and forms rills which eventually grow to form gullies.