Explanation:

Gully

Gully erosion is the removal of soil along drainage lines by surface water runoff. When rills increase in size, they become gullies. Once started, gullies will continue to move by headward erosion or by slumping of the side walls. Gullies formed over a large area gives rise to badland topography (Chambal Ravines). When a gully bed is eroded further due to headward erosion, the bed gradually deepens and flattens out, and a ravine is formed. The depth of a ravine may extend to 30 metres or more.