What is one of the four processes of overland erosion?

Gully formation is indeed one of the four processes of overland erosion. Overland erosion refers to the movement of soil and sediment by the action of water, primarily during rainfall events. When heavy rainfall occurs, water can accumulate and flow over land surfaces. As it flows, this water can create small channels, which grow larger over time due to the continuous movement of water and sediment. These channels are known as gullies.

Gullies represent a form of concentrated erosion as they represent the deepening and widening of the landscape caused by the persistent flow of water. They often indicate areas where soil has been stripped away significantly, which can lead to greater erosion and sediment transport downstream. This process is significant for understanding how landscapes change over time and underscores the importance of effective erosion control practices.

In contrast, river flow and wave action refer to erosion processes primarily within established water bodies, while flooding is a temporary event that may contribute to erosion but is not a process in itself. Gullies, therefore, represent a specific manifestation of overland erosion that illustrates the impact of surface water movement on landscapes.