The National Soil Erosion Research Laboratory
Classical gullies are an advanced stage of channel erosion. They are formed when channel development has progressed to the point where the gully is too wide and too deep to be tilled across. These channels carry large amounts of water after rains and deposit eroded material at the foot of the gully. They disfigure landscape and make land unfit for growing crops.
Ephemeral gullies, on the other hand, can be plowed in and tilled across
depending upon their depth and width. They are somewhat transitory rather
than permanent like classical gullies. Ephemeral gullies will reform in the
same location in a field where flow from upslope regions concentrates.
Creation of a grass waterway where an ephemeral gully forms can often
control this type of erosion.