The National Soil Erosion Research Laboratory
A channel is concentrated flow path for water leaving a field or watershed. Channels may be permanent waterways or may be tilled across (see ephemeral gully).
Erosion in channels is mostly caused by downward scour due to flow shear stress. Side wall sluffing can also occur during widening of the channel caused by large flows.
Channel erosion can be the first stage in development of a classical gully.