knickpoint

 In geomorphology, a knickpoint or nickpoint is part of a river or channel where there is a sharp change in channel slope, such as a waterfall or lake. Knickpoints reflect different conditions and processes on the river, often caused by previous erosion due to glaciation or variance in lithology. In the cycle of erosion model, knickpoints advance one cycle upstream, or inland, replacing an older cycle.

A knickpoint that occurs at the head (furthest upstream extent) of a channel is called a headcut. Headcuts resulting in headward erosion are hallmarks of unstable expanding drainage features such as actively eroding gullies.