knickpoint

A knickpoint is a point along a river or stream where there is a sharp change in the gradient of the bed profile, often appearing as a waterfall, rapid, or step in the channel. It marks a discontinuity in the longitudinal profile and represents a location where differential erosion by the stream has created a steep, resistant front against more erodible bedrock or sediment downstream.

Knickpoints form in response to changes in base level, tectonic uplift, or shifts in climate that alter discharge and incision rates. Common triggers include a relative drop in base level (such as sea level fall), uplift of the land, or variations in lithology and rock strength that produce a contrast in erodibility. Anthropogenic influences, such as dam construction and sediment retention, can also contribute by changing sediment supply and incision dynamics.

Once established, knickpoints tend to migrate upstream in a process known as knickpoint retreat or headward erosion. The rate of retreat depends on factors such as rock hardness, jointing and fracturing, channel slope, discharge, and resistance of the downstream bed material. Over time, a knickpoint may move several kilometers upstream, leaving behind fluvial terraces and a relict channel profile.

Significance in geomorphology lies in using knickpoints as indicators of incision rates, tectonic activity, or past climate change. They help reconstruct landscape evolution and timing of fluvial response to environmental change. Knickpoints occur in diverse settings, from mountain belts with rapid uplift to regions with strong lithologic contrasts along river corridors.