River rejuvenation is the renewal of the erosive activity of the river.
This means that the river starts eroding its channel more vigorously than it has been doing before due to changes that take place in the course of the river.
Rejuvenation can occur at any stage of the rive
River rejuvenation may occur due to the following reason.
Change in base level
The base level is the lowest level to which the river can erode by running water.
This is normally the sea level through the inland lakes can also be the base levels.
A horizontal layer of resistance rock can also be a temporary base level.
Change in sea level may be due to the following three factors.
A drop in sea level.
This can change the position of the river mouth to move further seaward.
A steeper gradient, therefore, occurs between the new and the old position of the river mouths.
The river starts to flow swiftly and the vertical erosion resume.
This deepens the river valley which progressively extends back into the flood plain as well.
Regional or local uplift of land
If the section of land along the course of the river slowly rises, the river may be powerful enough to continue down cutting.
The rising of the land, increases the gradient and makes the river flow swiftly. This increases its erosive power if originally the land was almost flat,
A new narrow and deep valley may cut into the old valley forming a rejuvenated gorge.
Unequal regional subsidence of land
If the land along the course of the river starts to sink unequally that is where the downstream side sinks more than the upstream side, an increase in gradient will occur causing the river to cut down more vigorously than before.
Rejuvenation caused by changes in sea level is known as dynamic rejuvenation
Increase in the discharge of the river.
The ability of the river to erode partly depends on the volume of the river. The rate of erosion is higher if the volume of the river is high.
An increase of the volume of the river far above average may be caused by the following factors,
An increase in precipitation
Climatic changes may cause the region around the basin of the river or river catchment area to receive higher rainfall than normal.
For example, an increase in temperature would cause ice to melt thereby releasing larger quantities of meltwater
Where a river captures the headwater of another river, an increase in its volume of water will be realized because of added water from the captured river.
River rejuvenation resulting from increased river discharge is known as static rejuvenation.