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 though the inland lakes can also be the base levels. A horizontal layer of resistance rock can also be a temporary base level. Change of 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 occur between the new and the old position of the river mouths. The river starts to flow swiftly and the vertical erosion resume . This deepen the river valley which progressively extend back into flood plain as well.
- Regional or local uplift of land. If the section of land along the rivers course slowly rises, the river may be powerful enough to continue down cutting. the rising of land , increasing the gradient and making the river to 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 start to sink unequally that is where the downstream side sink more than 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 river to erode partly depend 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 melt water
- River capture. Where river captures the head water 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.
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