ZIMSEC O Level Geography Notes: River Rejuvination
- Rejuvenation-occurs when there is a negative change in a river’s base level (i.e. when the river’s base level falls) which increases its potential energy and thus enables it to revive its erosive energy in the processes.
- A river’s base level is the lowest point to which a river can erode.
- A negative change in a river’s base level may be brought about by vertical uplift (for example isostatic uplift) or by a fall in the level of the sea for example due to tides.
- This change renews a river’s ability to erode due to an increased gradient.
- A rejuvenated river erodes vertically into the floodplain to produce new features that are different from those typically found in the flood plain.
Landforms resulting from rejuvenation
- Rejuvenation produces several features including: incised meanders, terraces and waterfalls/knickpoints.
River terraces and incised meanders
- River terraces are remnants of former floodplains
- Which following vertical erosion brought about by rejuvenation have been left high and dry above the current and present-day flood plain.
- If a river quickly erodes and cuts quickly into the floodplain a pair of terraces of equal height may be seen flanking the flood plain creating a valley into a valley feature known as paired terraces.
- Sometimes the river does quickly cut into the flood plain, allowing it to meander, resulting in one terrace being removed as the meander migrates downstream.
- This results in the formation of unpaired terraces.
- If uplift continues for sometime, incised meanders may form.
- These are meanders that have been cut deeply into the valley floor.
- Incised meanders are also known as entrenched meanders.
Knickpoint, rapids and waterfalls.
- Sometimes the point where the uplift occurs can be visible especially when the uplift or fall in base level is rapid.
- The point where the river crosses from the old plain into the new plain is known as knickpoint.
- A river may have to descent this knickpoint as either a rapid or waterfall.
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