Base level is the lowest point to which erosion by running water can occur. The graded profile of a river is upset by a negative change in base level.
This leads to a return to vertical erosion and the river has greater gravitational potential energy.
The fall in base level may be due to a fall in sea level or an increase in the relative height of the land in relation to the sea aka either the land goes up or the sea goes down.
In the UK rejuvenation has taken place several times due to rising sea levels and more recently as land slowly begins to rise isostatically.
Causes:
-Drop in sea level due to climate change or global sea levels falling
-Rise in land due to tectonic uplift
-Isostatic uplift (land lifting up after an ice sheet has melted)
Impact on Meanders:
Entrenched Meanders
-Cross Section is symmetrical
-Former where there is more resistant rock
-Same height on both sides
-Steep sides
-Quicker rejuvenation
-More vertical erosion than and incised meander
Ingrown Meanders
-Cross section asymmetrical
-One side steeper than the other
-Vertical erosion is less dominant allowing some lateral erosion to take place
-This leads to less steep banks
-Formed by the downward erosion of an existing meander
-Good for fortifications
Features of rejuvenation:
-Waterfalls and knick points
-Terraces (old flood plains) eg on the River Thames, like the Taplow Terrace and the Boyn Hill terrace
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