Rejuvenation

By Alex Jackson

Rejuvenation occurs when the river’s base level falls (i.e. when sea level falls). This can be a consequence of either a fall in the amount of sea water or the land rising. Both are the result of the comings and goings of ice ages. The effect on rivers is to produce features called “knick points” (which can be seen as waterfalls and rapids), river terraces and incised meanders.

Features Of Rejuvenation

Incised Meanders

Incised meanders are meanders which are particularly well developed and occur when a river’s base level has fallen giving the river a large amount of vertical erosion power, allowing it to downcut. There are two types of incised meanders, entrenched meanders and ingrown meanders. entrenched meanders are symmetrical and form when the river downcuts particularly quickly. Due to the speed which the river downcuts, there is little opportunity for lateral erosion to occur giving them their symmetrical shape. Ingrown meanders are asymmetrical. They form when the river downcuts at a less rapid pace, giving the river opportunity to erode laterally as well as vertically.

An entrenched meander along the San Juan River

An entrenched meander on the San Juan River, USA.

Copyright “Finetooth” from Wikimedia. Licensed under the Creative Commons 3.0 license.

River Terraces

A rejuvenating river can erode vertically into the former flood plain to produce features called river terraces. If vertical erosion is rapid then paired terraces are formed either side of the channel. If vertical erosion is slower though, unpaired terraces form as the river is given opportunity to meander. River terraces are particularly useful for settlements as they provide flat areas above the present floodplain. Oxford, Cambridge and London all developed on the river terraces of the Isis, Cam and Thames respectively.

A river terrace along the River Dovey.

Copyright Elaine Burt. Licensed under the Creative Commons 2.0 license.