river rejuvenation
DESCRIPTION
River rejuvenationTRANSCRIPT
River Rejuvenation
All your knowledge of rivers should help you to understand this final
process which forms a unique set of landforms.
RejuvenateTo restore to a former state; to make fresh or new again
Learning Outcomes
• To understand how changes in base level create different landforms.
• Explain the landforms produced by river rejuvenation (15 marks)
Base Level
• Listen to the explanation of base level and then produce a diagram to explain what it is and how it changes.
Base Level
• Base level is the lowest level to which erosion by running water can take place.
The River System
• River’s are always attempting to reach a state of dynamic equilibrium where there is a balance between the rate of erosion and deposition.
Dynamic Rivers
• In reality a river is rarely, if ever, in a state of dynamic equilibrium.
• Changes in discharge and sediment load are constantly changing the profile of the river.
For example….
• Waterfall• Erosion near the waterfall• Deposition lower downstream
• Lengthy period of heavy rain
Base Level changes
• Eustatic Change– Changes to sea Level
• Isostatic change– Glacial rebound
Changes
• Positive
Sea levels rise in relation to the land.
The river loses energy and as such deposition dominates and coastal areas flood.
• Negative
Sea levels fall in relation to the sea.
Land emerges from the sea, steepening the river gradient thus increasing the rivers erosional power.
Base Level
• Produce your diagram
Key Points
• Rivers begin to regrade from the point nearest the sea.
• It often happens again before a river has reached dynamic equilibrium giving it a partly graded profile.
• Knickpoints
• Incised meanders
• River terraces
• Waterfalls
Changes to the cross profile of the river
River in grade
Flood plain
Waterfall retreats cutting
a lower valley
Fall in sea level
River bluffs
New flood plain forms
New flood plain forms
River bluffs
Waterfall decreases in size to form rapids (knick point)
River Terrace
Terraces
Knickpoints and waterfalls
Incised Meanders
• The likely story is that the streams once flowed across nearly flat lowlands.
• Then, uplift of the rocks began, giving the streams a steeper slope to the sea and so speeding their flow and causing them to erode.
• But, the uplift was gradual enough that the streams held their old courses.
• The streams cut downward without a change in pattern, which is called incision.
Write three level descriptors for this question
Explain the landforms produced by river rejuvenation (15 marks)
Level 1 : BASICLevel 2 : CLEARLevel 3 : DETAILED
Review
BASE LEVEL
INCISION
ISOSTATIC UPLIFT
KNICK POINT