River rejuvenation occurs when a river's base level changes, altering the gradient of the river channel and increasing its erosive power. This causes the river to cut downward into its channel, forming landforms such as waterfalls, incised meanders, and river terraces. Changes in base level are typically caused by isostatic adjustments to sea level from glacial rebound or eustatic sea level changes.

1. River Rejuvenation All your knowledge of rivers should help you to understand this final process which forms a unique set of landforms. The big picture

2. Rejuvenate To restore to a former state; to make fresh or new again

3. Learning Outcomes To understand how changes in base level create different landforms. Explain the landforms produced by river rejuvenation (15 marks)

4. Base Level Listen to the explanation of base level and then produce a diagram to explain what it is and how it changes.

5. Base Level Base level is the lowest level to which erosion by running water can take place.

6. 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.

7. 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.

8. For example…. Waterfall Erosion near the waterfall Deposition lower downstream Lengthy period of heavy rain

9. Base Level changes Eustatic Change Changes to sea Level Isostatic change Glacial rebound

10. 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. rejuvenation

11. Base Level Produce your diagram

12. 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

13. River in grade Flood plain

14. Waterfall retreats cutting a lower valley Fall in sea level River bluffs New flood plain forms

15. New flood plain forms River bluffs Waterfall decreases in size to form rapids (knick point) River Terrace

16. Terraces

17. Knickpoints and waterfalls

20. Incised Meanders

25. 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.

26. Write three level descriptors for this question Explain the landforms produced by river rejuvenation (15 marks) Level 1 : BASIC Level 2 : CLEAR Level 3 : DETAILED

27. Review BASE LEVEL INCISION ISOSTATIC UPLIFT KNICK POINT