Meander Formation

This powerpoint looks at the formation of meanders. It leads students through their formation and then ends with an exam question.

1. Meander Formation

4. Learning Outcomes
You will be able to explain the sequence involved in the
formation of a meander.
You will be able to explain the sequence using the key
terminology.
KEY WORDS – helicoidal flow
sinousity
thalweg
centripetal force

6. Meander Formation
Riffles and Pools
Riffle – a shallow part of the
channel
Pool – a deep part of the
channel
On average pools occur 5-6 times the width
of the river bed

7. Meander Formation
The riffle reduces the hydraulic radius of that section of the
channel as the water flows inefficiently over it.

9. Asymettrical shape

10. The meandering Thalweg
Thalweg – the line of fastest flow in a river

11. Centripetal Force
At times of high flow
the water is thrown
around the riffles and
is thrown to the edge
by centripetal force
eroding and
undercutting it.
(MAINLY ABRASION
AND HYDRAULIC
ACTION)

12. Deposition
Slower flow on the inside of the bend leads
to depostion there.
It is slower because the reduction in the
rivers efficiency being reduced due to the
frictional contact with the river bed.

13. Helicoidal Flow
The movement of water in a meander has
been found to move from the outside to the
inside.
This helicoidal flow allows material eroded
from the outer bank to be moved to the
point bar on the inside of the next meander
downstream.

14. Helicoidal Flow
•Corkscrew motionCorkscrew motion
•In bends, water forced to outside of bend hits bank In bends, water forced to outside of bend hits bank
with forcewith force
•Water piles-up on outside of bendWater piles-up on outside of bend
•Forced downward along river cliff, back towards point Forced downward along river cliff, back towards point
barbar
•Transfers and reverses motion around next Transfers and reverses motion around next
alternating bendalternating bend

16. Exiting the meander
As the water exits the meander the
channel becomes shallower. This
reduces the hydraulic radius thus
increasing deposition.
As such new riffles are created.

18. Sinuosity
Actual channel length
Straight Line Distance
A sinuosity of 1.5 is the dividing line between a straight and
meandering channel.
= sinousity

19. Point Bar
River Cliff
Thalweg

20. Thalweg
Deposition
Point Bar
Helicoidal Flow
River Cliff
Abrasion
Hydraulic Action
Riffle
Pool
Sinuosity
Meander
Centripetal Force

21. Explain the formation of a meander
(8 marks)

24. Meander Formation
Explain the formation of a meander using
helicoidal flow
sinousity
thalweg
centripetal force