Meanders (Fluvial Erosion) Flashcards
How are meanders formed?
Rivers have alternating bars of sediment on their beds and the water has to move around them. This creates alternating shallow sections (riffles) and deeper sections (pools).
The swing of water directs the maximum velocity towards one side of the bank = undercutting. An outer concave bank is created. Deposition on the inside of the bend- the convex bank. Its sinuosity increases but it does not widen.
What is the cross section of a meander?
Asymmetrical- the outer bank forms a river cliff or bluff with a deep pool close to the bank. This bank is undercut with erosion, particularly abrasion and hydraulic action. The inner bank is s gently sloping deposit of sand and gravel called a point bar.
What are meanders?
Sinuous bends in a river.
How are meanders affected by helicoidal flow?
Meanders are perpetuates by a surface flow of water across to the concave outer bank with a compensatory subsurface return flow back to the inner bank.
Eroded material from the outer bank is transported away and deposited on the inner bank.
What is helicoidal flow?
Corkscrew-like movement of water.
How are point bars likely to be maintained?
By sediment from erosion at the bluff of the meander upstream on the same side of the channel.
Where is the greatest zone of erosion?
Downstream of the midpoint in the meander bend- because the flow of the strongest current does not exactly match the shape of the meander.
Why do meanders migrate downstream?
Erosion continues on the outer bank- it moves laterally and downstream.
What can be seen on the floodplains?
Imprints of former channels- aerial photographs.
