ZIMSEC O Level Geography Notes: Meanders and Ox-bow lakes
Meanders are pronounced bends in a river’s course
They are formed when a river twists and turn in wide bends.
They are common on the floodplain but can develop in any part of the river’s course.
Meandering is a common behaviour of fluids that avoid a straight path to flow in a twisting and turning path.
It is believed that meandering is a thermodynamics behaviour that maximizes velocity and reduces friction.
Other experts have theorized that Meanders start when friction with the channel bed and banks causes turbulence in the water flow.
This results helicoidal flow.
Helicoidal flow in a meander. Image credit uleth.ca
This is a corkscrew like movement of the water as it spirals downstream from bank to bank as shown in the diagram above.
This often occurs during floods and results in the formation of meanders and their associated features such as pools and riffles.
Helicoidal flow in a meander and the resulting features at each point. Image credit WordPress.com
Pools and riffles
Pool-this is a deep section in a meander where a lot of erosion takes place where the river’s energy builds up due to reduced friction and the water has higher velocity.
Riffle-this is a shallow section in a river where there is deposition due to reduced capacity in a river resulting from energy dissipation (reduction) in a river due to increased friction and a reduction in a river’s velocity.
The spacing of the pools and riffles are fairly regular in a river channel about six to five times the width of the channel.
Helicoidal flow is responsible for the erosion on the outside bends and then depositing it into the inside bends of meanders.