Transcript The Formation Of Meanders

The Formation Of Meanders
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Meanders are curves found in the middle and lower course of a river caused by
erosion and deposition and the change in speed of water causes the meanders.
They form when alternating pools (deep areas of water) and riffles (shallow
water) develop at equal spaces along a river.
The river channel are deeper in pools so they are more efficient so has greater
energy and erosive power. Energy is lost as the river travels over a riffle as there’s
friction.
The distance between the riffles and pools mean the rivers flow is uneven and
maximum flow is concentrated on one side of the river.
Turbulence increases in and around pools as the water speeds up so the water
begins to twist and coil.
This can cause a corkscrew like current in the water which spiral from bank to
bank between pools.
The flow causes more erosion and deepening of the pools and the eroded
material is then deposited on the inside of the next bend and the river will lose
energy.
Combination of the erosion and deposition helps expand the size of the meander.
Eventually this can lead to the formation of an oxbow lake.
River flow
movement
Pool
Deposition on inside
Riffle
Erosion on outside
The meanders are found in the lower part of
the course as all rivers flow down a slope
towards the sea and will take the easiest route
available. However, the geology of the land
means a river will rarely flow in a straight path
so this is why it will meander. The rates of
deposition and lateral erosion are highest at
this part of the river and also contribute to
meanders occurring due to little potential
energy but lots of kinetic energy allowing it to
flow faster forming a meander.
Inside bend
Lateral erosion
is dominant
As the
meanders
have migrated
downstream,
meander size
has increased
Slip off slope
created on
inside bend
Inside bend
has shallow
water and
slower flow
Outside bend (river cliff
can be created)
Corkscrew like
currents
Lateral erosion
by abrasion and
hydraulic action
forms river cliff
Deep water and
faster flow on
outside bend
The formation of an Oxbow Lake
On the inside of the loop,
the river travels more
slowly leading to deposition
of silt, while water on the
outside edges tends to flow
faster, eroding the outside
banks.
Over time the loop of the
meander widens until the
neck vanishes altogether
as the gap has been
narrowed by erosion.
•In the lower course of the river meanders can
become so pronounced that they can form ox-bow
lakes.
•In the lower course the lateral erosion cuts into the
neck of the meander, narrowing it considerably.
•Eventually the force of the river breaks through the
neck, and as this is the easiest way for the water to
go, the old meander is left without any significant
amount of water flowing through it.
•Quickly the river deposits material along the side of
its new course, which completely block off the old
meander, creating an ox-bow lake.
Eventually the
bend becomes
isolated from
the river's path
and an ox-bow
lake is formed.
The oxbow lakes occur in the lower course as this is where meanders occur and the river is able to take a quicker route by
discarding the meanders curve. They are more dominant in the lower course than the middle as meanders are larger so
there is more reason to reduce the amount of energy used by finding a quicker route.