Fluvial Landforms – Middle course of
river
River Channel:
 wider and deeper
 Volume of water greater than that in upper
course.
 Gradient is less than upstream portion of the
river course.
Fluvial Landforms – Middle course of
river
River Valley :
 More open V shape and wider valley floor.
 Lateral erosion of river more dominant.
 Weathering and mass wasting of valley sides.
Fluvial Landforms – Middle course of
river
Work of river :
 Vertical erosion is reduced.
 Increased volume of load and water in the river
is used mainly for lateral erosion.
 Some energy is also used for transportation.
 Some deposition also occurs.
Fluvial Landforms – Middle course of
river
Meanders, river cliffs and slip-off slopes
How meanders begin to form is uncertain.
They appear to have their origins in times of
flood and in relatively straight sections where
pools and riffles develop.
Fluvial Landforms – Middle course of
river
Fluvial Landforms – Middle course of
river
Pools: areas of deeper water.
Riffles: areas of shallow water.
Spacing between pools and rivers usually very
regular: 5x – 6x of river width
Fluvial Landforms – Middle course of
river
There is less friction in pools.
Thus, river flows faster and has more erosive
power.
Increased friction in the riffles slows water
down and more deposition takes place.
Continuous erosion in the pools and deposition
in the river accentuates the slight bends of a
river.
Fluvial Landforms – Middle course of
river
Fluvial Landforms – Middle course of
river
There exists a series secondary flow of water
in a river, other than the main flow.
One of these is called the helicoidal flow –
cockscrew movement of water.
Fluvial Landforms – Middle course of
river
Difference in velocity across the channel
causes unequal pressure distribution.
Current from the concave bank descends
downwards, undercutting and eroding the river
side.
Eroded material carried along the bed and up
the convex bank where it is deposited.
Fluvial Landforms – Middle course of
river
This current represents a cockscrew movement
of water because it continues downstream and
repeats the series of rotations.
Fluvial Landforms – Middle course of
river
As erosion continues to undercut the concave
bank, eroded materials slump down into the
river, forming a steep river cliff.
Fluvial Landforms – Middle course of
river
Continuous deposition on the convex bank
makes it shallow and deposition takes place.
These deposits on the convex bank build up
into a gently sloping slip-off slope.
Fluvial Landforms – Middle course of
river
Fluvial Landforms – Middle course of
river
The channel has an asymmetrical crosssection.
Continued erosion on the concave banks
and deposition on the convex banks cause
the meanders to migrate laterally.
Fluvial Landforms – Middle course of
river
Fluvial Landforms – Middle course of
river
References:
1. Chong, M. (2001) Aspects of Physical
Geography, Singapore: Pekoe Books.
2. Waugh, D. (2000) Geography – An
Integrated Approach, UK: Nelson