3. A. EROSION
A river can erode material from its bed and
banks Fluvial erosion occurs where a river is
flowing fast, so it has a lot of energy to erode
the bed and banks of the river. This mainly
occurs in the upper portion of the river. This
occurs in 3 different ways:
Abrasion
Hydraulic Action and
Attrition
4. • Abrasion – Moving water throws particles it is
carrying against the bed and banks of the river
which then dislodges more material
• Hydraulic Action - The sheer force of the water
pounding into the bed and banks can dislodge
material
• Attrition - Particles being carried downstream
knock against each other, wearing each other
down. This results in smaller, rounder particles as
you move downstream
5. B. Methods of Transportation
Fluvial transportation mainly occurs in the mid
section of the river. Rivers transport larger
material (e.g. rocks) where they have the most
energy and smaller material (e.g. ash0 where
they have the least energy. This occurs in four
main ways:
Solution
Suspension
Saltation
Traction
6. • Solution - Some minerals (particularly in
limestone areas) dissolve easily in water and are
not visible to the naked eye and are carried ‘in
solution’ downstream
• Suspension – As the speed or velocity of a river
increases, it is able to pick up and carry larger and
larger particles in its flow. Where particles are
carried along in the flow and are not in contact
with the river bed, they are said to be travelling in
suspension.
7. • Saltation - Heavier particles may not be held in
the flow all the time but may be bounced along the
bed
• Traction - The heaviest particles (eg boulders)
cannot be carried so are rolled along the river bed.
Such particles may only be moved when the river
has a large volume of water in it
8. C. Deposition
This occurs in a river when the kinetic energy is
LOW. This means the river speed is slow and
therefore the flow cannot carry the particles any
longer. This takes place mainly at the base of
the river where it is wide and slow.
9. Landforms Created
There are different landforms created at each
section of the river, as different processes
dominate
UPPER COURSE: Narrow channel, fast
moving, EROSION dominates
MIDDLE COURSE: Medium channel, medium
speed, TRANSPORT
DOMINATES
LOWER COURSE: Wide channel, slow
moving, DEPOSITION
dominates
10.
11. Upper Course Landforms
Here the river is fast flowing but there is little water
and load so does not have the power to erode the
hillsides. Instead it erodes downwards to create v-
shaped valleys
e.g. Whakapapaiti River
12. Middle Course Landforms
Here the river is wider and less steep. This means
there is a greater volume of water allowing the
river to erode sideways. This creates meanders
which can change the course of the river and ox-
bow lakes.
13. Lower Course Landforms
The river is at its widest and slowest at this point.
This drop in energy means that deposition
dominates forming braided channels and deltas.
Braided channel Delta
14.
15.
16.
17.
18.
19. It’s your turn …
• Draw a simple diagram
to represent each
process within the river
• Solution =
• Suspension =
• Saltation =
• Traction =
20. River Features
• Rivers are eroding, transporting and depositing
constantly within the drainage basin system.
• The river can be divided into 3 sections
• Upper Course at the Source,
• Middle Course
• Lower Course at the Mouth of the river.
• The river displays different characteristics at
each section
21. Fluvial (River) Processes
1. Fluvial processes create landforms.
2. These processes are affected by specific factors.
22. Also known as ‘Torrent’ or ‘Youth’ stages
Interlocking Spurs
In the Upper Course, the river is
fast flowing, but there is little
water and load. The river is
often called a stream and does
not have the erosive power to
remove the hillsides (spurs), but
erodes downwards instead.
EROSION TYPE: Vertical and Headward
24. Pothole
s
EROSION
TYPE: Vertical
( by EDDY
CURRENTS )
Boulders broken off by erosion that sit on the river bed create swirling
eddy currents as the water flows past as the river is not strong enough yet
to move the boulders by TRACTION. These eddies swirl the boulder
round and erode a pothole in the river bed by ABRASION.
25. Waterfall
and
Gorge 2
(PROFILE VIEW)
EROSION
TYPE: Vertical
and Headward
26.
27. Also known as the ‘Mature’ stage
Meanders 1
(Aerial View)
Meanders are formed
because the current swings
to the outside of a bend and
concentrates the erosion
there. Deposition occurs on
the inside of the bed where
there is not enough energy to
carry load.
EROSION TYPE: Lateral
28. Meanders 2
(Profile View / Cross
Section X - Y)
EROSION TYPE:
Lateral
This cross section clearly shows the eddy current (near ’X’)
formed by the velocity of the river being concentrated on the
outside of the bend. These UNDERCUT the bank causing the
formation of a RIVER CLIFF. On the inside (NEAR ‘Y’), a SLIP-
OFF-SLOPE is formed where current is too slow to carry any load.
29. Ox-Bow Lake 1
(Aerial View)
Ox-bow lakes are
formed when two
meander RIVER
CLIFFS are being
eroded towards each
other. These will
eventually meet,
causing the river to then
EROSION TYPE: Lateral
flow across the bottom
31. Braided Channels (Oblique Side View)
DEPOSITION
FEATURE: no
erosion in
the Lower
Course
In the Summer months, load is dropped by the low volume of low-energy
water in the river. These build up to form obstructions in the river and it
divides up to flow around them. In the winter, it is likely that the river
volume will increase and remove these obstructions.
32. This deposition feature is one
Delta (Aerial
of the largest. When the
View)
flowing river hits the non-
flowing sea, energy is suddenly
lost. This causes all of the load
in the river to drop in the river
MOUTH. This builds up over
time to create a delta – an area
of land. The river divides into
DISTRIBUTARIES to continue
to the sea, which is now some
way away from its original
meeting point.
33.
34. Ca
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