The River Course
Features of the Upper Course
Features of the Lower Course
• Potholes
• Flood Plain
• Waterfalls
• Meanders
• Rapids
• Ox Bow Lakes
• Levees
• Estuaries and Deltas
Features of the Middle Course
• Flood Plain
• Meanders
River Terraces
The Hydrologic Cycle
Formation of a Waterfall
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Resistant, hard rock lies on
top of softer rock type in a
river channel.
The underlying softer rock is
eroded more quickly than the
harder rock and so the
resistant rock is undercut.
Over time the resistant rock
will become increasingly
unsupported.
The harder rock will
eventually collapse under its
own weight.
Once it has collapsed, the
rocks which have shattered
will be swirled around at the
base of the waterfall, due to
the force of the water.
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This will cause the formation of
a plunge pool at the base of the
waterfall.
This process will happen
continuously, causing the
waterfall to move backwards
(retreat).
Waterfall retreats upstream
Overhang collapses
Hard Rock
Soft Rock
Plunge pool develops
undercutting
Where the 2 layers of rock are very thin,
there will be no obvious collapse, so the
water will just swirl round, causing rapids
Formation of a Flood Plain
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The river widens its valley by lateral
erosion (horizontally)
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The river uses much of it’s energy
transporting large quantities of
material
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When the river floods, after a
period of heavy rainfall, the
alluvium (sedimentary deposits) are
spread across the valley floor, and
deposited.
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Every time the river floods another
layer of alluvium is deposited and a
flood plain is formed.
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When the river is losing energy, for
example after a flood, the coarsest,
heaviest material is deposited first,
as this uses the most energy to
transport.
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Over time this can form a natural
embankment, called a levee.
Formation of a Meander
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In every river channel, even very
straight channels, riffles and pools
develop.
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Pools are deeper stretches of slow
moving water, usually with fine alluvial
deposits
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Riffles are shallower sections of faster
flowing water, flowing above coarser
material
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Once pools and riffles have developed
in a river channel, the river swings from
side-to-side
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This side-to-side motion is then
assisted by erosion and deposition of
the river channel
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The meander becomes more curved as
a result of erosion
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Erosion occurs on the outside bend
where velocity is strongest and the
water is deepest.
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On the other side, deposition occurs,
where the current is weakest
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Over time, the meander becomes more
and more curved, due to erosion and
deposition, but also because of the
movement downstream.
Formation of an Ox Bow Lake
• Oxbow lakes form during periods of flood
• The water is looking for the fastest, most direct route
and so instead of flowing round the meander, it cuts
straight across.
• Eventually the water inside the Oxbow lake will
either evaporate or silt up
Task 1:
Describe fully, with the aid of an annotated
diagram, how one of the following river
features is formed:
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Waterfall
Flood Plain
Meander
Ox Bow Lake
(6)
Formation of a River Terrace
• During glaciation, the land was
pushed downwards under the
weight of the massive ice
sheets
• Since the ice age ended, the
land has been slowly rising to
its former position
• Rivers try to adjust to this by
eroding back into its former
flood plain
• Areas of the floodplain remain
as river terraces
Formation of Estuaries and Deltas
• When a river enters the sea its
flow characteristics become
very different
• Velocity is reduced, and the
load has been deposited
• The mouth of the river
broadens to form an estuary
• Tides sweep up the mouth of
the river clearing it of any
remaining material, which is
then taken into the sea
• The sediments that is not
transported into the sea from
the estuary forms sand and
mud banks
Task 2:
For either a River Terrace or an Estuary,
describe in detail, how it is formed
(4)