River landscapes and processes
Geography GCSE WJEC
River Processes
Erosion - where parts of the river bed and
bank get eroded / removed from the
landscape
Transportation - where the eroded material
is carried from one place to another through
the river system
Deposition - where the river load becomes
too heavy for the river to carry and is
dumped down / deposited.
A river can erode material from
its bed and banks in 4 main ways
• Abrasion – Moving water throws particles it is
carrying against the bed and banks of the river
which 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
Can you remember the 4th type?
Methods of Erosion
• Abrasion –
• Hydraulic Action • Attrition • Solution-
Methods of Transportation
Rivers transport material in 4 main ways
•Solution - Some minerals (particularly in limestone
areas) dissolve easily in water and are not visible to
the naked eye
•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.
Methods of Transportation
• Saltation - Heavier particles may not be
held in the flow all the time but may be
bounced along the bed
• Traction - The heaviest particles are
rolled along the bed. Such particles may
only be moved when the river has a large
volume of water in it
solution
The V - Shaped Valley
Can you mark the V-shaped valley’s on this photo?
• In the UPPER STAGE the river erodes
downwards?
KEY
WORDS
Use this sketch to help explain how V shape valleys
form
Waterfalls and Gorges
1.
Draw the stages in the formation of a waterfall
2.
Explain in as much detail what is happening at 3
3. What is happening here? (see next slide)
??
Waterfall formation flash
Case study:
Niagara Falls
USA
Canada
USA
Canada
Canada Horseshoe
750 meters
52 meters
high
20 million visit the falls every year
Visitors !!!
Hard Resistant
Rock - Limestone
52 meters
Weak Rock Shale
Meanders
1. Can you mark the
fastest flow on this?
2. What type of erosion do you
think is happening?
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
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.
Ox- Bow Lakes
(Middle Course)
What is Meander Migration
…. What do you think might happen
here?
What is Meander Migration
Ox-Bow Lake 1
(Aerial View)
EROSION TYPE: Lateral
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 flow
across the bottom of the
diagram.
Ox-Bow Lake 2
(Aerial View)
Can you annotate this photo graph ?
Can you annotate this photo graph ?
What are Flood Plains and
levees?
•
Levees
Floodplain
Levees
Leeves
River
Leveés and Raised Beds 1
(Front View)
DEPOSITION
FEATURE: no
erosion in
the Lower
Course
Leveés are formed when rivers flood. The river water
overflows the banks of the river and immediately slows
down due to friction with the FLOODPLAIN. This drops the
larger particles first, building up a raised river bank called a
LEVEÉ.
Deltas
Delta
(Aerial View)
This deposition feature is one of
the largest. When the 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.
Can you work out what the river is trying to do by using this diagram?
Flooding in Boscastle
16th August 2004
Map of Boscastle.
Aerial Photo.
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
The Boscastle Drainage
Basin
The valley sides are
steep so …
Trees have been cut
down above the river.
This could make
flooding worse
because...
Settlements have
been built upstream.
This could mean…
Rainfall in this area is
The mouth of the
high so...
river is narrow so…
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
The narrow valley can be appreciated when looking
upstream from the harbour.
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
Causes of the flood:
1. Heavy localised rainfall. 89mm of rain fell in an hour.
2. Saturated ground from previous rainfall.
3. Topography of the land – the landscape upstream of
Boscastle acts as a funnel, directing vast volumes of
water into the village. The valley sides are steep
sided.
4. Narrow river channels in the village itself.
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
The river reaches
bankful stage. Any
further water will lead
to…
The velocity is..
The ground is
saturated so any
further rain can’t be
The discharge
is..so..
absorbed
The river is
discoloured
because..
The carrying capacity
of the river has
increased because..
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
In an operation lasting from mid-afternoon until 2:30 AM, a fleet of seven
helicopters rescued about 150 people clinging to trees and the roofs of
buildings and cars. Amazingly, no major injuries or loss of life were
reported. About 90% of Boscastle’s economy is tourism and about 2/3 of
this income usually occurred during the school holidays.
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
Impacts of the flood:
•Around 115 cars were washed into the sea
•Several boats were also lost,
•6 buildings were destroyed
•Loss of tourist trade
•Fall in house prices
•B3263 road was blocked by flood waters
•businesses destroyed including visitor centre
•Economic damage estimated 2006 = £300 million
•Seven helicopters rescued about 150 people
•No major injuries or loss of life were reported.
•About 90% of Boscastle’s economy is tourism based and
about 2/3 of this income usually occurred during the school
holidays.
•House prices fell as houses termed flood risks
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
How have decision makers responded?
A £4.5m scheme to improve flood defences.
Boscastle main car park.
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
The scheme stretches along the valley, incorporating
drainage, sewerage systems and land re-grading.
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
The river lies here.
Boscastle car park is being raised in height. This will
stop the river from bursting it’s banks so easily.
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
This drain allows water to run into the lower section
of the river quickly.
Boscastle flood defences.
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
The river channel is being made deeper and wider so
that it can accommodate more water.
The lower section of the village.
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
New sewerage systems are being put in place.
The lower section of the village.
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
Bridges that hindered the drainage of the floodwater
are being replaced by stronger bridges that are less
likely to get blocked.
Notice attempts to draw
in much needed custom.
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
So what’s been
done to mitigate
against flood
reoccurrence?
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
The bridge has
been raised and
widened
.
The narrow river
Valency channel has
now been widened
The river banks
have been raised
The channel has
been deepened
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
Whether flooding is prevented remains to be seen...
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
PROGRESS CHECK QUESTIONS:
Must…
Could..
What were the causes of the Boscastle
flood?
How did people make the Boscastle
flood worse?
Name 5 effects of the Boscastle flood.
Make 2 lists to show long term and
short term effects of the Boscastle
flood.
How can the risk of flooding be
reduced?
List 4 ways that flooding can be
reduced. For each, say how effective
the method would be.
MUST: Annotate images and diagrams to show the causes and effects of
the Boscastle flood.
Flood Management Strategies
1)
2)
3)
4)
Explain how each method works …
give good points & bad points of each strategy
Give viewpoints of different groups of people
Consider whether the strategy is sustainable
Sustainable
Planning - Land Use Zoning
Preparation - homes and businesses
Preparation – well beforehand
Preparation - beforehand
Preparation
River Management – hard engineering e.g. Dams
Hard options
tend to be
more
expensive and
have a greater
impact on the
river and the
surrounding
landscape.
They involve
engineering
(building) a
solution to
the flood
problem.
Building dams e.g. Talybont Reservoir
River Management – hard engineering
Building
flood walls
/ bunds –
permanent
defences
River Management – hard engineering
Altering the
channel –
widening,
deepening,
straightening
- lining in
concrete.
River Valency
Boscastle
2007.
Hard Engineering – flood relief channels
A channel can be
built to divert
some of the flood
water away from
the main channel
(like a road bypass)
Hard Engineering – flood protection
Individual
householders
can flood proof
their home for
about £20,000.
Businesses use
‘Floodguard’
too
A Flood Resilient Home
Temporary flood barriers
• Geodesign barriers- used in
Bewdley 24 times in last 4 years.
Take about 6 hours to put up
Soft Engineering - afforestation
Soft
options are
more
ecologically
sensitive.
e.g. encourage
landowners in
Upper Catchment
of R Severn to
plant more trees
Soft
Engineering
–
remove
drains
Restore
blanket
bogs on
moorlands
– remove
any
farmer’s
drains
Soft Engineering – natural floodpains
Allow
floodplains to
stay natural –
prevent
building on
floodplains.