Rivers and Coasts
1. Rocks
2. weathering and erosion of rocks
3. Limestone landscapes
4. Quarrying and uses of rocks
5. Hydrological cycle
6. Types of rainfall
7. How people affect the water cycle
8. Drainage (river) basin
9. Flooding
10. River basin management
11. Boscastle – example of a flood
12. River erosion
13.Landforms in uplands
14. Landforms in the lowlands
15. Estuaries and deltas
16. Coastal erosion
17. Cliffs and cliff erosion
18. Caves, arches and stacks
19. Coastal transport and deposition
20. Landforms of coastal deposition
21. Formation of beaches and spits
22. Coastal problems in UK
23. Coastal management
24. Scarborough example of
management
1Rocks
Types of rock
• Igneous – granite, basalt, formed by
volcanic activity
• Sedimentary – chalk, limestone,
clay, sandstone, is formed from
sediments
• Metamorphic – marble (from
limestone), slate (from clay) has
been altered by heat or pressure
Drainage
• Permeable rock eg chalk and
limestone, has spaces so that water
can pass through it. There will be
no surface streams
• Impermeable rock eg clay, granite,
does not let water to pass through
easily, there will be a lot of surface
water features – reservoirs, rivers,
lakes, bogs
Hardness
• Hard rocks eg granite are difficult to
erode
• Soft rocks eg clay are more easily
eroded
The rock type will affect
• Relief (height and steepness of the
land)
• Drainage
• Amount of weathering and erosion
• Economic use – quarrying and
farming
2 Weathering and erosion
Weathering is the breakdown of rocks
where it outcrops on the surface
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Physical weathering – break down
by mechanical processes of the
weather eg freeze thaw
Chemical weathering is the break
up by chemical processes that
change the composition of the rock,
especially calcium rich rocks like
limestone
Biological weathering – break down
by plants and animals eg tree roots
in joints and other weaknesses in
the rock
Erosion is the wearing away of the
earth’s surface by rivers, waves, wind
and ice.
River erosion involves hydraulic action,
attrition, corrasion (abrasion) and
corrosion
Wave (coastal) erosion involves the
same processes
Rocks with many weaknesses (joints,
bedding planes and faults) are likely to
be weathered and eroded more quickly.
3 Limestone landscapes
The chemical weathering of limestone
produces some special landforms
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Rivers may suddenly disappear
underground where they start to
cross limestone rock
Limestone pavements are large flat
areas of limestone rock which have
very little vegetation growing on
them
Caves and caverns are found
underground
Limestone is a valuable rock with
many uses so areas in England like
the Yorkshire Dales and Peak
District will have a number of
quarries
4 Quarrying and economic use of
rocks
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Limestone is used as a building
material, to produce lime for
fertiliser and as a cleanser in
steelworks and power stations. It is
mixed with clay to make cement
Granite is used as a building stone,
as bedding for railway tracks and
for sea defences
Clay is used to make bricks
Quarrying is an issue in some places
•
farmland is lost
•
wildlife habitats are destroyed
• People suffer from noise, dust,
heavy traffic on the roads and the
ugliness of the site whilst the
quarry is in use
But it does provide local jobs
Ways to reduce impact of quarries
• Wash lorry wheels
• Transport by train
• Limit working hours
• Limit size of quarry
• Plant trees round waste tips and
buildings
• Clean up environment when quarry
is no longer in use
Possible uses for old quarries
• Reclaim land for farming
• Partly reclaim it for wildlife habitats
• Waste tip for landfill
• Eden Project type attraction
5 (a) Hydrological (Water) Cycle
Key terms
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Precipitation – rain, snow, hail…
Runoff – water from precipitation
that flows over the surface usually
in rivers and streams
Interception – precipitation stopped
from reaching the surface by trees
and plants
Infiltration – movement of water
from surface into the soil
Groundwater flow – movement of
water down slope in the rocks
Through flow – movement down
slope through the soil
Evapotranspiration – loss of water
from surface, plants, lakes, trees …
into atmosphere
•
Condensation – water vapour that is
changed into water droplets in the
atmosphere by cooling. Leads to
clouds forming
Precipitation – usually rain triggers off
the cycle. People can affect the water
cycle by
• chopping down trees – more rapid
surface runoff and possible
flooding
• building urban areas – less
infiltration, so more rapid surface
runoff and possible flooding
• planting trees to reduce flooding
downstream of towns and cities
• building reservoirs – means more
evaporation from the surface.
5 (b) Hydrological Cycle
6 Types of rainfall
The cause of rainfall is air rising and
cooling. When moisture in air cools to
its dew point, it condenses and forms
cloud. Rainfall is classified into three
types;
• Relief rainfall – moist are is forced
to rise to rise over mountains most
rain falls on mountain tops where
the air is at its coolest.
• Frontal rainfall – moist, warm air is
forced to rise above denser cold air.
This happens above warm and cold
fronts in a depression (low
pressure). Rain forms along trhese
fronts.
• Convection rainfall – great heating
at the surface warms up the air,
making it lighter so that it rises. Air
rises cools down and moisture
condenses to form tall cumulus
clouds and heavy rain.
7 How people affect the water cycle
LAND USE CHANGES
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For centuries, woodland has
been cleared for farming.
Deforestation is still happening,
especially in LEDCs such as
Brazil
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More and more people are living
in cities. Cities grow, farmland
and woodland is lost.
Vegetation is replaced by
buildings, roads and other hard
surfaces
EFFECTS ON THE WATER CYCLE
• Interception decreases – crops
are smaller than trees and give
less shelter
• Evapotranspiration decreases –
less water is being held and
used by plants
• Runoff increases – more
precipitation reaches the
surface; there is less to hold
back surface flow
Runoff increases greatly
• Hard surfaces reduce
infiltration
• Pipes, drains and sewers
collect water and take it straight
to the river
8 Drainage (river) basin
Drainage basin – An area of land
drained by a river and its tributaries.
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Highest land is around the edges
(watershed), so that all runoff is fed
into streams and rivers inside the
basin.
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Rivers are at their widest and
deepest just before going into sea.
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Different landforms found along the
river’s course – waterfalls and V
shaped valleys higher up and
meanders and floodplains lower
down
Factors leading to a high risk of
flooding
• High land at the topprecipitation is heavier in the
hills
• Steep slopes- gravity speeds up
water flow
• Impermeable rocks- these
reduce infiltration and
groundwater flow
• Small size- all the basin is
affected during a great
downpour
• Land use- large urban areas,
many factories and roads
9 (a) Flooding
There is too much water for the river
channels to hold, especially in flat lowlying areas.
Natural causes
• Persistent rain – Once the ground
becomes saturated (cannot hold
any more water), all water flows
over the surface as run-off.
• Heavy rain – Too much water falls
too quickly for it to infiltrate into
the ground, e.g. in a thunderstorm.
• Melting snow and ice – Alpine rivers
are full of water in spring and
summer when the sun is at its
strongest.
It is quite normal for rivers to flood, and
that is the reason why the flat land to
the sides of river is called its
floodplain.
9 (b) Flooding
Human causes
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Land use changes – deforestation
and building of urban areas
increases runoff
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Building on floodplains – hard
impermeable urban surfaces
increase runoff (and drains quickly
take water to the river)
•
Disasters linked to humans – dam
bursts – but these are very rare
It is normal for rivers to flood and that
is why the flat land either side of the
river is called the floodplain.
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10 River basin management
Rivers have many uses – water supply,
recreation, navigation, food source,
sewage disposal, and wildlife habitat.
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Control land uses – include planting
trees (aforestation) and stopping
uncontrolled logging, especially on
steep slopes
The main aim of river management is to
reduce flooding
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Hard engineering solutions are
expensive and only justified where
the costs of flooding in terms of
people and property will be high. In
some places farmland areas
upstream of cities are allowed to
flood and the water drains away
later.
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Dams and reservoirs – control river
flow so that water is stored in wet
periods and released during dry
times of the year
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Channel works, such as
embankments (increase height of
the natural levees along the sides)
and dredging (removing silt from
the river bed) make the channel
deeper and able to hold more water
before it floods. Walls or barriers
control rivers in urban areas
11 Boscastle, August,2004
Causes
• 200mm of rain fell in 4 hours.
• Two rivers meet in Boscastle, both
flow in narrow, steep sided valleys
The flood
• A 3 m high wall of water swept
through the village. No one was
killed as it happened during the day
and rescue services were there
quickly
Effects
• Two riverside shops were
destroyed and houses badly
damaged
• Cars were washed into the sea
• 100 people needed rescuing by
helicopter from roofs and trees
12 River Erosion
Types of erosion
• Hydraulic action – force of the water
eroding, the channel bed and banks
• Attrition – river load particles
becoming smaller and more
rounded through contact with other
particles and with channels sides
• Corrasion (or abrasion) – river load
wears away the channel bed and
banks while it is being transported
• Corrosion – Chemical action of
water dissolves minerals in rocks
especially in limestone
Refer to river processes every time you
are asked to explain how river
landforms are formed through erosion.
Remember the processes of erosion
using HACC – Hydraulic Action,
Attrition, Corrasion, Corrosion
Types of river erosion
Vertical erosion – the river cuts
downward into the land, especially
in the uplands
Forms
• steep sided, V-shaped valley
• interlocking spurs
• waterfalls and gorges
Lateral erosion – the river cuts
sideways into the land, especially in
lowlands
Forms
• floodplain
• meanders and oxbow lakes
13 Landforms in the uplands
Steep-sided V-shaped valley
• Erosion is concentrated in the part
of the river channel where the river
flows, the river cuts deep into the
land – vertical erosion
Interlocking spurs
• The river follows a winding course
flowing from side to side in the
valley bottom, as it flows it cuts
vertically into the land, ridges of
high ground are left
Waterfall and gorges
• Formed when harder rock outcrops
over softer rock. The softer rock is
eroded more quickly, the hard rock
is undercut, forms an overhang
which eventually collapses
14 Landforms in the lowlands
Meanders and oxbow lakes
• The river flows faster on the outside
bend, lateral erosion forms a river
cliff. On the inside bend it is slower
and deposition takes place
Levee
• During a flood a river deposits new
layers of silt on its banks.
Floodplain
• During a flood flat land next to a
river is covered by river water full of
silt
• When the land dries out a layer of
silt is deposited
• After many floods a thick layer of
fertile silt (alluvium) builds up
15 (a) Estuaries and Deltas
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Found at the mouths of rivers.
If the mouth of a river has only
one channel, it is known as an
estuary. If a river splits up into
many channels (called
distributaries), it forms a delta.
Most rivers in the UK, like the
Thames and Severn have
estuaries. At low tide, large
areas of mud and salt marsh
can be seen. Often there is a
deepwater channel in estuaries,
which ships can use. Most of
the world’s rivers such as the
Nile and the Mississippi, form
deltas. The land is fertile, but
floods are a problem.
15 (b) Estuaries and deltas
Why big rivers form deltas:
• They transport large loads of silt
• When crossing flat land near the
sea, they are slow-flowing, don’t
have enough energy to carry
sediment and deposit some of it
• They are held back by meeting
denser sea, water, increasing
deposition
• The main river channel blocks up
with silt and divides into separate
channel
• Distributaries deposit silt when they
flood, forming a wide area of flat
land
• Examples – Mississippi and Nile
16 (a) Coastal Erosion
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Hydraulic Action – The force of the
water eroding the land as waves
break against the rocks
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Attrition – The break up of boulders
and pebbles into smaller particles
of sand.
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Corrasion – The wearing away of
cliffs by the rocks and pebbles
thrown at them by the waves
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Corrosion – The chemical action of
salt water on rocks such as
limestone
Most erosion takes place during
storms as destructive waves break
against the coast
16 (b) Coastal erosion
17 Cliffs and cliff erosion
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The bottom of a rock outcrop is
eroded by destructive waves
between the high and low water
mark
A wave-cut notch is formed at the
base of the cliff
Eventually the overhang collapses
and the cliff retreats inland
Erosion is fastest where the rocks
are soft and have many
weaknesses, the cliffs have a gentle
slope. Where the rock is more
resistant the cliffs are high and
vertical
As the cliff retreats, it leaves a
wave-cut platform
18 Caves, Arches and stacks
• The sea attacks a vertical line
of weakness eg a fault
• The crack gets larger and
develops into a small cave due
to hydraulic pressure
• On a headland the waves may
break through to the other side
of the cliff – an arch is made
• Eventually the waves remove
more rock and the arch
collapses leaving a stump
The Needles off the Isle of Wight
is an example
19 Coastal transport and deposition
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Eroded materials are moved
along the coast by longshore
drift.
How longshore drift works
• When waves break along a
coastline at an angle, they carry
sand and pebbles up the beach
at this angle.
• Pebbles always roll back down
the beach at right angles to the
coastline.
• The same pebbles are picked
up by the next wave and moved
further along the coast.
• Repeated many times, this
process gives a zigzag
movement of sand and pebbles
along the coast.
20 Landforms of coastal deposition
Constructive waves build up material
• Beach – area of sand and shingle
between the high and low
watermarks, which slops down
towards the sea
• Spit – long ridge of sand and
shingle, with one end attached to
the land and the other end finishing
in the open sea
• Bar – ridge of sand and shingle
across the entrance to a bay or
river mouth
• Tombolo – ridge of sand and
shingle linking an island to the
mainland
Waves keep adding or taking away
sand and shingle. Materials taken away
in winter storms may be replaced in
summer when weather and seas both
calm down again
21 Formation of beaches and spits
Beach formation
• Longshore drift transports sand and
shingle, deposition happens in a
sheltered area at the head of a bay
• Sand and shingle deposits build up
over time to form a beach
Spit formation
• Deposition happens at a bend in the
coastline or in the shelter of a bay
• Sand and shingle are deposited
• Over time the end of the spit away
from the coast may become curved
22 Coastal problems in the U.K
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Soft sand cliffs in eastern England
are collapsing
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Sea levels continue to rise from the
last Ice Age
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Global Warming – world
temperatures are rising and sea
level is rising as result
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Southeast England is sinking as it
recovers from the weight of ice
which lay on it during the last Ice
Age
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It costs at least £1000 per metre to
place rocks at the bottom of cliffs
and much more to build sea walls.
Example East Yorkshire – evidence
of recent cliff collapse
• The road is broken
• Vegetation – Covered rock from
the cliff top has fallen down the
cliff.
• The coast line is not straight; in
places it has been pushed back.
Who will be affected?
• Caravan and holiday – home
owners on the cliff top are
gradually losing their property.
Key point: It costs at least £1000
per metre to place rocks at the
bottom of cliffs and much more
to build a sea wall.
23(a) Coastal management
The seaside is no longer entirely
natural, because it is managed by
people and usually there is a sea
wall and a promenade; sometimes,
lines of groynes can be seen along
the beach.
Methods of coastal management
Sea wall:- A concrete wall built between
the sea cliffs so that the waves can
no longer reach and erode the cliffs.
• Advantage- most effective method
of sea defence.
• Disadvantage- expensive to build
and to maintain; can only be used
for short stretches of coast
23(b) Coastal management
Blocks of rocks:- these are placed at
the base of cliffs to reduce direct wave
attacks.
• Advantage- cheaper alternative to
sea walls in rural locations
• Disadvantage- not fully effective;
waves in big storms may go over
them.
Groynes:- lines of wooden boards built
out into the sea, at right angles to the
coastline.
• Advantage- trap beach materials,
maintaining beach width and depth
for visitors
• Disadvantage- resorts further along
the coast are deprived of beach
materials.
24 Scarborough - an example of
coastal management
Reasons why it is needed
• Old sea wall no longer protects
promenade during storms
• Sandy rocks being easily eroded
• Major seaside resort
Cost – estimated at £26 million, likely to
be over £50 million
Management methods
• Build a new sea wall, further out to
sea than the old one
• Place blocks of granite in front of
the headland to protect the cliffs
• Place concrete blocks on top of the
rocks
• New defences are intended to
absorb wave energy before waves
reach the coastline