Transcript Crowded Coasts - SLC Geog A Level Blog

Unit 3 Increasing Risks
•Describe and explain the causes of rapid erosion
on the Holderness coast.
•Evaluate the impact of rapid erosion on the
residents of the Holderness coast.
With ever increasing numbers of people choosing
to live near the coast the risks presented by
coastal erosion and rising sea levels have also
increased
Coastlines are worn away (eroded) by wind
action, tidal currents, wave currents, or
drainage.
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For centuries there has been an erosion problem
along the Holderness coast, which stretches
between Flamborough Head in the North and
Spurn head in the South.
On average 2m of coastline are lost each year – the
fastest in Europe.
Since Roman times it has eroded by 4km and 29
villages have been lost.
Other villages are disappearing now.
In 1967 a storm caused the loss of 10m in one night
and 12 bungalows near Bridlington were so near
the sea that they had to be destroyed.
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The shape of the coastline
Width of beach
Length and direction of the fetch
Where the wave breaks
Height or steepness of wave
Wave energy
Rock resistance
Structure
Human activity
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The three main reasons for the rapid erosion at
Holderness are:
Geology
Fetch
Longshore drift and beach material
The boulder clay has very
little resistance to erosion,
especially when wet,
making it very susceptible
to erosion
The two main types of
rock on the Holderness
coast are Boulder clay
and chalk
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Most of the coastline is boulder clay, which is
also known as glacial till.
It is a mixture of fine clays, fine sands and
boulders deposited by glaciers after the last ice
age.
It has very little resistance to erosion, especially
when wet.
It produces shallow sloping cliffs, between 5
and 20m high.
These cliffs are rapidly eroding, on average 2m
a year.
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Waves are caused by the transfer of energy
from wind to the sea water – it is the form of
the wave that moves forward, not the water
Height and power of wave depends on the
strength of the wind, the amount if time it has
been blowing and the fetch.
As waves reach shore – water depth decreases
– wave energy concentrated in a narrowing
zone – changing the form of the wave until it
collapses and water is thrown on the beach –
releasing the wave energy.
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With waves the greater the wind the
greater the frictional drag and therefore
the size of wave
Those that travel short distances and are
the result of local waves are seen as sea
waves
Those that are formed from distant storms
and travel large distances are known as
swell.
Holderness is exposed to winds and waves
from the north-east, which have a fetch of
about 500-800km. This is not far, but the coast
at Holderness is attacked by other factors,
affecting the ferocity of the waves.
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Currents – or swell – which circulate around the UK from the
Atlantic and into the North sea. The Atlantic fetch is 5000km or
more, and its currents add energy to waves in the North sea.
Therefore, there are often powerful destructive waves along this
coastline.
Low pressure weather systems passing over the North sea are
often intense, and locally produce very strong winds and waves.
Small, almost enclosed seas, like the North sea, often generate
huge waves during storms. Waves move within the sea but cannot
disperse their energy – rather like water slopping up against the
side of a washbasin
The sea floor is deep along the Holderness coast. Therefore, the
waves reach the cliffs without first being weakened by friction
with shallow beaches.
SO WAVES CAN BE HUGE ON THE NORTH SEA COAST!!
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CREST
TROUGH
WAVE PERIOD
LENGTH
VELOCITY
STEEPNESS
ENERGY
SWELL
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CREST – Highest point of the wave
TROUGH
WAVE PERIOD
LENGTH
VELOCITY
STEEPNESS
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CREST – Highest point of the wave
TROUGH – lowest point of the wave
WAVE PERIOD
LENGTH
VELOCITY
STEEPNESS
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CREST – Highest point of the wave
TROUGH – lowest point of the wave
WAVE PERIOD – Time taken for wave to
travel one wave length
LENGTH VELOCITY
STEEPNESS
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CREST – Highest point of the wave
TROUGH – lowest point of the wave
WAVE PERIOD – (T) Time taken for wave to
travel one wave length
LENGTH – (L) Distance between two
successive waves
VELOCITY STEEPNESS
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CREST – Highest point of the wave
TROUGH – lowest point of the wave
WAVE PERIOD – (T) Time taken for wave to
travel one wave length
LENGTH – (L) Distance between two
successive waves
VELOCITY – (C) speed of movement of a crest
in a given period of time
STEEPNESS –
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CREST – Highest point of the wave
TROUGH – lowest point of the wave
WAVE PERIOD – (T) Time taken for wave to travel
one wave length
LENGTH – (L) Distance between two successive
waves
VELOCITY – (C) speed of movement of a crest in a
given period of time
STEEPNESS – (H/L) ratio of wave height divided by
length it can not exceed 1:7 (0.14) as it will break
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CREST – Highest point of the wave
TROUGH – lowest point of the wave
WAVE PERIOD – (T) Time taken for wave to travel one
wave length
LENGTH – (L) Distance between two successive waves
VELOCITY – (C) speed of movement of a crest in a
given period of time
STEEPNESS – (H/L) ratio of wave height divided by
length it can not exceed 1:7 (0.14) as it will break
Cliff foot through a number of processes:
Hydraulic action
Corrasion/Abrasion
Solution/Corrosion
Cliff face processes:
Weathering
Physical
Biological
Chemical
Mass movement
Due to the fact that coastlines are usually not
found as straight lines, it is unusual to find an
area where waves hit the coastline at right
angles.
As a result waves will often hit the coast obliquely
leading to a process called long shore drift
which is due to reflection of the waves.
This process results in the movement of
sediment along the coast
Longshore Drift and removal of material may also
occur as a result of Tidal movement.
Tides move in Flows and Ebbs.
This movement may be at right angles to the coast
or along the coast (especially if the direction of
flow is through a narrow channel).
The beaches at Holderness are its main problem.
Boulder clay erodes to produce mainly clay particles,
which are easily transported out to sea, rather than
accumulating close to the cliffs as beach sand.
Although there are beaches, there is never enough sand
to stop the waves reaching the cliff base at high tide.
What little sand is produced is taken southwards by
longshore drift, leaving the Holderness cliffs poorly
protected against wave attack. Eventually, a small
amount of beach material reaches a spit at Spurn Head,
where it accumulates.
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Case Study: Rapid erosion of the Holderness Coast
You are required to research three areas of the Holderness coast:
Withernsea, Mappleton, Flamborough
Identify the coastal processes that are changing the shape of the coast at
each of the locations
Identify evidence in the form of specific landforms and/or damage to
property at each of the three locations.
Suggest likely impacts to residents of the processes at work in each
location.
Suggest likely impacts on the natural environment of such rapid erosion.
E.g. will there be damage to coastal wetlands?
You should then work to annotate a map of the coastline with details of
the erosion and impact at each location with the aim of creating a wall
display of the information. You may wish to supplement your
information with images of each area that show landforms and impacts.
Websites to use:
http://maps.google.co.uk/maps?hl=en&tab=wl
http://www.geography.learnontheinternet.co.uk/topics/holdernesscoas
t.html
http://www.sln.org.uk/geography/schools/blythebridge/WLA2Coasts.
htm
Other resources to use:
Ordnance survey maps of the Holderness coast.
AS Geography for Edexcel, Oxford Publications photocopy
Location
Flamborough
Mappleton
Withernsea
Processes
Evidence/ landforms
Impacts on residents
Impacts on
environment
Hard Engineering Techniques:
Wooden groynes at Hornsea
These have been built to trap sediment carried by
longshore drift, keeping the beach in place at
Hornsea, which in turn protects both the cliffs and
the town.
However, south of Hornsea the village of
Mappleton was being starved of sediment
being trapped due to the groynes. Waves
eroded the cliffs so much in the early 1990’s that
nearly 4 metres was being lost every year and the
village was in danger of disappearing.
Rock Groynes at Mappleton
After a campaign by residents to protect Mappleton,
Humberside council built two rock groynes to protect
the village. These are boulders of granite, laid out like
groynes, and cost almost £2million. The cliff face was
also rebuilt to make it less steep and therefore more
stable.
After this, at Cowden (3km south of Mappleton)
sediment starvation was also causing these cliffs to be
eroded, with the rate of erosion increasing from 2.5
metres per year in 1991 to 3.8 metres per year in 2007.
This process is called terminal groyne syndrome and
happens frequently when groynes are stopped.
Revetments at Easington
A rock revetment has been built to protect
Easington’s gas terminal. Like stone
groynes, a revetment consists of large
granite boulders. The boulders are placed
like a wall in a line of defence along the
shoreline/ It works by absorbing – not
reflecting – wave energy using large air
spaces between the boulders and a broad
surface area. Revetments are very expensive
but lone lasting.
Sea walls at Withernsea
Withernsea replaced its old straight sea wall with
a recurved wall at a cost of 6.3 million pounds.
The cost benefit analysis showed that it was
worth investing in the wall to protect the local
properties and save tourism employment.
Negatives are the noise of the waves crashing
against the wall and views from the hotels are
restricted. Some tourists argue that the rip rap
at the base of the sea wall are unattractive.
Soft Engineering Techniques
Beach nourishment at Hornsea
This had added sediment to the beach at
Hornsea, by dredging and pumping from
offshore straight onto the beach.
This was to:
- create a wider beach to protect the cliff line
- to add sediment into the coastal system so
that areas downdrift benefit.
The downside is that its sediment can be
taken away in a single storm, and so it has to
be replenished every one or two years.
Coastal Zoning
This is also known as red-lining, and is a
device used by planners to divide stretches of
coast into land use zones. Red-lining identifies
those zones at risk to erosion where the costs of
protection exceed the possible benefits.
Decisions are then made as to which areas need
protecting, and zones that are decided to not,
are denied planning permission for anything
along the coast that may protect the coast.