Key Idea 5: Coastal Processes and Coastal Management
5.1 How do geomorphological processes contribute to the development of distinctive coastal
landforms?
Processes
There are 3 main processes active on the coast: - Erosion, Transportation and Deposition
Different amounts of energy result in different processes occurring.
Erosion
Hydraulic action
Corrasion/abrasion
Attrition
Solution
The wearing away of the landscape
the power of the water forcing itself into
cracks in the rock cause it to break up
waves uses material/rock to rub against
the cliff and wear away/ rub away the cliff
rocks bang together and break up
becoming smaller and smoother
chemicals in the water dissolve minerals in
the cliff / rocks
What Factors will change the rate of erosion at the coast?
- Geology (Rock Type) – hard rock will erode slower than soft rock. Clay cliffs will slump instead of
collapsing.
- Waves (Strength and Type) – the bigger the wave, the more powerful the wave. This is affected
by how far the wave has travelled (the fetch), the strength of the wind and the length of time the wind
has been blowing for.
The swash of a wave is when it rushes up the beach. The backwash is it returning to the sea. With a constructive wave, the
swash is stronger than the backwash. With a destructive wave, the backwash is stronger than the swash.
Transportation
The process of longshore drift transports sediment along the coast
1.Waves attack the beach at an
angle that is determined by the
direction of the wind
2.The swash of the wave carries
material up the beach at the
same angle as the waves attack
3.The force of gravity causes the
backwash of the wave to carry
material back to sea at right
angles. Backwash is always
straight; the swash always
matches the wind direction.
Deposition
When a river loses energy and places / puts down the material it was carrying.
5.2 What landforms are produced?
Erosion:
Wave-cut Platform
- The waves attack the base of the cliff through the processes of abrasion,
corrosion, hydraulic action and attrition.
- Over time the cliff will be undercut and a wave-cut notch is formed.
- Eventually the cliff becomes unstable and collapses. Further cliff retreat will
form a wave-cut platform.
Cliff Slumping – Clay Cliffs
Headlands and Bays – a discordant coastline. Form where there are bands of hard and soft rock next to each other.
Erosion of a headland – Headlands becomes exposed and at risk of further erosion from wave attack on all sides. This
forms cracks, caves, arches, stacks and stumps.
Weak areas (CRACKS) are attacked by waves and
are opened to form a CAVE. (Due to erosion eg
Hydraulic Action and abrasion)
Cave widened and deepened by erosion to form an
ARCH (eg Durdle Door, Dorset)
As the roof of the arch is continually undercut (by
weathering/erosion) it eventually collapses leaving
an isolated STACK (eg Old Harry, Dorset)
Headland Retreating
The stack is continually eroded, eventually forming
a STUMP (eg Old Harry’s Wife, Dorset)
Deposition: Different landforms develop when there is a break in the coastline and waves lose energy as this means
they deposit material. They will deposit heavier material first and then finer particles as the energy decreases.
Beaches
Sand and shingle being transported along the coast by longshore drift will, in time, reach an area where the water is
sheltered and the waves lack energy, e.g. a bay. The material may be temporarily deposited to form a beach. Beaches are
not permanent features as their shape can be altered by waves every time the tide comes in goes out. Shingle beaches
have a steeper gradient than sandy beaches.
Sand Dunes are small ridges or hills of
sand found at the top of a beach, above
the usual maximum reach of the waves.
They form from wind-blown sand that is
initially deposited against an obstruction
such as a bush, driftwood or rock. As
more sand particles are deposited the
dunes grow in size, forming rows at
right angles to the prevailing wind direction.
Sand Spits: A spit is a permanent landform resulting
from marine deposition. It is a long, narrow
accumulation of sand or shingle, with one end
attached to the land, and the other projecting at a
narrow angle either into the sea or across a river
estuary. Many spits have a hooked or curved end.
They form where longshore drift moves large
amounts of sand and shingle along the coast, and
where the coastline suddenly changes direction to
leave a shallow, sheltered area of water.
Bar: Longshore drift can continue across an entire small bay. If it
blocks the bay totally it is called a bar. The area of water behind is
called a lagoon.
Tombolo: If longshore drift and deposition continue out into the
sea they may eventually join up with an island. This feature is
called a tombolo.
SUMMARY OF DEPOSITIONAL LANDOFORMS:
5.3 Why do coastal processes need to be managed?
Coastal erosion is an issue in many countries and especially certain parts of the UK. It is an issue that will be increasing in
the future because of:
Sea level rise
More frequent /
bigger storms…
Postglacial
rebound…
…climate change leads to the melting of ice caps and sea level rise. This means more areas will be
attacked by waves and erosion and flooding need to be prevented.
…as a result of climate change there will be worse weather meaning erosion will be more of an issue
in the future and more land / homes / business will be at risk
…during the ice age the north of the UK was under ice and weighed down. Over thousands of years
this is now changing back and so some areas are sinking and getting closer to sea level so will be
more at risk from erosion and flooding.
Reasons to protect coast from erosion…
What is at risk
Roads and rail links that
run down the coast
would be lost…
Businesses close to the
coastline eg cafes,
caravan sites, hotels…
Electricity cables and
water pipes often run
close to the coast and
are at risk from the
erosion so…
Beach access can be
dangerous…
Many homes are at risk
from falling into the sea
so become uninsurable
and worthless…
So What…why would it be bad if this wasn’t
protected
…it would cost more to reposition them than to stop the
erosion destroying the. Roads and rail links are essential
for the economy of coastal areas and may be the only
access along the coast.
...these need protection so that people’s income and jobs
are saved. Local areas need to make money to generate
taxes and support local populations. If they were left to
erode or flood they would lead to unemployment and
areas becoming rundown and less successful / attractive.
Thousands of pounds would be lost.
...this infrastructure needs protecting to save the money
and disruption of moving it inland. It is necessary as
homes and businesses need supplies to remain
operational.
…meaning that tourists no longer visit and the economy
of an area becomes weaker, leaving people out of work.
It may also lead to accidents and potential injury.
...so these are protected so that there is no need to move
people and provide new homes / compensation.
Rehousing thousands would be a large and unpopular
task.
Example from Holderness
Coast Case Study
The B1242 (an important access
road) runs close to the coast
through the village of Mappleton
so the village has had rock
armour and a rock groyne built.
Bridlington and Hornsea are
major tourist centres where sea
defences have been built to
protect them.
Easington has a major gas
terminal for North Sea Gas which
is then distributed to places all
around the UK. It has been
protected with a rock groyne and
rock armour.
Withernsea has been protected to
allow it to continue to be a tourist
destination and save the access
and businesses in the village.
Bridlington and other smaller
villages have been protected as
there are enough homes / people
to make it financially worth
defending.
These reasons combined with the greater risk from more storms and rising sea levels means that coastal management and
defence are key areas for governments / councils to consider.
5.4 How are coastlines managed?
Choosing which methods of coastal protection is most appropriate for an area of coastline may take into account the
following:
- COST : concrete sea wall is expensive. Wood revetments are cheaper
- LIFETIME: rock groynes may last decades. Beach rebuilding will have to be carried out every few months
- ENVIRONMENTAL IMPACT: offshore reefs will not affect the look of the beach but concrete revetments will look
awful and put tourists off using the coastline
- SUSTAINABILITY: using hardwood from tropical rainforests for timber groynes is not sustainable –they will
deteriorate and need replacing faster than new hardwood trees grow. Beach rebuilding is sustainable as you are
moving sand from where it has been deposited, to where it has been eroded from.
Hard Engineering
Soft Engineering
Building or creating something which will interfere with coastal processes–usually to reduce the power
of breaking waves against cliffs.
Working with the natural processes of sea and sand in a more environmentally sustainable way. Using
the natural processes to bring about an intended effect.. They are usually more long-term and
sustainable, with less impact on the environment.
Strategy
Concrete Sea Wall
(HARD technique)
Deflects the waves
(Withernsea, East Yorkshire)
Revetment
(HARD technique)
Inter-locking concrete slabs or wooden boards to
deflect the waves.
(Hornsea, East Yorkshire)
Gabions
(HARD technique)
Wire cages filled with stones/rocks stacked along
the cliff base
(Easington, E. Yorkshire)
Rock Armour / Rip-Rap
(HARD technique)
Granite boulders (very resistant)
(Withernsea, East Yorkshire)
Groynes / Breakwater
(HARD technique)
Wooden or boulder ‘fences’ designed to trap &
accumulate sand.
(Hornsea, East Yorkshire)
Cliff Drainage
(HARD technique)
Removing water from a cliff quickly so it’s less
likely to Slump
(Scarborough, North Yorkshire)
Offshore Reef
(SOFT technique)
Man-made artificial reefs are built just out to sea
to for the waves to break on them and create
calmer water at the coast
(East Anglia coast)
Beach Nourishment
(SOFT technique)
Dredge sand from estuary or sea bed and put it
back on the beach
(Pevensey Bay, East Sussex))
Advantages
Deflects Waves
•Strong
•Effective
•Lasts a long time
Provides hard face to cliff
•Easily installed
•Cheaper than sea wall
•Deflects wave power
Disadvantages
Expensive
•Likely to need repair fairly regularly
•Deflected waves can ‘scour’ sea bed
and undermine the sea wall foundations
Can be eroded from below easily
•Needs frequent repair
•Not very attractive
•Easily installed
•Cheaper than sea wall
•Not very attractive
•Needs frequent checking & repair
•Not easy for people to get over to get to
beach
•May contain rats nests
•Popular option in recent
•Not very attractive
years – seen to be effective •Not easy for people to get over to get to
•Cheaper than sea wall
the beach (broken ankles)
•Rats may live in spaces
•Builds up the beach
•Need repairs
•Makes a wider beach
•OK with medium waves –but strong
•Provides calm water
waves still get to cliff face
•Encourages tourism
•Leads to faster cliff erosion down the
coast by robbing it of potential beach
material.
•Can reduce slumping of
clay or sandy cliffs
•Only useful where slumping is an issue
•Can be made to Blend in
•Needs to operate with other solutions
with the coastal landscape like groynes or rock armour as well.
•Provides inshore area of
calm water
•Effective at preventing the
cause of cliff erosion
•Adds to tourist amenity by
making bigger beach
•Attractive
•Works with the natural
processes of the coast
•Very expensive
•Need openings for fishing boats to get
to sea
•Damages fish nets.
•Can be ‘breached’ in stormy conditions
and need repair.
•Needs frequent renewal of more sand
•Does not protect cliff face from winter
storm waves.
5.5 Why does coastal management create controversy?
It is natural that people who live near the coast expect to be protected from erosion and flooding. However, the usual
strategies of hard and soft engineering are expensive and, in the face of rising sea-levels, may not be sustainable. Planners
now believe that a mixture of engineering strategies and coastal land-use zoning is needed to manage coastlines in the
future. These zones will include some urban areas where future building will be prevented and other where homes will be
rebuilt further inland and coastal retreat will be managed.
Building se defences on one part of the coastline has an effect further down the coast:
-
Less erosion or the trapping of sediment by groynes means that erosion is greater where the defences end. This
means different view exist on whether they should be built and where they should be built
-
Sea defences are very expensive so they are only built where there is sufficient benefit to justify the cost – small
villages / isolated farms are left without protection and can lose their homes / businesses without compensation
-
This means different groups will have different views on whether defences should / should not be built at a location
Local residents on the
coast
Will want their homes protected no matter the cost
They will feel they should be protected and the local authority should pay for and
build the defences
Local businesses on
The benefit that the businesses bring to the local economy make defences more
the coast
likely than just for some houses.
They will want to keep the voters happy – if there are lots of voters on the coast
Local politicians
they will want to protect them and stay in office so will support sea defences
Sea defences are expensive so if money is spent on these it wont be spent on
Local taxpayers (inland) other things. Living away from the coast means they will not benefit directly from
the defences and will see them as a waste of money
They would like the coast to be left as natural as possible so that the erosion will
allow natural processes of transport and deposition to continue and to keep the
Environmentalists
coast as it should be. (eg Spurn Head needs some erosion of the Holderness
Coast as otherwise it will be eroded and disappear which is bad as it is an
important habitat for wildlife / birds)
They will not want the defences as they will be worried that erosion will increase
People living down the
at their home and they could lose their property with no compensation / help to
coast from sea
rehome. They will think it unfair that they are not protected when other homes
defences
are.
FOR
FOR /
AGAINST
AGAINST
AGAINST
AGAINST
Sustainable Coastal Management
Managed retreat is a method whereby we humans concede defeat to the power of the sea and allow it to erode and create
salt marshes for example. We can also allow cliff erosion to occur in areas of low value farmland and just compensate
farmers for their losses, rather than construct more expensive coastal defences. This can only work where the coasts of
compensation are significantly less than the coasts of building coastal defences, and can be a cheap option. It can also be
beneficial to plants and animals by providing new habitat. This method is highly controversial however, as land is lost and
the human cost can be greater than just financial. Imagine a farmer told to quit land and a family home that could have
been in the family for generations because the council do not want to build a sea defence - the trauma of this is huge.
This can also involve Integrated Coastal Zone Management (ICZM) which involves looking at the coastline as a whole and
working out which areas should be protected and which sacrificed for the best overall solution.