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What do all these pictures have
in common?
3 answers required
Coastal Defences?
• Coastal Defences are ways of protecting the
coastline from erosion.
• They are normally man made, and generally
very expensive.
• But they have to be built in many places to
stop the cliffs eroding.
PREDICTION:
Which do you think is the most and
least effective defence, and why?
How can the coastline be protected?
Generally speaking, the most effective
protection is a large beach. Why?
Because the beach acts like a natural
barrier between the waves and cliffs. The
beach breaks the wave. This means that it
absorbs the most of the wave’s energy
before it reaches the cliff
How can the coastline be protected?
Sea Wall
Rip Rap
Gabions
Groynes
Beach Nourishment
Offshore Reef
Managed Retreat
Large rocks placed in front of the cliff.
Gets rid of energy, can be cheap
depending on rock type, effective for
many. Can make the beach difficult for
tourists to get to, unattractive, doesn’t
work in storm conditions.
Cost £300 per metre
RIP RAP
Walls usually made up of concrete. The
modern ones have a curved surface.
Reflects & absorbs energy, very visiblemakes residents feel safe, effective for
many years. Ugly-puts tourists off,
expensive to build.
Cost £3,000 per metre
RECURVED SEA WALL
This is placing more sand and pebbles on the
beach. Looks natural, provides a beach for
tourists and is a natural form of defence,
cheap. It may affect the animal & plant life.
The beach needs regular top ups as sand gets
washed away. Disruption to homes whilst sand is
being replaced
Cost £5,000 per 100m
BEACH REPLENISHMENT
Usually made of wood that stretch out into the
sea. Prevents longshore drift as sand builds up
on one side of the groyne, keeps the beach in
place and is effective for many years.
Unattractive & makes it difficult to walk along
the beach, they disrupt the natural processes
of the beach
Cost £5,000 each
GROYNE
These are wire cages filled with stone used to
reduce erosion.
Cheaper than other forms of protection, rock
cages absorb energy. Wire cages can break &
need to be securely tied down, not as efficient
as other methods.
Cost £11 per metre
GABIONS
This means allowing the sea to
gradually flood the land or erode the
cliffs. Creates new habitats for
plants and birds. Cheap method. It is
upsetting for land owners to lose
land.
Cost – depends on coastal area
MANAGED RETREAT
These are enormous blocks and
natural boulders which are sunk
offshore to change the wave
direction and absorb energy from
waves and the tides.
Cost £1950 per m
OFFSHORE REEF
Coastal Defences can be put into two
categories…Hard and Soft engineering
Hard Engineering
Soft Engineering
Involves major
construction work
Works with natural
processes - unobtrusive
Large Scale, immediate
impact, expensive
Does not involve major
construction
Man Made Interference
with natural processes
Cheap, Small Scale, slow
impact
Rip Rap
• Large rocks are place in front of a cliff £300 per metre
• Normally hard rocks which are very
resistant to erosion. This means they are
long lasting.
• This dissipates (breaks up) the wave
energy so their erosive force is reduced
when they hit cliffs. However, not during
storms.
• Relatively cheap
• Can create unpleasant views and access
problems for beach visitors
Recurved Sea Wall
• Usually made of concrete with a
recurved face to reflect and absorb wave
energy back out to sea.
• This can sometime deflect waves onto
one particular area – wave scoruing
• £3,000 per metre
• A very visible reassuring defence and
long lasting. However this can spoil
views
• They can add to Longshore Drift
Gabions
• Wire cages filled with stone to reduce
erosion. The cages absorb the wave energy
and reduce erosive power.
• £11 per metre (cheaper than others)
• The cages will eventually break so they
need tying down effectively.
• Compared to others Gabions are not that
effective, and certainly damage the view.
• When the water drains through them
cages, the material is deposited which can
create beach
Beach Replenishment/Nourishment
• Placing of sand and pebbles on a beach artificially. Sand is a
natural (and the best) defence as it absorbs energy.
• Creates a cheap and natural appearance to beach for tourists
• This is an unnatural addition and may damage wildlife.
• The sand be easily be washed away which means it needs
replacing again.
• £5,000 per 100m
Managed Retreat
• Do nothing
• Allow the sea to erode the cliffs naturally. This normally involves
councils making a decision as to the value of land.
• The only cost may be compensation for landowners
• New habitats are created and it is cheap in the long run, but
predicting rates of erosion can be hard.
Offshore Reef
• Enormous concrete blocks and boulders are sunk offshore to
alter wave direction and dissipate energy. This means waves
break further from sea and waves reaching the cliff are weak.
• This will mean more constructive waves to create a beach
• £1,950 per metre and difficult to install
Groynes
• Usually made of wood, although
sometimes stone. Stretch out into sea to
trap material caused by Longshore Drift.
• This retains the beach (which is a natural
absorber of waves energy) and prevent s
erosion as well as for tourists.
• £5,000 each
• Effective for many years (20-30) but wood
will eventually rot.
• Effective, but can disrupt beach walks and
interferes with natural processes which
means beaches further downcoast will be
starved of sand.
• EG, Mappleton (first 10 mins)