Transcript Coastal Protection - Withernsea High School Humanities College

Coasts : Coastal Protection / Hard and Soft Engineering Strategies
There are many different ways to reduce the rate of coastal erosion. Some are more
expensive than others, some last longer, some are less of an eye-sore ..etc. There are 2
main categories of coastal protection:
Key Terms :
Coastal protection
HARD Engineering Strategies : Building or creating something which will interfere with
coastal processes – usually to reduce the power of breaking waves against cliffs.
Coastal management
SOFT Engineering Strategies : 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.
Hard engineering solutions
Choosing which methods of coastal protection is most
appropriate for an area of coastline may take into
account the following:
Protection strategies
Soft engineering solutions
Sustainable protection strategies
Example / Case-Study :
Holderness coast
Easington Gas Terminal
COST : concrete sea wall is expensive. Wood
revetments are cheaper
Withernsea
LIFETIME : rock groynes may last decades. Beach
rebuilding will have to be carried out every few months
Mappleton
ENVIRONMENTAL IMPACT : offshore reefs will not
affect the look of the beach but concrete tetrapods 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.
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Hornsea
Possible Questions :
Why might certain coastal
protection methods be selected
instead of others?
What is the difference between
Hard and Soft coastal protection
techniques?
Weblinks
http://www.bbc.co.uk/schools/gcsebitesize/geo
graphy/coastal/coastalmanagementrev2.shtml
Coasts : Coastal Protection / Hard Engineering Strategies
Type / Location
Concrete Sea Wall
(HARD technique)
Deflects the waves
Advantages
•Deflects Waves
•Strong
•Effective
•Lasts a long time
(Withernsea, East
Yorkshire)
Revetment
(HARD technique)
Inter-locking concrete
slabs or wooden boards
to deflect the waves.
(Hornsea, East
Yorkshire)
•Provides hard face to
cliff
•Easily installed
•Cheaper than sea wall
•Deflects wave power
Gabions
(HARD technique)
Wire cages filled with
stones/rocks stacked
along the cliff base
(Easington, E. Yorkshire)
•Easily installed
•Cheaper than sea wall
Rock Armour / Rip-Rap
(HARD technique)
Granite boulders (very
resistant)
(Withernsea, East
Yorkshire)
•Popular option in
recent years – seen to
be effective
•Cheaper than sea wall
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
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Key Terms :
Hard engineering
Concrete Sea wall
Revetment
Gabions
Rock Armour / Rip-Rap
Example / Case-Study :
Holderness coast
Easington Gas Terminal
Withernsea
Hornsea
•Not very attractive
•Needs frequent
checking & repair
•Not easy for people to
get over to get to beach
•May contain rats nests
•Not very attractive
•Not easy for people to
get over to get to the
beach (broken ankles)
•Rats may live in spaces
Mappleton
Possible Questions :
Which coastal protection would
you suggest for a coastal resort –
and which would you reject – and
why?
Which of these hard engineering
techniques is most effective?
Weblinks
http://www.bbc.co.uk/schools/gcsebitesize/geo
graphy/coastal/coastalmanagementrev2.shtml
Coasts : Coastal Protection / More Hard Engineering Strategies
Type / Location
Advantages
Disadvantages
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Key Terms :
Hard engineering
Tetrapods
(HARD technique)
Interlocking concrete
shapes which can be
made where they are to
be used.
(50% of Japan’s coast)
•Popular option in
Japan – seen to be
effective
•Can be built on-site
•Allows some waves
through – so less
‘reflected’ wave damage
•Not attractive at all
•Almost impossible for
people to get over to get
to the beach
•Dangerous to
swimmers & small boats
– stick out.
Tetrapods
Groynes / Breakwater
Cliff Drainage
Example / Case-Study :
Holderness coast
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)
•Need repairs
•OK with medium waves
– but strong waves still
get to cliff face
•Leads to faster cliff
erosion down the coast
by robbing it of potential
beach material.
•Builds up the beach
•Makes a wider beach
•Provides calm water
•Encourages tourism
•Can reduce slumping
of clay or sandy cliffs
•Can be made to Blend
in with the coastal
landscape
Surface
Water
Drainage
Pipe
•Only useful where
slumping is an issue
•Needs to operate with
other solutions like
groynes or rock armour
as well.
Easington Gas Terminal
Withernsea
Hornsea
Mappleton
Possible Questions :
Which coastal protection
technique is most appropriate for
a section of cliff which has a
history of slumping – and why?
Which coastal defence technique
would be best for a coastal
industry – and why?
Weblinks
http://www.s-cool.co.uk/alevel/geography/deltas-andestuaries-and-changes-to-coastal-areas/human-influencesat-the-coast.html
Coasts : Coastal Protection / Soft Engineering Strategies
Type / Location
Advantages
Disadvantages
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Key Terms :
Soft Engineering strategies
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)
•Provides inshore area
of calm water
•Effective at preventing
the cause of cliff erosion
Beach Re-Cycling
(SOFT technique)
Moving sand from areas
it has accumulated to
areas it has been eroded
from.
(Pevensey Bay, East
Sussex))
•Adds to tourist amenity
by making bigger beach
•Attractive
•Works with the natural
processes of the coast
Beach Re-Building
(SOFT technique)
Dredge sand from
estuary or sea bed and
put it back on the beach
(Pevensey Bay, East
Sussex))
•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.
•Needs frequent renewal
of more sand
•Does not protect cliff
face from winter storm
waves.
Offshore Reef
Beach Re-cycling
Beach Re-building
Example / Case-Study :
East Anglia
Pevensey Bay, East Sussex
Possible Questions :
Why are soft engineering
strategies more sustainable?
What are the advantages of soft
engineering coastal defences over
hard engineering defences?
Weblinks
http://www.scool.co.uk/alevel/geography/deltas-andestuaries-and-changes-to-coastalareas/human-influences-at-the-coast.html
Coasts : Coastal Protection / Hard Engineering Case-Study : Mappleton Location
Why have they built 2 rock groynes?
Why is one larger than the other ?
Are they working ? How can you tell?
Mappleton was given a £3m coastal
defence scheme in 1992 due to the
danger to the main north-south coast
road being lost if erosion continued.
This would have severely affected trade
and emergency transport in the region.
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Coasts : Coastal Protection / Hard Engineering Case-Study : Mappleton Strategies
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Coasts : Coastal Protection / Hard Engineering Case-Study : Mappleton Evaluation
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Key Terms :
Longshore Drift
Active cliff
Accumulation
Beach-robbing
Precedent
Evaluation
Successful Outcomes of
the Mappleton Defences
•Erosion
has
been
effectively stopped behind
the defences. The grass
growing on the landscaped
cliffs shows they are no
longer ‘active’ – in contrast
to the cliffs downcoast.
Less Successful Outcomes of the Mappleton Defences
•Erosion has increased downcoast. Material moved by
Longshore Drift is successfully ‘trapped’ at Mappleton by
the rock groynes – but this means it is not moving down the
coast to accumulate on beaches there. As a result beaches
south of Mappleton are robbed of sand, becoming narrower
and erosion is faster than it used to be before the scheme
•The road has been
‘saved’ – along with the
village.
•Other villages under threat of coastal erosion say that a
precedent has been set – and their villages should now be
protected like Mappleton – otherwise it is unfair.
•Tourism in the area has
increased as a result of the
wider beach and the
interest in the scheme.
•Erosion is still taking place north of Mappleton, so in the
future the protected area is likely to become a peninsula as
the coast to the north and south retreats westward. So
more money will have to be spent protecting the sides of it.
Example / Case-Study :
Mappleton, East Yorkshire
Possible Questions :
Why are there sometimes
negative consequences of
protecting some parts of the coast
and not others?
What conflicts of interest might
arise as a result of coastal
protection measures?
Weblinks
View this BBC video clip
And this one BBC video clip
Coasts : Coastal Protection / Easington Gas Terminal – A Controversial Issue
20% of Britain’s gas comes onshore at the Easington Gas terminal from the undersea gas pipeline stretching from
Norway. Protecting this piece of coastline is therefore vital. The following issues occur though:
•Which form of coastal protection should be selected? What criteria would you select for your basis of choosing (cost?,
effectiveness?, environmental impact? Sustainability?...
•Who should pay for any coastal protection here? (The government? East Yorkshire Council? British Gas? Gas customers?)
•Who could be negatively affected by protecting this area of coastline? (look further along the coast beyond the gas terminal)
•Should there be any compensation for anyone negatively affected? If so – who should pay it?
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Coasts : Coastal Protection / Soft Engineering Case-Study – Pevensey Bay
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The Pevensey Bay
Beach Replenishment Project
Suffolk Coast South England
Using Soft Engineering
Coastal Protection techniques
to Hold the Line on a coast
under threat.
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Reasons behind the Beach Replenishment scheme at Pevensey
Reason 1 : Almost all of the 150 wooden Groynes had deteriorated and either
needed repair or replacement. Both would be very expensive and use a lot of
hardwood – which isn’t a sustainable solution. They were removed in 2007.
Reason 2 : The beach environment has
many valuable plant species and these
needed to be protected and encouraged to
thrive.
Reason 3 : There are many coastal homes
looking out over the beach – and their
protection, but also their views needed
preserving.
Removing the old groynes
Technique 1 :
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Beach Replenishment
Sand and gravel is hoovered up
by a dredger ship off the coast,
and sprayed onto the lower
beach at high tide.
At low tide, bulldozers push the
material up the beach to raise
the height of the beach
This takes place 3 times a year
– in early Autumn after the
holiday season, in January
before the main winter storms,
and at Easter just before the
holiday season and to correct
winter storm damage to the
beach.
Technique 2 :
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Beach Recycling
There is strong Longshore Drift from
West to East along the bay
Bulldozers dig up the accumulated
sand at the eastern end of the bay
and transfer it to trucks.
Trucks take the beach material back
along the beach to the western end –
so that Longshore Drift can distribute
it along the length of the beach over
the year.
Technique 3 :
Before
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Beach Re-profiling
Re-profiling
This means changing the gradient of
the beach to the best one for
absorbing the wave energy.
Winter storms remove lots of the
lower beach with their strong
backwash.
After
Bulldozers spread the sand evenly
across the beach in Spring to create
a more even profile – which is better
at absorbing wave energy.