Transcript GG4 Revision

Key questions:
• Why do coastal environments need to be
managed?
• What are the methods used to manage
coastal environments and how successful
are these strategies?
Coastal Management: What does it
mean?
• Management means controlling development and
change in the coastal zone and undertaking work
according to agreed principles and criteria.
Stages in management:
• Understand the causes of the problems
• Undertake works to reduce or solve the problems.
• Improve prediction and make contingency plans.
Why?
• As things like coastal tourism have become
more frequent, humans have found it
increasingly necessary to attempt to
control the effects of the sea. The main
reasons for coastal management are:
• to protect the coast from the erosive
effects of the sea.
• to increase the amount of sand on the
beach.
Successful management
areas depends on:
of
coastal
1. understanding the differing interests of
those who want to use coastal land in
different ways, and
2. understanding the physical processes
impacting on the coast, such as erosion and
longshore drift.
Coastal Management in the UK
• In the UK, MAFF (Ministry of Agriculture,
Fisheries and Food) is responsible for the
management of coastal flooding in Britian;
since 1985 it has also managed coastal
protection works, including erosion control.
• Shoreline Management Plans (SMPs) have
been produced on behalf of local councils,
government agencies and other interested
parties, to co-ordinate planning along
designated sections of coastline.
• The aim of each SMP is to provide the basis
for sustainable coastal defence policies and
to set objectives for future management of the
shoreline.
• Physical, environmental, engineering and
planning constraints are taken into account.
MAFF guidelines identify four
coastal defence options:
• 1. Do nothing – carry out no new coastal defence
activities (except for safety measures)
• 2. Retreat the Existing Defence Line – move by
intervention the exisitng defence landward
• 3. Hold the existing defence line – by intervention,
with additional defences where and when necessary.
• 4. Advance the Existing Defence Line – by
intervention to move the existing sea defence
seaward.
Interested parties in coastal management
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There are many different land uses found in coastal areas - for
example, tourism, industry, fishing, trade and transport. This
means that there are many different groups of people who have an
interest in what happens in coastal areas and how they are
managed.
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Some of the common-interest
management issues are:
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Local residents
Environmental groups
Developers
Local councils
National governments
Tourist boards
National Parks Authorities,
such as the Pembrokeshire National Park Authority
groups
involved
in
coastal
• Each of these interest groups may have a different view
about what should be done to protect and manage coastal
areas. A difference of opinion can cause conflict between
interest groups
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There many reasons why groups of people might be
concerned about the coast:
erosion is threatening beaches or coastal settlements
people want to develop tourism in the area - or existing
tourism is declining
there is a danger of flooding if sea-levels rise
there is a problem with sewage and/or pollution.
Management options:
Techniques for managing these physical processes can be divided
into hard engineering options (such as building sea walls) and soft
engineering options (such as beach nourishment and managed
retreat).
Hard Engineering
• Hard engineering options tend to be expensive and short-term
options. They may also have a high impact on the landscape or
environment. The table shows the most common hard engineering
solutions.
Soft engineering
• Soft engineering options are often less expensive than hard
engineering options. They are usually also more long-term and
sustainable, with less impact on the environment. There are two
main types of soft engineering.
Building a sea wall
- Often built in front of seaside resorts.
- Very expensive.
- They aim to completely block the waves and their
effects.
- Life span of approximately 75 years.
- Can cause the erosion of the beach in front of
them.
- Socially reassuring for local residents.
Building groynes
- Wooden barrier built at right angles to the coast.
- They aim to stop the movement of material along
the beach due to long shore drift.
- Their primary intention is to build up the amount of
sand on the beach.
- They have a life span of approximately 25 years.
Advantages
Protects the base of cliffs against erosion. Can
prevent coastal flooding in some areas. Land and
buildings are protected from erosion.
Disadvantages
A sea wall is expensive to build. Curved sea walls
reflect the energy pf the waves back to the sea.
This means that the waves remain powerful. Over
time the wall may begin to erode. The cost of
maintenance is high.
Advantages
Prevents the movement of beach material along the
coats through the process of longshore drift.
Allows the build up of a beach (a natural defence
against erosion and an attraction for tourists).
Disadvantages
Can be seen as unattractive.
Can be costly to build and maintain.
Advantages
Rip Rap/Rock armour or boulder barriers
Absorb the energy of the waves.
– large boulders of 10 tonnes or more are piled up on the
Allows the build up of a beach.
beach and used to absorb the energy of waves and encourage
the build up of beach material.
Disadvantages
- The gaps between the rocks allow water through, which
Can be expensive to obtain and transport the
means that the energy of the waves is dissipated very
boulders.
effectively.
- It is important that the boulders are big enough to
withstand being eroded themselves and therefore becoming
part of the coastal system.
Gabions
Advantages
Large steel mesh cages filled with large rocks.
- Aligned at right angles to the coastline.
-They aim to do a similar job to wooden groynes.
-Usefull solution where armour rock is considered
inappropriate or too costly. Various forms
available. Can be buried by sand and vegetation.
Permeable face absorbs wave energy and
encourages upper beach stability.
Disadvantsages
Expected life span of 20 – 25 years, as the steel
will rust.
Limited life, leading to unsightly and hazardous
wire baskets along beach and the release of nonindigenous cobbles to the beach system. Wire
affected by saltwater, vandalism and abrasion by
trampling or gravel beach impacts.
Revetments
Structures placed on banks or cliffs in such a way as
to absorb the energy of incoming water or
explosives. They are usually built to preserve the
existing uses of the shoreline and to protect the
slope, as defense against erosion,
Wooden, steel, or concrete fence-like structures
that allow sea water and sediment to pass through,
but the structures absorb wave energy. A beach can
Soft engineering options:
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Soft engineering
Soft engineering options are often less expensive than hard engineering options. They
are usually also more long-term and sustainable, with less impact on the environment.
There are two main types of soft engineering:
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Beach nourishment
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This replaces beach or cliff material that has been removed by
erosion or longshore drift.
The main advantage is that beaches are a natural defence
against erosion and coastal flooding. Beaches also attract
tourists.
While it can be a relatively inexpensive option it requires
constant maintenance to keep replacing the beach material as it
is washed away.
Managed retreat
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This is where areas of the coast are allowed to erode and flood
naturally. Usually this will be areas considered to be low value.
The advantages are that it encourages the development of
beaches (a natural defence) and salt marshes (important for the
environment) and cost is low.
While this is a cheap option, it will not be free as people will
need to be compensated for loss of buildings and farmland.
Disadvantages of Coastal Management
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Cost: Most of the solutions detailed are very costly, and in many
places questions are being asked as to whether they are actually
worth the money.
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Problems of disrupting the natural coastal system: Whenever you
tamper with nature there are going to be knock on effects, which
could, in time, become worse than the original problem.
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Coastal defence strategies are often very localised, and can cause
problems further down the coast. One such example could be seen
where groynes are used to trap sediment. Further down the coast
there could be a reduction in the amount of material available to
protect the coast there. This in turn would mean an increased
amount of coastal erosion.
3 contrasting coastal
management case studies in UK
All three are very
different and have
varying outcomes
and effects.
Case Study 1 - Hallsands
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The loss of Hallsands was originally branded as a natural disaster,
however, after some research it is clear to see that the loss of the
village was due to human interference.
In order to build a new docklands at nearby Plymouth, large
amounts of shingle, used to make concrete were dredged from
Hallsands.
BBC - Learning Zone Class Clips - Hallsands - destruction of
coastland - Geography Video
Hallsands
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With no shingle beach to protect the vulnerable cliffs, the waves
began eroding underneath the village and eventually it crumbled into
the sea.
Hallsands Today
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Butlins is situated on the Somerset Coast in the town of Minehead.
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Butlins is built on an area of marshland prone to flooding.
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In order to combat the damaging effects of flooding it was decided
that a £12.5 million flood defence should be built.
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A curved concrete wall has been built along the coast in order to
deflect some of the power of the waves
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In front of this structure is an armour of huge boulders, averaging 7
tonnes each
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This constructed sea wall has cost £12.5 million but there is a high cost
to benefit ratio.
Problem
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Porlock's coast primary use is farmland
At the moment Porlock coasts, shingle is doing just fine, at stopping
the storms and high tides.
This natural defence system however is changing and will not be
able to prevent flooding of the land
Porlock Beach’s
natural defences
Shingle acts as wall to
protect the farmland
behind
Solutions
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Does the national trust, who looks after most of the farmland and
coast; pay huge sums of money to help stop it?
Or
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Do they let the land behind flood and let nature take its course?
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BBC - Learning Zone Class Clips - Coastal management strategies sea defences and managed retreat - Geography Video
The Outcome
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After assessing the area, there was only one answer
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This was to flood the land. Although it may loose some farmland, it
would stop the surprise flooding.
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Building sea defences would be pointless, as they would only be
destroyed in high tides and storms.
Bournemouth
Coastal Management
Examples From Dorset Coast
Bournemouth & Barton
Bournemouth
Challenge: Produce a presentation on the implication of groynes as a
method of coastal management using Bournemouth as a supporting
case study.
Implications Of Groynes
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Scour hole
Erosion to replace volume of trapped sand
Total erosion usually much higher.
Cost-benefit analysis in coastal management
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Bournemouth is a major resort town. The appearance of the beach is important to the town’s
image as a modern international centre of business, learning and leisure. This growth in business
has made the beach an even more valuable asset than ever before.
But Bournemouth has always had a problem holding on to its sand: longshore drift, which is very
active here, tends to carry it away in vast quantities. To stop this process, groynes were built —
wooden barriers to hold back the sand. But wrestling with nature is an expensive business: a
single groyne costs almost a quarter of a million pounds.
Barton-on-Sea
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Along the coast at Barton-on-Sea, there is a different problem. Starved of
material by the groynes in Bournemouth, the town’s beach has been reduced to
a fraction of its original width. In fact, at high tide there is no beach at all. Waves
act directly on the cliffs. Coupled with the local geology — layers of clays and
sands — this leads to rotational cliff slumping on a regular basis. Slumped
coastlines are very unstable and dangerous and trying to control them is a
serious business. Any kind of coastal protection in areas like this requires huge
and expensive engineering works.
How much to spend and where to spend it often depends on a very simple
formula: if the clifftop property is valuable, spend the money; if it isn’t, don’t. This
is more or less what happens at Barton.
• To the west of the town there is a fairly heavily
defended stretch of coastline, with groynes and
revetments and cliff draining works; these have
arrested the erosion, protecting the valuable
properties. But to the east of the town it would be
difficult to introduce an effective coastal protection
programme. The property on the top of the cliffs —
mainly holiday chalets — is relatively low-value, and
the management strategy adopted here is simply to
pick them up and move them backwards when they
get within an unsafe distance of the clifftop.
Scour Hole
Cost v Benefit
Barton-on-Sea
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On the Dorset coast, east of Bournemouth, is a headland of
resistant sandstone called Hengistbury Head. A large concrete
breakwater or groyne has been built there. The groyne was built in
1938. Before that time there was a narrow beach along the full
length of the headland. It is clear that the groyne has caused a
large build up of sand to the west of the groyne, and a reduction of
sand to the east.
At high tide there is no beach at all east of the groyne; whilst to
the west, sand dunes have developed. This could not have happened
unless there was a movement of beach material along the coast,
from west to east, at Hengistbury Head. This movement is called
longshore drift.
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Since the 1930’s, rapid coastal erosion had occurred in
Christchurch Bay, most notably at Barton-on-Sea The cliffs at
Barton are 30m high, but are formed in relatively weak sands and
clays. The foot of the cliff is attacked by the sea and the cliff
face is prone to slumping and rotational slip.
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A massive engineering scheme was carried out to protect the cliffs,
at a cost of over £6 million. A sea wall and groynes were built at
the foot of the cliff and sheet steel was driven into the cliff face.
Despite this, the cliff still collapsed following heavy rain in 1975.
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Engineers has tried to prevent the natural processes of erosion –
and failed. One reason was that longshore drift had probably been
lessened due to the groyne at Henigstbury, 7km to the west of
Barton. Barton also faces the full force of the south-westerly
gales.
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Since 1975 the scheme
has been renewed with
the
addition
of
thousands of limestone
boulders along the cliff
foot and a complex
drainage
system
through the cliff face.
Strong
promontories
have been built into the
sea and an artificial
beach has been made.
Will this save Barton?
Only time will tell.
Questions:
1.Describe the coastal defence engineering scheme at Barton on
Sea.
2.How successful do you think the scheme has been?
3.Make a plan for measures to reduce further erosion at Barton.
Draw up your plan as a report, including suitable maps and diagrams.
The Holderness Coast
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The Holderness Coast is
on the NE coast of the
UK, facing the North
Sea. The coastline is
mainly made up of cliffs
(20-30m high), consisting
of soft, easily eroded
boulder clay.
The Holderness Coast is located between the Humber Estuary to the
South and Flamborough Head to the North and forms part of a
designated Heritage Coast.
The Holderness Coast
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The Holderness Coast is one of Europe's fastest
eroding coastlines. The average annual rate of
erosion is around 2 metres per year.
The main reason for this is because the bedrock is
made up of till. This material was deposited by
glaciers over 18,000 years ago.
Geology
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The soft brown clay, known as boulder clay as it contains randomly
distributed pebbles and boulders was deposited by glacial action
and remains unconsolidated (not turned to rock). As a result it is
easily eroded by destructive storm waves and the fine nature of
the clay means it is transported away from the beach in suspension
by longshore drift. Undercutting of the cliff leads to large-scale
slumping along the coastline.
Hengistbury Head
• Bournemouth cliffs have been stabilised by the construction of a concrete
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promenade with long groynes. The consequent containment of loss of material
from Bournemouth cliffs had essentially increased the erosion at Hengistbury
Head as the arrival of material from the South-west had decreased . The
building of groynes at Hengistbury has helped to contain this loss. Highcliffe had
a very large concave beach defence erected in the 1960's below Steamer Point
and considerable work has also been done at nearby Barton. Interestingly the
beaches at Mudeford and Highcliffe have built up considerably in the last 30
years while the trailing sandbank off Mudeford Spit new seems less prominent.
The end of Mudeford Sandspit has also been reinforced with a rock groyne
While the sea defences erected at Bournemouth and at Hengistbury Head have
significantly slowed the erosion, regrettably it is difficult to see how full
equilibrium can now be restored within this area, without the utilisation of new
techniques. There has been concern of a breach across barn Field which would
turn Hengistbury Head into an Island. There are mixed opinions regarding this
possibility with some considering such a disaster almost inevitable within the
next 50 years while others put the risk at 3% or less
The Holderness Coast
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The Holderness Coast is one of the fastest eroding coasts in the world.
The village of Mappleton lies on the coast which is made of
unconsolidated glacial till – it leaves the cliffs vulnerable to erosion.
Why
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is
Cliff
Erosion
such
a
problem
here?
1. The cliffs are made up of soft glacial material (Boulder Clay made up of sands and gravels). This is easily eroded by the waves
and the cliffs are easily undermined.
2. The Holderness Coast is very exposed; approaching waves have
a long fetch over the North Sea.
3. The waves are mainly destructive - eroding the base of the
cliffs (hydraulic action etc.)
4. Most of the Material eroded from the cliffs is washed out to
sea, the rest is moved by longshore drift - the beaches are
therefore narrow and do little to protect the coastline. (If the
beaches were wider, the waves would break on the beaches
reducing their erosive power).
5. The coastline is threatened further by sea-level rise.
Mappleton
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Situated approximately 3km south of Hornsea lies the village of
Mappleton. Supporting approximately 50 properties, the village has
been subject to intense erosion at a rate of 2.0m per year, resulting in
the access road being only 50m from the cliff edge at its closest point.
Geology
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Mappleton lies upon unconsolidated till. This material was deposited by glaciers
during the last ice age 18,000 years ago.
The two rock groynes at Mappleton have helped develop wide and steep sandy
beaches.
•
Mappleton has been the focus
of coastal management and
controversy. Here the cliff has
been regarded and grassed to
make it gentler and less prone
to slumping. Two large groynes
built of huge gneiss boulders
have been erected with the aim
of trapping sediment to build up
the beach and so protect the
cliff
from
direct
wave
attack.
Rock armouring has
been placed along the foot of
the cliff to dissipate wave
energy before it reaches the
soft boulder clay behind. This
does
appear
to
have
been successful in reducing the
rate of erosion on the village of
Mappleton but has; it has been
argued resulted in more rapid
erosion
further
downdrift
where the beaches are being
starved of sediment.
Deposition
along
the
Holderness
Coast
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Spurn
Head
Spurn Head is an area of deposition that occurs at the southern
end of the Holdeness Coastline. Here the coastal processes and
fluvial (river) processes interact and sediment transported by
longshore drift is deposited to form a spit.
The spit is in danger of being breached every time there is a major
storm as several sections of it have become very narrow as
sediment has been transported to the distal end of the spit.
Flamborough Head
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The most striking aspect of Flamborough
Head are the white chalk cliffs that
surround it. The chalk lies in distinct
horizontal layers, formed from the
remains of tiny sea creatures millions of
years ago.
Above the chalk at the top of the cliffs
is a layer of till (glacial deposits) left
behind by glaciers 18,000 years ago,
during the last Ice Age. As the cliffs
below are worn away by the action of the
waves, the clay soil often falls into the
sea in huge landslips.
Coastal Management
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In 1991 two rock groynes and a rock revetment were built, as a consequence a
substantial beach accumulated between the groynes halting erosion.
However, further south the rate of erosion has increased significantly. This is
because material which is being carried south is not being replaced (it is trapped
within the groynes). Therefore there is no beach to protect the cliffs. Even
during a neap tide ( a tide which is 30% less than the average tidal range) the
sea reaches the base of the soft cliffs and erosion occurs.
Spurn Head
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The area known as Spurn forms the southern extremity of the Holderness coast
and includes the unique feature of Spurn Head, a sand and shingle spit 5.5km
long, reaching across the mouth of the Humber.
Spurn is made up of the material which has been transported along the
Holderness Coast. This includes sand, sediment and shingle.
Spurn Head
Step 1: Longshore drift
moves material beyond the
change in coastline
Step 2: The spit is formed
when
the
material
is
deposited
Step 3: Over time the spit
grows in length and may
develop a hook if wind
direction changes further
out
Step 4: Waves cannot get
behind the spit, creating a
sheltered area where silt is
deposited and mud flats or
salt marshes form
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Spurn Head is an example of a feature
geographers call a spit.
The spit forms a sweeping curve
which continues the line of the
coast. The sand which forms the spit
has been transported along the
Holderness Coast by longshore drift.
The energy in the waves transporting
the material reduces where the
North Sea meets the Humber
Estuary. As a result the material is
deposited. This process is known as
deposition.
Easington Gas Terminal
Easington
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Easington, also situated on the Holderness Coast, is the gas
terminal for gas from the North Sea which supplies most of
Britain.
This needs to be protected from the sea – it would be very costly
to relocate the terminal.
Some ideas have already gone into practice, but are not long term
solutions. For instance bolstering the cliff face with rocks has
already become battered by the sea.
Easington – Long term solutions
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They have decided to build groynes on the beach in order to
protect the terminal.
Cliffs south of Easington, prior to groynes.
Cliffs after the construction of
groynes.
Conflicts which have occurred over the
construction of the groynes at Easington
have mainly centred over the sand spit Spurn
Head. The spit is an SSSI and the question is
to protect the spit and relocate the gas
terminal. Economically, protecting
Easington would be worthwhile. Realistically,
North Sea gas only has around a 30 year
lifespan and so the groynes could be removed
and the spit allowed to reform.
Chesil Beach,
Chiswell and the
Isle of Portland
Dorset Coast
Chesil Beach is known throughout the world as an impressive shingle storm beach. The
beach acts as a vast natural defence, but in very heavy storms the area behind the beach
may be flooded.
Chesil beach is a natural barrier, 27 km long and 200m wide. It is a coastal feature of
international significance, being one of the three major shingle beaches in Britain. Until
1972, beach material was excavated for commercial activities.
Huge waves pounding against the beach
force water through the pebbles to the
back of the beach. The biggest waves
sometimes overtop the ridge, sending
water and shingle onto the road behind. In
recent years extensive flood alleviation
schemes have been implemented by the
Environment Agency and the Ministry of
Agriculture Fisheries and Food (MAFF) to
minimise the impact of such flood events,
and a flood warning system alerts
residents in the area if a major flood event
is predicted.
The area has long been associated with
shipping disasters because of its exposed
nature and stormy seas. The loss of life
from ships wrecked during heavy seas has
even been recognised in the local name of
the bay off Chiswell - "Deadman's Bay." In
1775 a convoy of merchant ships and their
escorts perished in a severe gale. 6 ships
sunk with the loss of 298 lives. In 1824 the
Fleet was flooded to a depth of over 20
feet causing extensive damage to property
and loss of life. The 'Adelaide' ran aground
in 1872 and her debris can still be found
washed up on the beach.
How was Chesil Beach formed?
Barrier Beach or Tombolo?
The evolution of Chesil Beach and the Fleet has been the subject of much
discussion and remains the focus of considerable research today. Understanding
where the beach came from is essential in order to determine what may happen
to it and the land behind it in the future.
There is no full agreement on the formation of the beach or any theory that can
account for all of the observable phenomena. The traditional view is that Chesil
Beach was driven onshore with rising sea levels at the end of the last Ice Age. As
the sea advanced, material from what is now Lyme Bay was swept up to form the
beach, trapping the Fleet lagoon in the process.
More recently it has been proposed that a large volume of the beach was derived
from the landslides of East Devon and West Dorset. During the last Ice Age, these
landslides would have been very active indeed and as sea levels rose, erosion cut
into the debris, sending a huge ‘pulse’ of material, by long shore drift, to the east.
This might explain the older, finer beach that underlies what we see today. This
beach moved onshore, trapping the Fleet lagoon and reaching its present position
some 4 to 5,000 years ago. It was then buried by the pulse of shingle that forms the
beach that we see today.
Chiswell settlement is located immediately behind the Chesil Beach shingle
ridge, on the north-east side of the Isle of Portland. It has been flooded many
times. The first major recorded event occurred in November 1824, when 26
people and approximately 80 houses were destroyed or damaged in a
devastating storm. Since 1824, 22 storm events have occurred at Chiswell
that have endangered lives and put property at risk.
Coastal protection and sea defence works were first undertaken during 196975. This has formed the basis of the long term protection of Chiswell. Since
then, a number of new protection schemes have been built, at the same time
providing an important local amenity; the promenade at the south end of
Chiswell.
CHISWELL
• The village of Chiswell lies at the point where the massive
bank of Chesil Beach joins the Isle of Portland to the
mainland of Dorset. Property and the access on and off the
Island has always been subject to flooding from the sea:
indeed, the beach faces the full force of the Atlantic. On a
calm day it is impossible to gain a measure of the sea and
the power that it is capable of unleashing on a mobile beach
composed from nothing more than pebbles. However, storm
and ocean swells are capable of breaking over the beach,
which stands 15 metres above the high water mark.
• The only road from the mainland runs behind the beach
along with services such as power, water and sewerage.
Maintaining these facilities is fundamental to the social and
economic wellbeing of the Island, which is home to more
than 15,000 people. Two flooding events during the winter
of 1978 and 1979 brought devastation and disruption to the
village and the Island, forcing measures to be taken to
protect against inundation by the sea.
13th Feb 1979
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Flooding behind the beach
during the storm of December
1978. The Island of Portland
was effectively cut of from the
mainland
Waves overtopping the beach during the
storm of February 1979.
13 December 1978
•
A deep depression swept in from the Atlantic Ocean and created storm
conditions. A combination of heavy rain and strong winds meant that waves of
over 4.5 m attacked the shore at regular 12 second intervals. These steep
destructive waves with their strong backwash carried away beach material. As
the storms continued, Chesil beach was progressively reduced in height and
became even more unstable. Water broke over the highest part of the beach
and ran down the other side, eroding the landward slope.
•
Meanwhile, huge quantities of sea water percolated through the pebbles of
Chesil beach and seeped out through its landward face. Thus, overtopping and
percolation led to Chiswell being flooded to a depth of 1.2m.
•
Over 30 commercial and residential properties were flooded and families were
evacuated to emergency rest centres. Gas, water and electricity lines were cut
for 24 hours and emergency services were needed for five days.
13 February 1979
On the morning of 13 February 1979, Chesil Beach was overwhelmed by
constructive waves attacking the shore at 18-second intervals. The waves
pushed shingle beach forward and tonnes of shingle overspilled the top of
Chesil, flattening it out. This allowed water to break over the top of the beach
and on to Chiswell below.
Portland was temporarily cut off from the mainland because of the overtopping
waves. Over 30 Chiswell properties were flooded and the relevant families
evacuated. Again, water, gas and electricity supplies were cut and emergency
services were needed for ten days.
After the 1979 flood, everyone has agreed that something had to be done to
prevent future flooding.
Consequences
•
On 14th February 1979, a firm of consultant engineers were contracted to
identify and find ways of reducing the flood hazard at Chesil Beach. Funded
mainly by the government, the engineers produced an undated flood control
system. The systems cost approximately £3 million and was built in four main
stages.
•
•
An innovative scheme was completed in 1986, the bulk of which lies within the
beach in the form of an interceptor drain and gabion basket blanket over the
beach crest. Developing this scheme required a major investigation into the
structure of the beach and the nature of the threat.
Today the scheme has returned confidence to the local community even though
it does not provide complete protection from the worst that the sea can deliver.
As a result, the long-term future of the village remains the subject of
considerable debate.
The Scheme
•
The scheme involved gabion baskets on the
beach crest, some improvement to the
existing sea walls and a sunken culvert drain
within the beach linking to an open channel
draining into Portland Harbour. The main
road behind the beach was also raised in
order to alleviate flooding.
Sea Defences
•
Gabion baskets filled with local coarsely crushed
Portland Limestone
Sea Wall
• Casting of the wave return wall on top
of the existing sea wall in front of
the Cove Inn
Interceptor Drain
•
The shingle lies on an impermeable layer.
The interceptor drain was located at the
boundary, thereby ensuring that the
water was collected
•
Pile driving along the line of the drain in
February 1996
Success of the scheme
• With the exception of the recommended
1500-metre length of gabion crest
protection, the scheme was completed
in 1988. A severe storm attacked
Portland on 16 December 1989 and
proved the efficiency of the sea defence
scheme. Flooding was minimal and the
interceptor drain flowed at its maximum.