Coastal Management
Lesson Objective:
Understand why methods of engineering to protect the
coast have advantages and disadvantages
MANAGING THE COASTLINE
“Cliff collapse
in Egypt leaves
24 dead”
“Hundreds of thousands of
tonnes of chalk fell 500ft
to the beach on Sunday
morning, in what is thought
to have been the biggest
sudden loss of coastline in
Britain in living memory.”
“Holbeck
Hall Hotel
crashes
into the
sea”
“Beach hit by 200 tonne cliff
collapse”
“Beach closes after cliff
collapse”
“My house
is only
worth £1!”
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 eyesore ..etc. There are 2 main categories of 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.
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.
Possible Questions :
Why might certain coastal
protection methods be selected
instead of others?
What is the difference between
Hard and Soft coastal protection
techniques?
17
How can the coastline be protected?
HARD ENGINEERING
How do groynes work?
Groynes trap the sand which is carried along the coast by
longshore drift.
The sand acts as a natural protection against the force of the
waves. The waves break onto the beach and not the cliffs.
Groynes
•
•
•
•
•
These are built at right angles to the coastline.
They aim to slow down longshore drift and trap sediment.
They can be made of timber, concrete or rock.
Wood groynes are around £5,000 each.
Rock groynes cost around £200,000 each.
Advantages:
• More beach material to dissipate wave energy which slows down
cliff erosion.
• Cheap in comparison to other hard engineering methods
Disadvantages:
• Beaches further along the coast are starved of beach material due
to their affect on long shore drift.
What are the disadvantages of groynes?
Mappleton is located on the
Holderness Coastline.
In 1991 a rock revetment and two
rock groynes were built. Sand
accumulated and halted erosion.
South of Mappleton, the rate of
erosion has increased significantly.
Material that usually moves south
via longshore drift is becoming
trapped within the groynes.
Now there is no beach to protect
the cliffs - the sea reaches the base
of the soft cliffs and erosion occurs.
Sea Walls
•
•
•
•
Sea walls aim to prevent erosion by providing a barrier.
They reflect the seas energy.
The walls are placed parallel to the shore.
They are usually expensive and can cost up to £5000 per square
metre.
Advantages:
• Provide excellent defence where wave energy is high
• They reassure the public
• They have a long life span.
Disadvantages:
•
•
•
•
Expensive
Ugly- can put off tourists
They can make it harder to access the beach
Recurved sea walls cause greater erosion at the base of the wall
What problems do sea walls create?
Why might a sea wall cause more coastal erosion?
Rip rap/ Rock Armour
• These are often large boulders placed along the base of
a cliff to absorb energy from waves.
• They cost about £3000 per metre
Advantages:
Cheap and efficient
Disadvantages:
• Ugly
• Dangerous access to beach
• Costs increase when rock is imported
Gabions
• These are steel wire baskets filled with rock and built into an eroding
cliff to improve stability
• They are fairly cheap, costing about £350 per metre.
Advantages:
• Cheap
• Fairly effective
Disadvantages:
• Unattractive
• They cannot withstand strong waves
Revetments
• Traditionally these have been wooden slatted barriers
constructed towards the rear of beaches to protect the
base of cliffs. Energy from waves is dissipated by them
breaking against the revetments.
• Cost: £2000 per metre
Advantages:
• Less beach material is eroded compared to a sea wall
• Cheaper and less intrusive than a sea wall
Disadvantages:
• Short life span
• Unsuitable where wave energy is high
Offshore reef
• Enormous concrete and natural blocks are sunk offshore to alter the
wave direction
• Cost £1,950 per metre
Advantages
• The waves break further offshore so reduce erosive power
• The allow the build up of sand
Disadvantages
• May be reduced by heavy storms
• Difficult to install
SOFT ENGINEERING
Beach Replenishment
Beach replenishment is also known as beach
nourishment.
Beach nourishment is the process of dumping or pumping sand
from elsewhere onto an eroding shoreline to create a new beach or
to widen the existing beach.
Beach nourishment does not stop erosion, it simply gives the
erosional forces (usually waves) something else to "chew on" for
awhile.
The waves erode the nourished sand instead of destroying houses,
roads or parking lots. Because nourishment doesn't stop erosion,
nourishment must be repeated to maintain the beach.
Beach nourishment/
repenishment
• Beaches are built up, usually by pumping sand onto the beach
• The source of the material is usually from offshore dredging.
• This has to be undertaken on a regular basis (once every five, or
less, years).
• Pumping material can be expensive (at least £1,250 per cubic
metre) unless it is a by-product of channel dredging.
Advantages:
• Retains the natural appearance of the beach
Disadvantages:
• Off shore dredging of sand and shingle increases
erosion in other areas and affects ecosystems.
• Large storms will require beach replenishment,
increasing costs.
• Can be expensive, depending on the source of the sand
Managed retreat
• This is when areas of coast are allowed to erode.
• This is usually in areas where the land is of low value.
• Cost: depends on amount of compensation that needs to
be paid to people affected by erosion.
Advantages:
• Managed retreat retains the natural balance of the
coastal system.
• Eroded material encourages the development of
beaches and salt marshes.
Disadvantages:
• People lose their livelihood e.g. farmers. These people
will need to be compensated.
Cliff regrading
Making the cliff face longer so that it is less steep
Advantages:
• Cheap
• Natural- will encourage wildlife back into the area
Disadvantages:
• Not effective on its own- need other defences at the
base of the cliff
• Some homes on the cliff may need to be demolished
What may influence decision
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 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.
How can the coastline be protected?
Hard engineering techniques aim to stop coastal processes from
occurring. Soft engineering methods try to work with nature to protect
the coast.
Match the following statements to
your pictures of hard and soft
engineering worksheet.
Write in pencil if you are unsure!
If you finish, use page 58/59 of the textbook to
add more detail.
How does it work?
Advantages
Disadvantages
Wooden structures break the force
of the waves and trap beach
material behind them.
Much cheaper than a sea wall.
Effective at breaking the force of the
waves.
Less durable than a sea wall – may
need replacing quicker.
Does not give total protection to the
base of the cliff.
Cost approx £1000 per metre
Large boulders on the beach –
lesson the force of the waves by
absorbing the wave energy within
the gaps between the rocks.
Relatively cheap.
Use natural material/rocks
Environmentally ugly . Can be
removed by the waves due to the
washing away of sand and shingle
beneath.
Build up the beach by replenishing
beach material, particularly at the
base of structures to provide a
‘natural’ solution to absorbing wave
energy.
Provides a natural solution.
Natural looking – meaning it is
difficult to tell management is taking
place.
Can be expensive to keep
transporting large amount of sand –
sediment moved by longshore drfit
so will need frequent replenishment
unless used with other defences.
Concrete wall, curved under side to
deflect the power of the waves.
They reflect rather than absorb
wave energy.
Most effective means of preventing
erosion.
Most expensive (up to £2.5
million/km).
Deflected waves often scour the
base, undermining it – it may
collapse in the future.
Cages of boulders built into the cliff
face – small rocks help to absorb
the wave energy.
Effective where severe erosion and
cheaper than sea walls.
Environmentally ugly (usually used
in large numbers)
Cost is approx £350 per metre.
Wooden or in some cases steel
structures that stop longshore drift
and build up/ anchor the beach,
protecting the base of a cliff.
Stops longshore drift encouraging
the build up of the beach and
effectively reducing erosion.
Can increase erosion further down
the coast by stopping longshore
drift and starving areas further
down the coast of sediment. Cost
approx £5-6000 each.
Links to Holderness case study
• http://www.youtube.com/watch?v=AG9eO
C-ErO0
Consider….
1. Why are settlements defended while
agricultural land is left to the actions of the
sea?
2. Some people are for coastal protection
schemes and others are against. Explain
these different opinions.
Past exam question