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 WallRip RapGabionsGroynes

Beach NourishmentOffshore 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 visible- makes 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)