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Slide 1

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DEFENCES…read more

Slide 2

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There are many techniques used for reducing the power of
waves before they erode a coastline. The photos illustrate
some methods used in areas of weak rocks in Britain and
· Rip-rap is a sheet of boulders used at the toe of a slope to
add weight and break the force of the waves. Rip-rap is
made of resistant rocks, often gabbro, dolerite, granite or
gneiss, which will not weather or break down. Because the
blocks are angular, they fit together tightly, but still allow
water to drain through back to the sea.
· Concrete walls are usually slightly curved at the top so that
waves are deflected slightly so that water is returned to the
sea. They may have drainage holes so that any water
which overtops the wall can drain back into the beach.…read more

Slide 3

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· Concrete shapes can be arranged to nest together so
that they are wedged tightly enough not to be moved by
large waves. They allow water to drain back to the
beach and also allow sand to build up around them,
which helps to stop sand from washing out to sea.
· Geotextiles can fix slopes which have been reduced in
angle and encourage vegetation to grow back. Marram
grass grows in pure sand, has very long roots and can
cope with waves and dry conditions.
· Offshore breakwaters break the force of the waves and
ensure that wave energy is dispersed. They also allow
the build-up of sand in the low energy areas next to the
shore.…read more

Slide 4

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Le Croisic, Brittany
This coastline is made
of schists which are
very unresistant and
easily eroded by the
sea.…read more

Slide 5

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The houses are protected from the sea by rip-rap -
large boulders of resistant rock brought from
outside the area. They absorb the energy of the
waves but are permeable so that water can drain
through them back to the sea.
Le Croisic, Brittany…read more

Slide 6

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Some houses have had to build their own sea defences.
Walls take up little land area, but need to be slightly
curved towards the top to absorb wave energy. This
one has drainage holes to allow water from the garden
behind to drain onto the beach, to reduce water
pressure on the wall.
Curved profile Drainage holes
Le Croisic, Brittany…read more

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