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The Impacts of Different Sea Defences 15.3.11
A sea wall is a large coastal defence, mainly made out of tough rocks and not easily
eroded materials like reinforced concrete or boulders or other long lasting
materials. They are constructed on the inland part of a coast to reduce the effects of
strong waves. Modern seawalls tend to be curved to reduce as much as possible
the sea's effect of corrasion and abrasion and to deflect as much of the waves
energy as possible.
An example of a place using the seawall defence is Pondicherry near the Indian
Although seawalls are quite effective at breaking waves and reflecting them back at
the sea, they have quite high maintenance costs. They also look very ugly, especially
in little fishing villages.
The cost of a seawall is in the hundred thousands if not the millions because they
are very expensive to maintain and the waves they block are often very destructive
and have a lot of hydraulic power. This could affect people's tax.
There isn't much environmental impact from building seawalls, the only one that I can
say is that animals that come in at high tide that might live on the cliff face, might
have no habitat to live in. Also when corrasion happens on the seawall, bits might
come off, which could be eaten by little animals living on the seafloor, but this is a
very small threat.
Groynes are mainly built to interrupt water flow, which in turn prevents movement of
sediment and loose shingle on the beach. Groynes can create beaches, and they
also prevent beaches being washed away by longshore drift. The area between
each groyne is called a groyne field. Groynes are usually made of wood or concrete
or other strong materials.
An example of a groyne defence is on the Isle of Wight in Sandown, England.
Groynes are basically natural barriers to the sea, and if a groyne is constructed
correctly, then not too much sediment are built up at one time. Although groynes are
very good at their job, they are very unsightly, and ruin a beaches beauty in some
places, because they are so ugly, they immediately come across as man made and
unnatural, and make a beach seem less organic, and more influenced by man.
The cost of a single groyne is about five thousand pounds per metre due to
maintenance and the constant weight that the defence has to take from sediment
Animals don't really get affected by groynes because they don't reach that far into
the sea, also habitats don't really get destroyed.
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Gabions are really effective in breaking up a wave's energy, and at the same time
preventing the wave from reaching inland. A gabion is a basket or a cage mainly
made of netting, which is then filled with medium sized stones. This defence is so
effective because the stones are allowed to move a little in the cage, which lessens
the wave's energy a little.…read more
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Rock armouring is basically using piles of rocks to protect shorelines from erosion
and corrasion. Rock armouring or Riprap is mainly limestone or granite, which can
last a long time, as long as the water is not too acidic. The way they work is that they
absorb wave's energy, like a gabion, which means that the ripraps are often
damaged and require a lot of maintenance. Rock armouring is permeable because
it uses rocks which have many gaps.…read more