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Groynes (and breakwaters)
 Groynes
come in many shapes and sizes are specifically built to help hold material on
a beach and slow down longshore drift (see picture opposite). Artificial breakwaters
are normally built offshore and designed to shelter the coast by forcing waves
to 'break' and lose much of their energy before they reach the shore.
Caption:
Wooden groyne creating a build up of shingle on the up-drift (left hand side)
with a lower beach on the down-drift (right hand side), Porlock (Annex 01),
Somerset.
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Guidance: Groynes (and breakwaters) can appear to be successful
and in some instances are able to support the maintenance of a beach for
many years. There are however limitations to their use, which are increasingly
being recognised, namely:
- storms, which can move material onshore and offshore may cause a
rapid depletion of the beach. This may involve the pebbles either being
moved offshore into deeper water where they can be effectively 'lost'
to the system or onshore as the shingle beach 'rolls-over' the land;
- as material is held up on one section of the coast it can 'starve'
adjacent sections 'down-drift' of the groynes.
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