Sea defenses and coastal protection structures like seawalls, breakwaters, gabions, revetments, groynes, rock armor, and concrete blocks are used to prevent coastal erosion and flooding. Seawalls are durable structures that protect the coast from erosion and flooding. Gabions are wire baskets filled with stone that can be placed vertically or sloping to limit wave run-up. Groynes are structures built perpendicular to the shoreline to reduce beach material loss from longshore drift. Breakwaters are large concrete blocks or boulders sunk offshore to alter wave direction and reduce their energy before reaching the shore.

1. What Are They?

2. Sea Defense or Costal protection are defenses that
stop erosion, flooding, silting up of harbors etc.
Walls, breakwaters and other measures designed to
prevent coastal erosion.

3. SEAWALLS
Seawalls are durable structures designed to protect the coast against erosion and
flooding by the sea. They are sometimes additionally used for amenity purposes
or to protect reclaimed land from erosion. Because of the potential for scouring at
the toe (bottom) of the structure, seawalls are often used together with some
system of beach control such as groynes or a nourished beach

4. Gabions are wire baskets filled with stone, cobbles or small rocks. They can be
placed as either a vertical wall or as as a sloping revetment, where their
permeability helps to limit wave run-up and overtopping. Gabions are most
commonly used to stabilise shorelines against erosion, or as earth retaining
walls.

5. Revetments are simply described as an earth embankment core
covered by a protective surface layer. A revetment may be
either rigid or flexible, depending on the material from which
the protective surface layer is constructed. The main types of
revetment construction used for coastal defences are Rock
Armor, Concrete Blocks (often inter-connected), Gabions or by
way of Earth Reinforcing Geotextiles.

6. Groynes are beach control structures designed to reduce the loss (or rate of loss) of beach
material due to long shore drift. Groynes are narrow structures usually built at right angles to
the shoreline, most commonly built using timber planking between timber piles, however
groynes can also be built from rock and concrete. Across the partnership area there are
several examples of different types of groynes, the Hayling Island Southern frontage has over
60 groynes, mostly of timber construction, with rock groynes found at the Eastern end of the
beach. Groynes can also be found to the east of Gilkicker Point, Gosport.

7. Also known as riprap, rock armour is large rocks piled or placed at the foot of
dunes or cliffs with native stones of the beach. This is generally used in areas
prone to erosion to absorb the wave energy and hold beach material. Although
effective, this solution is unpopular due to the fact that it is unsightly.
Also, longshore drift is not hindered. Rock armour has a limited lifespan, it is not
effective in storm conditions, and it reduces the recreational value of a beach.
The cost is around £3000 per metre, depending on the type of rocks used.

8. Enormous concrete blocks and natural boulders are sunk offshore to alter wave direction and to
filter the energy of waves and tides. The waves break further offshore and therefore reduce their
erosive power. This leads to wider beaches, which absorb the reduced wave energy, protecting
cliff and settlements behind. The Dolos which was invented by a South African engineer in East
London has replaced the use of enormous concrete blocks because the dolos is much more
resistant to wave action and requires less concrete to produce a superior result. Similar concrete
objects like the Dolos are the A-jack, Akmon, Xbloc and the Tetrapod, Accropode