seawall

An example of a modern seawall in Ventnor on the Isle of Wight in the UK.

A seawall (also written as sea wall) is a form of hard and strong coastal defense constructed on the inland part of a coast to reduce the effects of strong waves.

In the UK, sea wall also refers to an earthen bank used to create a polder, or a dike. The term is also sometimes used for walls used to make artificial harbours and port facilities.

Seawalls may be constructed from a variety of materials: most commonly, reinforced concrete, boulders, steel, or gabions. Additional seawall construction materials may include vinyl, wood, aluminum and fiberglass composite.

Seawalls can be expensive to build, today costing between $4000 to $7000 per meter^{[citation needed]}. Modern concrete seawalls tend to be curved to reflect the wave energy back out to sea. Poor designs require constant maintenance as waves erode the base of the seawall.

Design principles and types

A range of seawall types can be envisaged in relation to wave energy, resembling cliff and beach profiles. Vertical seawalls are built in particularly exposed situations. These reflect wave energy and under storm conditions standing waves (clapotis) will develop. In some cases piles are placed in front of the wall to lessen wave energy slightly.

Curved or stepped seawalls are designed to enable waves to break and to dissipate wave energy and repel waves back to the sea. The curve can also prevent the wave over topping the wall, and provide additional protection for the toe of the wall.

A series of rubble mound-type structures (revetments, riprap) are used in less demanding settings. The least exposed sites involve the lowest-cost bulkheads, or revetments of sand bags or geotextiles. These serve to armour the shore and minimize erosion. They may be either watertight, covering the slope completely, or porous, to allow water to filter through after the wave energy has been dissipated.

History

Pondicherry

On December 26, 2004, when towering waves of the 2004 Indian Ocean earthquake crashed against India's south-eastern coastline killing thousands, the former French colonial enclave of Pondicherry (now Puducherry) escaped unscathed. During the city's nearly three centuries as a French colony, French engineers had constructed and maintained a massive stone seawall, which kept Pondicherry's historic center dry even though tsunami waves drove water 24 feet above the normal high-tide mark.

The barrier was initially completed in 1735. Over the years, the French continued to fortify the wall, piling huge boulders along its 1.25-mile (2-kilometer) coastline to stop erosion from the waves pounding the harbour. At its highest, the barrier running along the water's edge reaches about 27 feet above sea level. The boulders, some weighing up to a ton, are weathered black and brown. The sea wall is inspected every year. Whenever gaps appear or the stones sink into the sand, the government adds more boulders to keep it strong.

The Union Territory of Pondicherry recorded some 600 deaths from the huge tsunami waves that struck India's coast after the mammoth underwater earthquake (which measured 9.0 on the moment magnitude scale) off Indonesia, but most of those killed were fishermen who lived in villages beyond the artificial barrier.

See also

• Breakwater
• Retaining wall
• Accropode
• Dike
• Alaskan Way Seawall
• Galveston Seawall
• Georgetown Seawall
• Gold Coast Seawall
• Saemangeum Seawall
• Vancouver Seawall
• The Embarcadero (San Francisco)

References

• De Centre d'études maritimes et fluviales. (2007). Rock Manual. The use of rock in hydraulic engineering. Ciria. ISBN 0860176835.
• N.W.H. Allsop. (2002). Breakwaters, coastal structures and coastlines.Thomas Telford. ISBN 0727730428.
• M. N. Bell, P. C. Barber and D. G. E. Smith. The Wallasey Embankment. Proc. Instn Civ. Engrs 1975 (58) pp. 569--590.

External links

Wikimedia Commons has media related to: Seawalls

Look up seawall in Wiktionary, the free dictionary.

• Channel Coastal Observatory - Seawalls
• Constructing a new sea wall and defences at Lyme Regis in Dorset
• Seawalls and defences on the Isle of Wight

Gallery

Seawall in production in Galveston, TX, USA, 1905	Remains of the first seawall of Canvey Island built c.1622.	Seawall in Bembridge, UK
Seawall in Sicily	Seawall in Poland‎	Seawall on Goat Island in Newport, Rhode Island, USA