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Seawalls

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The following article discusses fixing of the coastline using seawalls.

Method

Fig. 1. Examples of seawall structures.

A seawall is constructed at the coastline, at the foot of possible cliffs or dunes. A seawall is typically a sloping concrete structure; it can be smooth, stepped-faced or curved-faced. A seawall can also be built as a rubble-mound structure, as a block seawall, steel or wooden structure. The common characteristic is that the structure is designed to withstand severe wave action and storm surge. A rubble-mound revetment often protects the foot of such non-flexible seawalls. A rubble-mound seawall bears a great similarity to a rubble-mound revetment; however a revetment is often used as a supplement to a seawall or as a stand-alone structure at less exposed locations. An exposed dike, which has been strengthened to resist wave action, is sometimes referred to as a seawall.

Functional characteristic

The nearly vertical seawall, which was mainly used in the past, had the unfortunate function of reflecting some of the wave energy, whereby the erosion was aggravated, resulting in accelerated disappearance of the beach. However, all kinds of seawalls involve beach degradation as they are used at locations where the coast is exposed to erosion. The seawall will fix the location of the coastline, but it will not arrest the ongoing erosion in the coastal profile. On the contrary, it will to a varying degree, accelerate the erosion. It is quite normal that the beach disappears in front of a seawall, and it will most often be necessary, after some years, to strengthen the foot of the seawall with a rubble revetment.

A seawall will decrease the release of sediments from the section it protects and will have a negative impact on the sediment budget along adjacent shorelines.

Applicability

A seawall is a passive structure, which protects the coast against erosion and flooding. Seawalls were (are) often used at locations off exposed city fronts, where good protection was needed and where space was scarce. Promenades have often been constructed on top of these seawalls. They are also used along other less inhabited coasts, where combined coast protection and sea defence is urgently needed. Seawalls are primarily used at exposed coasts, but they are also used at moderately exposed coasts.


References

Mangor, Karsten. 2004. “Shoreline Management Guidelines”. DHI Water and Environment, 294pg.

See also

Coastal protection techniques



The main author of this article is Mangor, Karsten
Please note that others may also have edited the contents of this article.