Tetrapods are a type of structure in coastal engineering used to prevent erosion caused by weather and longshore drift, primarily to enforce coastal structures such as seawalls and breakwaters. Tetrapods are made of concrete, and use a tetrahedral shape to dissipate the force of incoming waves by allowing water to flow around rather than against them, and to reduce displacement by interlocking.
Tetrapods were originally developed in 1950 by Pierre Danel and Paul Anglès d'Auriac of Laboratoire Dauphinois d'Hydraulique (now ARTELIA) in Grenoble, France, who received a patent for the design. The name was derived from Greek, with tetra- meaning four and -pode meaning foot, a reference to the tetrahedral shape. Tetrapods were first used at the thermal power station in Roches Noires in Casablanca, Morocco, to protect the sea water intake.  Their success saw Tetrapods become popular across the world, particularly in Japan where their manufacture and dispersal still create jobs and contracts for construction companies. It is estimated that nearly 50 percent of Japan's 35,000 kilometers (22,000 mi) coastline has been covered or somehow altered by Tetrapods and other forms of concrete. The proliferation of Tetrapods on the island of Okinawa, a popular vacation destination in Japan, has made it difficult for tourists to find unaltered beaches and shoreline, especially in the southern half of the island.
The Tetrapod inspired many similar concrete structures for use in breakwaters, including the Modified Cube (United States, 1959), the Stabit (United Kingdom, 1961), the Akmon (The Netherlands, 1962), the Dolos (South Africa, 1963), the Stabilopod (Romania, 1969), the Seabee (Australia, 1978), the Accropode (France, 1981), the Hollow Cube (Germany, 1991), the A-jack (United States, 1998), and the Xbloc (The Netherlands, 2001), among others. In Japan, the word tetrapod is often used as a generic name for wave-dissipating blocks including other types and shapes.
- Artificial reef
- Breakwater (structure)
- Coastal management
- Coastal erosion
- Ocean surface wave
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