Breakwaters create safe harbors, but can also trap sediment moving along the coast. Long Beach Peninsula in Long Beach, California, April, 1998.

Breakwaters are structures constructed on coasts as part of coastal defense or to protect an anchorage from the effects of weather and longshore drift. Image File history File links Breakwater_break1_new(USGS). ... Image File history File links Breakwater_break1_new(USGS). ... Nickname: Location within Los Angeles County in the state of California Coordinates: Country United States State California County Los Angeles County Government  - Mayor Bob Foster Area  - City  65. ... 1998 (MCMXCVIII) was a common year starting on Thursday of the Gregorian calendar, and was designated the International Year of the Ocean [1]. // Coated in ice, power and telephone lines sag and often break, resulting in power outages. ... Coastal defenses are objects and engineering techniques used to defend coasts against erosion and flooding. ... Weather is a term that encompasses phenomena in the atmosphere of a planet. ... In geography, longshore drift (LSD) (shore drift or littoral drift) is a process by which sediments move along a beach shore. ...

Purposes of breakwaters

Defense against coastal erosion

Schematic of shifting coastline with breakwaters

Offshore breakwaters, also called revetments or bulkheads, reduce the intensity of wave action in inshore waters and thereby reduce coastal erosion. They are constructed some distance away from the coast or built with one end linked to the coast. The breakwaters may be small structures, placed one to three hundred feet offshore in relatively shallow water, designed to protect a gently sloping beach. Breakwaters may be either fixed or floating: the choice depends on normal water depth and tidal range. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Rugged coast of the West Coast of New Zealand The coast is defined as the part of the land adjoining or near the ocean. ... Rugged coast of the West Coast of New Zealand The coast is defined as the part of the land adjoining or near the ocean. ... The Beach in Calella, Spain. ...

When oncoming waves hit these breakwaters, their erosive power is concentrated on these structures some distance away from the coast. In this way, there is an area of slack water behind the breakwaters. Deposition occurring in these waters and beaches can be built up or extended in these waters. However, nearby unprotected sections of the beaches do not receive fresh supplies of eroded sediments and may gradually shrink due to erosion. This article is about waves in the most general scientific sense. ... Rugged coast of the West Coast of New Zealand The coast is defined as the part of the land adjoining or near the ocean. ... Slack water is the time during which no appreciable current in flowing in a body of water. ... It has been suggested that this article or section be merged into sediment. ... Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid. ... Severe soil erosion in a wheat field near Washington State University, USA. For erosion as an operation of Mathematical morphology, see Erosion (morphology) Erosion is displacement of solids (soil, mud, rock and other particles) by the agents of ocean currents, wind, water, or ice by downward or down-slope movement...

Seawalls are subject to damage, and overtopping by big storms can lead to problems of drainage of water that gets behind them. The wall also serves to encourage erosion of beach deposits from the foot of the wall and can increase longshore sediment transport.

3 of the 4 breakwaters forming Portland Harbour

The eight offshore breakwaters at Elmer, UK

ImageMetadata File history File links Download high resolution version (820x615, 51 KB) The southern ship channel, site of the wreck of HMS Hood (1896), at Portland Harbour, England. ... ImageMetadata File history File links Download high resolution version (820x615, 51 KB) The southern ship channel, site of the wreck of HMS Hood (1896), at Portland Harbour, England. ... Two RIBs at Castletown, Portland Harbour Portland Harbour is located beside the Isle of Portland, off Dorset, on the south coast of England. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...

Protection of anchorages

An anchorage is only safe when ships anchored there are protected from the force of high winds and powerful waves by some large underwater barrier which they can shelter behind. Natural harbours are formed by natural barriers such as headlands or reefs. Mobile harbours, such as the D-Day Mulberry harbours were floated into position and acted as breakwaters. Some natural harbours, such as those in Plymouth Sound, Portland Harbour and Cherbourg, have been enhanced or extended by breakwaters made of rock. Italian Full rigged ship Amerigo Vespucci in New York Harbor, 1976 A ship is a large watercraft capable of deep water navigation. ... An underwater scene just beneath the surface. ... A harbor (or harbour) or haven is a place where ships may shelter from the weather or are stored. ... The bay at San Sebastián, Spain A headland is an area of land adjacent to water on three sides. ... A reef surrounding an islet. ... Land on Normandy In military parlance, D-Day is a term often used to denote the day on which a combat attack or operation is to be initiated. ... A Mulberry harbour was a type of temporary harbour developed in World War II to offload cargo on the beaches during the Allied invasion of Normandy. ... Map of the UK showing the location of Plymouth Sound at 50. ... Two RIBs at Castletown, Portland Harbour Portland Harbour is located beside the Isle of Portland, off Dorset, on the south coast of England. ... Cherbourg is a city of Normandy, in northwestern France, in the Manche département, of which it is a sous_préfecture. ...

Types of breakwater structures

A breakwater is constructed some distance away from the coast or built with one end linked to the coast. Breakwaters may be either fixed or floating: the choice depends on normal water depth and tidal range. A breakwater structure is designed to absorb the energy of the waves that hit it. This is done either by using mass (e.g. with caissons) or by using a revetment slope (e.g. with rock or concrete armour units).

Caisson breakwaters typically have vertical sides and are usually used where it is desirable to berth one or more vessels on the inner face of the breakwater. They use the mass of the caisson and the fill within it to resist the overturning forces applied by waves hitting them. They are relatively expensive to construct in shallow water, but in deeper sites they can offer a significant saving over revetment breakwaters. A caisson is: In engineering, a retaining structure used, for example, to work on the foundations of a bridge pier. ... Look up berth in Wiktionary, the free dictionary. ...

Revetment breakwaters use the voids in the structure to dissipate the wave energy. Rock or concrete armour units on the outside of the structure absorb most of the energy, while gravels or sands are used to prevent the wave energy continuing through the breakwater core. The slopes of the revetment are typically between 1:1 and 1:2, depending upon the materials used. In shallow water revetment breakwaters are usually relatively cheap, but as water depth increases, the material requirements, and hence costs, increase significantly. Rocky revetment at a restoration site along Keene Creek, Duluth, Minnesota. ...

See also

• Akmon
• Dolos invented by South African engineer in East London
• Groyne
• Harbour
• Jetty
• Pier
• Port
• Tetrapod
• Xbloc

Akmons protecting the runway at Wellington International Airport from Cook Strait. ... Wikipedia does not yet have an article with this exact name. ... East London (Afrikaans: Oos-Londen, Xhosa: Imonti) is a city in southeast South Africa, situated in the Eastern Cape Province at 32. ... A groyne on the East coast of England Wikimedia Commons has more media related to: Groyne A groyne (groin in the United States) is a method of coastal defense against erosion. ... A harbor (or harbour) or haven is a place where ships may shelter from the weather or are stored. ... Alternate meanings: See Jetty (web server) Alternate meanings: See Jettying in buildings The term jetty, derived from the French jetie, and therefor signifying something thrown out, is applied to a variety of structures employed in river, dock and maritime works which are generally carried out in pairs from river banks... For the type of foundation, see Deep foundation. ... Seaport, a painting by Claude Lorrain, 1638 The Port of Wellington at night. ... In coastal engineering a tetrapod is a four-legged concrete structure used as armour unit on breakwaters. ... The Xbloc interlocking concrete block An Xbloc is an interlocking concrete block or armour unit designed to protect shores, harbour walls, seawalls, breakwaters and other coastal structures from the direct impact of incoming waves. ...

External links

Wikimedia Commons has media related to:

Breakwater

• USGS Oblique Aerial Photography - Coastal Erosion from El-Niño Winter Storms October, 1997 & April, 1998
• Channel Coastal Observatory - Breakwaters