Breakwater (structure)
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Breakwaters are structures constructed on coasts as part of coastal defense or to protect an anchorage from the effects of weather and longshore drift.
Coastal defense
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.
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 occurs in these waters and beaches can be built up or extended in these waters. However, nearby unprotected sections of the beaches does not receive fresh supplies of eroded sediments and may gradually shrink due to erosion.
Anchorage
An anchorage is only safe when ships anchored there are protected from the force of high winds and big 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.
See also
- Dollos invented by South African engineer in East London
- Groyne
- Harbour
- Jetty
- Port
External links
- [USGS] Oblique Aerial Photography - Coastal Erosion from El-Niño Winter Storms October, 1997 & April, 1998
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