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Causeway

[kawz-wey]

In modern usage, a causeway is a road or railway elevated by a bank, usually across a broad body of water or wetland. A transport corridor that is carried instead on a series of arches, perhaps approaching a bridge, is a viaduct. In the U.S. a short stretch of viaduct is called an overpass. The distinction between the terms causeway and viaduct becomes blurred when flood-relief culverts are incorporated, though generally a causeway refers to a roadway supported mostly by earth or stone, while a bridge supports a roadway between piers (which may be embedded in embankments). Some low causeways across shore waters become inaccessible when covered at high tide.

Etymology

When first used, the word appeared in a form such as “causey way” making clear its derivation from the earlier form “causey”. This word seems to have come from the same source by two different routes. It derives ultimately, from the Latin for heel, calx and as near certainly as may be, comes from the trampling technique for consolidating earthworks. In antiquity, the construction was trodden down, one layer at a time, often by slaves or a flock of sheep. Today, a machine does the job. The same technique would have been used for road embankments, raised river banks, sea banks and fortification earthworks. (The layers, though not the trampling action, can be seen in the Bayeux Tapestry: Building Hastings Castle.)

The second derivation route is simply the hard, trodden surface of a path. The name by this route came to be applied to a firmly-surfaced road. It is now little-used except in dialect and in the names of roads which were originally notable for their solidly-made surface. The word is comparable in both meanings with the French chaussée, from a form of which it reached English by way of Norman French. The French adjective, chaussée, carries the meaning of having been given a hardened surface, and is used to mean either paved or shod. As a noun chaussée is used on the one hand for a metalled carriageway, and on the other for an embankment with or without a road. Other languages have a noun with similar dual meaning. In Welsh, it is sarn. The Welsh is relevant here, as it also has a verb, sarnu, meaning to trample. The trampling and ramming technique for consolidating earthworks was used in fortifications and there is a comparable, outmoded form of wall construction technique, used in such work and known as pisé, a word derived not from trampling but from ramming or tamping.

Engineering

The modern embankment may be constructed within a cofferdam: two parallel steel sheet pile or concrete retaining walls, anchored to each other with steel cables or rods. This construction may also serve as a dyke that keeps two bodies of water apart, such as bodies with a different water level on each side, or with salt water on one side and fresh water on the other. This may also be the primary purpose of a structure, the road providing a hardened crest for the dike, slowing erosion in the event of an overflow. It also provides access for maintenance as well perhaps, as a public service.

Examples

Notable causeways include those that connect Singapore and Malaysia (the Johor-Singapore Causeway), Bahrain and Saudi Arabia (25-km long King Fahd Causeway) and Venice to the mainland, all of which carry roadways and railways. In the Netherlands there are a number of prominent dykes which double as causeways, including the Afsluitdijk, Brouwersdam, and Markerwaarddijk. In Louisiana, two very long bridges, called the Lake Pontchartrain Causeway, stretch across Lake Pontchartrain for almost 38 km, making them the world's longest bridges (if total length is considered instead of span length). They are also the oldest causeways on the Gulf Coast that have never been put out of commission for an extended period of time following a Hurricane. In the Republic of Panama a causeway connects the islands of Perico, Flamenco, and Naos to Panama City on the mainland. It also serves as a breakwater for ships entering the Panama Canal. The oldest engineered road yet discovered is the Sweet Track in England, dating from the 3800s BC.

Causeways are also common in Florida, where low bridges may connect several man-made islands, often with a much higher bridge (or part of a single bridge) in the middle so that taller boats may pass underneath safely. Causeways are most often used to connect the barrier islands with the mainland.

The Churchill Barriers in Orkney are of the most notable sets of causeways in Europe. Constructed in waters up to 18 metres deep, the four barriers link five islands on the eastern side of the natural harbour at Scapa Flow. They were built during World War II as military defences for the harbour, on the orders of Winston Churchill.

Precautions

Causeways affect currents and may therefore be involved in beach erosion or changed deposition patterns. This, for instance, has been a problem at the Hindenburgdamm in northern Germany. Causeways are often a problem with an approaching hurricane or strong tropical storm, because the high winds and waves make them dangerous. Along with traffic jams, this is a major reason for the early emergency evacuation of island residents during a weather emergency.

References

Oxford English Dictionary. 1971. ISBN 0-19-861212-5.
Collins Robert French Dictionary, 5th edn. 1998. ISBN 0-00-470526-2.
Nouveau Petit Larousse Illustré, Paris. 1934.
Grape, W. The Bayeux Tapestry. Prestel, Munich and New York. 1994. ISBN 3-7913-1365-7.
Evans, H.M. and Thomas, W.O. The New Welsh Dictionary (Y Geiriadur Newydd). Llyfrau'r Dryw, Llandybie. 1953.