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 TheJohor–Singapore Causeway supports over 100 million annual international border crossings. | |
| Ancestor | None. (SeeFord (crossing)) |
|---|---|
| Related | None. (SeeStep-stone bridge) |
| Descendant | None. (SeeViaduct) |
| Carries | Traffic,Rail, Cyclists, Pedestrians |
| Material | Concrete, Masonry, Earth-fill |
| Movable | No |
| Design effort | medium |
| Falsework required | No |
Acauseway is a track, road or railway on the upper point of anembankment across "a low, or wet place, or piece of water".[1] It can be constructed of earth,masonry, wood, or concrete. One of the earliest known wooden causeways is theSweet Track in theSomerset Levels, England, which dates from theNeolithic age.[2]Timber causeways may also be described as bothboardwalks andbridges.
When first used, the wordcauseway 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 most likely comes from the trampling technique to consolidateearthworks.
Originally, the construction of a causeway used earth that had been trodden upon to compact and harden it as much as possible, one layer at a time, often by slaves or flocks ofsheep. Today, this work is done by machines. The same technique would have been used for road embankments, raised river banks, sea banks andfortification earthworks.
The second derivation route is simply the hard, trodden surface of a path. The name by this route came to be applied to any 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 1911 Encyclopædia Britannica states: "causey, a mound or dam, which is derived, through the Norman-Frenchcaucie (cf. modernchaussée),[3] from the late Latinvia calciata, a road stamped firm with the feet (calcare, to tread)."[4]
The word is comparable in both meanings with theFrenchchaussée, from a form of which it reachedEnglish by way ofNorman French. The French adjectivechaussée carries the meaning of having been given a hardened surface and is used to mean either paved or shod. As a nounchaussée 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. InWelsh, it issarn. The Welsh is relevant here, as it also has a verbsarnu, 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. The Welsh wordcawsai translates directly to the English word 'causeway'; it is possible that, with Welsh being a lineal linguistic descendant of the original native British tongues, the English word derives from the Welsh.[citation needed]
A transport corridor that is carried instead on a series of arches, perhaps approaching a bridge, is aviaduct; a short stretch of viaduct is called anoverpass. The distinction between the termscauseway andviaduct becomes blurred when flood-reliefculverts 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 hightide.
The Aztec city-state ofTenochtitlan had causeways supporting roads and aqueducts. One of the oldest engineered roads yet discovered is theSweet Track inEngland. Built in 3807 or 3806 BC,[5] the track was a walkway consisting mainly of planks ofoak laid end-to-end, supported by crossed pegs ofash, oak, andlime, driven into the underlying peat.
InEast Africa, the Husuni Kubwa (the "Great Fort"), situated outside the town ofKilwa, was an early 14th-century sultan's palace and emporium that featured causeways made from blocks of reef and coral nearly a meter high. These acted asbreakwaters, allowing mangroves to grow which is one of the ways the breakwater can be spotted from a distance. Some parts of the causeway are made from the bedrock, but usually the bedrock was used as a base. Coral stone was also used to build up the causeways, with sand and lime being used to cement the cobbles together. However, some of the stones were left loose.[6]
InScotland, the skirmish known as Clense the Calsey, orCleanse the Causeway, took place in theHigh Street of Edinburgh in 1520.[7]
In the 18th century,Dahomey lacked an effective navy hence it built causeways fornaval purposes starting in 1774.[8]
The modern embankment may be constructed within acofferdam: twoparallel steel sheetpile orconcreteretaining walls,anchored to each other with steel cables or rods. This construction may also serve as adyke that keeps two bodies of water apart, such as bodies with a different water level on each side, or withsalt water on one side andfresh 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.
Notable causeways include those that connectSingapore andMalaysia (theJohor-Singapore Causeway),Bahrain andSaudi Arabia (25-km longKing Fahd Causeway) andVenice to the mainland, all of which carry roadways and railways. In theNetherlands there are a number of prominent dikes which also double as causeways, including theAfsluitdijk,Brouwersdam, andMarkerwaarddijk. In the Republic ofPanama a causeway connects the islands of Perico, Flamenco, and Naos toPanama City on the mainland. It also serves as a breakwater for ships entering thePanama Canal.
Causeways are also common inFlorida, where low bridges may connect several human-madeislands, often with a much higher bridge (or part of a single bridge) in the middle so that tallerboats may pass underneath safely. Causeways are most often used to connect thebarrier islands with themainland. In the case of theCourtney Campbell Causeway, however, the mainland (Hillsborough County) is connected by a causeway to a peninsula (Pinellas County). A well-known causeway is theNASA Causeway connecting the town ofTitusville on the Florida mainland to the rocket-launching facility at theKennedy Space Center onMerritt Island.
TheChurchill Barriers inOrkney are some 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 atScapa Flow. They were built duringWorld War II as military defences for the harbour, on the orders ofWinston Churchill.
The Estrada do Istmo connecting the islands ofTaipa andColoane inMacau was initially built as a causeway. The sea on both sides of the causeway then became shallower as a result of silting, and mangroves began to conquer the area. Later, land reclamation took place on both sides of the road and the area has subsequently been namedCotai and become home to several casino complexes.
A major drawback of causeways is that, unlike tunnels or bridges, they prevent shipping through the strait they cross. In some cases, causeways have been built with "gates" or other facilities to permit shipping to pass through.
Causeways affect currents and may therefore be involved inbeach erosion or changed deposition patterns; this effect has been a problem at theHindenburgdamm in northern Germany. Duringhurricane seasons, the winds and rains of approachingtropical storms—as well as waves generated by the storm in the surrounding bodies of water—make traversing causeways problematic at best and impossibly dangerous during the fiercest parts of the storms. For this reason (and related reasons, such as the need to minimizetraffic jams on both the roads approaching the causeway and the causeway itself),emergency evacuation ofisland residents is a high priority for local, regional, and even national authorities.
Causeways can separate populations of wildlife, putting further pressure onendangered species.
Causeways can cause a mineral imbalance between portions of a body of water. For example, theLucin Cutoff, built across theGreat Salt Lake has caused the northern half of the lake to have much higher salinity, to the point that the two halves show a major color imbalance. Furthermore, the difference in salinity has become so severe that nativebrine shrimp cannot survive in much of the waters, with the northern part being too salty and the southern part being insufficiently salty.
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