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34-587: The station was shut down in April 2019, after the Canadian Science Advisory Secretariat found substantial fish mortality caused by the turbine, and a crucial component failed within the generating system. For example, research from the 1980s showed almost one quarter of the American shad passing through were killed. The station operated 34 years, mostly with minimal regulatory scrutiny. A causeway on

68-648: 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. 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

102-542: 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 . The Aztec city-state of Tenochtitlan had causeways supporting roads and aqueducts. One of the oldest engineered roads yet discovered is the Sweet Track in England . Built in 3807 or 3806 BC,

136-407: 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

170-543: A landscape, usually by bridging a river valley or other eroded opening in an otherwise flat area. Often such valleys had roads descending either side (with a small bridge over the river, where necessary) that become inadequate for the traffic load, necessitating a viaduct for "through" traffic. Such bridges also lend themselves for use by rail traffic, which requires straighter and flatter routes. Some viaducts have more than one deck, such that one deck has vehicular traffic and another deck carries rail traffic. One example of this

204-455: A long elevated railway or road. Typically a viaduct connects two points of roughly equal elevation, allowing direct overpass across a wide valley, road, river, or other low-lying terrain features and obstacles. The term viaduct is derived from the Latin via meaning "road", and ducere meaning "to lead". It is a 19th-century derivation from an analogy with ancient Roman aqueducts . Like

238-412: A major color imbalance (as can be seen in the image at right). Furthermore, the difference in salinity has become so severe that native brine shrimp cannot survive in much of the waters, with the northern part being too salty and the southern part being insufficiently salty. Viaduct A viaduct is a specific type of bridge that consists of a series of arches, piers or columns supporting

272-418: A meter high. These acted as breakwaters , 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. In Scotland ,

306-535: 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 . In the case of the Courtney Campbell Causeway , however, the mainland ( Hillsborough County ) is connected by a causeway to a peninsula ( Pinellas County ). A well-known causeway is the NASA Causeway connecting

340-595: A repurposed rail viaduct provides a garden promenade on top and workspace for artisans below. The garden promenade is called the Coulée verte René-Dumont while the workspaces in the arches below are the Viaduc des Arts . The project was inaugurated in 1993. Manhattan's High Line , inaugurated in 2009, also uses an elevated train line as a linear urban park . In Indonesia viaducts are used for railways in Java and also for highways such as

374-402: A time, often by slaves or flocks of sheep . Today, this work is done by machines. The same technique would have been used for road embankments, raised river banks, sea banks and fortification 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

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408-410: 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. The Welsh word cawsai translates directly to

442-470: Is a high priority for local, regional, and even national authorities. Causeways can separate populations of wildlife, putting further pressure on endangered species . Causeways can cause a mineral imbalance between portions of a body of water. For example, a causeway built in the Great Salt Lake has caused the northern half of the lake to have much higher salinity, to the point that the two halves show

476-500: Is built across land rather than water, the space below the arches may be used for businesses such as car parking, vehicle repairs, light industry, bars and nightclubs. In the United Kingdom, many railway lines in urban areas have been constructed on viaducts, and so the infrastructure owner Network Rail has an extensive property portfolio in arches under viaducts. In Berlin the space under the arches of elevated subway lines ( S-Bahn )

510-883: Is the Prince Edward Viaduct in Toronto, Canada, that carries motor traffic on the top deck as Bloor Street , and metro as the Bloor-Danforth subway line on the lower deck, over the steep Don River valley . Others were built to span settled areas, crossing over roads beneath—the reason for many viaducts in London. Viaducts over water make use of islands or successive arches. They are often combined with other types of bridges or tunnels to cross navigable waters as viaduct sections, while less expensive to design and build than tunnels or bridges with larger spans, typically lack sufficient horizontal and vertical clearance for large ships. See

544-407: Is used for several different purposes, including small eateries or bars. Elevated expressways were built in major cities such as Boston ( Central Artery ), Los Angeles, San Francisco, Seoul , Tokyo and Toronto ( Gardiner Expressway ). Some were demolished because they were unappealing and divided the city. In other cases, viaducts were demolished because they were structurally unsafe, such as

578-464: The Annapolis River created a reservoir which powered a water turbine . Sluice gates in the causeway allowed the reservoir to be refilled by the incoming tide, and retain the water in the reservoir when the tide recedes. Power was only generated when the tide was out, for about five hours, twice a day. Construction began in 1980, and it opened in 1984. It was constructed by Nova Scotia Power, at

612-526: The Chesapeake Bay Bridge-Tunnel . The Millau Viaduct is a cable-stayed road-bridge that spans the valley of the river Tarn near Millau in southern France. It opened in 2004 and is the tallest vehicular bridge in the world, with one pier's summit at 343 metres (1,125 ft). The viaduct Danyang–Kunshan Grand Bridge in China was the longest bridge in the world as of 2011 . Where a viaduct

646-629: The Embarcadero Freeway in San Francisco, which was damaged by an earthquake in 1989. However, in developing nations such as Thailand ( Bang Na Expressway , the world's longest road bridge ), India ( Delhi-Gurgaon Expressway ), China, Bangladesh, Pakistan, and Nicaragua, elevated expressways have been built and more are under construction to improve traffic flow, particularly as a workaround of land shortage when built atop surface roads. Other uses have been found for some viaducts. In Paris, France,

680-530: The Roman aqueducts , many early viaducts comprised a series of arches of roughly equal length. The longest viaduct in antiquity may have been the Pont Serme which crossed wide marshes in southern France. At its longest point, it measured 2,679 meters with a width of 22 meters. Viaducts are commonly used in many cities that are railroad hubs , such as Chicago, Birmingham, London and Manchester . These viaducts cross

714-584: 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. A transport corridor that is carried instead on a series of arches, perhaps approaching a bridge, is a viaduct ; 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

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748-518: The harbour, on the orders of Winston Churchill . The Estrada do Istmo connecting the islands of Taipa and Coloane in Macau 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 named Cotai and become home to several casino complexes. Various causeways in

782-498: The large railroad yards that are needed for freight trains there, and also cross the multi-track railroad lines that are needed for heavy rail traffic. These viaducts provide grade separation and keep highway and city street traffic from having to be continually interrupted by the train traffic. Likewise, some viaducts carry railroads over large valleys, or they carry railroads over cities with many cross-streets and avenues. Many viaducts over land connect points of similar height in

816-780: The mainland, all of which carry roadways and railways. In the Netherlands there are a number of prominent dikes which also double as causeways, including the Afsluitdijk , Brouwersdam , and Markerwaarddijk . 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 . Causeways are also common in Florida , where low bridges may connect several human-made islands , often with

850-517: 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-French caucie (cf. modern chaussée ), from the late Latin via calciata , a road stamped firm with the feet ( calcare , to tread)." The word is comparable in both meanings with the French chaussée , from

884-399: The river banks. The causeway housed the power house and sluice gates. The blocking of water flow by the causeway has resulted in increased river bank erosion on both the upstream and downstream sides. The causeway is also known as a trap for marine life. In 2004, a mature humpback whale swam through the open sluice gate at slack tide, ending up trapped for several days in the upper part of

918-602: The river before eventually finding its way out. Causeway A causeway is a track, road or railway on the upper point of an embankment across "a low, or wet place, or piece of water". It can be constructed of earth, masonry , wood, or concrete. One of the earliest known wooden causeways is the Sweet Track in the Somerset Levels , England, which dates from the Neolithic age. Timber causeways may also be described as both boardwalks and bridges . When first used,

952-620: The skirmish known as Clense the Calsey, or Cleanse the Causeway , took place in the High Street of Edinburgh in 1520. In the 18th century, Dahomey lacked an effective navy hence it built causeways for naval purposes starting in 1774. 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

986-613: The time a provincial crown corporation . The decision to build the facility was partly prompted by the promise of federal funding for this alternative energy project, and the existence of a rock-filled causeway which had been built on the Annapolis River in 1960 by the Maritime Marshlands Reclamation Authority to block the Bay of Fundy tides from entering the river to replace the function of the existing dykes along

1020-642: The town of Titusville on the Florida mainland to the rocket-launching facility at the Kennedy Space Center on Merritt Island . The Churchill Barriers in Orkney 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 at Scapa Flow . They were built during World War II as military defences for

1054-530: The track was a walkway consisting mainly of planks of oak laid end-to-end, supported by crossed pegs of ash , oak, and lime , driven into the underlying peat. In East Africa , the Husuni Kubwa (the "Great Fort"), situated outside the town of Kilwa , was an early 14th-century sultan's palace and emporium that contained causeways and platforms at the entrance of the Harbour made from blocks of reef and coral nearly

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1088-435: The winds and rains of approaching tropical 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 minimize traffic jams on both the roads approaching the causeway and the causeway itself), emergency evacuation of island residents

1122-524: The word causeway 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 consolidate earthworks . 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

1156-493: The world: Unlike tunnels or bridges, causeways do not permit shipping through the strait which can cause problems. In some cases, causeways were built with "gates" or other facilities to permit shipping to pass through. Causeways affect currents and may therefore be involved in beach erosion or changed deposition patterns; this effect has been a problem at the Hindenburgdamm in northern Germany. During hurricane seasons,

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