A naviduct is a special class of

navigable aqueduct Navigable aqueducts (sometimes called navigable water bridges) are bridge structures that carry navigable waterway canals over other rivers, valleys, railways or roads. They are primarily distinguished by their size, carrying a larger cross-se ...

, in which the

waterway A waterway is any Navigability, navigable body of water. Broad distinctions are useful to avoid ambiguity, and disambiguation will be of varying importance depending on the nuance of the equivalent word in other ways. A first distinction is ...

also includes a

lock Lock(s) or Locked may refer to: Common meanings *Lock and key, a mechanical device used to secure items of importance *Lock (water navigation), a device for boats to transit between different levels of water, as in a canal Arts and entertainme ...

. One example of a naviduct has been built at

Enkhuizen Enkhuizen () is a municipality and a city in the Netherlands, in the province of North Holland and the region of West-Frisia. History Enkhuizen, like Hoorn and Amsterdam, was one of the harbour-towns of the VOC, from where overseas trade ...

on the

Houtribdijk The Houtribdijk is a dam in the Netherlands, built between 1963 and 1976 as part of the Zuiderzee Works, which connects the cities of Lelystad and Enkhuizen. On the west side of the dike is the Markermeer and on the east is the IJsselmeer. The ...

in the

Netherlands , Terminology of the Low Countries, informally Holland, is a country in Northwestern Europe, with Caribbean Netherlands, overseas territories in the Caribbean. It is the largest of the four constituent countries of the Kingdom of the Nether ...

on the instructions of the

Rijkswaterstaat Rijkswaterstaat, founded in 1798 as the ''Bureau voor den Waterstaat'' and formerly translated to Directorate General for Public Works and Water Management, is a Directorate-General of the Ministry of Infrastructure and Water Management, Ministry ...

. This cost over €55 million and was completed in 2003. It is big enough to simultaneously transfer two large

Rhine The Rhine ( ) is one of the List of rivers of Europe, major rivers in Europe. The river begins in the Swiss canton of Graubünden in the southeastern Swiss Alps. It forms part of the Swiss-Liechtenstein border, then part of the Austria–Swit ...

river-barges from the

Markermeer The Markermeer () is a lake in the central Netherlands in between North Holland, Flevoland, and its smaller and larger neighbors, the IJmeer and IJsselmeer. A shallow lake at 3 to 5 m in depth, matching the reclaimed land to its west, nor ...

to the

IJsselmeer The IJsselmeer (; , ), also known as Lake IJssel in English, is a closed-off freshwater lake in the central Netherlands bordering the Provinces of the Netherlands, provinces of Flevoland, North Holland and Friesland. It covers an area of with a ...

or vice versa. The structure was chosen because a busy waterway crosses a

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aqua ...

carrying a busy road, but the space available for separate aqueduct and lock facilities was restricted.

Name and definition

The term is derived from the words for navigation and aqueduct, which are in turn partly derived from the Latin words ''navis'' meaning ship and ''ducere'' meaning to lead or conduct. It can also be thought of as a lock system with an underpass under the lock for road traffic. The term is introduced and used extensively in the Netherlands for referring to the works near Enkhuizen in Dutch and English language texts.

Krabbersgat Naviduct

The world's only operational naviduct is near Enkhuizen, and is part of works commissioned in 1995 and administered in the Netherlands by the Rijkswaterstaat. This location is at the western end of the Houtribdijk in the province of

Flevoland Flevoland () is the twelfth and newest province of the Netherlands, established in 1986, when the southern and eastern Flevopolders, together with the Noordoostpolder, were merged into one provincial entity. It is in the centre of the countr ...

, which separates the Markermeer from the IJsselmeer. This dam was built as a possible northern dike to build the

Markerwaard 200px, The Markerwaard would be on what is now the Markermeer The Markerwaard is the name of a proposed, but never built, polder adjoining the IJsselmeer in the central Netherlands. Its construction would have resulted in the near-total reclama ...

polder A polder () is a low-lying tract of land that forms an artificial hydrology, hydrological entity, enclosed by embankments known as levee, dikes. The three types of polder are: # Land reclamation, Land reclaimed from a body of water, such as a ...

in 1975. Although construction of this polder has been permanently shelved and was officially abandoned in 2003, the dam is still called a dike. Until the building of the naviduct, marine transport between the two lakes had to cross the dike at the Krabbersgat lock (near Enkhuizen) or the Houtrib lock (near

Lelystad Lelystad () is a Dutch Municipalities of the Netherlands, municipality and the capital city of the province of Flevoland in the central Netherlands. The city, built on reclaimed land, was founded in 1967 and was named after Cornelis Lely, who en ...

) due to the differing lake levels. The two lakes have the same target level, but wind surge and feed flows affect the two water bodies differently. Without a lock on the naviduct, the flow of water through the aqueduct could become too high for navigation. Highway N302 runs along the dike between the two towns, with

bascule bridge A bascule bridge (also referred to as a drawbridge or a lifting bridge) is a moveable bridge with a counterweight that continuously balances a span, or leaf, throughout its upward swing to provide clearance for boat traffic. It may be single- o ...

s at the two lock locations. Prior to the official opening of the naviduct at 11am on 26 April 2003 by

Roelf de Boer Roelf Hendrik de Boer (born 9 October 1949) is a retired Dutch politician and businessman who was a member the Pim Fortuyn List (LPF) and briefly served as Deputy Prime Minister from 2002 to 2003. Biography De Boer served as a reservist in the ...

, delays often arose for both road and water traffic, which could not pass the lock location simultaneously, and this was a particularly acute problem at the Enkhuizen end of the dike.

Technical details

The naviduct is constructed in a specially designed

, having an artificially managed water table depth of -12.00 m

NAP A nap is a short period of sleep, typically taken during daytime hours as an adjunct to the usual nocturnal sleep period. Naps are most often taken as a response to Somnolence, drowsiness during waking hours or as a means to supplement before ...

. The polder is diamond-shaped with a length of 500m and a width of 160m, while its embankment is elevated to +6m NAP. The road under the naviduct reaches a depth of -10.80m NAP. The polder guide dams were built using the

geotextile tube A geotextile tube is a large, tube-shaped bag made of porous, weather-resistant geotextile and filled with a sand slurry, to form an artificial coastal structure such as a breakwaters, dune or levee. Geotextile tubes are a component of the liv ...

method, where porous sausage-shaped bags are pumped full of sand slurry. The slurry is dewatered as the pumps fill the bags, forming a stable structure that is subsequently covered with quarried stone. Both locks have a length of 125 meters, a width of 12.5 meters and meet the ''Va'' requirements of the

CEMT Class The Classification of European Inland Waterways is a set of standards for interoperability of large navigable waterways forming part of the Trans-European Inland Waterway network within Continental Europe and Russia. It was created by the European ...

(i.e. each is suitable for a large Rhine river-barge). Special waterproof concrete was used for the locks, as they are designed to operate without the need for maintenance resulting from surface wear. The completed project cost €55 million before tax.

Other naviducts

Disused

The

Seneca Aqueduct Seneca Aqueduct — or Aqueduct No. 1 — is a naviduct that carries the Chesapeake and Ohio Canal (C&O) over Seneca Creek (Potomac River), Seneca Creek in Montgomery County, Maryland. The C&O built eleven aqueducts along its length. Seneca Aque ...

on the

Chesapeake and Ohio Canal The Chesapeake and Ohio Canal, abbreviated as the C&O Canal and occasionally called the Grand Old Ditch, operated from 1831 until 1924 along the Potomac River between Washington, D.C., and Cumberland, Maryland. It replaced the Patowmack Canal ...

is a disused naviduct, consisting of a lock (Riley's Lock) and an aqueduct. The lock is located next to the aqueduct, but both are part of a single structure made out of sandstone. It was used from 1833 to 1924. One of the arches of the aqueduct collapsed in 1971, so it can no longer contain water.

Planned

The Dutch government is currently considering whether to replace some of its existing lock and opening bridge combinations with naviducts. Naviducts have a high construction cost compared to standard locks and bridges, but benefit the economy by reducing delays. The former State Secretary for Infrastructure and the Environment,

Joop Atsma Johannes Jan "Joop" Atsma (born 6 July 1956) is a Dutch politician of the Christian Democratic Appeal (CDA) party and sport administrator. He was a member of the Senate since between 9 June 2015 and 12 June 2023. Biography Joop Atsma is the son ...

, issued a statement in 2012 detailing the factors influencing the decision to build a new naviduct on the

Afsluitdijk The Afsluitdijk (; ; "closure dyke") is a major dam and causeway in the Netherlands. It was constructed between 1927 and 1932 and runs from Den Oever in North Holland province to the village of Zurich, Friesland, Zurich in Friesland province, o ...

Kornwerderzand Kornwerderzand ( West Frisian: Koarnwertersân) is a village on the Afsluitdijk, a major dam in the Netherlands that links Friesland with North Holland. Overview Kornwerderzand is located approximately 4 kilometers from the coast of Friesland, on ...

. Strengthening of the existing locks was costed at €33 million, building new locks at €91 million and a naviduct and new locks at €200-450 million, depending on the size of locks and size of highway. A naviduct would give waiting time annualised benefits of €3 million to maritime traffic and €13 million to road traffic, based on the bridge opening 7,000 times a year.

Cost–benefit analysis Cost–benefit analysis (CBA), sometimes also called benefit–cost analysis, is a systematic approach to estimating the strengths and weaknesses of alternatives. It is used to determine options which provide the best approach to achieving benefits ...

of all potential solutions were considered, and for the present time, the locks will be strengthened. However, it is quite possible that a naviduct will be built to replace the locks when they reach the end of their useful life in 2050.

Sources

{{DEFAULTSORT:Lock (Water Transport) Navigable aqueducts Water transport infrastructure Locks (water navigation) Dikes in the Netherlands Buildings and structures in Flevoland Zuiderzee Works Buildings and structures in North Holland