Navigable aqueducts (sometimes callednavigable water bridges orcanal bridges) are bridge structures that carrynavigablewaterwaycanals over other rivers, valleys, railways or roads. They are primarily distinguished by their size, carrying a larger cross-section of water than most water-supplyaqueducts. Roman aqueducts were used to transport water and were created in ancient Rome. The 662-metre (2,172 ft) longsteelBriare aqueduct carrying theCanal latéral à la Loire over the RiverLoire was built in 1896. It was ranked as the longest navigable aqueduct in the world for more than a century, until theMagdeburg Water Bridge in Germany took the title in the early 21st century.
Early aqueducts such as the three on theCanal du Midi had stone or brick arches, the longest span being 18.3 metres (60 ft) on theCesse Aqueduct, built in 1690. But, the weight of the construction to support the trough with the clay or other lining to make it waterproof made these structures clumsy. In 1796Longdon-on-Tern Aqueduct, the first largecast iron aqueduct was built byThomas Telford atLongdon-on-Tern on theShrewsbury Canal. It has a total length of 57 metres (187 ft) across three intermediate piers. Within ten years Telford had completed the far more ambitiousPontcysyllte Aqueduct in Wales on theLlangollen Canal over theRiver Dee valley, with a total length 307 metres and a height of 38 metres, making it the tallest navigable aqueduct in the world. Other cast-iron aqueducts followed, such as the single-spanStanley Ferry Aqueduct on theCalder and Hebble Navigation in 1839, with its innovative 50-metre (160 ft)through arch design.
There were 32 navigable aqueducts on theErie Canal, constructed 1817–1825 inNew York State, United States.
Benjamin Outram's 44 ft long (13 m) single-span Holmes Aqueduct on theDerby Canal inDerby was the world's first navigablecast iron aqueduct, narrowly pre-datingThomas Telford's 186 ft long (57 m)Longdon-on-Tern Aqueduct on theShrewsbury Canal, sometimes described as the world's firstlarge-scale navigable cast iron aqueduct. The oldest currently navigable cast-iron aqueduct is Outram's Stakes Aqueduct on theHuddersfield Narrow Canal atStalybridge, built c1801 to replace an original, stone-built, four arch structure, which had been swept away in the floods of August 1799.
Pontcysyllte Aqueduct (307 metres, 1,007 ft) carries theLlangollen Canal over the River Dee valley in northWales; it was designed byThomas Telford, opened in 1805 and is the highest navigable aqueduct in the world. The same canal, which includes a tunnelled section, crosses a second valley on theChirk Aqueduct (1796–1801). This navigable canal also supplies water to the former borough ofCrewe and Nantwich.
SirArthur Cotton planned the aqueduct atP. Gannavaram,Andhra Pradesh inIndia to cater for the needs of farmers in theKonaseema area while he was constructing theDowleswaram barrage. Originally a non-navigable aqueduct was constructed in 1859 with a length of 700 metres (2,300 ft). In 2000, a new navigable aqueduct and road bridge was constructed across theRiver Vynateya (a tributary of theGodavari River) near Gannavaram, to facilitate the crossing of theGannavaram Canal and also to irrigate a farming land.
Following construction of theM6 Toll Motorway the building of theLichfield Canal Aqueduct ran into construction difficulties. The UK parliament passed legislation preventing a road being built in the path of a canal being renovated without providing a tunnel or aqueduct for canal traffic to pass.
The Magdeburg Water Bridge seen from the shores of theElbe
Notes:1 Containscanalised river.2 Partly or mostly navigable, and/or under restoration.3 A system of canals. Canals which form part of this system are not listed here individually.
