Navigable aqueducts 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-section of water than most water-supply aqueducts. Although Roman aqueducts were sometimes used for transport, aqueducts were not generally used until the 17th century when the problems of summit level canals had been solved and modern canal systems were developed. The long steelBriare aqueduct carrying the Canal latéral à la Loire over the River Loire was built in 1896. It was ranked as the longest navigable aqueduct in the world for more than a century, until the Magdeburg Water Bridge in Germany took the title in the early 21st century. Early aqueducts such as the three on the Canal du Midi had stone or brick arches, the longest span being on the Cesse 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 1796 Longdon-on-Tern Aqueduct, the first large cast iron aqueduct was built by Thomas Telford at Longdon-on-Tern on the Shrewsbury Canal. It has a total length of across three intermediate piers. Within ten years Telford had completed the far more ambitious Pontcysyllte Aqueduct in Wales on the Llangollen Canal over the River Dee valley, with a total length 307 metres. Other cast-iron aqueducts followed, such as the single-span Stanley Ferry Aqueduct on the Calder and Hebble Navigation in 1839, with its innovative through arch design.
Notable navigable aqueducts
Benjamin Outram's single-span Holmes Aqueduct on the Derby Canal in Derby was the world's first navigable cast iron aqueduct, narrowly pre-dating Thomas Telford's Longdon-on-Tern Aqueduct on the Shrewsbury Canal, sometimes described as the world's first large-scale navigable cast iron aqueduct. The oldest currently navigable cast-iron aqueduct is Outram's Stakes Aqueduct on the Huddersfield Narrow Canal at Stalybridge, built c1801 to replace an original, stone-built, four arch structure, which had been swept away in the floods of August 1799.
Pontcysyllte Aqueduct carries the Llangollen Canal over the River Dee valley in north Wales; it was designed by Thomas Telford and opened in 1805. The same canal, which includes a tunnelled section, crosses a second valley on the Chirk Aqueduct. This navigable canal also supplies water to the former borough of Crewe and Nantwich.
Sir Arthur Cotton planned the aqueduct at P. Gannavaram to cater for the needs of farmers in the Konaseema area while he was constructing the Dowleswaram barrage. Originally a non-navigable aqueduct first constructed in 1859 with a length of. In 2000, a new navigable aqueduct and road bridge was constructed across the River Vynateya near Gannavaram, to facilitate the crossing of the Gannavaram Canal and also to irrigate a farming land.
The Briare aqueduct near Châtillon-sur-Loire, France, carries the Canal latéral à la Loire in a steel channel over the Loire River. At, it was the longest canal aqueduct in the world for a century.
In recent years the building of the Lichfield 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 in Germany connects the important Mittellandkanal over the river Elbe to the Elbe-Havel canal. Nearly long, it is the longest navigable aqueduct in the world.
