Navigable aqueducts (sometimes called 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-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 started to appear.
01. Pontcysyllte Aqueduct — UK
The Pontcysyllte Aqueduct is a navigable aqueduct that carries the Llangollen Canal over the valley of the River Dee in Wrexham County Borough in north east Wales. Completed in 1805, it is the longest and highest aqueduct in Britain, a Grade I Listed Building and a World Heritage Site. Built by Thomas Telford and William Jessop, it is 307 m. (1,007 ft.) long, 3.4 m. (11 ft.) wide and 1.6 m. (5.25 ft.) deep.
The towpath is mounted above the water, with the inner edge carried on cast-iron pillars in the trough. This arrangement allows the water displaced by the passage of a narrow boat to flow easily around it, enabling relatively free passage. Every five years the ends of the aqueduct are closed and a plug in one of the highest spans is opened to drain the canal water into the River Dee below, for inspection and maintenance of the trough.
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16 more Navigable Aqueducts after the break...