If you need a canal to cross another canal, you simply build a water bridge across, with one canal on top of another. If you need to build a land bridge across a waterway, you can make the bridge split in two or swing aside when tall ships need to pass. But what do you do when you need to have a canal make room for large ships on another canal? That was the situation in Manchester, UK, in 1885. Originally the smaller Bridgewater Canal crossed the Manchester Ship Canal on an arched bridge. But now the region needed to move large ships — too large to fit under the Bridgewater Canal — through the Manchester Ship Canal. So the bridge was replaced with an aqueduct that would swing out of the way of traffic on Manchester Ship Canal:
It was replaced by a unique swing aqueduct that was opened in 1893 and was an even more daring structure than the original aqueduct, consisting of a channel that could be sealed off at each end to form a 235 feet long and 18 feet wide tank, holding 800 tons of water, that swung round on its pivot, situated on an island in the middle of the Ship Canal.In the links, you can find a video of the swinging aqueduct in action.
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