The Falkirk Wheel is a rotating boat lift, connecting the Forth and Clyde Canal with the Union Canal. It is named after the nearby town of Falkirk. The two canals were previously connected by a series of 11 locks, but by the 1930s these had fallen into disuse, were filled in and the land built upon them.
The plan to regenerate the canals of central Scotland to reconnect Glasgow with Edinburgh was led by British Waterways with support and funding from seven local authorities, the Scottish Enterprise Network, the European Regional Development Fund and the Millennium Commission. It was decided early on to create a dramatic 21st century landmark structure to reconnect the canals, instead of simply recreating the historic lock flight. Designs were submitted for a boat lift to link the canals, with the Falkirk Wheel design winning. As with many Millennium Commission projects the site includes a visitors' centre containing a shop, café and exhibition centre.
The difference in the levels of the two canals at the wheel is 24 metres (79 ft), roughly equivalent to the height of an eight-storey building. The Union Canal, however, is 11m higher than the aqueduct which meets the wheel, and boats must pass through a pair of locks to descend from this canal onto the aqueduct at the top of the wheel. The aqueduct could not have been positioned higher due to conflicts with the historically important Antonine Wall.
The wheel has an overall diameter of 35 metres (115 ft) and consists of two opposing arms which extend 15 metres beyond the central axle and take the shape of a Celtic-inspired, double-headed axe. Two sets of these axe-shaped arms are attached about 25 metres (82 ft) apart to a 3.5 metres (11 ft) diameter axle. Two diametrically opposed water-filled caissons, each with a capacity of 80,000 imperial gallons (360,000 l; 96,000 US gal), are fitted between the ends of the arms.
These caissons always weigh the same whether or not they are carrying their combined capacity of 600 tonnes (590 LT; 660 ST) of floating canal barges as, according to Archimedes' principle, floating objects displace their own weight in water, so when the boat enters, the amount of water leaving the caisson weighs exactly the same as the boat. This keeps the wheel balanced and so, despite its enormous mass, it rotates through 180° in five and a half minutes while using very little power. It takes just 22.5 kilowatts (30.2 hp) to power the electric motors, which consume just 1.5 kilowatt-hours (5.4 MJ) of energy in four minutes, roughly the same as boiling eight kettles of water.
The wheel is the only rotating boat lift of its kind in the world, and is regarded as an engineering landmark for Scotland.