|Date||22 December 2011|
|Location||Falkirk||NS 85257 80131; 56.00033°N, 3.84144°W|
The 35-mile-long Forth & Clyde Canal was built between 1768 and 1790 to provide a shipping route across central Scotland from the Firth of Forth in the east to the Firth of Clyde in the west. A route from its eastern end to Edinburgh — a distance of about 31 miles — was created with the construction of the Union Canal between 1818 and 1822. The two canals were connected by a flight of 11 locks at Falkirk, where their difference in height was 35 metres.
Competition from the railways spelt the demise of the canals. Commercial use of the Union Canal came to an end in the 1930s and the flight of locks at Falkirk was filled in and built over. The Forth & Clyde Canal ultimately fell into disuse in the 1960s when it was closed in order to avoid having to build a motorway crossing.
British Waterways, with support from a number of sources, including National Lottery funding via the Millennium Commission, led an £84.5m project to revitalise the two canals. The Millennium Link was the UK’s largest canal restoration project and its centrepiece was the Falkirk Wheel — the world’s first and only rotary boat lift.
The Falkirk Wheel was officially opened in May 2002 and cost £17.5m. Its overall diameter is 35 metres and its shape was inspired by a Celtic double-headed axe. Boats can transfer through the lift in about 15 minutes, with a half rotation of the wheel taking 4 minutes, during which time a water-filled gondola at the lower level swaps position with its counterpart at the upper level. The wheel is always in perfect balance due to Archimedes’ principle — a floating object displaces its own weight in water — so as a boat enters a gondola, a volume of water equal to the weight of the boat is forced out, preserving the original net weight of the gondola plus water. The energy required to operate the wheel is only 1.5 kWh, roughly equivalent to that needed to boil 8 kettles of water.
The upper level of the Wheel is connected via a reinforced-concrete aqueduct to a 180-metre-long tunnel ending in a basin which in turn connects to the Union Canal via a double lock. The Roughcastle tunnel was built when the Wheel was constructed so as not to disturb the Roman remains of the Antonine Wall, under which it passes.