CANALSThe great canal of Darius I: 6th century BC

The cutting of for irrigation has been an essential part of the civilization of Mesopotamia, controlling the water of the Euphrates and the Tigris. Several link the two rivers, and small boats use these waterways. But the world’s first canal created purely for water transport is an incomparably more ambitious affair.

Between about 520 and 510 BC the Persian emperor, Darius I, invests heavily in the economy of his newly conquered province of Egypt. He builds a canal linking the Nile and the Red Sea. Its access to the sea is close to modern Ismailia, which much later becomes the terminus of another great waterway, the Suez canal.

The Grand Canal: 3rd century BC – 13th century AD

The Chinese (the greatest early builders of canals) undertake several major projects from the 3rd century BC onwards. These waterways combine the functions of irrigation and transport.

Over the centuries more and more such canals are constructed. Finally, in the Sui dynasty (7th century AD), vast armies of labourers are marshalled for the task of joining many existing waterways into the famous Grand Canal. Barges can now travel all the way from the Yangtze to the Yellow River, and then on up the Wei to the western capital at Xi’an.

Along this great Chinese thoroughfare the rice harvest of the Yangtze is conveyed to the centres of political power in the north.

From the 13th century there is a new northern capital. Kublai Khan establishes himself at Beijing, which becomes the capital of the Mongol or Yüan dynasty. The Mongols extend the Grand Canal all the way north to join Beijing’s river at T’ien-ching.

Flash locks and pound locks: 10th – 15th century AD

From the very first construction of canals, some method is necessary to cope with differences in water level. The simplest solution is a weir, to hold up the water on the higher side, with a gap in the middle which can be opened to let a boat through. The removal of the barrier, however achieved, is inevitably followed by a sudden rush of water – carrying the vessel easily through in one direction, but making passage very difficult in the other. A primitive lock of this kind is known, for obvious reasons, as a flash lock.

The development of the more sophisiticated pound lock is traditionally credited to an engineer, Chiao Wei-yo, working on the great Chinese canal system in the 10th century AD.

It is said that Chiao is required to construct two flash locks on the Grand Canal only about 200 yards apart. He realizes that he has created a pool which will be at the upper or lower level of the canal depending on which of the two barriers is open. Moreover the barrier separating patches of level water can be opened without the obstruction of water pressure.

The result is the pound lock, standard on all modern canals. The first in Europe is believed to have been built in the Netherlands in 1373 at Vreeswijk, where a canal from Utrecht joins the river Lek.

At this stage the barrier is a simple sluicegate which has to be raised and lowered like a guillotine. The process is laborious, and the water pressure against the flat surface requires a very strong construction to hold it.

The last missing piece in the design of the modern lock is the mitred lock gate. On this system each end of the lock is closed by a pair of wooden gates slightly too large to close in a normal flush position. They meet with mitred edges pointing in the direction of the higher water level. Water pressure holds them tightly together, until the level is the same on either side – at which point the gates can be easily pushed open.

The first lock with mitred gates is probably the one built in Milan in about 1500 to join two canals of differing levels. Known as the San Marco lock, it is likely that its design is by Leonardo da Vinci. As his notebooks reveal, Leonardo is interested in all aspects of hydraulic engineering; and he is employed at this time by the duke of Milan.

From the 12th century Europeans have been busy constructing canals, even with the primitive device of the flash lock. The mitre lock makes possible increasingly ambitious projects.

European canals: 12th – 17th century AD

In one area of Europe, the Netherlands, canal building is an integral part of economic development. The primary purpose is drainage; an efficient transport network is a welcome bonus. But in Italy, in the late 12th century, an ambitious canal is constructed without any subsidiary motive of drainage or even irrigation.

It is the Naviglio Grande, built between 1179 and 1209 to bring marble from near Lake Maggiore for the construction of the cathedral in Milan. The barges float down the river Ticino before diverting into the canal, which has a fall of 110 feet in its length of 31 miles. The next comparable project, a century later, is a canal with a different purpose – to improve trade.

From 1391 the Stecknitz canal is constructed southwards from the city of Lübeck. Its destination is the Elbe, which is reached early in the 15th century. The new waterway joins the Baltic to the North Sea.

This canal rises some 40 feet from Lübeck to the region of Möllner and then falls the same amount again to reach the Elbe, all in a distance of 36 miles. This must be about the limit which can be safely achieved with flash locks. With mitre locks, from the 16th century, anything is possible. And the most ambitious projects are undertaken in France.

The Briare canal, completed in 1642, joins the Seine to the Loire; at one point it has a staircase of six consecutive locks to cope with a descent of 65 feet over a short distance. Even more remarkable is the Canal du Midi, completed in 1681, which joins the Mediterranean to the Atlantic by means of 150 miles of man-made waterway linking the Aude and Garonne rivers. At one point this canal descends 206 feet in 32 miles; three aqueducts are constructed to carry it over rivers; a tunnel 180 yards long pierces through one patch of high ground.

The potential of canals is self-evident. It falls to Britain, in the next century, to construct the first integrated system of waterborne traffic.

Bridgewater Canal: AD 1759-1761

In 1759 a young self-taught engineer, James Brindley, is invited to visit the duke of Bridgewater. The duke is interested in improving the market for the coal from a local mine which he owns. He believes his coal will find customers if he can get it more cheaply into Manchester. He wants Brindley to build him a canal with a series of locks to get barges down to the river Irwell, about three miles from the mine.

Brindley proposes a much bolder scheme, declared by some to be impossible but accepted by the duke. He will construct a more level canal, with less need for time-wasting locks. He will carry it on an aqudeuct over the Irwell on a straight line to the heart of Manchester, ten miles away.

On 17 July 1761 the first bargeload of coal is pulled along the completed canal. Brindley’s aqueduct (replaced in 1894 by the present swing aqueduct) crosses the Irwell at Barton. The strange sight of a barge floating in a gutter high up in the air becomes one of the first great tourist attractions of the Industrial Revolution. The investment in this private canal rapidly pays off. The price of the duke’s coal is halved in the Manchester market.

The Bridgewater canal is the first in Britain to run its entire length independently of any river. It is the start of the country’s inland waterway systerm, for which Brindley himself will construct another 300 miles of canals.

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