canals and inland waterways

Ancient works

Most of the improvement of rivers and construction of artificial waterways in antiquity was for irrigation purposes. In the 7th century bce the Assyrian king Sennacherib built a stone-lined canal 80 km (50 miles) long and 20 metres (66 feet) wide to bring fresh water from Bavian to Nineveh. The work, which included a stone aqueduct 300 metres (330 yards) long, was constructed in one year and three months, according to a plaque that survives on the site. Surprisingly advanced techniques were used, including a dam with sluice gates allowing regulation of the flow of the water stored. The Phoenicians, Assyrians, Sumerians, and Egyptians all constructed elaborate canal systems. The most spectacular canal of this period was probably Nahrawān, 122 metres (400 feet wide) and 322 km (200 miles) long, built to provide a year-round navigation channel from near Sāmarrāʾ to Al-Kūt, using water provided by damming the unevenly flowing Tigris. Many elaborate canals are known to have been built in Babylonia. In Egypt the Nile was dammed to control its floodwaters, and an extensive system of basin irrigation was established. The Persian king Darius in the 5th century bce cut a canal from the Nile River to the Red Sea.

The Romans were responsible for very extensive systems of river regulation and canals in France, Italy, the Netherlands, and Great Britain for military transport. The legions in Gaul canalized one of the mouths of the Rhône River to protect their overseas supply route. In the 1st century bce the Roman consul Marcus Livius Drusus dug a canal between the Rhine and IJssel rivers to relieve the Rhine of surplus water, and the Roman general Corbulo linked the Rhine and Meuse with a canal 37 km (23 miles) long to avoid the stormy North Sea passage from Germany to the coast. Attempting to reclaim the Fens in England, the Romans connected the River Cam with the Ouse by a 13-km (8-mile) canal, the Nene with the Witham by one 40 km (25 miles) long, and the Witham with the Trent by the Fosse Dyke (ditch), still in use.

Outside Europe and the Middle East, between the 3rd century bce and the 1st century ce, the Chinese built impressive canals. Outstanding were the Ling Canal in Guangxi in southeastern China, constructed to connect the headwaters of the Xiang River, flowing north into Hunan province, with the Li River, and the Bian Canal in Henan. Of later canals the most spectacular was the Grand Canal, the first 966-km (600-mile) section of which was opened to navigation in 610. This waterway enabled grain to be transported from the lower Yangtze River (Chang Jiang) and Huai River valleys to Kaifeng and Luoyang. These canals had easy gradients (changes in water levels). At about 5-km (3-mile) intervals there were single gates of stone or timber abutments with vertical grooves up or down along which the log closure was manually hauled by ropes to hold or release the water, thus controlling the water level. A few more elaborate gates had to be raised by windlasses. Where water level changes were too great for such simple devices, double slipways were built and vessels were hauled up the inclines.

Medieval revival

In Europe, canal building, which appears to have lapsed after the fall of the Roman Empire, was revived by commercial expansion in the 12th century. River navigation was considerably improved, and artificial waterways were developed with the construction of stanches, or flash locks, in the weirs (dams) of water mills and at intervals along the waterways. Such a lock could be opened suddenly, releasing a torrent that carried a vessel over a shallow place. The commercially advanced and level Low Countries developed a system of canals using the drainage of the marshland at the mouths of the Schelde, Meuse, and Rhine rivers; about 85 percent of medieval transport in the region went by inland waterway.

Because shipping was handicapped where barges had to be towed over the weirs with windlasses or manually, the lock and lock basin were evolved to raise boats from one level to another. Although a primitive form of lock had been in operation as early as 1180 at Damme, on the canal from Brugge to the sea, the first example of the modern pound lock, which impounded water, was probably that built at Vreeswijk, Netherlands, in 1373, at the junction of the canal from Utrecht with the Lek River. Outer and inner gates contained a basin, the water level of which was controlled by alternatively winding up and lowering the gates. In the 15th century the lock-gate system was much improved with the addition of paddles to control the flow of water in and out of the lock chamber through sluices in the gates or sides of the lock.

Commercial needs soon encouraged canal construction in less ideal locations. The Stecknitz Canal, built in Germany (1391–98), ran 34 km (21 miles) from Lake Möllner down to Lübeck, with a fall of 12 metres (40 feet) controlled with four stanches; the canal was later extended south to Lauenburg on the Elbe to establish a link between the Baltic and the North Sea. To deal with a fall from the summit to Lauenburg of 13 metres (42 feet) in 24 km (15 miles), two large locks were built, each capable of holding 10 small barges.

Italy, the other principal commercial region of medieval Europe, also made important contributions to waterway technology. The Naviglio Grande Canal was constructed (1179–1209) with an intake on the Ticino River, a fall of 33.5 metres (110 feet) in 50 km (31 miles) to Abbiategrasso and Milan, the water level being controlled by sluices. To facilitate transport of marble from the quarries for the building of Milan’s cathedral, the canal was linked with an old moat, and in Italy the first pound lock with mitre instead of the earlier portcullis gates was constructed to overcome differences in water levels.

China surpassed Europe in canal building. Between 1280 and 1293 the 1,126.5-km (700-mile) northern branch of the Grand Canal was built from Huai’an to Beijing. One section, crossing the Shandong foothills, was in effect the first summit-level canal, one that rises and then falls, as opposed to a lateral canal, which has a continuous fall only. The Huang He (Yellow River) was linked with a group of lakes about 161 km (100 miles) south, where the land rose 15 metres (50 feet) higher, and, to overcome water lost through operation of the lock gates, two small rivers were partially diverted to flow into the summit level.