Arteries of the Empire

The Great Yu, the semi-mythical founder of the Xia Dynasty in the 21-20th century BC, was the father of China's early water control system. Through the succeeding millennia, his descendants were among the earliest developers of hydraulic engineering in the world - a system of immense scale and technical sophistication, whose legacy survives and is still in use today.

While escaping the wrath of periodic floods remained a primary emphasis, these works were also the key to China's agricultural productivity and the basis of an extensive inland water-borne transport system. Sima Qian, the 2nd-century BC historian discusses 11 major canal projects built before his own time, most of which were consciously designed to provide both transportation and irrigation.

One of these, near present-day Chengdu in Sichuan, is the Capital River Weir. Built in about 240 BC, it "made, and still makes today, the Chengdu plain the most fertile area in all of China," according to Lyman Van Slyke, a Stanford University sinologist. The designer, Li Bing, cut through the shoulder of a hill to open a new channel off the Min River. And to ensure a constant flow in the channel, he built an artificial island buttressed with stone weirs dividing the waters upstream. The deep, narrow (30m wide) cut in the hill limits the amount of water that can pass through, forcing excess water back across the island to the main stream through a spillway when the river is high. The system is still in use today, supplying water to Chengdu city and nearby areas containing more than 5 million people.

The major rivers in China run west-to-east dividing the country into distinct north-south regions. Canal transport was crucial to the unification of China as a continental empire. Near present-day Guilin in Guangxi province, the 30-km "Magic Canal" connects the north-flowing Xiang River, a tributary of the Yangtze (alsoYangzi), to the Li River, which joins the Gui River to flow south to the West River and then to Canton. Built at about the same time as the Capital River Weir, it is the first contour transport canal ever built in the world, and it is the reason why southeast China is part of China. This canal provided direct waterborne transport from north China to as far south as Canton.

The "Magic Canal" is unusual in that it was built exclusively for military purposes. Sima Qian records that the Qin Emperor sent fighting men on "boats with deckcastles to conquer the tribes of southeast China.

Lu's scheme uses a diversion head and a series of spillways similar to that of the Capital River Weir to precisely control the amount of water flowing in the canal in all seasons. A separate 2.5km lateral canal cuts across a bend in the Xiang River to moderate its flow near the canal intake. The banks of the canal are lined with stone. In the 12th century it could accommodate barges and other vessels of up to 35 tonnes capacity.

Untold numbers of war barges, soldiers and supplies crossed the divide from present-day Hunan on this canal during the Han Dynasty to complete the conquest of southeast China.

The Grand Canal is the most well-known example of pre-modern Chinese hydraulic engineering. The main course of the original Grand Canal, completed in 605 by connecting several pre-existing canal sections, facilitated shipment of grain from the productive lower Yangtze valley to the Sui capital near Loyang.

South of the Yangtze, the canal continued through the rich delta region as far as Hangzhou, forming the main trunk of a dense network of canals with connections to every town and important village. A sophisticated culture developed in this highly productive region, focused on wealthy canal cities such as Suzhou, Changzhou, Hangzhou and Shaoxing. A new canal section extended north of the Yellow River to near present-day Peking, forming a Y-shaped system totaling about 2,500 km.

A new canal was constructed after the Mongol invasion in the 13th century to ship Yangtze Valley grain direct to the new Yuan capital at Peking. This modern Grand Canal has continued in uninterrupted use to the present day, though there has been no through traffic since 1855, when a drastic change in the course of the Yellow River made part of the mid-section of the canal impassable.

This was not just a big ditch. North of the Yangtze, the canal must ascend a gradual slope to a summit more than 40 m higher than its starting point, requiring a complex system of locks, feeder lakes and lateral canals to maintain the appropriate water level in different sections o the canal as boats were slowly raised up the hill.

During Ming times (1355-1644), the Grand Canal carried from as much as 350-400,000 tonnes of grain every year, the lifeblood of the empire. The Ming eventually followed the Yuan Dynasty precedent by relocating its capital in Peking to direct the large garrisons in the north to counter the threat of renewed Mongol invasion from beyond the Great Wall.

Robert Delfs. Reprinted with permission from the Far Eastern Economic Review, 15 March 1990, pp. 28-29.

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