Aerial view of the Dujiangyan Irrigation System. PHOTO BY RUTH MOSTERN.
Dujiangyan (The Weir on the Capital River) is a 2,300-year-old hydrological engineering works situated in the middle reaches of the Min River, the largest and longest of the Yangzi (Chang) headwaters. It is the oldest surviving water management system in the world, initially built by the Qin kingdom as a strategic element in defeating its rivals to the north and south.
Dujiangyan (The Weir on the Capital River) is a huge irrigation system located at the western edge of the Chengdu Plain, where the waters of the Min flow from a gorge to an alluvial fan plain. The Dujiangyan system is located at the highest point of the plain, allowing the whole irrigation network to run by gravity. Prior to the construction of Dujiangyan in the fourth century BCE, the natural course of the Min River followed the edge of the western foothills, and its unregulated spring flow caused massive floods. Dujiangyan regulated the floodwaters and diverted the river into the middle of the Chengdu Plain. Its canal system irrigated 126,000 ha during the Han dynasty (206 BCE–220 CE), and that capacity has expanded to almost 660,000 ha in thirty-six counties today. It has made the Chengdu Plain into one of the most dependably fertile and densely populated agricultural regions in the world. Still functioning as designed in the third century BCE, the Dujiangyan system consists of three primary and interrelated components that regulate the flow of water into the Chengdu Plain while preventing flooding and silt buildup.
As the Min River flows downstream, the Yuzui (Fish’s Mouth) levee splits it into an inner and an outer channel. The outer channel, following the original course of the river, discharges excess water, while the inner channel leads to the irrigation canals. Surface water flows into the concave inner channel, while the deeper silt-carrying water flows into the convex outer channel and can be easily dredged. The Baopingkou (Precious Bottleneck) culvert cuts through the rock face of Mount Yulei and is the gate to the inner channel. It prevents excessive water from entering the Chengdu Plain by diverting it over the Feisha (Flying Sands) spillway and into the outer channel. The Feisha spillway is located at the downstream end of the Yuzui levee. During flood season, when the water level in the inner channel exceeds a fixed point, surplus water and silt flow over the Feisha spillway and into the outer channel. The spillway discharges more than 90 percent of the silt carried in the river. During the peak farming months, when water flow in the inner channel is low, the Feisha spillway blocks water from entering the outer channel and ensures that it is available for irrigation.
Annual dredging and maintenance has been essential to the operation of Dujiangyan since its construction. During autumn, when the flow of water is at a minimum and the farm season is slack, workers create temporary diversion dams to direct all of the water into the inner channel. The bed of the channel is cleared, and any necessary repairs are carried out. In February, the dams are erected in the inner channel, and the outer channel is dredged. Branch canals are maintained by the farmers themselves. The entire Dujiangyan system has historically been built from locally accessible and easily assembled materials, though these have been replaced by concrete since the 1960s.
Dujiangyan and Chinese History
It is no exaggeration to say that the creation of Dujiangyan allowed the Chinese Empire to be unified for the first time. In 316 BCE, the armies of the kingdom of Qin, one of several contenders for dominance in north China, drove the state of Chu out of Sichuan. The Qin rulers recognized that in order to prevail against their northern rivals, they would have to produce enough food to field vast armies capable of wearing down their opponents; while to eliminate Chu in the south, they should mount attacks by riverboat. The construction of Dujiangyan was the key to both of these strategies.
In 277 BCE, Sichuan governor Li Bing was commissioned to conduct an extensive hydraulic survey and build a waterworks on the Min. Tens of thousands of workers hauled bamboo baskets filled with rocks into the middle of the river, and the Yuzui levee was completed in four years. It took eight more years to cut through the mountain to create the Baopingkou culvert, using controlled fires to heat the rocks, and then dousing them with cold water to crack them. Dujiangyan was completed after fourteen years of labor by local residents, Qin colonists, and subjects of defeated Qin rivals. Timber was floated down the newly navigable river to a shipyard in Chengdu to construct warships. Additional irrigation canals transformed the Chengdu Plain into fertile farmland, and more than 100,000 people from the Qin heartland moved to Sichuan, which quickly became China’s largest granary. In 223 BCE, Qin troops sailed down the Min River from Chengdu, defeating the state of Chu. Two years later, Qin armies in the north, bellies full of Sichuan rice, unified the north. The king of Qin renamed himself as the First Emperor, initiating China’s imperial era.
The system continued to expand throughout the imperial era. As governor, Li Bing staged a ritual confrontation with the dragon spirit of the Min River, long revered by locals. By the Han dynasty, some people came to believe that Li Bing himself had become a god, commemorated for vanquishing the dragon spirit and ending human sacrifices to it. During the Song dynasty (960–1279), civil officials, committed to extending cultural conformity throughout the empire, reinvented Guankou Erlang, an ancient Min River water-taming god who still commanded sacrifices of 40,000 sheep each year, as a Confucian official and son of Li Bing. Finally, it was at Qingcheng Mountain overlooking Dujiangyan that centenarian hermit Zhang Daoling is said to have ascended to heaven as an immortal in 143 CE. His successors transformed Daoism from a set of philosophical principles into a sectarian religion under the Heavenly Master school. Most of the original twenty-four dioceses of Heavenly Master Daoism are located in and around the watershed of the Dujiangyan irrigation system.
Since 2000, Dujiangyan and Mount Qingcheng have together been inscribed as a UNESCO World Heritage site drawing almost a million visitors each year. Dujiangyan remains the key to intensive agriculture in the Chengdu Plain, which supports an urban and rural population of more than 15 million people and boasts one of the world’s highest rural population densities. In recent years, a number of hydroelectric projects have been completed on the Min River. There are currently fifteen dams in operation or under construction on the river. These dams, which critics believe may constrain urban and agricultural access to water and threaten the continued viability of Dujiangyan, are controversial both in China and internationally.
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Closer view of the Dujiangyan Irrigation System. PHOTO BY RUTH MOSTERN.
Dujiangyan Irrigation System (D?ji?ngyàn Shu?lì G?ngchéng ???????)|D?ji?ngyàn Shu?lì G?ngchéng ??????? (Dujiangyan Irrigation System)