Dujiangyan Irrigation System: Li Bing's 2,200-Year-Old Waterworks

The Dujiangyan Irrigation System is an ancient water-management scheme on the Min River in Sichuan, south-west China, begun around 256 BC under Li Bing, a governor serving the state of Qin. Instead of damming the fast, flood-prone river, its builders divided and guided it, protecting the Chengdu Plain from floods and watering its fields. Still working after more than 2,200 years, it turned Sichuan into one of the most productive farming regions in China.

A river that flooded and starved the plain

The Min River rises in the mountains of the eastern Tibetan Plateau and rushes down onto the Chengdu Plain, a broad, flat basin in what was then the land of Shu. In spring and summer, snowmelt and monsoon rains turned the river into a torrent that flooded the plain. In dry seasons, much of the land to the east of the river lacked water, because a ridge called Mount Yulei blocked its flow.

Qin conquered Shu in 316 BC, during the Warring States period. For Qin, the region was both a frontier to be secured and a potential granary for its long wars against rival states. Making the plain safe and fertile became a strategic goal.

Li Bing and the building of the system

Li Bing was appointed governor of Shu by King Zhaoxiang of Qin, probably in the 250s BC. Very little is known about his life. The historian Sima Qian, writing around 100 BC, mentions him briefly as the official who cut through the hill and divided the river. A fuller account appears in the Huayang Guozhi, a history of the region written in the 4th century AD.

Tradition dates the start of construction to about 256 BC, and the work probably took many years. Later legend gave Li Bing a son, Erlang, who helped him and fought river dragons; this figure is not mentioned in early sources and is generally treated as folklore. Both father and son came to be worshipped at the Erwang Temple overlooking the works.

How Dujiangyan works

The genius of Dujiangyan lies in three linked structures that use the shape of the river and the force of the water itself.

The Fish Mouth (Yuzui). A long levee, its tip shaped like a fish’s head, stands in the middle of the river and splits it into two. The outer river carries the main flow and floodwater away along the old riverbed. The inner river leads towards the irrigation network. Because of the river’s curve and the shapes of the two channels, the inner river receives a larger share of the water in the dry season and a smaller share in floods. Traditionally this is described as roughly 60 per cent in the dry season and 40 per cent in the flood season.

The Flying Sand Weir (Feishayan). Downstream, a low spillway connects the inner river back to the outer one. When the inner channel is too full, water spills over it into the outer river. The swirling flow at a bend also throws much of the sand and gravel carried by the river over the weir, keeping the irrigation channels from silting up.

The Bottle-Neck Channel (Baopingkou). Finally, the inner river passes through a narrow gap cut through Mount Yulei into the plain. Its fixed width limits how much water can enter, acting as a natural control gate. Without explosives or iron tools of the modern kind, the workers are said to have heated the rock with fire and then doused it with cold water to crack it, a method recorded in later accounts.

From the Bottle-Neck, a branching network of canals spreads water across the plain by gravity, with no pumps or locks.

What makes the design unusual is that it works with the river rather than against it. A high dam would have trapped sediment, blocked fish and needed constant reinforcement. By dividing the flow, letting surplus water and gravel escape and fixing the size of the intake, the builders created a system that largely regulates itself through the seasons.

Simple materials, careful upkeep

The original works used local materials. Long cylindrical baskets woven from bamboo and filled with river stones, known as zhulong, formed the levees and could be replaced when they wore out. Wooden tripods called macha were used to block or divert flows during maintenance.

Every winter, in the low-water season, officials organised the dredging of the channels and the repair of the levees. A famous principle, often attributed to Li Bing and carved at the site, sums up the method: dig the riverbed deep and keep the weir low. Accurate depth markers helped workers judge how much silt to remove. This yearly maintenance, carried out by successive dynasties, is the main reason the system has lasted so long.

In 1974, workers found a stone statue of Li Bing in the riverbed. Its inscription dates it to AD 168 during the Eastern Han dynasty, showing that Li Bing was already honoured as a hero four centuries after his death. The statue may also have served as a water-level gauge.

The Land of Abundance

Dujiangyan transformed the Chengdu Plain. Freed from regular floods and supplied with reliable water, its fields produced rich harvests of rice and other crops. The region became known as the Land of Abundance (Tianfu zhi guo), a name still used for Sichuan today.

For Qin, Shu became a source of grain, men and supplies in the final wars that led to the unification of China in 221 BC. Together with other great Qin projects such as the Zhengguo Canal north of the Wei River, it gave the state an economic base that its rivals could not match.

Over the following two millennia the network was extended many times. Modern estimates of the farmland it serves run to hundreds of thousands of hectares, far more than in ancient times, and it also supplies water to the city of Chengdu. Concrete structures and modern sluices have been added, but the basic layout remains Li Bing’s.

Recognition and resilience

In 2000 UNESCO inscribed Mount Qingcheng and the Dujiangyan Irrigation System together on the World Heritage List, praising the system as a major example of ancient Chinese hydraulic engineering. The nearby temples, including the Erwang Temple and the Fulong Temple, attract large numbers of visitors.

On 12 May 2008 the Wenchuan earthquake, centred only a few tens of kilometres away, devastated the town of Dujiangyan and the surrounding region. The core waterworks cracked but did not fail, and they were repaired and kept in service, an event often cited as evidence of the soundness of the original design.

Timeline

• 316 BC: Qin conquers the kingdom of Shu in what is now Sichuan.
• c. 256 BC: Work begins on the Dujiangyan system under governor Li Bing, by tradition.
• c. 100 BC: Sima Qian records Li Bing’s work in his treatise on rivers and canals.
• AD 168: A stone statue of Li Bing is carved and placed in the river.
• 1974: The Han-dynasty statue of Li Bing is rediscovered during works on the river.
• 2000: Mount Qingcheng and the Dujiangyan Irrigation System become a UNESCO World Heritage Site.
• 2008, 12 May: The Wenchuan earthquake damages the region; the waterworks survive and are repaired.

Why it matters

Dujiangyan is one of the oldest water-control systems in the world still doing its original job. It shows how careful observation of a river, simple materials and steady maintenance could produce an engineering work that has fed a region for more than two thousand years.