Taming the river without a dam
In 256 BC, the state of Qin commissioned governor Li Bing to solve a problem: the Min River, which flooded the fertile Chengdu Plain each spring with snowmelt from the Tibetan Plateau. Instead of building a dam, which would have blocked military vessels—Li Bing developed a system that works in harmony with the river's natural forces. The approach transformed the area into the "Land of Abundance" and is still in use today, irrigating over 668,700 hectares of farmland.
The system relies on three main structures. First, the Yuzui, or "Fish Mouth Levee," is a man-made island that divides the Min River into an Inner and Outer River. During the dry season, the Inner River carries approximately 60% of the water toward the irrigation network. In the flood season, this ratio automatically flips, with the wider Outer River carrying about 60% of the excess water safely away.
The second component is the Feishayan, or "Flying Sand Weir." This low spillway, with an opening 200 meters wide, has two purposes. It allows excess water from the Inner River to flow into the Outer River, preventing floods. The natural swirl of the water at this point also forces heavier silt and sediment out through the weir, effectively self-cleaning the irrigation channel.
Finally, the Baopingkou, or "Bottle-Neck Channel," is a narrow passage that Li Bing's workers gouged through a mountain. Before the invention of explosives, they achieved this by repeatedly heating and cooling the rock to crack it. This channel is a final control gate, regulating the volume of water entering the vast network of canals that feed the Chengdu Plain.
A legacy of maintenance
The long-term success of the Dujiangyan system is due to a strict maintenance regimen established by Li Bing. The guiding principle was a six-character mantra: "Shen Tao Tan, Di Zuo Yan," which translates to "dredge the shoals deep, keep the dikes low." Annual dredging during the dry winter season was essential to remove accumulated silt from the Inner River.
To ensure the dredging was done correctly, stone markers were originally placed in the riverbed. By the Eastern Han dynasty, these were replaced by three stone statues, each about 2 meters high, that indicated the proper water levels. Later, four iron bars were buried in the riverbed to serve as gauges for the annual cleaning. The construction of the levees themselves used local materials: long bamboo cages called zhulong were filled with stones and held in place by wooden tripods.
The system's design is so efficient that the frequency of major dredging has decreased over time. The entire project was inscribed as a UNESCO World Heritage Site in 2000 for its remarkable and enduring approach to hydraulic engineering. A nearby temple, Erwang Temple, honors Li Bing and his son for their ingenuity.