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2,200 year-old irrigation system still operating in Dujiangyan

Dujiangyan Scenic Area wide angle photo from the top of the Yulei mountain. It shows the Fish mouth and the Flying sand weir.
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16/05/2026

Written by Jean Werk, PCC web developer

In March, during our holidays in China, we visited the famous irrigation system at Dujiangyan in Sichuan province. We had less than 2 hours to visit the place. While it was scenic, I couldn’t figure out how it worked until I researched it once I was back home.

Historical background

In the 3rd century BCE, the plain around Chengdu, the current capital of Sichuan province was going through a cycle of drought and flood every year. The Min river carries a lot of sediment. In the dry season, this would stop water flowing towards the plain. And during the wet season, the plain would flood.

Li Bing, the province governor and an engineer, was tasked by the ruler of the Qin kingdom to tame the river. Military ships still needed to navigate so a dam was out of question. With the help of tens of thousands of workers, Li Bing designed and built an irrigation system that still helps feeding 10 million people in Chengdu today.

Construction of the main elements

  • (A) The Fish mouth is a levee on an artificial island. On the above photo shot from the mountain on the East shore, it is the platform on the right side. It was originally built from sausage-shaped baskets of bamboo filled with rocks. Its purpose is to split the Min river into the outer and the inner river. On the West side it the outer river which is wide and shallow and then becomes the main river. On the East side is the inner river which is narrow and deep. It feeds the irrigation system.
  • (B) The Flying sand weir is a 200m wide weir, also originally built with bamboo baskets. It links the inner and the outer river. On the photo, it is the sandy area on the left side of the artificial island.
  • (C) The Bottleneck channel is a narrow deep channel, 80m long and 20m wide carved into the mountain. Remember that gunpowder had not been invented yet! Rocks were cracked through fire heating & rapid water cooling.
  • (D) The final part of the system is a network of irrigation channels in the Chengdu plain.

How it works

During the dry season, 60% of the Min river flows into the inner river at the Fish mouth (A).

The Flying sand weir (B) is slightly higher and stops the water from escaping into the outer river.

So it all flows into the Bottleneck channel (C) and then towards the Chengdu plain (D).

Diagram of the water flow in the Dujiangyan irrigation system during the dry season. 60% in the inner river and 40% in the outer river. Location of the 4 main elements.
River flow during dry season

When the wet season arrives, the Fish mouth (A) behaves differently and only 40% of the Min river flows into the inner river.

The concave shape of the inner river creates a current that swirls and throws the excess water with most of the sediment over the Flying sand weir (B), hence its name. See the red arrow on the diagram.

And the narrow Bottleneck channel (C) also limits the amount of water flowing into the irrigated plain (D).

Diagram of the water flow in the Dujiangyan irrigation system during the wet season. 40% in the inner river and 60% in the outer river. Location of the 4 main elements.
River flow during wet season

Ongoing maintenance

While most of the silt and sediment is naturally expelled into the outer river, some accumulates in the inner river over time. Li Bing was conscious of this and placed statues in the inner river to indicate droughts, floods and whether mud needed to be removed during the dry season.

An example of sustainable design

This irrigation system is unique in the world because of its geography. After more than 2 millennia, it still functions as the primary water source for a modern metropolis of 20 million people. Concrete has replaced bamboo baskets and various gates have been added to river. But the core system still works. By collaborating with nature, Li Bing created a masterpiece of sustainable engineering. Sichuan grew rich and was able to feed the massive army of the Qin kingdom that united China a few decades later.

One hour by train from Chengdu, Dujiangyan scenic area is a beautiful place to visit, with the Erwang temple in the mountain and the Guanxian ancient city next to the Bottleneck channel.

For more information