A bird's-eye view of Dujiangyan. (PHOTO:VCG)

By Staff Reporters

Dujiangyan is a renowned ancient flood control and irrigation system in Sichuan province, southwest China. It was first built around 256 B.C. as a large-scale water conservancy project by Li Bing, a hydraulic engineer who served the state of Qin as a governor of Shu County.

This project has been in operation for more than 2,000 years, irrigating more than 30 counties and cities with a total area of nearly 10 million mu (one mu is about 666.7 square meters), giving rise to the folklore that the Chengdu Plain was "a Land of Heaven." It is also the oldest operating grand water conservancy project, featuring diversion instead of damming, in the world.

The Chengdu Plain was once a place of severe floods and droughts in ancient times, which were brought on by Minjiang River, the longest tributary of the Yangtze River, on which the Dujiangyan project was developed. The Minjiang River flows from its source through the steep mountains, and once it reaches the Chengdu Plain, the water slows down abruptly, blocking the river course with so much sediment and rocks that the nearby areas are prone to floods.

In order to solve the problem of floods and droughts, the Dujiangyan project was initiated. The overall plan of Dujiangyan was to divide the water flow of the Minjiang into two, with one side being redirected into the dry Chengdu Plain to irrigate fields. The main project included three components, the Yuzui, Feishayan and Baopingkou.

Yuzui, a key part of the structure, is an artificial levee that divides the water into an inner and an outer flow. The inner flow is deep and narrow, while the outer flow is relatively shallow and wide to protect local people from being plagued by floods or droughts. This is done by controlling the amount of water that the inner flow carries.

Feishayan is a 200-metre wide opening connecting the inner and outer flows, allowing the natural whirlpool flow of water to drain excess water from the inner to the outer flow to prevent flooding.

Baopingkou, an important part of the system, is a channel cut through the mountains. The channel distributes water to the agricultural fields of the Chengdu Plain, while its narrow entrance, from which it derives its name, acts as a check gate, creating a whirlpool flow that carries excess water over sand and rocks to ensure against flooding.

Dujiangyan encapsulates ancient Chinese wisdom, and is a symbol of harmony achieved between human and nature.