China's 2,000 year-old irrigation system still tames floods

Nov 20, 2016

Since its construction two thousand years ago, agricultural production has improved and the size of irrigated land expanded, from 126,000 hectares to over 660,000 hectares covering 36 counties

In China's central province of Sichuan, the city of Dujiangyan is home to an ancient irrigation system that still tames floods and irrigates plains to support agriculture.

The Dujiangyan irrigation system was built over 2,200 years ago around 250 BC under the guidance of Li Bing, the then governor of the Shu Prefecture of the Qin State.

Historical accounts show that the Minjiang River, on which the irrigation system was built, often flooded and wrecked havoc across the vast Chengdu Plain.

Part of the astounding engineering project involved cutting a channel through the surrounding Mount Yulei.

In the middle of the river a dyke was then created, dividing it into two: an inner river and an outer river, each with its own distinct function.

Two spill ways were built at the end of the dyke, creating a gravity irrigation system that soon stopped the floods, yet at the same time diverted water for agriculture.

Since its construction two thousand years ago, agricultural production has improved and the size of irrigated land expanded, from 126,000 hectares to over 660,000 hectares covering 36 counties.

 The 'fish mouth' divides the Minjiang River into two rivers

The ancient irrigation system made Sichuan the most agricultural production region of China and still draws thousands of tourists and scientists from across the world for leisure or study.

The Dujiangyan consists of three parts: Yuzui, a ‘fish-mouth' dyke; Feishayan, a spillway for discharging flood and silt, and the Baopingkou, a channel cut through Mount Yulei.

 

How the ancient system works

During the flood season, the Yuzui dyke diverts 40% of the water from the Minjiang River into the inner river while 60% of it is pushed into the outer river, helping keep a balance.

However, during the dry season, the reverse is what happens. The system also pushes 90% of silt into the outer river, ensuring that the main Minjiang River is free from debris that leads to floods.

The Baopingkou, shaped like an inverted ladder, plays the function of regulating water flow while the Feishayan spillway discharges flood and silt from the inner river into the outer river.

The complex irrigation system is still a puzzle to scientists and marks in many respects the ingenuity of ancient Chinese when it comes to flood control and engineering.

Dujiangyan is both a scenic spot surrounded by mountains and a UNESCO World Heritage Site.

In his honour, a shrine was built in remembrance of Li Bing on the east side of Dujiangyan.

Another popular feature around the Dujiangyan is a suspension bridge connecting the artificial island to both banks of the river.

Made of wooden plates and bamboo handrails, walking across the bridge is exciting as it sways with every movement. It is known as one of the Five Ancient Bridges of China.

 

 

(adsbygoogle = window.adsbygoogle || []).push({});