Dujiangyan irrigation system

The Dujiangyan () is an ancient irrigation system in Dujiangyan City, Sichuan, China. Originally constructed around 256 BC by the State of Qin as an irrigation and flood control project, it is still in use today. The system's infrastructure develops on the Min River (Minjiang), the longest tributary of the Yangtze. The area is in the west part of the Chengdu Plain, between the Sichuan Basin and the Tibetan Plateau. Originally, the Min would rush down from the Min Mountains and slow down abruptly after reaching the Chengdu Plain, filling the watercourse with silt, thus making the nearby areas extremely prone to floods. King Zhao of Qin commissioned the project, and the construction of the Dujiangyan harnessed the river using a new method of channeling and dividing the water rather than simply damming it. The water management scheme is still in use today to irrigate over of land in the region. The Dujiangyan, the Zhengguo Canal in Shaanxi and the Lingqu Canal in Guangxi are collectively known as the "three great hydraulic engineering projects of the Qin."

History

Planning

During the Warring States period, people who lived along the banks of the Min River were plagued by annual flooding. Qin hydrologist Li Bing investigated the problem and discovered that the river was swelled by fast flowing spring melt-water from the local mountains that burst the banks when it reached the slow moving and heavily silted stretch below.

One solution would have been to build a dam, but the Qin wanted to keep the waterway open for military vessels to supply troops on the frontier, so instead an artificial levee was constructed to redirect a portion of the river's flow and then to cut a channel through Mount Yulei to discharge the excess water upon the dry Chengdu Plain beyond.

Construction

King Zhao of Qin allocated 100,000 taels of silver for the project and sent a team said to number tens of thousands. The levee was constructed from long sausage-shaped baskets of woven bamboo filled with stones known as Zhulong held in place by wooden tripods known as Macha. The construction of a water-diversion levee resembling a fish's mouth took four years to complete.

Cutting the channel proved to be a far greater problem, as the tools available at the time, before gunpowder was invented, could not penetrate the hard rock of the mountain, so a combination of fire and water used heat and cool the rocks until they cracked and could be removed. After eight years of work, a -wide channel had been gouged through the mountain.

Legacy

After the system was finished, no more floods occurred. The irrigation made Sichuan the most productive agricultural region in China. The construction is also credited with giving the people of the region a laid-back attitude to life; by eliminating disaster and ensuring a regular and bountiful harvest, it has left them with plenty of free time.

The original Dujiangyan Irrigation System was destroyed by the 1933 Diexi earthquake. The current Dujiangyan Irrigation System was rebuilt by Zhang Yuan and his sons after the Diexi Earthquake in 1933. Zhang Yuan and his son refer to Zhang Yuan (张沅) and his son Zhang Shiling (张世龄).

In 2000, Dujiangyan became a UNESCO World Heritage Site. Today it has become a major tourist attraction in Sichuan.

2008 Sichuan earthquake

On May 12, 2008 a massive earthquake struck a vast portion of west Sichuan, including the Dujiangyan area. Initial reports indicated that the Yuzui Levee was cracked but not severely damaged. Diversion of flow could still be seen as the river turns.

Engineering Constructions

Irrigation Head

The Irrigation System consists of three main constructions that work in harmony with one another to ensure against flooding and keep the fields well supplied with water:

The Yuzui or Fish Mouth Levee, named for its conical head that is said to resemble the mouth of a fish, is the key part of the construction. It is an artificial levee that divides the water into inner and outer streams. The inner stream is deep and narrow, while the outer stream is relatively shallow but wide. This special structure ensures that the inner stream carries approximately 60% of the river's flow into the irrigation system during dry season. While during flood, this amount decreases to 40% to protect the people from flooding. The outer stream drains away the rest, flushing out much of the silt and sediment.

The Feishayan or Flying Sand Weir has a -wide opening that connects the inner and outer streams. This ensures against flooding by allowing the natural swirling flow of the water to drain out excess water from the inner to the outer stream. The swirl also drains out silt and sediment that failed to go into the outer stream. A modern reinforced concrete weir has replaced the original weighted bamboo baskets.

The Baopingkou or Bottle-Neck Channel, which was gouged through the mountain, is the final part of the system. The channel distributes the water to the farmlands in the Chengdu Plain, whilst the narrow entrance, that gives it its name, works as a check gate, creating the whirlpool flow that carries away the excess water over Flying Sand Fence, to ensure against flooding.

Anlan Suspension Bridge

Anlan or Couple's Bridge spans the full width of the river connecting the artificial island to both banks and is known as one of the ''Five Ancient Bridges of China''. The original Zhupu Bridge only spanned the inner stream connecting the levee to the foot of Mount Yulei. This was replaced in the Song Dynasty by Pingshi Bridge which burned down during the wars that marked the end of the Ming Dynasty.

In 1803 during the Qing Dynasty a local man named He Xiande and his wife proposed the construction of a replacement, made of wooden plates and bamboo handrails, to span both streams and this was nicknamed Couple's Bridge in their honour. This was demolished in the 1970s and replaced by a modern bridge.

Temple Sites

Two Kings Temple

Erwang or Two Kings Temple is on the bank of the river at the foot of Mount Yulei. The original Wangdi Temple built in memory of an ancient Shu king was moved, so locals renamed the temple here.

The 10,072 m² Qing Dynasty wooden complex conforms to the traditional standard of temple design except that it does not follow a north-south axis. The main hall, which contains a modern statue of Li Bing, opens up onto a courtyard facing an opera stage. On Li Bing's traditional birthday, 24th day of the 7th month of the lunar calendar, local operas were performed for the public, and on Tomb Sweeping Day a Water Throwing Festival is held.

The rear hall contains a modern statue of the god Erlang Shen. Some say Erlang Shen was Li Erlang, but historic records do not confirm this, and it is possible that he was invented by locals as a false god. Guanlantin Pavilion stands above the complex and is inscribed with wise words from Li Bing such as, ''When the river flows in zigzags, cut a straight channel; when the riverbed is wide and shallow, dig it deeper.''

Dragon-Taming Temple

Fulongguan or Dragon-Taming Temple in Lidui Park was founded in the third century in honour of Fan Changsheng. Following Li Bing's death a hall was established here in his honour and the temple was renamed to commemorate the dragon fighting legends that surrounded him. It is here that Erlang Shen, the legendary son of Li Bing, is said to have chained the dragon that he and his 7 friends had captured in an ambush at the River God Temple when it came to collect a human sacrifice. This action is said to have protected the region from floods ever since.

During the East Han Dynasty a statue of Li Bing was placed in the river to monitor the water flow, with the level rising above his shoulders to indicate flood and falling beneath his calves to indicate drought. Recovered from the river in 1974 and placed on display in the main hall, this is the oldest known stone statue of a human in China.

See also

* Turfan water system
* Grand Canal of China

References

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AAAAA-rated tourist attractions
Canals in China
Chinese architectural history
Chinese inventions
Irrigation in China
Irrigation projects
Major National Historical and Cultural Sites in Sichuan
National parks of China
Qin (state)
Tourist attractions in Chengdu
World Heritage Sites in China
Qin dynasty architecture

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