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An ancient irrigation sensation
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TUOSHANYAN, or Tuoshan Weir, that meets the sea and hills in Ningbo, Zhejiang Province, is one of the greatest ancient irrigation systems in Chinese history. It has harnessed the terrain’s unruly water and blessed its people with bumper harvests for over 1,100 years.
Built in AD 833 on the Yinjiang River, the weir functioned for centuries to prevent tidal sea water from accessing the riverbanks, controlled its flow and stored fresh water for irrigation and civil use in severe drought.
Before the dam was set up, the sea water flooded the Yongjiang River and its farmlands, devastating crops that were greatly halogenated by the high salt-content in water. Therefore, local people designed the weir under the supervision of Wang Yuanwei, the administrator of Yinjiang County, to prevent any further damage.
The stone dam was established between Tuoshan Hill and Siming Hill on the upper stream of Yinjiang River.
The top of the dam, 140 meters long, was made of 80 square stones, while the body, more than 134 meters long and 3 meters tall, was a mixture of wood and stone, supported by giant wooden posts. In addition, molten iron was injected to consolidate the whole structure.
The dam worked to ensure the farm irrigation of seven counties nearby, covering an area of about 16,000 hectares, and also served Ningbo’s downtown area through the Nantang River.
In the shape of a bow, the weir could withstand big flood and cleverly control its flow. When the flooding season came, 70 percent of the water ran to the inner river and the rest was discharged to the outer river.
During the drought period, the situation was reversed — 70 percent to the outer river and 30 percent to the inner river. The bottom of the dam was paved with gravel, which became closer and tighter when they were shaken under the attack of a flood.
In 1242, the head of the province, Chen Kai, ordered a sluice to be built to control the silt, located 150 meters away at the northwest of the weir. When the flood water that carried mud and sand was blocked in front of the weir, it changed its direction and sped to the sluice, where whirlpools were created to remove the silt quickly.
As the ancient canals have been changed many times. The sluice is out of use today and is a relic of the past. Only four old bollard grooves remain from it. The second bollard from the western side was used to measure water level, while the third one was carved with “Huisha Sluice.”
Tuoshan Weir gave a great boost to the development of the coastal Ningbo, which experienced rapid growth due to the stability of water supply.
Ningbo was an important link of the Maritime Silk Road in ancient times, and has leaped to be one of the world’s largest harbor cities today.
Yinjiang County’s administrator Wang was remembered by locals for his efforts to construct the weir and raise funds. People built a temple on the top of the Tuoshan Hill in the name of Wang, while nearby another temple was erected to commemorate the 10 workers who died during its construction.
Every year on the third day of the third lunar month, and the 10th day of the 10th lunar month, it’s been a folk tradition for the locals to hold temple fairs and cultural festivals worshiping Wang, who was 33 years old when the dam was completed. The 10th day of the 10th month was his birthday.
During the Song (AD 960-1279) and Qing (1644-1911) dynasties, maintenance and restructuring of the weir were continuously carried out.
In 1536, the dam’s top was increased by about 33 centimeters, while in 1857, it went through a big renovation.
In 1914, a thorough clean-up project made the canals smoother. By the early 1920s, the Tuoshan Weir was a combo project of nine supplementary dams and 13 ponds to drain off flood waters.
After centuries, the weir is kept intact and today still functions well to block seawater, store fresh water and perfectly adjust the flows with the river course. But it cannot irrigate the farms anymore because of the modern urban planning.
In 1988, the weir was listed as a Major Historical and Cultural Site under State-level Protection, and also recognized as one of the four most important water conservation projects in ancient China.
The other three are the Zhengguo Canal in Shaanxi Province, Lingqu Canal in the Guangxi Zhuang Autonomous Region and Dujiangyan or Dujiang Weir in Chengdu, Sichuan Province.
In 1996, Tuoshanyan Weir Memorial Hall was opened free to the public. It exhibits more than 100 photos and paintings by famous artists, as well as nine statues, four models to explain the architectural techniques, five old inscribed stone steles, construction tools and more than 20 geological samples.
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