Chapter 21 Section 3 Water Conservancy of Dujiang in Han, Tang and Song Dynasties

Since Li Bing built the Dujiang Water Conservancy, due to its remarkable economic benefits, it has been valued by future generations. For more than 2,000 years, not only attention has been paid to maintenance, but also expansion and innovation. The Han Dynasty was the initial development period of Dujiang water conservancy.In the last years of Emperor Jing of the Western Han Dynasty (156 BC-141 BC), the famous local official at that time, Wen Weng, the prefect of Shu County, organized manpower to dig a canal at the top of Guankou Mountain (northwest of Guanxian County today) to divert the water from the river to the northeast. The streams irrigate 1700 hectares of farmland in Fan County (where the government is located in the northwest of Peng County today).This newly opened irrigation canal became the later Puyang River, one of the main canals in the Dujiang Irrigation District.This project expanded the Dujiang irrigation area to the northern part of the Chengdu Plain.During the Eastern Han Dynasty, a canal of more than 20 miles was dug in Guangdu County (roughly equivalent to today's Shuangliu County) to divert water from the lower reaches of the Pijiang River to irrigate the farmland around Wangchuanyuan, and expanded the Dujiang irrigation area to the southwest of Chengdu.

During the Tang and Song Dynasties, the water conservancy system of the Dujiang River was further developed, the canal head project was gradually completed, the canal system was increased, and the irrigation area was expanded. During the Longshuo period of Emperor Gaozong of Tang Dynasty (661-663 A.D.), Shilang Weir and Baizhang Dike were built.The Baizhang embankment is located on the left side of the Neijiang River. The purpose of construction is to protect the embankment on the left side, so that drift trees can enter Baopingkou along the embankment in the south.Shilang Weir is located under the opposite bank of Hutouyan. Because of its special flood discharge and sediment discharge function, the excess flood and sediment in the water entering the Neijiang River are turned over and discharged to the Outer River. Later generations renamed it Feisha Weir.Together with Baopingkou and Dayuzui, it is called the three canal head projects of Dujiang Water Conservancy.According to contemporary measurements, when the Minjiang River generates water and the flow of the Neijiang River exceeds 1,000 cubic meters per second, 40% of the flood and 98% of the sediment will be discharged from the Feisha Weir.Due to technical limitations, the effect of flood discharge and sand discharge may not be as good as that of modern times, but the difference will not be too far.The reason why Shi Lang Yifei Sand Weir has good flood discharge and sand discharge effects is that it follows Li Bing's important principle of "low-level weir", and it is because of the appropriate location.It is located under the opposite bank of Hutouyan, and Hutouyan is a protruding rock mass, which can guide the flood water and sediment in the inner river to Feishayan and discharge it to the outer river.It is not far from Baopingkou, which has a good water control effect. Even if the flow of Neijiang reaches as high as 3,000 cubic meters per second, the water intake of Baopingkou is about 700 cubic meters.In this way, the flood formed a whirling flow outside the mouth of the treasure bottle, causing a large amount of water and sand to overturn the Shilang Weir and discharge it to the outer river.

When Li Bing built the Dujiang water conservancy, he had already built stone man water gauges in the three rivers, and put forward the principle of "deeply sweeping the beaches and making low weirs".Regarding Shentaotan, it is said that Li Bing once buried a stone horse in the riverbed under Fengqi Nest as a mark.There is no regulation on the standard of low-zuo weirs. By the Song Dynasty, after long-term practice, both of them had been greatly improved.At that time, a 10-stroke water ruler was engraved on the stone wall at the mouth of the treasure bottle, each stroke was one foot.The water can meet the needs of irrigation when the water reaches six strokes. If there is excess water, it will be discharged from the Shilang Weir to the outer river.In order to match the water inflow in the six strokes of Baopingkou, the height of the Shilang Weir has been stipulated as follows: "When the Shilang Weir is built at the age of one year, bamboo must be used as a rope to lead from the north to the south, and the fourth is the height of the quasi-water. degree."

While improving the canal head project, in addition to repairing the old canals, many new canals were dug in the irrigation area. In the Tang Dynasty, the more important ones were that during the reign of Wu Zetian (AD 684-704), the long history Liu Yi dug canals in Tangchang (northwest of Pixian County) and Jiulong (Pengxian County) and also diverted water from Jiangtuo. , irrigated the farmlands of the two counties, and further expanded the irrigation area opened up by Wenweng in the Western Han Dynasty.This irrigation canal is the upper section of today's Renmin canal.The more important project drilled in the Tang Dynasty was the Yuanji (also known as Tongji) Weir.In the 28th year of Kaiyuan (740 A.D.), Yuanji Weir was dug by Zhang Qiu Jianqiong, a local official in Yizhou.It leads the canal southward from the mouth of the Qiongjiang River (Nanhe River) in Xinjin, 120 miles long, to Meizhou (now Meishan County where the government is located) and enters the Minjiang River, irrigating 160,000 mu of land.At the end of the Tang Dynasty, Yuanji Canal was renamed Tongji Canal, and Zhang Lin, governor of Meizhou, renovated and expanded it. The area of ​​irrigated fields increased significantly, reaching 15,000 hectares according to historical records.Because of their great contributions to water conservancy construction, there was a poem praising them later:

There was Zhang Qiu before and Zhang Gong later, and the water conservancy was dredged and the japonica rice was abundant. Nanyang is not the same, why not use it to cut down the work of heaven. The Song Dynasty also attached great importance to the maintenance and expansion of Dujiangyan.It has an annual repair system, and when it is repaired every year, it also requires that the construction situation, such as the height, width, depth, and size of the river, the size of the irrigated field area, the name and quantity of materials used, the number of people involved in the construction, and the name of the presiding official, etc. must be detailed. Recorded in the book for year-end assessment.And built many projects.More importantly, in the Neijiang irrigation area, the Shiqu water system divided into nine branches was dug.It was the predecessor of Jiang'an River, one of the four major canal systems in the Neijiang irrigation area.In Waijiang Irrigation District, Tongji Canal was restored under the auspices of Sichuan appeasement envoy Li Qiu (Qiu Qiu).The restored Tongji Canal can be irrigated.After maintenance and expansion in the Song Dynasty, Dujiangyan Irrigation District developed to 12 counties.

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