The establishment of Dujiangyan has its specific historical roots. During the Warring States Period, people suffering from war longed for the early reunification of China. Coincidentally, after Shang Yang's political reform, Qin was once famous all over the world, virtuous and virtuous, and the country became stronger and stronger. They correctly recognized the special strategic position of Ba and Shu in the process of reunifying China, saying that "if you gain Shu, you will gain Chu, and if Chu dies, the world will be merged" (Sima Cuo's words).

Under this historical background, at the end of the Warring States Period, Zhao Haoqi of Qin appointed Li Bing, who was familiar with astronomy and geography and lived in seclusion, as the prefect of Shu County. After Li Bing came to power, he first made up his mind to eradicate the flood in Minjiang River, develop agriculture in western Sichuan, benefit the Chengdu Plain and create an economic foundation for Qin to unify China.

Chengdu Plain, known as "Land of Abundance", was a place where floods and droughts were very serious in ancient times. The lamentation and tragic situation of "until two rulers crowded past in the foggy age of this area" and "man or fish became a turtle" in Li Bai's Shu Dao Nan is a true portrayal of that era. This situation is caused by the "bad" natural conditions in Minjiang River and Chengdu Plain.

There are more than 90 tributaries in Minjiang River, with Heishui River and Zagunao River in the upper reaches. Dujiangyan irrigation area in the middle reaches includes Heishi River, Jinma River, Jiang 'an River, Zouma River, Baitiao River and Puyang River. There are Qingyi River, Dadu River, mabian river and Yuexi River downstream. The main water source comes from the steep right bank of the mountain, and the big tributaries all overflow from the gap of the mountain on the right bank. Rainfall is mainly concentrated in the rainy season, so the water in Minjiang River fluctuates quickly and the water potential is fast.

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Every year, when the rainy season comes, the water potential of tributaries such as Minjiang River soars and often floods. When there is insufficient rain, it will cause drought again. Two or three hundred years before Dujiangyan was built, Du, an ancient Shu kingdom, opened an artificial river at the foot of the Minjiang River to drain the water from the Minjiang River into the Tuojiang River to eliminate floods.

In the fifty-first year of Qin Dynasty (256 BC), Li Bing was in charge of Shu County. On the basis of previous water control, Li Bing built Dujiangyan in guanxian, where the Minjiang River flows into the plain, relying on the local people.

Dujiangyan's master plan is to divide the Minjiang River into two branches, one of which is introduced into Chengdu Plain, which can not only divert floods and reduce disasters, but also divert water to irrigate farmland and turn harm into benefit. The main works include Yuzui diversion dike, Sha Fei weir spillway and Baojiangkou water intake.

Baidu encyclopedia-Dujiangyan