Why did Dujiangyan, built by Li Bing, have no major floods for more than 2, years, while other places flooded every year?

Every summer, there are floods there, causing serious losses. Disasters exist not only in modern times, but also in ancient times. There are countless droughts, insect pests and locust plagues. Someone once recorded that there was a relatively large-scale disaster every three years from the Yellow Emperor to the Qing Dynasty. The disaster has come, which has brought endless harm to the people, displacement and even homelessness.

with the development of modern science and technology, we have built many large-scale water conservancy projects, which should be able to ensure that the floods are not so rampant, but contrary to expectations, the floods are still out of control and bring losses to people every year. But what makes us wonder is that during the Qin Dynasty, Dujiangyan, which was built by Li Bing, has been in that area for more than two thousand years, and why there has been no major flood.

Time goes back to ancient times. At that time, the Chengdu Plain was also a place flooded, but it could produce a large amount of grain for the army. Although it was used to produce grain and cultivate land, it would also suffer from floods. It's not the same as Guanzhong in Qin State. There is little rain in Guanzhong. If it doesn't rain, it's no use asking grandpa to worship grandma.

Chengdu Plain is just the opposite of Guanzhong. There is never a shortage of water here, but the flood reduced the grain production, which made Qin Guojun have a headache. At this time, Li Bing, who knew astronomy and lost geography, appeared, so he was named the prefect of Shu County to control the flood. After surveying the terrain, Li Bing decided to build Dujiangyan in today's Dujiangyan city, so that the water content of the Minjiang River can be divided into two sections, generally called Waijiang outside and Neijiang inside.

In this way, Li Bing can kill two birds with one stone by making the water from the outer river flow out when the flood comes, and by making the water from Neijiang ensure the irrigation of crops when the water is in short supply. It also spared the people along the way from the troubles of floods and ensured the worries of Qin's grain. Li Bing did not expect that the Dujiangyan he built took more than 2, years and is still in use. People specially built a statue for him to commemorate him.

some people say that the current floods are different from the previous ones, and the river courses have also changed. In addition, the construction of large-scale water conservancy projects makes the river have nowhere to discharge when it rains, so when it rains, there will be floods. Facts have proved that Li Bing's technology of building Dujiangyan, even after more than 2, years, has been in use. Why not learn it to benefit the people?