Dujiangyan was built in Qin dynasty, with a history of two thousand years, and it can still be put into use. So how does Dujiangyan make itself a water conservancy project that spans the Millennium dimension?
In this issue, Ziya Tongqu Knowledge Bureau will learn the secret of Dujiangyan standing for thousands of years with you.
(A) the historical background of Dujiangyan
Dujiangyan is a super water conservancy project, built by Li Bing and his son two thousand years ago. Dujiangyan consists of fish mouth, flying sand weir and bottle mouth. Dujiangyan has been playing the role of flood control and irrigation for more than 2000 years, and it is precisely because of its existence that Chengdu Plain has become a rich and fertile "land of abundance".
Today, Dujiangyan irrigation area has reached more than 30 counties and cities, and Dujiangyan irrigation area is nearly 10 million mu.
Dujiangyan is also the oldest and only well-preserved water conservancy project in the world, which has been used to this day, and the most prominent feature is dam-free water diversion.
Dujiangyan embodies the industriousness and science of working people in ancient China, and is the crystallization of people's wisdom at that time.
So how does such a super-large Huimin project operate and how does it supervise water conservancy?
First of all, we must first understand why such a project should be built.
Chengdu Plain is located in the inland of the motherland, far away from the ocean, but the terrain of Chengdu Plain is vast and open, surrounded by mountains. Therefore, the weather in Chengdu Plain will have two extremes:
In the rainy season, Chengdu Plain is open and there is no shelter on the ground, so in the rainy season, the Minjiang River floods, and the whole Chengdu Plain will become a Wang Yang, which will bring great trouble to people's production and life.
In the dry season, the land in Chengdu Plain is cracked due to lack of water, which is because its terrain is not close to the sea, the weather is very dry and it doesn't rain. Therefore, it seriously hindered the survival and production of the ancient Shu people.
After Shang Yang's political reform, a large number of talents appeared in Qin State. Under such circumstances, the then ruler ordered the construction of Dujiangyan, which was a water conservancy project for the benefit of Chengdu people.
According to the natural conditions of Chengdu Plain at that time, Dujiangyan must have two most important functions, flood control and irrigation.
Minjiang River is the most abundant tributary of the Yangtze River, and the terrain of Chengdu Plain is inclined to the southeast, so Minjiang River is like a river covering the whole plain.
The area built by Dujiangyan reaches the inland of Chengdu Plain, and the drop between the two places is as high as 273 meters. Such a "suspended river" will become very dangerous for Chengdu Plain in rainy season.
If the Minjiang River is used reasonably, the drought in the dry season of Chengdu Plain can be effectively solved, so the builders use their brains to rationally allocate water resources and use Dujiangyan to realize their ideas.
The overall planning of Dujiangyan project construction is to divide the water of Minjiang River into two streams, one is introduced into Chengdu Plain, the other is mainly used for evacuation, and the excess river water is introduced into the main branch and leaves Chengdu Plain. Doing so can not only alleviate the local drought, but also avoid floods.
(B) Dujiangyan's three major structures and functions
The main construction project of Dujiangyan mainly includes three parts: the fish mouth, the treasure bottle mouth and the flying sand weir.
The bottle mouth was first built in these three projects. Bottle mouth plays a role of "control gate" in Dujiangyan project, which can automatically control the amount of water entering Neijiang.
Before the construction, libing and his son first found local residents with relevant water control experience, and together they surveyed the nearby topography and water regime. Under the discussion of a group of people, everyone unanimously decided to cross Leiyushan to get water.
They used fire to crack the stone and successfully blasted Leiyushan into a mountain pass with a width of 20 meters, a height of 40 meters and a length of 80 meters.
Because it is shaped like a bottle mouth, they named this mountain pass Baokou. And those stone piles separated by digging Lei Yu are called "retaining piles".
After the success of Lei Yu Mountain, the water of Minjiang River smoothly entered the eastern arid area through Baokou, and the rich river water of Minjiang River was used for agricultural production and irrigation of fertile fields.
This can not only immediately alleviate the flood problem in the western plain, but also reasonably lead the water to the east, benefiting the arid areas in the east, which can be described as killing two birds with one stone.
After the formal construction of the bottle mouth was completed and put into use, the construction party started the second main project-the water distribution fish mouth.
As the name implies, the function of fish mouth is to divert water and give full play to Dujiangyan.
The shape of the front end of this diversion weir is very similar to the fish head, especially the mouth part, so it is officially named as the diversion fish mouth.
The reason for building the water-separating fish mouth is that although the bottle mouth plays the role of water diversion and irrigation, it is difficult for the river to flow into the bottle mouth because of the high terrain in Jiangdong.
Even if it flows into the bottle mouth, the flow of the river will become extremely unstable because of the terrain, and the adjustment function of Dujiangyan will be greatly reduced, so the builder built a water-separating fish mouth to make up for this deficiency.
The "fish mouth" is actually a diversion weir, which can divide the river into two tributaries by topography. The river in the east is called Neijiang, which will be forced to enter the bottle mouth and become the irrigation water in the east. The water in the west is called the Waihe River, and they will flow down the Minjiang River and join the mainstream of the Minjiang River.
Because the Neijiang River is narrow and deep, while the outer river is wide and shallow. In the dry season when the water level drops, nearly 60% of the water will flow into Neijiang and become the daily water for people living in Chengdu Plain. When the rainy season comes, the Minjiang River floods fiercely and the water level rises, and most of the water will flow away along the wider surface of the Minjiang River. People call this design "46 water division".
Because it is far from enough to control the Minjiang River only by relying on the bottle mouth, in order to achieve better flood control and disaster reduction, builders built a flying sand weir.
First, they built a flat sink and a spillway at the bottle mouth. A bend was built in front of the spillway to control the flood and let the river form a circulation here.
During the rainy season, when the water level rises, the river will not cross the weir crest. At this time, the flood with sediment will flow along the water flow to the outer river, thus ensuring that the irrigation area in Chengdu Plain will not be flooded.
Secondly, when sediment and stones pass through the flying sand weir, they will encounter the vortex formed by the rotation of water flow. At this time, due to the centrifugal force, they will be thrown over the flying sand weir, which is why it is named "flying sand weir".
Throwing away stones and sediment in this way will greatly reduce the accumulation of sediment around the bottle mouth and ensure that the bottle mouth can work all the year round. In order to observe and control the water quantity in Neijiang, Li Bing carved three stone statues and put them into the water, based on which the water level was determined, and it was also used as the dredging standard when the water quantity was the least.
Baokou, Fenshuiyuzui and Sha Fei Weir constitute a complete Dujiangyan. The three main projects complement each other and jointly become a big barrier of Chengdu Plain, coordinating the water resources of Minjiang River and ensuring the water resources balance of Minjiang River. It has protected the lives and property of people in Chengdu Plain for thousands of years.
Dujiangyan, which took eight years to build, brought good news to Chengdu people and improved the flood and drought disasters in Chengdu Plain. Dujiangyan played an important role in Chengdu Plain's transformation from "no grain harvest" to "land of abundance".
End—
Xiaomiao