What is the function and significance of Dujiangyan?

Dujiangyan is the earliest water conservancy project in China, located on the Minjiang River, at the foot of Lei Yu Mountain and west of Dujiangyan City. It was called Du 'an weir in ancient times, and Dujiangyan after Song and Yuan Dynasties. Known as the "treasure of Zhenchuan", Dujiangyan is the oldest and only grand water conservancy project in the world, with a history of more than 2,200 years, and it still plays a huge role.

Before Dujiangyan was established, Bashu area had been hit by Minjiang River flood. Minjiang River is a large tributary of the upper reaches of the Yangtze River. Whenever mountain torrents occur in spring and summer, the river rushes down and enters the Chengdu Plain, which often leads to floods due to the narrow river channel. In addition, Leiyushan on the east bank of Minjiang River blocked the eastward advance of the river, causing drought in the east and waterlogging in the west, which made the people of Shu miserable.

In the fifty-first year of Qin Xiang (256 BC), after the Western Zhou Dynasty was destroyed by Qin State, Bashu area was incorporated into the territory of Qin State. In 300 BC, the king of Qin appointed Li Bing as the magistrate of Shu County and began to build Dujiangyan. After years of hard work, Li Bing and his son scientifically solved the problems of automatic river diversion, automatic sediment discharge and inflow control, eliminated floods, and made the western Sichuan Plain a land of abundance.

Dujiangyan hub project is mainly composed of fish mouth, flying sand weir and bottle mouth, which are mutually restricted and adjusted, and the structure is scientific and ingenious. Historically, the position of the fish mouth has been changing, and it was first located not far downstream of the Baisha estuary. It is located at 2050 meters downstream of Baisha Estuary, which was determined during the overhaul of 1936. Fish mouth is a water diversion project in Dujiangyan, named after it looks like a fish mouth. It holds its head high in the middle reaches of the Minjiang River, leading the turbulent river into the inner and outer rivers. Waijiang in the west, commonly known as "Jinma Township", is the main stream of Minjiang River flowing into the Yangtze River through Dujiangyan, Leshan and Yibin, with a total length of more than 700 kilometers, which is mainly used for flood discharge; Neijiang, located at the foot of the eastern mountain, is an artificial channel, which flows into Chengdu Plain under the control of the bottle mouth and is mainly used for irrigation. The arrangement of fish mouths is very clever, which determines the diversion ratio of the inner and outer rivers and is the key to the whole Dujiangyan project. The intake width of Neijiang is 150m, and that of Waijiang is 130m. Fish mouth skillfully uses topography to complete the task of water diversion, and plays the role of automatically adjusting the water quantity at different water levels in flood and dry seasons. In spring, the water flow of Minjiang River is very small. In order to ensure irrigation water, the main stream of Minjiang River goes straight to Neijiang, accounting for about 60% of the water, and the outer river accounts for about 40%. In the flood season, the proportion of the two is reversed, 40% in Neijiang and 60% in Waijiang, so that the irrigation area is not affected by floods. This is the "four or six, flat poverty and drought" in the San Zi Jing. In addition, in ancient times, the fork was used to artificially change the diversion ratio of internal and external rivers. Chacha is an interceptor with several logs as the skeleton, covered with bamboo mats and filled with sediment. Generally, this method is used to intercept the outer river in spring when there is little water, so as to increase the water supply of Neijiang. After the spring ploughing ended and the water level rose, the dam stopped flowing and the water flow returned to normal.

1974 A reinforced concrete switch was built at the mouth of the Waijiang River on the west bank of Yu Zui, which replaced the previous temporary culvert project and was more flexible and reliable. There is a Baizhang levee on the east bank of the upstream of Yuzui, with a total length of1.950m, which pushes flood and sediment to the outer river and acts as a bank protection. Yu Zui Dam extends downstream to form Jingang Dam, followed by Sha Fei Dam and herringbone Dam.

Sha Fei weir is located on the right bank of Neijiang, at the lower end of Jingang dike, about 300 meters long. Formerly known as Shi Lang Weir, it was built during the Longshuo period in Tang Gaozong (66 1 ~ 663). It is a channel for flood discharge and sediment discharge in the middle section of Neijiang, hence the name. It follows the principle of "low weir", that is, the top of the dike is as low as the top of the standard platform on the other side, so that the internal river water exceeds the upper limit of Baokou flow. In order to observe and control the amount of water in Neijiang, Li Bing had three huge stone statues carved and stood in the water as an "automatic water level gauge", stipulating that "water cannot be exhausted without shoulders". Stone horses are also chiseled and placed in the middle of the river as a standard for scouring the beach when the water quantity is the least every year. If there is a serious flood. The flying sand weir will burst by itself, so that the flood entering Neijiang will be discharged into the outer river to ensure the safety of Neijiang irrigation area. Another function of flying sand weir is "flying sand". The Minjiang River runs down from Wanshan Mountain, with a lot of sediment and stones. If they are allowed to enter Neijiang, the bottle mouth and irrigation area will be blocked. Sediment and pebbles brought by the upstream can be thrown into the outer river (mainly by using centrifugal force skillfully), which effectively reduces the sediment deposition before and after Baokou and ensures the smooth flow of Neijiang. But in late autumn, the flying sand weir is particularly quiet. The river overflowing from Neijiang gurgles on the pebbles the size of weirs, and the stones are smooth and clear, so tourists can wade through them on foot. According to contemporary measurements, when the flow of Minjiang River exceeds 65,438+0,000 cubic meters per second, 40% of the flood and 98% of the sediment are discharged from Sha Fei weir. In ancient times, the flying sand weir was a temporary project built with bamboo cages and pebbles; Now it has been poured with concrete to ensure the effect once and for all.

Baokou Bottle, which is near the west gate of guanxian, is the gateway to control gravity irrigation in Chengdu Plain, and has the functions of water diversion and water control. According to the Military Records of Yongkang, "In spring ploughing, you need gold, and the title is' Golden Pass'", so the bottle mouth of Baokou was also called Golden Pass in ancient times. When the Du Jiang Weir was founded, with the help of his son Jiro, Li Bing invited farmers with experience in water control to make a field trip to the terrain and water regime of the Minjiang River flowing eastward, and decided to cut through Leiyu Mountain to divert water. He led the crowd to burn the stone, which burst and cut a mountain pass with a width of 20 meters, a height of 40 meters and a length of 80 meters. Because it looks like a bottle mouth, it is named "Baokou", and the stone pile separated from Leiyushan is called "Lidui". Strictly control the width and bottom height of the bottle mouth. The bottom width is 14.3m, and the top width is 28.9m The inner water inlet is 70m wide, and the outer water outlet is 40-50m wide. The ancients carved dozens of squares on the rock wall and named it "water gauge", which is the earliest water gauge in China. The cooperation between the bottle mouth and the flying sand weir has the function of controlling the water flow, which is the key to control the inflow of Neijiang. After the inland river flows into the bottle mouth, it passes through the main canal and the Yangtianwo sluice, dividing the river into two parts. Then it is divided into four parts by Pope and Zoujiang sluice, which are continuously diverted along the large and small diversion canals according to the topographic gradient of high in northwest and low in southeast, forming a self-flow irrigation canal system, which irrigates Chengdu Plain10 million mu of farmland. There are dozens of squares carved on the cliff on the left bank of the bottle mouth, each with a spacing of one foot, which is called "water gauge" to observe the fluctuation of water level. There were only ten strokes of water in the Song Dynasty and sixteen strokes in the Qing Dynasty. Now, the stone carving water on the cliff has reached 24 strokes. The rock foundation of Baokou has dried up for a hundred years because of the impact of the rushing river, and a huge suspended cave has appeared. In order to strengthen the rock foundation, in the winter of 1970, the people in the irrigation area blocked the mouth and drained the deep pool. From the foundations on both sides of the river, * * * poured more than 8 100 cubic meters of concrete, and built a great wall of steel at the goldfish pile and Baokoukou, making this bottle mouth that automatically controls the water volume in Neijiang more solid and reliable.

Dujiangyan Park near Dujiangyan has beautiful scenery and many cultural relics, including Fulongguan, Erwang Temple and An Lan Lock Bridge. Fulongguan, located at one side of the bottle mouth, is a shrine dedicated to Li Bing, also known as Laowang Temple. Legend has it that when Li Bing was in charge of water control, he lowered the dragon here and locked it under the pile in Longtan. Later generations set up a temple to worship this move. This view was founded in the Jin Dynasty and renamed as Fulongguan in the early years of the Northern Song Dynasty. The existing Triple Hall was rebuilt in the Qing Dynasty. There is a statue of Li Bingshi in the Eastern Han Dynasty (25 ~ 220) in the front hall, which is about 3 meters high and looks calm. There are also the ruins of the Eastern Han Dynasty weir stone tripod, and the scene when the sages and princesses in the Tang Dynasty became monks in Qingcheng Mountain. Erwang Temple has a history of 1500 years. It is backed by Leiyu Mountain and faces Minjiang River, and its scale is huge. The temple is dedicated to the gods of Li Bing and his son. Li Bing, dressed in a robe, is sitting in danger, holding a half-wrapped silk painting in his right hand, and his son Li Erlang is wearing sandals and casual clothes and holding tools. The plaques and couplets hanging on the doorposts in the corridor are eulogizing the tenacious perseverance and dedication of their father and son in inheriting Dayu, "benefiting the people" and "benefiting the whole Sichuan". An Lan Bridge, also known as Lovers Bridge, is located above the fish mouth of Dujiangyan, which is the most distinctive landscape of Dujiangyan. This bridge, formerly known as Zhupu Bridge and Shiping Bridge, was built before the Song Dynasty and was destroyed by war in the late Ming Dynasty. During the Jiaqing period of the Qing Dynasty, a teacher named He Xiande saw that it was difficult for pedestrians to cross the river, so he called for the reconstruction of a new cable bridge on the basis of the original bridge. He Xiande died before the bridge was completed, and his wife inherited his will. With the support of the masses, he finally built the bridge. After the completion of the new cable bridge, no matter how stormy it is, people can tide over the difficulties safely, hence the name "An Lan Bridge". The cable bridge is supported by wooden rafts and stone piers, and flies across the river with thick bamboo cables. The upper deck is paved with wooden boards, and bamboo cables are used as columns on both sides, with a total length of about 500 meters. The existing bridge moves down 100 meters, bamboo and wood are replaced with steel, and the wooden pier of the supporting cable is replaced with concrete pile.

Dujiangyan can be described as a great project that has benefited from the ages, and it is also one of the miracles of the Chinese nation to transform nature. Li Bing's contribution to water control is contemporary and beneficial to the future. In June 2000, Dujiangyan and Qingcheng Mountain were listed on the World Heritage List by the UNESCO Heritage Committee.