The place marked above is the location of Minjiang River.
"Constant" and "Change" of Water Conservancy
The Minjiang River, also known as Wenjiang and Du Jiang, originates from Gonggangling and Langjialing at the southern foot of Minshan Mountain, with a total length of 735 kilometers and a drainage area of 13588 1 square kilometer. The drop of the whole river is 3560m, with an average gradient of 8.2‰, and the annual runoff exceeds 654.38+0 billion m? . For Chengdu, the Minjiang River is like a sword of Damocles.
During the Warring States Period, Li Bing, the prefect of Shu County in Qin State, was a compound talent who could "know astronomy above and geography below" and "know all the water veins". He found that the Minjiang River, 50 kilometers away from Chengdu, was influenced by the Lei Yu Mountain, and its channel was inclined, forming a slope. He decided to build Dujiangyan here to change the unfavorable situation of Minjiang River to Chengdu Plain.
The whole project consists of three parts: fish mouth, flying sand weir and treasure bottle mouth, taking into account the functions of water diversion, flood discharge and sand discharge. After the completion of the weir, the harm of Minjiang River to Chengdu Plain was basically contained, and Du Fu praised it as "Shu people boast for thousands of years, and the flood is not close to Zhangyilou". The "unchanged" of Minjiang River and the "changed" of Dujiangyan collided with each other, which produced a good effect of promoting benefits and eliminating pests.
"Invariance" and "Change" of Engineering
Dujiangyan's water conservancy "black technology" tamed the restless Minjiang River. The research shows that the location of Dujiangyan is scientific and reasonable. Located at the junction of Minjiang River and Chengdu Plain, the maximum peak flow is 6400m? /s, the average minimum flow in February 107.
m？ /S. Dujiangyan's subsystems have different functions, coordinated cooperation, rational layout, and guided by the situation, thus solving the problem of drought and flood without sluice facilities.
"Water Classic Note" records: "From Jiang to Du 'an (now Dujiangyan City), the weir is on the right and stops at the left. It flows eastward, and the right of the Dan River is also." "Stop its left" means to control the water flow in Neijiang within a limited range. The "right weir" is an overflow weir built according to the route that the flood washed away the dike on the right bank, and the flood is diverted to all parts of the plain through these facilities.
This reflects the principle of water control put forward by Li Bing, that is, "one is divided into four or six, and the drought is flat". The Minjiang River changes course at the fish mouth. When the flow is large, it will be diverted to Waijiang and Neijiang at 6: 4. When the flow is small, the inner and outer rivers are diverted at 4: 6. The diversion of the river is not achieved overnight. 800 meters away from the fish mouth, there are two beaches. When the flow rate is less than 1300
m？ /s, the floodplain is exposed to the river, and when the water on the right side is large, it flows to Mazutuo, where the river center on the right bank protrudes, and forcibly enters Neijiang to the left. When the flow rate is greater than 1700,
m？ /s, the floodplain is submerged in the river, and the flood passes through the floodplain and goes straight to the outer river, and the diversion ratio is reversed.
Above _ Dujiangyan Project Layout
While meeting the irrigation demand, Dujiangyan is facing the problem of river siltation. Dujiangyan is located at the bend of Minjiang River, where Neijiang and Waijiang belong to concave bank and convex bank respectively. When the water flows through, the strong centrifugal force in the bend makes the surface water flow to Neijiang, and the bottom water flows to the outer river with sediment, which plays the role of "diverting water from the concave bank and discharging sediment from the convex bank".
The Neijiang water flow and Hutouyan on the north bank form a bend with a curvature radius of 850m, and the water flow is influenced by inertia. Under the dual effects of static pressure and impact, more than 90% of the sediment is discharged into the outer river by spiral flow through the flying sand weir, which plays the role of secondary sediment discharge. 1966 In the Minjiang River flood, a cement stone weighing about 1 ton was washed away by the sand-flying weir, which shows the strong sand-discharging ability of Neijiang. When the flow of Minjiang River exceeds 3000m? /s, too much water in Neijiang was blocked by Hutou Rock, and the water potential turned to the Sha Fei weir on the right bank to overflow the outer river, thus ensuring the relative stability of the water level in Neijiang.
Baokou Bottle Mouth is a bottleneck-shaped incision made manually on the rock protruding from the southern end of Lei Yu. It is 80 meters long, 20 meters wide and 40 meters high, which, together with the split pile in the middle of the left Neijiang River, causes local water accumulation and vortex flow. When a flood occurs, too much water flows through the flying sand weir and the miter dike, which plays the role of flood control and flow restriction. Dujiangyan responded to the "changing" Minjiang River with the "unchanged" top-level design, and built a safe and stable breakwater for Chengdu Plain.
Huayang County Records, also known as Huayang County Records, is a work of local chronicles written by Chang Qu of Han Dynasty in the Eastern Jin Dynasty.
"Invariance" and "Change" of Interests
Dujiangyan has an obvious effect on Chengdu Plain. Under the irrigation of Minjiang River, Chengdu Plain developed rapidly. "Historical Records" commented: "Guanzhong left the letter, right Longshu, fertile fields thousands of miles, this so-called Jincheng thousands of miles, the land of abundance is also." The good name of "Land of Abundance" spread like wildfire from now on. , a historian of the Eastern Jin Dynasty, also agrees with this view in Huayang Guozhi: "People follow floods and droughts, and hunger is unknown. When there is no famine, the world is called abundance. "
In the Tang Dynasty, there was a saying that "raising one benefits two". Chen Ziang, a litterateur, said in Military Biography of Shangshu: "The prosperity of Bashu is a treasure of abundance. Funded by the military of Longyou and Hexi, the postal route is given, and all business trips are taken. " By the Southern Song Dynasty, the annual fiscal revenue of Sichuan was 3,342 yuan, accounting for one third of the annual fiscal revenue of the Southern Song Dynasty, which played a decisive role.
Today, Dujiangyan has irrigated 0/0/20 of Sichuan's land, provided 0/4 of its grain production capacity, nurtured 0/3 of its population, and concentrated nearly half of its total economic output. Provide 3 billion m for Chengdu every year? Ecological environment of water supply. More than 800 small hydropower stations have been built in Dujiangyan irrigation area, transporting more than 400,000 cubic meters of timber. Fish ponds produce more than 500,000 Jin of fish and 6.5438+100,000 tons of sand and gravel, which has made extremely important contributions to Sichuan's economic progress and social stability. Dujiangyan, which is "unchanged", got rid of the shackles of time and space and adapted to the needs of the times.
Above _ Full Map of Sichuan in Qing Dynasty
"Invariance" and "Change" of Value
Dujiangyan not only creates economic value, but also has cultural value that cannot be underestimated. Before Qin unified the Central Plains, three major water conservancy projects were built, namely Dujiangyan, Lingqu and Zheng Guoqu. Only Dujiangyan has formed a well-functioning organic whole by using the functions of fish mouth to attract sand, flying sand weir to discharge sand, and bottle mouth to block water, which still plays an irreplaceable role and has not had any negative impact on the environment for more than 2200 years. This is a miracle in itself.
In the sixth year of Ding Yuan in the Western Han Dynasty (BC 165438+ BC 0 1), Sima Qian made a field trip to Dujiangyan and recorded Li Bing's achievements in Historical Records. During the Three Kingdoms period, Zhuge Liang, the prime minister of Shu and Han Dynasties, stressed: "We should take this as the foundation of agriculture and the capital of the country, and levy 2,200 people to protect it." Since then, Jin set up an official order to take charge of weir affairs, Song set up Yongkang Army and weir affairs, and set up water conservancy, so that Dujiangyan was properly maintained and an effective annual maintenance system was produced.
Above _ Kyle Poirot (1254 September 15—1324 June 5438+October 08), born in Kaul La Chu, Croatia, is an Italian traveler and businessman.
During the first year from Yuan Dynasty to Zheng Dynasty, Italian traveler Kelpolo visited Dujiangyan. In his Travels of Kyle Polo, he praised: "The Dujiang River system is very urgent, and there are many fish in Sichuan. There are many ships coming and going, carrying commercial goods and going upstream and downstream. " Dujiangyan has since become famous overseas. In the annual restoration process, people have summed up the principles of "deep scouring beach, low weir" and "cutting corners when encountering bends, and pulling out the heart when encountering the right direction", which have become the golden rule of river regulation. Under the constant irrigation of Dujiangyan, it has nurtured diverse cultural values.
Dujiangyan, surrounded by green mountains and green waters, is not only the perfect integration of ancient engineering technology and management technology, but also the successful practice of the traditional thought of "harmony between man and nature", and is known as "the originator of world water culture". German geographer Richthofen praised "the perfection of Dujiangyan irrigation method is unparalleled in the world". While benefiting Chuanchuan, it has also become the common wealth of mankind all over the world.