The current water level of Danjiang and Hanjiang rivers

The Danjiangkou Project is not only the largest water conservancy project in the Han River Basin, but also a large-scale water conservancy project with "all five benefits" built since the founding of New China. Following the footsteps of the Republic of China, From the beginning of construction in 1958 to the end of the century, it has gone through 41 years of ups and downs, withstood severe tests again and again, and played a great role again and again. This role is irreplaceable by other water conservancy projects. Today, looking at the Danjiang River at the turn of the century, re-understanding and re-evaluating the Danjiangkou Project is of very important strategic significance for us to make good use of this project and play its role. The Han River is one of the largest tributaries of the Yangtze River. It is located to the north of the Yangtze River, with a total length of 1,577 kilometers, a drainage area of ??159,000 square kilometers, and an average annual water flow of 55.4 billion cubic meters. The average annual precipitation in the basin is 800 to 1100 mm, and the precipitation from May to October accounts for about 75% of the whole year. Affected by the southeast monsoon, heavy rains often occur from July to September, which can easily form floods with large peak heights. The middle and lower reaches of the Han River are one of the important grain and cotton bases in Hubei Province, but floods occur frequently. According to records, from 1822 to 1955, the main embankment or main branch embankment breached 68 years ago, about once every two years. Flood prevention and disaster reduction is the primary task of managing the Han River, and the Danjiangkou Water Conservancy Project is the primary project to manage and develop the Han River. The Danjiangkou Dam is located at the junction of the upper and middle reaches of the Han River, controlling 60% of the Han River basin area. The average water inflow into the reservoir over the years is 38.9 billion cubic meters, accounting for 70% of the water volume of the Han River. According to the river basin plan and the construction scale approved in 1958, the dam crest elevation is 175 meters, the reservoir normal storage level is 170 meters, the corresponding storage capacity is 29.05 billion cubic meters, and the flood control storage capacity is 8-11 billion cubic meters. It can relieve the middle and lower reaches of the Han River equivalent to 1935 A once-in-a-century flood disaster. In 1966, with the approval of the State Council, the dam project was constructed in batches and the first phase of the project was completed. The initial dam crest elevation is 162 meters, the normal water storage level is 157 meters, the corresponding storage capacity is 17.45 billion cubic meters, and the flood control storage capacity is 5.6 billion to 7.8 billion cubic meters. Compared with the original approved construction scale, the reservoir storage capacity is reduced, and flood control in the middle and lower reaches is reduced. The standard can only reach a once-in-20-year event, and there are still flaws and deficiencies in preventing severe floods. Therefore, the reservoir flood control dispatch clearly stipulates that the flood limit water level from June 21 to August 20 is 149 meters, and the flood limit water level from September 1 to September 30 is 152.5 meters. From October 1, it is allowed to gradually store up to 157 meters. rice. Judging from the 32 years of operation from when the dam was lowered to impound water in 1967 to 1998, the Danjiangkou Project has played a significant role in five major benefits: flood control, power generation, irrigation, navigation, and breeding. Flood control: 67 floods with a peak flow of more than 10,000 cubic meters per second were blocked, a cumulative reduction of 935,000 hectares of inundated farmland, and a calculated loss reduction of 22.275 billion yuan. Power generation: The cumulative power generation is 102.8 billion kilowatt-hours, with a power generation output value of RMB 8.12 billion. Irrigation: The total water diversion volume is 12.9 billion cubic meters, and the cumulative irrigation area is 1.85 million hectares. Shipping: The total number of dam crossings is 3084. Breeding: The annual fishing volume in the reservoir area has reached more than 10 million kilograms. Among the five major benefits, the flood control benefit is the most significant. From this point of view, the Danjiangkou Project’s public welfare and social benefits are the first. In the summer of 1998, another basin-wide flood occurred in the Yangtze River Basin since the 1954 flood. As the main tributary of the Han River, the average rainfall in the upper reaches was 134.3 mm from July 4 to 16, causing the peak flow into the reservoir on July 11 to reach 14,300 cubic meters per second, with a total flood volume of 4.6 billion cubic meters. After being impounded by the Danjiangkou Reservoir, it was reduced The peak rate is 87%. In August, the average rainfall in the basin above Danjiangkou was 251.7 mm, 1.91 times the multi-year average, and the total water volume entering the reservoir was 11.07 billion cubic meters, 2.3 times the multi-year average. During the month, there were 3 floods with an inflow peak flow of more than 10,000 cubic meters per second at Danjiangkou. The maximum peak flow was 18,300 cubic meters per second. After being impounded by the Danjiangkou Reservoir, the peak flow was reduced by 60% to 93%, and the maximum discharge flow was only 1,780 cubic meters. ~5710 cubic meters per second, and even reduced to 1000 cubic meters per second for 60 hours. In mid-August, there were heavy to heavy rains in the entire Han River Basin. On the 16th, the inflow at Danjiangkou was 18,300 cubic meters per second. Another major flood occurred in the area from Danjiangkou to Zhongyang with a peak flow of 8,000 cubic meters per second. At this time, the sixth flood peak of the Yangtze River is coming, and the water level at Wuhan Pass has reached 28.9 meters. The Han River is blocked from entering the river and cannot be discharged smoothly, causing the water level downstream to rise. The flood control situation is very tense. The operation and operation of the Danjiangkou Reservoir is also in a difficult situation. According to the regulations, the response should be dispatched The discharge volume was increased to free up the reservoir to contain the third flood peak. However, in order to reduce the flood control pressure downstream, the Hanjiang Group Company actively coordinated with the Hubei Provincial Flood Control Headquarters, bravely took the risk, and locked the gates for 96 hours, successfully The peak of the third flood peak of the Han River and the sixth flood peak of the Yangtze River were realized. The Danjiangkou Reservoir was ordered to close its gates and stop flood discharge on August 15. As a result, the reservoir water level reached 154.65 meters on the 19th, exceeding the flood limit water level by 5.65 meters, exceeding the flood storage capacity by 2.7 billion cubic meters, and leaving only 1.7 billion cubic meters of effective storage capacity. This is For the first time, the Danjiangkou Reservoir stored water at extremely high levels during the flood season, shouldering the huge pressure of the dam operating at high water levels.

At that time, the flow rate at Huangzhuang, a control point in the middle and lower reaches, was 9,280 cubic meters per second, and the peak flow rate below Xiantao was 5,320 cubic meters per second. However, some people in Dujiatai Village in the middle and lower reaches of the Han River had already moved and were ready for flood diversion, but Due to the effective regulation of the Danjiangkou Reservoir, flood diversion from Dujiatai was avoided and the safety of the downstream embankment was ensured. The direct economic benefit this time alone reached 943 million yuan. Without the Danjiangkou Reservoir, all the floods in mid-to-late August would be released through the Hanjiang River Channel. With the inflow of about 8,000 cubic meters per second from Danjiangkou to Huangzhuang, the natural flow rate in Huangzhuang would likely reach 25,000 cubic meters per second. According to the Han River flood control plan, when the flow rate in the Huangzhuang section exceeds 21,000 cubic meters per second, flood diversion and storage will be required. At least Xiaojianghu and Dengjia Mining Diversion will cooperate with the flood diversion. This time alone, the flood diversion loss will be about 300 million yuan (according to 1990 year level). The Shayang Xincheng section in the lower reaches will continue to have a stable flow of 18,400 to 19,000 cubic meters per second. In the case of the natural diversion of the Dongjing River at 4,200 cubic meters per second, the mainstream flow in the river section below Zekou is still 14,000 to 15,000 cubic meters per second. second, only 5,000 to 9,000 cubic meters per second of flood water can be safely passed below the Xiantao section. Even under the condition of Dujiatai flood diversion, the peak flood volume of the main stream below Xiantao was still as high as 9,000 cubic meters per second. The highest water level in Hankou at that time was 29.43 meters. At this time, the flood flow from the Han River to the Yangtze River was only 6,300 cubic meters per second. If it continues again Increasing the flow rate by 3,000 cubic meters per second and discharging through the Han River channel will increase the water level of Hankou by 0.3 meters. Then the water level of Hankou may be close to or exceed the highest water level of 29.73 meters in 1954. Let’s not talk about the pressure on the embankments of the main stream of the Han River and the major issues of whether the safety of the embankments can be ensured. The Danjiangkou Reservoir plays a significant role in peak storage and peak-shaving, which has made a major contribution to alleviating the flood pressure in the middle reaches of the Yangtze River, especially in the Wuhan section. It is difficult to express in numbers. During the flood season of 1998, in order to reduce the flood control pressure on the middle and lower reaches of the Han River and Wuhan, the Danjiangkou Conservancy Project blocked floods of more than 7,000 cubic meters per second in the Han River five times. The cumulative flood volume was about 7.5 billion cubic meters, which is equivalent to Hubei Province. The flood inflow capacity of the flood diversion area in Gong'an County is 1.5 times, which shows the important role played by the Danjiangkou Conservancy Project during last year's flood season. Looking at the 32-year history of the Danjiangkou Water Conservancy Project since the lower gate was impounded, the author believes that there are three main obvious characteristics: First, the social benefits of flood control are significant. Since the completion of the Danjiangkou initial project in 1973, a flood control system has been formed in the middle and lower reaches of the Han River, with the Danjiangkou Reservoir as the main body, embankments on both sides of the bank, Dujiatai Flood Diversion Project, and temporary flood storage embankments in the middle and lower reaches. This has initially alleviated the problem of flooding in Wuhan City and the Jianghan Plain. Passive situation seriously threatened by floods. Since its initial project was impounded in 1967, it has intercepted and stored 67 floods with a peak flow of more than 10,000 cubic meters per second, 38 times with a peak reduction rate of more than 50%, and the rest of the flood peaks have also been reduced to varying degrees to avoid Flood diversion for civilian embankments was implemented 10 times, and flood diversion for the Dujiatai project was reduced 17 times. In 1983, a flood that occurred once in about 40 years occurred in the Han River Basin. Through the joint dispatch and operation of the Danjiangkou Reservoir and some flood diversion embankments in the Dujiatai Flood Diversion Area, the safety of the Han River Plain was ensured, and a total of 5.6 million acres of submerged cultivated land was reduced, with nearly 1 million hectares of flooded farmland reduced. people were protected from flooding. In ensuring the safety of the middle and lower reaches of the Han River and Wuhan City, the Danjiangkou Conservancy Project has played a huge role in flood prevention and disaster reduction. The Danjiangkou Water Conservancy Project was once called the reservoir project with the best comprehensive benefits by water conservancy experts. Second, the geographical location is important. The Danjiangkou Hydraulic Hub is located at the confluence of the Hanjiang River and the Danjiang River in northwest Hubei. It is not only an ideal water source for the Central South-to-North Water Diversion Project, but also a control project of the Hanjiang River. It plays a decisive role in flood control in the middle and lower reaches of the Hanjiang River and even in the Yangtze River. Take its dam top elevation of 162 meters as an example. The altitude level is more than 130 meters higher than that of central China, which is equivalent to the height of more than 40-story buildings. For the 13 million people in the middle and lower reaches of the Han River and even the more than 8 million people in Wuhan City, it is like A "basin" of water hanging above the head, once danger occurs, the consequences will be disastrous. Therefore, the author believes that from the perspective of flood control, it is also necessary to improve the Danjiangkou Dam heightening project. Third, the development prospects are broad. The Danjiangkou Reservoir has been considered by many water conservancy experts as an ideal water source for the Middle Line South-to-North Water Diversion. If the dam is raised to its completed elevation of 176.6 meters, not only will the water storage capacity of the reservoir be increased to 30 billion cubic meters, but an average of 150 million cubic meters of water will be transferred to the north over the years. billion cubic meters, and can improve the flood control standards in the middle and lower reaches of the Han River to a once-in-a-hundred-year event. In the long run, the heightening of the Danjiangkou Dam can achieve three benefits: first, it is beneficial to flood control of the Han River, second, it is beneficial to the south-to-north water diversion, and third, it is beneficial to the water diversion of the Yellow River. The Yellow River Basin has frequently dried up in recent years, which has sounded the alarm to people about water shortages. The heightening of the Danjiangkou Dam can realize the desire to divert water from the Han River into the Yellow River, improve the utilization rate of water resources, and solve the problem of the Yellow River's shortage. danger. According to the feasibility study report of the Yangtze River Water Conservancy Commission, the main construction volume of the Danjiangkou Dam heightening is 6.21 million cubic meters of earth and rock excavation and filling, 1.2 million cubic meters of concrete pouring, and 6,000 tons of metal structure installation. According to the survey data in 1992, 220,000 people need to be relocated in the reservoir area, and 235,000 acres of cultivated land will be submerged. The static investment is 7.348 billion yuan based on the 1995 price level, and the construction period is 6 years.

The funds used to complete the Danjiangkou Dam are similar to those used to strengthen the embankments and build civilian embankments in the middle and lower reaches of the Han River. If it is determined to complete the Danjiangkou project first and increase the flood control effect of the reservoir, the embankment defense standards in the middle and lower reaches of the Han River can be based on the 1964-type flood ( Once in 20 years) setting. If the Danjiangkou Project is not completed or is completed after a long time, the embankments and flood diversion and storage facilities in the middle and lower reaches of the Han River will not only be reinforced and raised according to the 1964 flood standards, but also be fortified according to the flood control standards of my country's major rivers. In this way , invest more funds. Therefore, in improving the flood control system in the middle and lower reaches of the Han River, it is most economical and effective to first implement the plan of raising the Danjiangkou Dam. Moreover, the Danjiangkou Dam is also the only large-scale water conservancy project in my country that has not yet been completed.