Danjiangkou Project is not only the largest water conservancy project in Hanjiang River Basin, but also a large-scale water conservancy project with "five major benefits" since the founding of New China. With the footsteps of * * * and China, it has gone through the stormy course of 4 1 year from its construction in1year to the end of this century, withstood severe tests again and again, and played a huge role again and again. This function is irreplaceable by other water conservancy projects. Today, it is of great strategic significance for us to look at Danjiangkou project at the turn of the century, re-recognize it and re-evaluate it. Hanjiang River is one of the largest tributaries of the Yangtze River, located in the north of the Yangtze River, with a total length of 1.577 km, a drainage area of 1.59 million square km, and an average annual inflow of 55.4 billion cubic meters. The average annual precipitation in the basin is 800 ~ 1 100 mm, and the precipitation in May ~1October accounts for about 75% of the whole year. Affected by the southeast monsoon, heavy rains often occur from July to September, which is easy to form floods with high peak flow. The middle and lower reaches of Hanjiang River is one of the important grain and cotton bases in Hubei Province, but floods are frequent. According to the data, from 1822 to 1955, the main dike or main branch dike burst for 68 years, that is, about two years. Flood control and disaster reduction is the primary task of harnessing the Han River, and Danjiangkou Water Control Project is the primary project of harnessing and developing the Han River. Danjiangkou Dam is located at the junction of the middle and upper reaches of the Han River, which controls 60% of the area of the Han River basin, with an average annual inflow of 38.9 billion cubic meters, accounting for 70% of the Han River. According to the river basin planning and the construction scale approved in 1958, the dam crest elevation175m, the normal storage level of the reservoir170m, the corresponding storage capacity is 29.05 billion cubic meters, and the flood control storage capacity is 8-1/0.00 billion cubic meters, which can alleviate the equivalent of the middle and lower reaches of the Hanjiang River. Initial scale: dam crest elevation 162m, normal water level 157m, corresponding storage capacity17.45 billion cubic meters, and flood control storage capacity of 5.6 billion to 7.8 billion cubic meters. Compared with the original approved construction scale, the reservoir capacity is reduced, and the flood control standard in the middle and lower reaches can only reach once every 20 years, so there are still defects and deficiencies in preventing catastrophic floods. Therefore, it is clearly stipulated in the reservoir flood control dispatching that the limited water level is 65,438+049 m from June 265,438+0 to August 20, and 65,438+052.5 m from September 65,438+0 to September 30, and it is allowed to be gradually stored to 65,438+0. From the 32-year operation of the dam 1967 to 1998, Danjiangkou project has brought into play five major benefits, including flood control, power generation, irrigation, shipping and aquaculture. Flood control: 67 floods per second with peak flow 1 10,000 cubic meters were intercepted, and the accumulated inundation of cultivated land was reduced by 935,000 hectares and the loss was reduced by 22.275 billion yuan. Power generation: cumulative power generation102.8 billion kwh, and power generation output value of 8 120 billion RMB. Irrigation: the total water diversion is 654.38+0.29 billion cubic meters, and the accumulated irrigation area is 654.38+0.85 million hectares. Shipping: the cumulative number of dam crossings is 3084. Breeding: The annual fishing capacity of the reservoir area reaches100000 kg or more. Among the five benefits, flood control benefits are the most significant. From this perspective, the public welfare and social benefits of Danjiangkou project are the first. In the summer of 1998, another basin flood occurred in the Yangtze River basin after 1954 flood. As the main tributary of the Han River, the average rainfall in the upper reaches from July 4th to June 6th was 134.3mm, which led to the peak flow of +0 1 day on July 4th reaching 14300 m3/s, and the total flood volume was 4.6 billion m3, which was impounded by Danjiangkou Reservoir, and the peak clipping rate was 87%. In August, the average rainfall in the watershed above Danjiangkou was 25 1.7mm, which was 1.9 1 times of the multi-year average, and the total inflow was 1 1.07 billion cubic meters, which was 2.3 times of the multi-year average. During the month, the flood of Danjiangkou Reservoir with the peak flow exceeding 10000 m3/s was counted for three times, with the maximum peak flow of 18300 m3/s, the peak was cut by 60% ~ 93%, and the maximum discharge was only 1780 ~ 57 10 m3/s, or even some. In mid-August, the whole Hanjiang River basin was flooded with heavy rain. On June 65, 438+06, the inflow of Danjiangkou was18300m3/s, and another flood with a peak flow of 8000m3/s occurred between Danjiangkou and Zhongyang. At this time, the sixth flood peak of the Yangtze River came, and the water level of Wuhan Pass was as high as 28.9 meters. The Hanjiang River was blocked from entering the river, which caused the downstream water level to rise and the flood control situation was very tense. Danjiangkou reservoir is also in a difficult situation. According to the regulations, it is necessary to increase the discharge to make room for the storage and discharge of the third flood peak. However, in order to reduce the pressure of downstream flood control, Hanjiang Group actively coordinated with Hubei Flood Control Headquarters, bravely took risks and locked the floodgates for 96 hours. Danjiangkou Reservoir was ordered to close the gate and stop flood discharge on August 15, resulting in the reservoir water reaching154.65m on August 19, the flood limit water level was 5.65m, the flood was 2.7 billion cubic meters, and the effective storage capacity was only1700 million cubic meters. This is the first time that Danjiangkou Reservoir has greatly exceeded the storage in flood season, which has put tremendous pressure on the high water level operation of the dam. At that time, the flow of Huang Zhuang at the control point in the middle and lower reaches was 9280 cubic meters per second, and the flood peak flow below Xiantao was 5320 cubic meters per second. However, some people in the Dujiatai levee in the middle and lower reaches of the Han River have moved to prepare for flood diversion. However, due to the effective operation of Danjiangkou Reservoir, Dujiatai flood diversion was avoided and the safety of the downstream main dike was ensured. The direct economic benefit reached 943 million yuan this time. Without Danjiangkou Reservoir, all the floods in August will be discharged through the Hanjiang River in the middle and late period, and with the inflow of about 8,000 cubic meters per second from Danjiangkou to Huang Zhuang, the natural flow of Huang Zhuang will probably reach 25,000 cubic meters per second. According to the flood control plan of Hanjiang River, when the flow of Huang Zhuang reaches more than 2 1 1,000 cubic meters per second, the People's Embankment is needed to hold back the flood, at least in Xiaojiang and Deng Jiamin. There will be a steady flow of 1.84 million ~ 1.9 million cubic meters per second in the downstream Shayang Xincheng reach. In the case that the Dongjing River naturally diverts 4200 cubic meters per second, the mainstream of the river below Zekou is still 14000 ~ 15000 cubic meters per second, and only 5000 ~ 9000 cubic meters of flood water per second can pass safely in the river below Xiantao. Even in the case of Dujiatai flood diversion, the flood peak of the main stream below Xiantao was as high as 9000 cubic meters per second, while the highest water level in Hankou was 29.43 meters at that time. At this time, the flood from the Han River into the Yangtze River is only 6300 cubic meters per second. If the flow rate of 3000 cubic meters per second is increased and discharged through the Hanjiang River, the Hankou water level will rise by 0.3 meters, and the Hankou water level may approach or exceed the highest water level of 29.73 meters 1.954. We don't talk about the pressure of embankments in the main stream of the Han River, and we don't talk about whether the safety of embankments can be guaranteed. Just because Danjiangkou reservoir plays an important role in storing and cutting peaks, it is difficult to express its great contribution to alleviating the flood pressure in the middle reaches of the Yangtze River, especially in Wuhan. During the flood season of 1998, Danjiangkou Water Control Project held more than 7,000 cubic meters of flood water per second for five times, with a total amount of about 7.5 billion cubic meters, equivalent to 1.5 times the flood inflow capacity of the flood storage area in Gongan County, Hubei Province. This shows that Danjiangkou water conservancy project played an important role in the flood season last year. Throughout the 32-year history of Danjiangkou Water Control Project since its impoundment, the author thinks that there are three obvious characteristics: First, the social benefits of flood control are remarkable. 1973 since the completion of the initial Danjiangkou project, a flood control system has been formed in the middle and lower reaches of the Han River, which is composed of Danjiangkou Reservoir as the main body, dikes on both sides of the river, Dujiatai flood diversion project and temporary flood storage and detention dikes in the middle and lower reaches, initially alleviating the passive situation that Wuhan City and Jianghan Plain are seriously threatened by floods. Since the initial impoundment of 1967, * * * has intercepted 67 floods with peak flow greater than 10000 cubic meters per second, 38 floods with peak clipping rate exceeding 50%, and other flood peaks have also been reduced to varying degrees, avoiding the artificial flood diversion of 10 and reducing the flood diversion of Dujiatai Project by 65433. During 1983, the Hanjiang River Basin was flooded once every 40 years. After the joint operation of Danjiangkou Reservoir and Dujiatai flood diversion area, the safety of Hanjiang Plain was ensured, the flooded farmland was reduced by 5.6 million mu, and nearly one million people were spared from the flood. Danjiangkou water conservancy project has played a great role in flood control and disaster reduction in ensuring the safety of the middle and lower reaches of the Han River and Wuhan City. Danjiangkou water control project was once called the reservoir project with the best comprehensive benefit by water conservancy experts. Second, geographical location is important. Danjiangkou water control project is located at the intersection of Hanjiang River and Danjiangkou in the northwest of Hubei Province. It is not only an ideal water source for the Middle Route of South-to-North Water Transfer Project, but also a control project of the Han River, which plays an important role in flood control in the middle and lower reaches of the Han River and even the Yangtze River. Taking its crest elevation of 162m as an example, its altitude is more than 130m higher than that of Central China, which is equivalent to the height of a 40-story building. For the middle and lower reaches of the Han River 13m people and even more than 8 million people in Wuhan, it is like a basin of water hanging overhead. Once danger occurs, the consequences are unimaginable. Therefore, from the perspective of flood control, it is also necessary to improve the Danjiangkou dam heightening project. Third, the development prospects are broad. Danjiangkou Reservoir was once considered by many water conservancy experts as the ideal water source for the Middle Route Project of South-to-North Water Transfer. If the dam is raised to the completion elevation of176.6m, not only will the reservoir capacity increase to 30 billion cubic meters, but the average water transfer from the north for many years will be1500 million cubic meters, and the flood control standard in the middle and lower reaches of the Hanjiang River will be raised to once in a hundred years. In the long run, the heightening of Danjiangkou dam can achieve three benefits: first, it is beneficial to the flood control of Hanjiang River, second, it is beneficial to the South-to-North Water Transfer Project, and third, it is beneficial to the Yellow River Water Transfer Project. In recent years, the frequent interruption of the Yellow River basin has sounded the alarm for the shortage of water resources, and the heightening of Danjiangkou dam can realize the desire of diverting Han River into the Yellow River, improve the utilization rate of water resources and solve the danger of the interruption of the Yellow River. According to the feasibility study report of the Yangtze River Water Conservancy Commission, the main works for heightening Danjiangkou Dam are earthwork excavation of 62 1 10,000 cubic meters, concrete pouring10.2 million cubic meters, and metal structure installation of 6,000 tons. According to the investigation data of 1992, 220,000 people need to be relocated in the reservoir area, and 235,000 mu of cultivated land is flooded. According to the price level of 1995, the static investment is 7.348 billion yuan, and the construction period is 6 years. The funds used to complete Danjiangkou Dam are similar to those used for dike reinforcement and civil dike construction in the middle and lower reaches of Hanjiang River. If the Danjiangkou project is determined to be completed first and the flood regulation function of the reservoir is enhanced, the dike fortification standard in the middle and lower reaches of the Hanjiang River can be set according to the flood type of 1964 (once every 20 years). If the Danjiangkou project is not completed or completed for a long time, the dikes and flood storage facilities in the middle and lower reaches of the Han River should not only be reinforced and heightened according to the flood standard of 1964, but also be fortified according to the flood control standard of major rivers in China, so more funds will be invested. Therefore, in improving the flood control system in the middle and lower reaches of the Han River, it is the most economical and effective to implement the heightening scheme of Danjiangkou Dam first, and Danjiangkou Dam is also the only large-scale water conservancy project in China that has not yet been completed.