About there being so much sediment in the Yellow River

How many cubic meters of sediment is carried away by the Yellow River every year?

There are many reasons for the frequent flooding of the Yellow River, the most important of which is that a large amount of sediment blocks the river channel, and the water flow is not smooth and the embankment breaks. disaster.

A large amount of sediment has already turned the Yellow River into a watershed between the Haihe River and the Huaihe River. Most watersheds in the world are mountains or high hills, with rivers as watersheds. This is another world wonder of the Yellow River.

The Yellow River today is 6 meters higher than it was 50 years ago, with some being 13.5 meters above the ground. The riverbed in the Zhengzhou section has long been higher than the Zhengzhou "February 7th" Memorial Tower. The altitude of this section of the riverbed is 95 meters to 86 meters, while Beijing's Tiananmen Square is 43 meters above sea level, Tongxian and Daxing are only 12 meters above sea level, and Tianjin is 3 meters above sea level. The northern slope of the Yellow River from Zhengzhou to Kaifeng stretches 600 kilometers from Beijing to Tianjin. Once the floods on the north bank break the embankments, the Beijing and Tianjin areas will not escape misfortune. The situation on the south coast is even more severe. The floods of the Yellow River will plunge thousands of miles with waves tens of meters high. The tragic situation in history of diverting the Huai River into the sea and disorderly flowing the Huai River into the river will reappear today. Tens of millions of lives and hundreds of millions of yuan of property will be destroyed.

The essence of radical control of the Yellow River lies in the radical control of the hanging river and the radical control of sediment. At present, greening mountains and rivers and protecting vegetation are commonly practiced across the country. One of its significance is to reduce soil erosion and reduce the sediment content of rivers. This is the universality of things. There is also particularity within universality. Take the Yellow River as an example. Where is the source of its sediment? Why does this sediment deposit the river channel and raise the river bed? How can all this sediment be discharged from the river mouth?

The first person to theoretically answer these questions was Professor Qian Ning, a sediment expert and Tsinghua University.

Professor Qian Ning was born in Nanjing in 1922. At the age of 25, he went to the United States to study in the Department of Water Resources at the University of Iowa. At the age of 26, he won a scholarship from the University of California and changed his major to sedimentology. Obtained a doctorate from the University of California at the age of 29. His doctoral thesis "Research on the Balanced Sediment Transport Rate of Bedload" has both theoretical value and guiding significance for river sediment transport. Therefore, he was retained as an assistant research engineer and associate research engineer at the Institute of Engineering, mainly engaged in sediment transport. Research work. He returned to his motherland in 1955.

The rivers in the land of China provide him with a place to study sediment; the wandering channel of the Yongding River, the rolling tide of the Qiantang River, the ups and downs of the Yangtze River, and the peculiar posture of the Yellow River hanging in the sky are all like magnets. It attracted him to explore and study a series of sediment problems that had never been solved by predecessors, thus achieving fruitful scientific research results. In this process, he inherited and developed Einstein's theoretical system of sediment movement mechanics, advocated the study of the movement mechanism of high-sediment water flow, and played a pioneering role in the integration of river dynamics and geomorphology and the theoretical discussion of river bed evolution in my country. sexual effect. His representative works "Mechanics of Sediment Movement" and "Evolution of Riverbeds" have very important guiding significance for the sediment management of Chinese rivers.

In 1959, a Tang tomb was excavated during construction on the Huayuankou beach of the Yellow River. Professor Qian Ning, accompanied by colleagues from the Yellow River Commission, came to conduct an on-site inspection. From the excavated foundation pit alone, it was found that We can clearly see the sediment accumulated in various historical periods after the Tang Dynasty. This part of the sediment is much thicker than the sediment on the bed of the Yellow River.

This phenomenon attracted his great attention. After returning to Zhengzhou, he tried to collect drilling data from various sections of the riverbed and found that the sediment deep in the riverbed was thicker than the surface sediment, with most particles larger than 0.05 mm. From then on, people in the industry called it coarse mud. sand. According to hydrological statistics at that time, the amount of such coarse sediment was about 300 million to 400 million tons, accounting for 1/5 of the total sediment volume in the lower reaches of the Yellow River. The main culprit for why the Yellow River has become a hanging river is this coarse sediment.

The fact that these coarse sediments can accumulate on the river bed over time shows that the flow rate of the Yellow River cannot reach the driving force that causes the coarse sediments to flow into the sea. In other words, the fundamental reason why the Yellow River has become a hanging river is not because its flow rate is too large, but on the contrary, because its flow rate is too small. Especially after the flood season, the amount of water inflow is significantly reduced, the river flow rate is too slow, and the intensity of sand flushing is small. Therefore, a large amount of coarse sediment raises the river bed. This important discovery by Professor Qian Ning has produced a major breakthrough and leap forward in understanding and regulating the Yellow River.

It is Professor Qian Ning’s great wish to increase the flow of the Yellow River and increase the intensity of sand flushing. How to increase the flow of the Yellow River was something that was unthinkable at the time. But there is a problem that must be solved as soon as possible: Where does this coarse sediment come from?

In 1965, the Ministry of Water Resources organized an expert group to go to Zhengzhou to assist the Yellow River Water Conservancy Commission in formulating a plan to control the Yellow River. Professor Qian Ning was the head of the data group. Taking this opportunity, he and other experts mobilized more than 20 teachers and students from the Department of Geography of Nanjing University to go to various places in the middle reaches of the Yellow River to investigate the composition of surface materials. At that time, there were no special cars available, so they had to take a bus to the county seat, and then go to the investigation site on two legs to conduct on-site surveys. During this investigation, Professor Qian Ning and several young people first went to Yan'an to inspect Yanshui, then to Suide to inspect Wuding River and Dali River, and then went north to Yulin to inspect Yuxi River. Later, the Luhe River and Jiucheng Reservoir in Jingbian, the Qingshui River in Ningxia, and the Jinghe and Weihe rivers in Shaanxi-Gansu region all left their footprints.

After mastering a large amount of first-hand information, they came to this conclusion by analyzing the sedimentation caused by 103 flood peaks in the lower reaches of the Yellow River in the 19 years since the Sanmenxia Reservoir was built:

In the 430,000 square kilometers of soil erosion area on the Loess Plateau, 80% of the coarse sediment comes from 100,000 square kilometers, of which 50,000 square kilometers account for 50% of the coarse sediment. The 100,000 square kilometers area, that is, the tributary area between Shanxi and Shaanxi, the Baiyushan River source area in a broad sense, and the Liupanshan River source area with fine sediment. These areas should be the focus of soil and water conservation work. This scientific research achievement won the second prize of the National Natural Science Award in 1982.

Under the guidance of this correct theoretical basis, great progress has been made in combating pornography in various places.

Although the sediment content of the Yellow River can be greatly reduced through environmental protection activities such as returning farmland to forests, greening mountains and rivers, afforestation, and protecting vegetation, it is extremely difficult to restore vegetation on the arid Loess Plateau!

There is a folk song that says, "Plant trees in spring, harvest firewood in autumn, and do it again next spring." There are both responsibility issues and natural environment issues here. Changing this harsh natural environment is a long-term governance process. During this long management process, the Yellow River bed is still rising, and the river is at risk of flooding.

Guo Kai was greatly inspired by the scientific research results initiated by Professor Qian Ning. The Shuotian Canal he worked for diverted water from the Qinghai-Tibet Plateau to the Yellow River. One of its purposes was to flush sand into the sea and transform it into a river. The hanging river is an underground river. A paragraph from its feasibility report is copied below:

The critical value of the mud-carrying capacity (scouring and silting) of the lower reaches of the Yellow River is 20 to 25 kg/cubic meter, and the sand content per cubic meter of water is If it is less than 20 kilograms, it will be washed away, and if it is more than 25 kilograms, it will be silted.

Now, the Yellow River contains 37 kilograms of sand per cubic meter, so 400 million tons of sediment are deposited in the river below Zhengzhou every year, forming a suspended river 12 meters above the ground. Its discharge volume into the sea is 32.4 billion cubic meters, and the Shuotian Canal's south-to-north water diversion is 200.6 billion cubic meters, which is enough to ensure that the average annual runoff of the Yellow River is 2,500 cubic meters per second, and the annual discharge volume into the sea is 68 billion to 90 billion cubic meters. The sand content per cubic meter The amount will be reduced to less than 5 kilograms to 10 kilograms, which will ensure that the river channel will no longer be silted, and the flowing water will turn into scouring and strong scouring. In 16 years (if supplemented by a large dredger to stir the river bed, the efficiency will be greatly increased, 8 years will be enough) the river bed can be reduced by 15 to 20 meters, eliminating the hanging river. By then, the Yellow River from Zhengzhou to its mouth will become a flat river with a width of 600 meters to 1,000 meters and a water depth of 10 meters to 13 meters, which can be navigable for large ships of 100,000 tons. After the Yellow River disappeared below Zhengzhou, the river continued to scouring the river. When the river bed was 16 to 18 meters below the ground, that is, it dropped from the current altitude of 95 meters to 76 meters. The relative drop was smaller, the flow rate was slow, and the scouring stopped. , forming a benign state of neither erosion nor siltation. At this point, the Yellow River was truly cured. The discharge capacity of such a river can be as high as 40,000 cubic meters per second, and a flood that occurs once in ten thousand years will not cause disaster.

After such a benign river channel is formed, it will produce many beneficial benefits.

The current lower reaches of the Yellow River are 5 kilometers to 20 kilometers wide, but the future river channel will be only 1 kilometer wide, saving a lot of land in the river beach and flood discharge area;

The current hanging river is leaking It raises groundwater and salinizes much of the land. After turning into underground river channels, these saline-alkali lands immediately turned into fertile farmland;

20 billion tons of sediment accumulated in the river bed entered the sea, accelerating the progress of land reclamation.

With the above three side benefits alone, 20 million acres of fertile farmland can be obtained. This is of particular significance to the densely populated lower reaches of the Yellow River.

The biggest benefit lies in shipping. The current mouth of the Yellow River is only 3 kilometers away from the 10-meter deep sea line. After the benign river channel is formed and the mouth of the Yellow River extends to the deep sea area, siltation at the mouth of the river will stop forever, and the land-creating function of the Yellow River will also end. Because quicksand is swept away by strong ocean currents as soon as it reaches the deep sea, it will not accumulate in rivers or estuaries. This created a deep-water channel. This golden waterway can allow 100,000-ton ships to dock directly in Jinan and Zhengzhou, and 10,000-ton ships to sail to Xi'an. It can also go up to Wanjiazhai and connect to the Shuotian Canal. The prosperity of the Central Plains is just around the corner.