The Yellow River hangs again

The Yellow River, which has given birth to Chinese civilization and sons and daughters, is the "mother river" of the Chinese nation.

The Yellow River originates from the Bayan Kara Mountains on the Qinghai-Tibet Plateau and flows from west to east through nine provinces (autonomous regions) of Qinghai, Sichuan, Gansu, Ningxia, Inner Mongolia, Shaanxi, Shanxi, Henan and Shandong, and finally flows into the Bohai Sea. Heyuan to Hekou Town in Inner Mongolia Autonomous region in the upper reaches, Taohuayu in Henan Province in the middle reaches, and Taohuayu to the estuary in the lower reaches, showing a "few" distribution as a whole.

Li Bai, a poet of the Tang Dynasty, once described, "Don't you see that the water of the Yellow River comes from the sky, and the waves rush to the East China Sea and never look back?" Liu Yuxi described it as "thousands of miles of twists and turns of the Yellow River carrying silt, the waves rolling like a huge wind from the end of the world." We can see the characteristics of the Yellow River:

It is recommended to watch horizontally.

Haohukou Waterfall

First, there is more sand. Regardless of the annual sediment transport or the average sediment concentration, the Yellow River ranks first among the rivers in the world. The average annual sediment is 1.6 billion tons, which is piled into embankments 1 meter high and 1 meter wide, with a length of 27 circles around the equator, and an average sediment content of 35 kilograms per cubic meter, which is equivalent to 35 kilograms of sediment in one ton of water in the Yellow River.

Second, there are many bays and changeable flow directions, resulting in a large number of bays and loops.

Third, the combination of the new and the old, the downstream river after diversion, its formation time is only hundreds of years or even decades.

Fifth, the drop in the water surface is large, with a drop of 4480 meters from the source to the estuary.

Xiaolangdi flood discharge and sediment discharge

The sediment content of the Yellow River is large, according to statistics, about 89.1% comes from the "sandy and coarse sand area" in the middle reaches (1.182 billion tons), while in the lower reaches, due to the construction of embankments and other water conservancy projects, the river becomes narrower, and a large amount of sediment with a particle size greater than 0.05mm is deposited on the riverbed, causing the riverbed to rise, causing the river course 800km below Huayuankou to become a "overhanging river", also known as "first-class suspended river".

In the 1960s, with the construction of the water control project in the upper and middle reaches of the Yellow River, the number of major floods in the lower reaches decreased, and the sediment deposition in medium and small floods and low water periods mainly occurred on the main channel and Nentan. As a result, the bottom of the main channel from Dongbatou to Taochengpu in the lower reaches is higher than the beaches on both sides, forming a "secondary suspended river", and the Yellow River becomes a suspended river.

Schematic diagram of "overhanging river"

The reason for the formation of the "overhanging river" of the Yellow River is mainly affected by climate change and human activities.

About 5000 years ago, the climate of the Yellow River basin was warm and humid, the precipitation was abundant, and the vegetation was relatively lush. At that time, human beings were in the primitive era, the population was sparse, and the production tools used were very simple. The Loess Plateau is basically in a state of natural erosion.

From about after the Shang and Zhou dynasties to before the warring States period, the human economic activities in the Yellow River basin increased significantly, and the population gradually densed, but the productivity was still low, the climate was humid, the precipitation was more, and the forest and grass was more luxuriant. At that time, there was not only one channel in the lower reaches of the Yellow River, but wandered in the plain, forming multiple channels, so it was called "Nine Rivers". During this period, the riverbed silted slowly and the crevasse was not diverted much.

After the warring States period, due to the development of productive forces, people began to plant a large area of agriculture on the Loess Plateau, which changed the microclimate environment in the middle reaches of the Yellow River and made the vast area of the Loess Plateau dry. As a result, the surface of the Loess Plateau is fragmented and ravines are vertical and horizontal, which greatly accelerates the soil and water loss on the Loess Plateau. At the same time, large-scale dikes were built, and the flood of the Yellow River was classified into a fixed channel, forming a vast beach to detain the flood and settle sand, a large amount of sediment was concentrated between the levees on both sides of the strait year after year, and the riverbed continued to rise.

Night view of Li Yang

By the end of the Western Han Dynasty around 6 BC, it has been recorded that the riverbed near Liyang (now Junxian County, Henan Province) has been higher than the residential houses, forming a veritable "first-class suspended river".

The reasons for the formation of the "secondary suspended river" are mainly the following three aspects: first, the water and sediment conditions have changed significantly, the flood peak frequency and flood peak discharge have been significantly reduced, the bed-making effect of flood has been weakened, and the river plane and cross-section scale have been reduced. as a result, the siltation of the river is limited to the small and medium-sized main channel, and the main channel and tender beach have been silting all the time. Second, the boundary conditions of the river bed have changed greatly, and the construction of a large number of river regulation projects has made the main channel of the lower reaches relatively stable, creating a relatively stable place for sediment deposition. Third, the construction of the production dike in the beach area further narrows the flood discharge channel. When the great flood overflows the production embankment, the siltation thickness decreases gradually with the distance between the beach and the channel, which aggravates the channel shape with the beach lip high and the dike root low-lying.

After the Yellow River became a "suspended river on the ground", crevices and diversion occurred frequently. According to records, during the 2540 years from the pre-Qin period to the Republic of China (602-1938 BC), the Yellow River broke its mouth more than 1590 times and changed its course 26 times, including 9 major ones. There is a common saying that "two breaches in three years and one change in a hundred years" makes the people on both sides of the Yellow River miserable, and the safety problems in the lower reaches of the Yellow River are mainly caused by the continuous rise of the riverbed.

The Hebei-Shandong-Henan Yellow River Water Conservancy Commission was established (Director Wang Huayun on the right in the front row

Second platoon, right one, Academician Qian Zhengying)

In 1964, according to the experience gained in the application of Sanmenxia Reservoir, the strategy of controlling the Yellow River was adjusted to "upper stop and lower discharge". In 1975, a severe flood occurred in the Huaihe River, causing heavy casualties. Similar problems also occurred in the process of preventing and controlling the Yellow River, and the strategy for controlling the Yellow River was adjusted to "upper and lower drainage, separate stagnation on both sides".

Since the 1980s, with the improvement of the level of science and technology, the idea of sediment control has been constantly improved. finally, it has formed the contemporary strategy of "stopping, draining, regulating, releasing and digging" to control the Yellow River. "blocking" mainly refers to the