What is the concept of 2 billion tons of silt?
If 2 billion tonnes of silt were to be spread on a football field, it would be about 400 stories high.
If you change it to weight, it is about the same as the total weight of 10 million ordinary cars.
And this is the dilemma that the Three Gorges Dam is facing now.
According to the Ministry of Water Resources, in the 17 years from 2006 to 2023, the cumulative silt in the Three Gorges Reservoir area has reached 2.08 billion tons.
If left unchecked, the silt will accumulate more and more until the Three Gorges Reservoir is affected and its water storage capacity is seriously affected.
At that time, the Three Gorges Dam will face the same fate as the Sanmenxia Dam, millions of people in the lower reaches of the Yangtze River will be affected, shipping on the Yangtze River will be cut in half, and the lower reaches of the Yangtze River will face the threat of flooding.
Fortunately, the silt problem was taken into account long before the dam was built.
Why is so much silt accumulating?
Although the Yangtze River does not have much sediment compared to the Yellow River, its runoff far exceeds that of the Yellow River, so it carries a lot of sediment every year.
As we all know, the Yellow River flows through the Loess Plateau and has always been the hardest hit area of soil erosion, and the downstream river channel is tens of meters above the ground for a period of time.
Ancient Chinese books record that "the Yellow River fights water, and mud dwells in its seventh". In modern times, the Yellow River has carried an average of 1.6 billion tons of sediment into the sea every year, with an average of 35 kilograms of sediment per cubic meter of water.
Long before the construction of the Three Gorges Dam, many people recognized this, the most famous of which was a water conservancy expert named Huang Wanli.
This expert has clearly pointed out that the main stream above the Three Gorges belongs to the section of the river with reduced slopes, and a large amount of pebbles and sediment have accumulated in the river. Before the dam is built, the sediment flows out into the sea along the Yangtze River.
In addition, although the upper reaches of the Yangtze River are not like the Yellow River, where soil erosion is serious, some areas have been deforested and reclaimed for steep slopes.
When the rainy season comes, it is easy for this part of the land to slide into the river with heavy rains.
In the past, the Yangtze River, which has a huge flow, was able to wash this part of the sediment into the sea, and even if there was some residue, it would not have much impact.
But the Three Gorges Project changed all that.
The originally unobstructed river channel was cut off by the middle barrage, forming a reservoir, and the sediment that had been impacted from the upstream had nowhere to go, so it had to accumulate here.
According to statistics, since the completion of the Three Gorges Dam, more than 2.7 billion tons of sediment have accumulated in the reservoir, and only 630 million tons have left the Three Gorges Reservoir area, and more than 2 billion tons of sediment remain.
This silt is undoubtedly a major challenge for the Three Gorges Reservoir area.
Dredging challenges
In fact, as the longest demonstration project, these issues must have been taken into account before the construction of the project began.
As for the problem of silt, the Three Gorges Dam mainly relies on "storage and drainage" to deal with it.
To put it simply, during the flood season, the flood peak, which carries a large amount of sediment, is released downstream to reduce silt.
After the flood season, the water is accumulating and waiting for the next sand discharge.
In the 18 years since its completion, the Three Gorges Reservoir area has been rescued and cleared many times, during which the total amount of sediment discharged has reached more than 500 million tons, which has greatly alleviated the silt situation of the reservoir.
Based on scientific principles, the engineers hypothesized that the sediment in the water flow would form a uniform slope at the bottom of the reservoir, so that the sediment would naturally move downstream with the flow during drainage.
In addition, in the main part of the dam, a large number of sand discharge holes, sluice gates and other devices have been built, which will create a strong flow of water and discharge the sediment when the water level is right.
In addition to this, before the construction of the Three Gorges, a number of dams were built upstream, which intercepted a large part of the silt, and the results of soil and water management along the route are gradually emerging, and the sediment upstream will only become less and less.
In 2023, only 200 million tons of sediment will be accumulated in a year, which is a cliff-like decline compared to previous years.
However, this sediment is not randomly arranged.
Excessive discharge will lead to the destruction of the downstream ecological environment and affect the reproduction of aquatic animals.
Therefore, the specific arrangement should be decided according to the actual situation.
It is estimated that the Three Gorges Reservoir receives more than 500 million tons of sediment every year, and theoretically speaking, in the 18 years since its completion, the cumulative savings should exceed 9 billion tons.
But no.
According to the Ministry of Water Resources, by the end of 2023, a total of 2.02 billion tonnes of silt had been accumulated, much lower than initially forecasted.
It can be said that the original design of the project was very effective, and the silt problem did not affect the Three Gorges Dam at all.
The project of the century - the Three Gorges Dam
If there is any project that can be called the project of the century, then the Three Gorges Dam can definitely be among them.
In 1994, the construction of the Three Gorges Dam officially began, and before that, the Three Gorges Dam had undergone 40 years of demonstration, a time that is unique even in the world.
The construction period lasted 12 years and the investment was as high as 250 billion yuan, and it was not until 2006 that the Three Gorges Dam was fully completed.
Before the construction, many people questioned whether the project could return to its original cost, whether it would cost so much, and it was basically useless in the end.
In fact, for this problem, it can only be said that it is absolutely back to basics.
In terms of shipping alone, before the construction of the Three Gorges Dam, the navigable capacity of the waterway from Chongqing to Shanghai was only 10 million tons, but after the completion of the project, it increased to 50 million tons.
This alone has indirectly provided more than 30 billion benefits for the shipping industry.
Looking at the tourism industry again, the Three Gorges Dam was rated as a 5A scenic spot in 07, received more than 3.2 million tourists in 2023, and has a cumulative income of more than 60 billion since its completion.
And these are not the main purposes of the construction of the Three Gorges Dam, the main function of the Three Gorges Dam is to generate electricity, and power generation has been in operation since 03.
According to reports, the daily power generation capacity in 2020 was close to 400 million kilowatt hours, and in 2018, the Three Gorges Power Station produced a total of 100 billion kilowatt hours of electricity.
Since its completion, this alone has provided more than 100 billion yuan of income for the mainland, not to mention the industrial production of several provinces that have benefited from it.
With such a high rate of return, the Three Gorges Dam can truly be called a project of the century that absolutely benefits the country and the people.
Moreover, the Three Gorges Dam has only been built for 18 years, and its design life has reached 150 years, and because of its special structure, although it has a design life, it can be said that it is almost infinite.
epilogue
Today, the Three Gorges Dam has accumulated more than 2 billion tons of silt, but this will not affect the stability of the Three Gorges Dam, and with the gradual passage of time, the amount of new silt added each year decreases, and the capacity to discharge silt gradually increases, and this silt will only become less and less.
So, there's no need to worry about something that almost never goes wrong.
So what do you think about this? Welcome to leave a message to discuss......
Source: Ministry of Water Resources of China 2024-05-21 2023 China River Sediment Bulletin
Source: China Sand and Gravel Association 2024-03-07"In-depth Study|Can More Than 2 Billion Tons of Sediment Accumulated in the Three Gorges Reservoir Be Used? How to use it? 》
Source: Hubei Daily 2024-06-02 "3.93 million cubic meters of sediment scoured and the desilting and desilting dispatch at the tail of the Three Gorges Reservoir was successfully completed"
Source: Gezhouba, China 2020-11-01 "Historic Moment! The Three Gorges Project has been completed and accepted》
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