The bed-building water disappears and the river "becomes thinner"
Inner Mongolia section of the Yellow River is located in the middle and upper reaches of the Yellow River, with a total length of more than 890 kilometers, accounting for one fifth of the total length of the middle and upper reaches of the Yellow River. For thousands of years, the Yellow River has bred the grassland coal city Wuhai, grassland steel city Baotou, Hetao plain and Tumochuan plain with its mother's milk-like river water, and it is known as "the Yellow River is harmful but only rich".
However, since the 1990s, the natural inflow of the Yellow River has decreased, and the Longyangxia and Liujiaxia reservoirs in the upper reaches have been jointly operated, resulting in the leveling of the flood peak of the Yellow River, the disappearance of bed-making flow and the "slimming" of the river course.
According to the statistics of the Yellow River Water Conservancy Commission, the average annual runoff of the Yellow River is 58 billion cubic meters, but since the 1990s, the average annual natural runoff has dropped to 45 billion cubic meters, a decrease of 65.438+0.3 billion cubic meters.
In addition, a large number of reservoirs and dams have been built in the upper reaches of the Yellow River, which has had a certain impact on the runoff law of the Yellow River. Under the premise of constant precipitation, the runoff has decreased. Especially after Longyangxia and Liujiaxia Reservoirs were put into storage, the upstream inflow decreased obviously.
Martin Zhang, director of the flood control office in Bayannaoer City, Inner Mongolia, said that at present, the river width in Inner Mongolia has shrunk from an average of1.500m more than a decade ago to about 500m. In the past, the Yellow River could pass through floods at a flow rate of 3,000 cubic meters to 4,000 cubic meters per second. Now, when the flood reaches 700 cubic meters per second, it will leave the river and go to the beach
Sediment deposition is aggravated, and the river becomes "thick"
The Yellow River is a river with high sediment concentration. In the past, these sediments mainly relied on large-flow floods in flood season to achieve the balance of erosion and deposition. Wang Zhenyu, deputy director of the Flood Control Office of the Yellow River Committee, said that before 1986, the Inner Mongolia section of the Yellow River was in a state of erosion and siltation, and the sand was washed away as soon as the flood came. At present, the base flow in the upper reaches of the flood season is reduced, the big flood has become a small flood, the middle flood has disappeared, and the flood peak has been leveled. The river does not have such a large sediment carrying capacity, which leads to an increase in sediment deposition.
The reporter scooped up a glass of water in Dalat Banner District, Ordos City, Inner Mongolia. After one hour, the deposited sediment is half a cup. People from the local flood control office told reporters that more than a decade ago, the sediment in a cup of Yellow River water was only about one third. Zhang Wuzhong of Inner Mongolia Hydrological Bureau Station said: "Every year, more than 1.286 and 5438+0.400 tons of sediment enter the Yellow River in Inner Mongolia, which mainly comes from the top ten holes on the south bank. According to monitoring, all the sediments in the first ten holes were deposited in the middle reaches of Inner Mongolia. "
The top ten hole piles refer to the top ten seasonal mountain torrents distributed in Ordos Plateau in Inner Mongolia section of the Yellow River. According to the data, in the past 30 years, only the sand dam formed by ten big holes in the central and western regions of Liugou blocked the main stream of the Yellow River seven times. Due to the intensification of sediment deposition in Inner Mongolia section of the Yellow River, the river channel is blocked, the storage capacity of the water control project is reduced, and the water and sediment regulation capacity is lost. Wang Jijun, director of the Yellow River Water Conservancy Bureau in Inner Mongolia, told the reporter: "The original design storage capacity of the Yellow River three sheng public water conservancy project is about 400 million cubic meters, and now more than half of it has been silted up, leaving only about1.400 million cubic meters."
There is a trend of "secondary suspended river" in the upper reaches of the Yellow River.
With the aggravation of sediment deposition, the riverbed of Inner Mongolia section of the Yellow River rises rapidly, forming a "suspended river on the ground" in just over ten years. According to the monitoring of hydrological stations along the Yellow River, in recent ten years, the average elevation in Inner Mongolia has reached about 3 cm, and the local reach has reached more than 2 meters.
Referring to the Yellow River today, Wang, deputy director of the Municipal Flood Control Office who lives in Linhe District of Bayannaoer City, is worried: "Now the riverbed of the Yellow River has been' suspended' on the roof of my house. It is a bit mysterious to say that "the water of the Yellow River moves to heaven", but it is not an exaggeration to say that "the water room of the Yellow River goes upstream". If this levee collapses, you can't hide from standing on the roof. "
Some experts from the Yellow River Committee pointed out that due to the continuous siltation and elevation of the inner Mongolia section of the Yellow River, some sections of the Yellow River have a tendency to develop into "secondary suspended rivers". The so-called "second-class suspended river" is the river type of "the river is higher than the beach, and the beach is higher than the bottom of the river". Even if there is a small or medium flood, the main channel is difficult to accommodate, which will inevitably lead to major river regime changes, and it is easy to appear cross rivers and oblique rivers, increasing the risk of breach.
Experts believe that the Inner Mongolia section of the Yellow River has reached the point where it must be controlled, and the best way to control the "suspended river on the ground" is to adjust water and sediment. However, if we want to realize the water and sediment regulation of the whole Yellow River, we still face many problems. In addition to the contradiction between water resources and power generation, Ningxia and Inner Mongolia also have great demand for agricultural water. If the Yellow River water is used to wash the river, it may reduce the agricultural water consumption. In addition, the Yellow River needs to build at least seven water control projects to regulate water and sediment in the main stream, but now there are only four in the Yellow River, and three more need to be built.