Sanmenxia Reservoir is the first large-scale reservoir built in in Yellow River in my country, and it is also the backbone reservoir for controlling the silt of the Yellow River. Since its inception, Sanmenxia Reservoir has experienced multiple stages such as water storage and sand blocking, flood detention and sand discharge, and storing and cleaning and discharge of , and is still being optimized.
The sand control model of Sanmenxia Reservoir changes frequently, and the root cause is still the "water-sand relationship" in the middle reaches of the Yellow River. While controlling sand, Sanmenxia Reservoir has also played a significant role. First, it provides sand discharge water for Xiaolangdi Reservoir , and second, it can jointly respond to the Yellow River floods, assist in flood detention and peak reduction, which will help ensure the safe flood flow in the lower reaches of the Yellow River.
Sanmenxia Reservoir: Why are the resources of "fish reservoirs" limited?
Sanmenxia Reservoir is a "old-level" artificial reservoir in my country and is also the pride of the people of Sanmenxia . The reservoir was officially opened to the gate in September 1960. Over the past 62 years, the reservoir area has formed a unique ecosystem and natural environment.
Sanmenxia Reservoir Area includes the main stream section between the Yellow River Longmen- Sanmenxia Dam , and also includes the following Weihe section and Beiluo River below Lintong. The main body of the river dam is 106 meters high, the corresponding elevation of the dam top is 353 meters, and the total designed storage capacity is 34.5 billion m³, which creates a huge water surface for the development of the fishery economy.
However, affected by silt, the biological resources in the Sanmenxia Reservoir area are not as rich as those in the south, and the development of fishery resources is greatly restricted. In 2016, the Henan Academy of Fisheries Science conducted a survey on Fenglingdu, the middle reaches of the reservoir area, and the middle reaches of the reservoir area, and the Lingbao City in the Hubin District in front of the dam. There were only 18 species of fish found, and was less than There are 28 types of reservoir area in Xiaolangdi, and 148 types of in Sanxia Reservoir Area in .
Among them, the catch of meal strips is the most, accounting for as high as 60%, followed by catfish (13.46%), crucian carp (12.54%), and carp (5.82%). Overall, there are not many economic fish species in the Sanmenxia Reservoir area, only a few species such as yellow croaker, silver carp , croaker , grass carp , etc. The rest are all such as snake croaker , croaker Small, low-value fish such as sausage , , sausage , etc.
However, during the period of water and sand diversion, a special "flowing fish" wonder will appear downstream of the dam. Water and sand are adjusted for about 20 days each time. During this period, the amount of silt and sand in the main river of the Yellow River increased sharply. These silt particles are small, which not only adhere to the gills of fish and blocks breathing, but also leads to a decrease in the dissolved oxygen content of and a drastic change in the water environment.
At this time, a large number of indigenous fish such as carp, catfish, bream fell out of the water due to lack of oxygen, and fishermen on both sides of the Taiwan Strait took the opportunity to "wait for the rabbit." For example, in July 2015, when the Sanmenxia Reservoir opened its gates and water was released, the phenomenon of "flowing fish" occurred in the Pinglu River section of Shanxi. Thousands of people were spread across the Yellow River, more than 20 kilometers, and many residents were holding 6 to 7 meters of scribbling nets in hand. The fishing catch ranges from dozens of kilograms to hundreds of kilograms, and the scene is quite spectacular.
Water storage is restricted: the water level does not exceed 318 meters. What are the impacts?
Sanmenxia Reservoir is different from Wanjiazhai Reservoir. Although both are located in the main stream of the Yellow River, the "silt and sand burden" of Sanmenxia Reservoir is obviously greater.
From the geographical location, it can be seen that Sanmenxia Reservoir is located in the lower section of the middle reaches of the Yellow River, , and regulates the largest sediment distribution section of the Yellow River. The reservoir area controls an area of 688,400 square kilometers, accounting for 91.5% of the total basin area. The water volume regulated by it accounts for 89% of the Yellow River water volume, and the amount of silt and sand controlled reaches 98% .
The importance of Sanmenxia Reservoir in the Yellow River's desertification control is self-evident. However, its water storage capacity is also limited, so why?
The main reason is that the high water level of will aggravate the sinking of silt and sand, and the lifting speed of Tongguan elevation will be accelerated. The ultimate threat is the flood control safety of Guanzhong Plain and even Xi'an. Therefore, the water level must be limited in the Sanmenxia Reservoir area.
Time went back to 1960. At that time, the Sanmenxia Reservoir's idea of sand control was mainly "blocking", but the facts proved that this method was not in line with reality, so that the end of the reservoir silt continued to extend. It was not until March 1962 that the application ideas began to change, that is, changed to "sand blocking" to "sand discharge" , and the reservoir gates remained fully open during the flood season, and were vigorously discharged to reduce the amount of silt in silt.
Tongguan elevation change chart
At the same time, Tongguan elevation also ushered in a peak, reaching 327.4 meters in 1969, which was more than 5 meters higher than the original 322 meters. In order to prevent the abnormal increase in Tongguan elevation, the Sanmenxia Reservoir area had to limit the water storage capacity and lower the water storage level. Since 2003, my country has put forward new restrictions on the basis of Sanmenxia's "storage and discharge of muddy": during the non-flood season, the water level in the reservoir area shall not exceed 318 meters.
The water level in the reservoir area does not exceed 318 meters. What impact will it have?
First of all, limiting the water level is conducive to increasing the sand delivery volume and stabilizing the elevation of Tongguan. After 2003, the reservoir area implemented "storage, clearing, and muddy discharge + low water level operation", and open and leaking applications became the mainstream, and Tongguan elevation became stable, which is the biggest benefit of the new operating model.
Secondly, low water level operation also has corresponding disadvantages. During the flood season, the average water level in the Sanmenxia Reservoir area was only 306 meters, and the non-flood season was generally maintained at around 317 meters, which means that the reservoir area could not maintain the ideal storage capacity, and the benefits of water supply, irrigation, etc. were affected.
2020, the water level change chart of Sanmenxia Reservoir
On the other hand, the storage capacity of Xiaolangdi Reservoir is only 1 billion m³, which cannot meet the sand flushing needs, and can only "borrow water and drain sand" from the upstream reservoir. The Sanmenxia Reservoir is the first reservoir upstream. The distance between the two is only 130 kilometers, the sand flushing process is shorter and the kinetic energy is stronger. However, after reducing the water storage capacity, the Sanmenxia Reservoir area can no longer provide sufficient water, resulting in insufficient subsequent sand flushing power in Xiaolangdi Reservoir area and reduced sand flushing efficiency.
In short, maintaining low water level operation has both advantages and disadvantages. However, considering the importance of Tongguan elevation, the control of 318 meters of water level is still the best trade-off based on reality.
After 20 years of water and sand adjustment, how serious is the silt in the reservoir area?
Since 2002, my country has fully formed a comprehensive yellow control plan of "interception, discharge, discharging, adjusting and digging". Among them, water and sand are the main means to erode river silt, and have achieved remarkable results in the past 20 years.
During water and sand adjustment for 20 years, what is the current situation of silt silt in the Sanmenxia Reservoir Area?
The Yellow River Sediment Bulletin shows that in 2020, the silt in the Sanmenxia Reservoir area was both eroded and silted, but was still generally manifested as siltation . From October 2019 to October 2020, the silt volume in the reservoir area was .0271 billion m³; from 1960 to 2020, the cumulative silt volume was 6.3127 billion m³.
The main stream of the Yellow River in 2020 has very complex changes in time and space. From the Sanmenxia to Tongguan River section, the riverbed still has a small amount of siltation, with a siltation volume of .0423 billion m³; in the Xiaobei main stream section, the riverbed mainly manifests as erosion, with a erosion volume of .0267 billion m³. Among the two tributaries of Beiluo River and Wei River in the reservoir area, the overall silt is also manifested as silt, with a total silt of 11 million m³.
At the intersection of the Yellow River and Wei River
In sharp contrast to it, the Xiaolangdi reservoir area downstream is manifested as "the erosion is greater than the siltation", with a total of 60 million m³ erosion in 2020.
Comprehensively with the two major reservoirs, the effect of water and sand diversion is still worthy of recognition, and ecological construction has begun to show results. In the future, with the continuous progress of soil and water conservation work on the Loess Plateau, and the gradual implementation of returning farmland to forests and grasslands, the amount of sediment in the middle reaches of the Yellow River will surely continue to decline, and the prospects for yellowing control are promising.
The future of Sanmenxia Reservoir: Is it expected to play a greater role?
According to the water and sand monitoring data of Tongguan Hydrological Station, the silt and sand transportation volume of the Yellow River has dropped to .24 billion tons of from 2000 to 2019. What is this data concept? You should know that from 1919 to 1960, the average annual sand volume of the Yellow River reached 31.6 billion tons of , which means that in recent decades, the sand volume of the Yellow River has decreased by more than 80% of .
Changes in sand volume in Sanmenxia Reservoir
Many phenomena show that the current Yellow River is becoming clearer and the water quality is also getting better. The contradiction of "less water and more sand" is gradually easing. For example: In early May 2022 and August 2021, a river of "green water" appeared in Hukou Waterfall in the Yellow River. The turbid Yellow River water turned into a thick green, and the change in the water color made people shine.
In the context of the improvement of the ecology and the decrease in the amount of sand coming, the Sanmenxia Reservoir Area is also expected to play a greater role. For example: According to the actual sand conditions, the water level can be appropriately raised to further improve the flood control capacity of the main stream of the Yellow River, and at the same time reduce the hidden dangers of " hanging river " downstream, and improve the flood control standards in the downstream beach areas.
More importantly, the Sanmenxia Reservoir in the future is expected to play a role in actively regulating sand. On the one hand, it is conducive to the expansion of the Yellow River Estuary wetlands, and on the other hand, it is also conducive to restoring its own reservoir capacity and improving the service life of the reservoir. In the future, the Sanmenxia Reservoir will still be responsible for the desertification control of the Yellow River.
