Yellow River is a famous sandy river in my country. It has less water and more sand aggravates silt, and the middle and lower rivers have formed "Hanging river on the ground ". In order to reduce the silt rate of silt, my country has built Xiaolangdi Reservoir in the last canyon in the middle reaches of the Yellow River. Through the reservoir, water and sand are adjusted to reshape the water and sand relationship, and the ecology of the Yellow River has undergone significant improvements.
In October 1999, Xiaolangdi Reservoir was lowered to store water, and silt silt occurred in the reservoir area that year; in 2002, my country conducted a water and sand diversion test in the Yellow River for the first time, with the goal of flushing sand and reducing silt, increasing the operating years of the reservoir, and providing conditions for the benefits of water supply, irrigation, power generation, etc.
After 20 years of verification, the Yellow River's water and sand diversion are undoubtedly successful: with Xiaolangdi Reservoir as the core, the discharge and silt reduction exceed expectations, the main trough of the downstream river channel is stable, and the Yellow River Estuary wetland has also become a paradise of life.
Xiaolangdi Reservoir: The reservoir’s silt reduction exceeded expectations, how important is the sand discharge effect?
After Sanmenxia Reservoir , Xiaolangdi Reservoir is highly expected because of its huge storage capacity. Water conservancy experts regard it as a backbone project for the management of the Yellow River. According to the plan, Xiaolangdi Reservoir is designed according to the flood frequency of ,000-year , and the flood check of once in 70,000 years , with a total storage capacity of 12.65 billion m³ , of which: the reserved storage capacity of silt is 7.55 billion m³ , and the long-term effective storage capacity of 5.1 billion m³ .
It is not difficult to see that the silt storage capacity accounts for a larger proportion, which is also a special design made in combination with the current silt and sand of the Yellow River. According to the analysis of water conservancy experts, Xiaolangdi Reservoir can eventually intercept 10 billion tons of silt, reducing the silt of 7.8 billion tons of for at least the downstream river channel. Through intelligent scheduling, the actual role of the reservoir far exceeds the initial setting of "reducing silt".
In fact, water and sand adjustment have begun to show results after 4 years of operation. Judging from the silt and silt situation of the silt, Xiaolangdi Reservoir does not simply reduce silt, but also washes downstream riverbeds, avoiding the flooding of small and medium-sized floods on the beach area. According to the hydrological monitoring results, in 2006, the minimum flat-slope flow in the lower reaches of the Yellow River has increased from the original 1800m³/s to 3500m³/s, which means that the main trough of the river channel is improved and the overflow capacity is enhanced.
What is even more rare is that the role of Xiaolangdi Reservoir is not limited to the "early stage" and is still effective today. As of 2021, the Yellow River has operated more than 20 times of water and sand diversion, and the disaster reduction benefits have become more and more obvious. The downstream main trough has basically achieved the full scrubbing of on all line, the flatbed flow has increased to 4480m³/s, and the average elevation of the riverbed has dropped by 2.6m. These data show that the risk of "secondary hanging rivers" not only no longer increases, but has decreased, and the probability of occurrence of "homogenous rivers" and "slanted rivers" has been significantly reduced.
Overall, Xiaolangdi Reservoir is a comprehensive reservoir that benefits the country and the people, and its contribution is of great significance. The flood control capacity in the lower reaches of the Yellow River has been enhanced, the probability of small and medium-sized flood flooding has decreased, the area of delta wetlands has increased, and the ecology of mudflats has improved. These are all benefits brought by water and sand diversion.
Of course, the sand regulation method in the future will continue to improve, taking into account water storage and sand discharge and ecological protection. "People's control of yellow yellow" will also be "scientific control of yellow yellow" and "ecological control of yellow yellow".
water and sand have been adjusted for 20 years. How much silt is the reservoir area?
I believe everyone is very curious: Xiaolangdi Reservoir has outstanding sand discharge benefits, is there still silt in the reservoir area? After 20 years of water and sand diversion, how much silt is there in the reservoir area?
First of all, the silt content in the middle reaches of the Yellow River is relatively high. Xiaolangdi reservoir area has more than 10 tributaries including Dayu River, Guangshui River, and Boqing River. The valley width ranges from 500 to 1000m. The reservoir area has a narrow and long curved shape, and silt silt is inevitable. Especially during the water storage period, the sand discharge holes of the hub dam are closed, the water flow slows down, and the silt and sand are all under, and the silt effect is the most obvious at this time.
However, after water and sand adjustment, sand silt-silt discharge can basically achieve dynamic balance. In some years, the amount of sand discharge is more than the amount of sand silt, resulting in a net erosion. However, in most years, the discharge ratio is less than 100%, and water and sand can not completely discharge the silted silt sand. Therefore, the total amount of silt shows a trend of slowly increasing.
According to reports from Sun Dongpo and other scholars, from 2002 to 2015, the total amount of sand silt in the Xiaolangdi reservoir area increased year by year to 3.048 billion m³ , and the average sand discharge ratio for many years was 21% . As mentioned above, the sand blocking capacity of Xiaolangdi Reservoir is 7.55 billion m³ . From calculations, it can be seen that the utilization level of sand blocking capacity has reached 40.4% .
In order to slow down the siltation speed, experts from the Yellow River Commission proposed the "one high and one low" scheduling idea in 2018, and the sand discharge efficiency has increased significantly. Water and sand monitoring data shows that from 2018 to 2020, the Xiaolangdi Reservoir has discharged a total of 1.3 billion tons of sand in three years, with an average annual discharge of more than 400 million tons. Thanks to the new model, the total amount of silt has been basically controlled, and it will remain at 3.146 billion m³ in 2020, accounting for 41.6% of the designed storage capacity.
3.1 billion m³ is not a small number, but compared with Sanmenxia Reservoir, the Xingli reservoir of Xiaolangdi Reservoir is more than enough and has a much longer service life. Since 2018, the minimum discharge ratio of Xiaolangdi Reservoir is 95% and the highest is 193%. The net erosion has been achieved many times, and the silt silt situation has been continuously improved.
On the other hand, my country has carried out greening and tree planting projects on Loess Plateau for a long time, and the forest coverage rate in the loess area has been continuously improved, reducing soil erosion from the source. Taking Shanxi Province as an example, Shanxi's ecological environment was fragile in the past, with the forest coverage rate in 2010 only 18.03%. After the climax of afforestation and greening rose, the coverage rate increased to 23.57% in 2020. Tens of millions of acres of mountainous areas are changing from "yellow" to "green" at a speed visible to the naked eye, and the ecological Yellow River has become a reality.
Xiaolangdi Reservoir contains a lot of silt and sand, so why not use to silt ship to silt?
monitoring data shows that the average annual sand transport of the Yellow River is decreasing, and the river water in the middle and lower reaches is beginning to "clear". Hukou Waterfall has seen the spectacular scene of "green waterfall rushing" many times, and the contrast of water color is shocking. The reason is that cascade reservoirs have stored water and blocked sand, planted trees and reduced sand in afforestation.
A large amount of silt is accumulated in the reservoir, providing the best place for the comprehensive utilization of silt. Regarding the sediment precipitated in the reservoir area, domestic scholars have also put forward suggestions for development and utilization: According to the natural sorting effect, coarse sand with a larger specific gravity of is deposited at the end of the reservoir, with shallow water level and large harvestable area. can directly use sand extraction boat to extract ; the sediment in the middle of the reservoir area is mainly medium coarse sand, and the water level is deep. can use jet pumping or self-priming pipelines to extract sand, transport silt and sand along the pipeline to a suitable site, artificially sink and sort.
. In front of the dam, the silt particle size is around 0.025~0.06mm. According to the provisions of the "SL 42-2010 River Sediment Particle Analysis Regulations ", this particle size can be classified as silt . is between sand and gravel, and has a low utilization value of ; in addition, the deepest water level is, and it is difficult to develop. The most direct treatment method is sand discharge and out of the warehouse .
, but it is different from the style you imagined. There has never been a large-scale sand mining ship in the Xiaolangdi reservoir area, and individual sand mining is strictly prohibited. First, because sand mining will damage the river environment, disrupt hydrological laws, threaten the safety of dam facilities, and near-shore stacking is not conducive to flood transportation and sand transportation; second, because of the low efficiency and high difficulty, the main sand control method in the reservoir area is to adjust water and sand. First, increase the sand content of the water body, and then naturally discharge it with water belt sand. This method is low in cost, good effect, rich in experience, and mature technology.
What about the ecological dredging test? If ecological dredging is carried out in the Xiaolangdi reservoir area, it is necessary to take into account the geological conditions of the dredging point, avoid mining in geologically fragile areas, and provide a scientific and rigorous assessment of the impact of the sand mining plan. In fact, my country is currently promoting the comprehensive utilization of silt in the middle reaches of the Yellow River, and ecological dredging is its main method, and Sanmenxia Reservoir has taken the first step in the pilot.
silting ship in Sanmenxia Reservoir
According to experts, the silt sediment in the Sanmenxia reservoir area exceeds 3 billion m³ . The ecological silting in the reservoir area has the significance of exploratory, innovative and leading .The dug out not only frees up the storage capacity, but can also be used to fill gullies, build fields and repair slopes, with wide benefits. Since it is a "leading" project, it means that it may be promoted in other reservoirs of the Yellow River in the future, including Xiaolangdi Reservoir, we will wait and see.
summary
Xiaolangdi Reservoir has stored water for 23 years. The ecological environment of the Yellow River has improved significantly, the sand transport volume has shown a trend of decreasing, and siltation and erosion have reached a dynamic balance. At present, there are more than 3.1 billion m³ of silt in Xiaolangdi Reservoir. How to avoid the rapid increase in silt and sand is testing the dispatching wisdom of water conservancy experts.
The silt and sand of the Yellow River are also valuable resources, and the ecological silt that attracts thousands of people is being piloted in an orderly manner in the Yellow River. I believe that the Yellow River in the future can also present a beautiful picture of few sands and many fish, clear water and green mountains.
