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The middle route of the South-to-North Water Diversion Project, as a large-scale cross-basin water diversion project in the mainland, plays an important role. With an average annual water transfer of 8.54 billion m³ from the Danjiangkou Reservoir to Tuancheng Lake in Beijing's Summer Palace, it not only meets the drinking water needs of the people of North China, but also presents remarkable achievements from an ecological point of view.
This grand project spans the four major river basins of the Yangtze River, the Huaihe River, the Yellow River and the Haihe River, covering the northern subtropical, warm temperate zone and temperate zone, and its complex climate environment is breathtaking. The whole project can be seen as a vast ecosystem, consisting of the Danjiangkou Reservoir, the main canal and the hoarding reservoir, in which abundant fish stocks thrive in this complex ecosystem.
The South-to-North Water Diversion Project is divided into three water transmission channels: the eastern, central and western routes, and the middle route project is eye-catching. Compared with the Eastern Route Project, the water quality of the Middle Line Project is better because its source of water is the Danjiangkou Reservoir, known as the "Asian Tianchi" reservoir located in the middle and upper reaches of the Han River, which is the largest artificial freshwater lake in Asia. Since the first water storage in 1967, the Danjiangkou Reservoir has been expanding, and after the dam height project in 2012, its water quality has reached the standard of first-class water source protection zone, the water body is highly transparent, and the water in the core area can even be directly drinkable.
In order to ensure that the water quality in the main canal of the middle line meets the standard, a series of water retention measures have been adopted for the project. First of all, protected areas and ecological isolation belts have been set up on both sides of the Danjiangkou Reservoir and the main canal to prevent water pollution caused by human activities. Secondly, the middle line water transmission channel adopts a variety of facilities, such as pipelines, tunnels, culverts, aqueducts, etc., to avoid contact with natural water bodies, and the inner slope and bottom are lined with concrete, which will not negatively affect water quality. Finally, four water quality monitoring centres have implemented real-time monitoring to ensure water quality safety.
The fish in the central canal also benefit from the excellent water quality. In the 2015 resource survey, a total of 19 species of fish were found, of which carps were overwhelmingly dominant, and the largest body length was less than 24 cm, representing species such as wheat ear fish, meal fish, goby, etc. In the 2018 survey, the number of fingerlings increased to 23, including horsemouth and dinner fish. In addition, some large predators such as anchovy, grass carp and carp also appear in the dry canal.
Fish is one of the spectacular carnivorous fish, wild anchovy can grow up to 2m and weigh more than 100 pounds. These spectacular underwater "tigers" are also common in the Danjiangkou Reservoir. Grass carp can grow to more than 1 meter, but their growth may be limited in the special aquatic environment of the midline trunk channel. As for carp, they are more adaptable fish, growing up to 1.2m and weighing up to 40kg.
Although the ecology of the midline trunk canal is relatively homogeneous, the fish population here has gradually increased over time. The ecosystem of the main canal is gradually taking shape, and the number of fish is steadily increasing, which is a major success of the project.
Some people may ask, since the water quality of the main canal is excellent, why not release a large number of fish fry to further purify the water? In fact, this problem was taken into account in the early stages of construction, and fish nets were installed to prevent fish from the Danjiangkou Reservoir from entering the main canal. After all, the natural productivity of dry canals is limited and not suitable for large-scale stocking of wild fish.
In contrast, the most scientific method is to carry out breeding and releasing in the Danjiangkou Reservoir. The reservoir area has a vast water surface, complex shoreline and abundant food resources, which provide natural habitat and breeding grounds for fish. The Danjiangkou Reservoir also has a fish stocking station for releasing native fish such as silver carp, an initiative that has achieved significant economic and water purification benefits.
A good example is the growth of silver carp species, which can grow to 0.81.2 kg per 0.150.25 kg silver carp fingerling in one year, 24 kg in the second year and 610 kg in the third year. By stocking fish such as silver carp, the Danjiangkou Reservoir has effectively become the "water" of the midline water source
quality purifier". These fish continuously filter plankton in the reservoir area, purifying the water body, and then this clear water flows to the main canal, further improving the water quality and maximizing the comprehensive benefits.
Therefore, although the water quality of the middle line trunk canal is already excellent, it is a more scientific and effective method to carry out breeding and releasing in the Danjiangkou Reservoir, where the water source is located. This method can not only increase the reserve of biological resources, but also ensure the continuous purification of water quality, ensuring that the high-quality living water in the northern region continues to flow north.
On the whole, the success of the middle route of the South-to-North Water Diversion Project lies not only in ensuring the safety of drinking water in North China, but also in its outstanding achievements in ecological protection. Through scientific water quality management and reasonable fish breeding and release plan, this project has achieved a win-win situation between ecological environment and water resources. As one of the outstanding representatives of China's engineering construction, it has shown the world China's unique experience and achievements in large-scale water resources allocation and ecological protection.
In short, the successful experience of the middle route of the South-to-North Water Diversion Project tells us that scientific management and comprehensive consideration are crucial when dealing with the complex relationship between ecology and water resources. By protecting water sources, purifying water quality and increasing fish rationally, we can achieve ecological balance and provide valuable lessons for future water management. The success of this project not only shows China's strength in large-scale projects, but also allows us to cherish and protect precious natural resources.
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