500 million cubic meters of water in the Three Gorges will drop, and the water level will drop to 147 meters. Will it affect the fish in the reservoir?
In August of this year, affected by the continuous high temperature and little rain, the water level in the Yangtze River Basin dropped to varying degrees. Jianghan, Jiangnan and other places experienced the worst drought in decades. 17.64 million mu of crops. Many people will have such a doubt in their minds: Why is the main flood season so dry when it should be rainy?
As the subtropical high rises to the north, most of the south is affected by it. Not only does the temperature rise, but the typhoon cannot blow here, the rainfall is greatly reduced, and the evaporation is abnormally high, which leads to the situation of farmland without water.
In fact, in order to alleviate the drought, China has used many water conservancy facilities, and many reservoirs have opened gates and released water at the same time. Among them, the Three Gorges Reservoir has poured down 500 million cubic meters, and increased water supply to the middle and lower reaches of the Yangtze River. In the next few days, the water level will drop to 147 meters. . At the same time, the Baihetan, Wudongde and other hydropower stations in the upper reaches of the Yangtze River also opened flood discharge holes to replenish water downstream.
Everyone should know that the most important function of the Three Gorges is to prevent floods and droughts. In order to ensure that there will be no major floods in the Jingjiang section of the Yangtze River during the flood season, the Three Gorges Reservoir will release water in advance to lower the water level before the main flood season. The purpose is to free up enough water. space to intercept the flood peak. When there is a drought, the gate is opened to release water to ensure the water demand in the middle and lower reaches. Since this year is so dry, can we empty all the water in the Three Gorges?
Why can't the water level of the Three Gorges drop below 145 meters? In fact, the water level line was planned at the beginning of the design of the Three Gorges Dam. The dam crest elevation is 185 meters, and the normal operation water level is 175 meters. In order to ensure that the flood control reservoir in the reservoir has a capacity of 22.15 billion cubic meters, the flood control limit water level is set 145 meters, that is to say, 145 meters is the "dead water level" of the Three Gorges Reservoir. Unless there are very special circumstances, it is generally not allowed to empty to the dead water level, so as to give full play to the many benefits of the Three Gorges Dam. In the past few days, while the Three Gorges Reservoir is releasing water, the major cascade reservoirs of the Jinsha River will continue to replenish water. In addition to drought resistance, it also ensures that the water level of the Three Gorges will not drop below 145 meters.
Coincidentally, a severe drought occurred in the Yangtze River Basin in 2011. The precipitation at that time was 40-60% lower than that of the same period in many years, reaching the lowest level in 50 years. The land in the rice fields was cracked, and many cracks could even put four fingers at the same time. It is a pity that the sky is not beautiful, and the Three Gorges can only open the gates to release water. It has been 21 years since the completion of the Three Gorges Dam, and Gaoxia has become a paradise for all kinds of fish.
Especially since the 10-year ban on fishing in the Yangtze River in 2021, the ecology of the Yangtze River has achieved great recovery, and the fish that were once rare are not so mysterious now. But the Yangtze River is so dry, and after the Three Gorges sluice gates are opened, the water level has dropped a lot. Will this affect the fish in the library?
You must know that there are 424 species of fish living in the Yangtze River Basin. In addition to the common "four major fish", there are also rare species such as Chinese sturgeon and Dart's sturgeon.
The Three Gorges sluice gate is opened and the water level is lowered. Will it have any effect on the fish in the reservoir? The answer is yes. After the Three Gorges Reservoir supplies water to the middle and lower reaches, hydrological conditions such as water level, water temperature, and flow rate will change, which will affect the living environment of fish.
The first is the water level effect. Compared with normal, the water level dropped after the reservoir gushed, and most fish spawned in shallow water areas. The drop in water level will inevitably have an impact on the spawning of fish, and the number of fish spawned is relatively small, affecting the reproduction of the entire fish group. .
Next is the water temperature. After the water level drops, the water with higher surface temperature is lost, and the water with low temperature at the bottom surges. The suitable spawning temperature for fish is generally 16-18°C. When the fish return to the shallow water to spawn, they find that the water temperature is not the same as before. The number of eggs laid naturally decreased.
Finally, in terms of flow rate, even after the fish have successfully spawned, the eggs still need to avoid predators during the incubation period. In order to successfully escape, the water flow rate is a very important factor. Taking the four major fish as an example, in order for their eggs to float safely, the water velocity needs to exceed 0.25m/s. After the water level drops, the water flow decreases, which is not conducive to the hatching of the eggs.
It can be seen that the opening of the gates of the Three Gorges Reservoir has brought some negative impacts on the reproduction of fish in the reservoir, but these impacts may not be worth mentioning compared with the water demand of hundreds of millions of acres of farmland downstream.
In general, the Three Gorges Dam has advantages and disadvantages from construction to operation, but it is undeniable that the advantages far outweigh the disadvantages, not to mention the economic benefits such as shipping and power generation. It fights the flood peak every year and ensures the lives and property of the people in the Jingjiang section. Safety and the fight against drought have made a huge contribution. What do you think of this?