When it comes to land or lake reclamation, first thing that comes to mind is Netherlands. Initially, a quarter of land in Netherlands was below sea level, but due to land reclamation, area of the Netherlands has increased by 5,200 square kilometers. In 1920, Netherlands launched Zuiderzee project, aim of which was to build a dam in Zuiderzee to block sea, turning Zuiderzee into a lake. Since then, people have drained sea water and turned the Zuiderzee into a freshwater lake.
The new lake was named IJsselmeer with a total area of 3440 square kilometers. The lake provides Netherlands with a large amount of fresh water resources, improves ecological situation of coastal areas, and restrains coastal salinization. It can be said that Zuiderzee project is one of greatest projects of mankind in 20th century, and it is a milestone for mankind to claim land from ocean.
Can we build a similar project in China? Looking at a map of China, we found that Bohai Sea is a rather special existence. The Bohai Sea, located in northern China, is China's largest inland sea. The exit to Bohai Sea is guarded by Shandong Peninsula and Liaodong Peninsula. The distance in a straight line from Shandong Peninsula to Liaodong Peninsula is more than 120 km, in middle are Miaodao Islands. If we build a super dam between two peninsulas, can Bohai Sea be turned into China's largest inland lake?
Some people have pointed out that if Bohai Sea becomes a freshwater lake, it will provide Beijing, Tianjin, Hebei, Liaoning, Shandong and other regions with more fresh water resources, which will help solve problem of water shortage around Bohai Sea. Once dam is built, railroads and highways can be built on dam, shortening time for northeast to reach hinterland and encouraging economic revitalization of northeast. At same time, dam blocking sea goes deep into sea, which will add another charming scenery and promote tourism in North China and Northeast China. It can be seen that if Bohai Sea becomes a lake, it can indeed bring certain economic benefits.
Some people have also pointed out that after construction of a dam blocking sea, ports in Bohai Sea will become unnavigable. From experience of Zuiderzee, I can say that this concern is completely unnecessary, because people can build locks on dam so that ships can pass.
So is it realistic to build a dam in Bohai Sea to block sea?
First of all, first difficulty we face is problem of engineering quantity. The construction of a sea-blocking dam in Bohai Sea will far exceed number of sea bridges and underwater tunnels, and investment will be astronomical. The Bohai Sea is shallowest sea in China, with an average depth of only 18 meters. However, it is still fantastic to build such a huge monster in sea. The reason Netherlands was able to build Zuiderzee Dam is because Zuiderzee is only 4 to 5 meters deep and dam is only 30 kilometers long. If a dam is built on Bohai Sea, it is estimated that it will take a hundred years.
Second, problem of pollution. Bohai District is area with most severe water pollution in China, and nearby Haihe and Liaohe river basins have been severely affected by water pollution. If Bohai Sea and Yellow Sea are separated, water in Bohai Sea will quickly become polluted and cannot be exchanged with outside world or purified. Thus, even if Bohai Sea becomes a freshwater lake, it is just stagnant water.
The problem of water pollution in Bohai
Thirdly, Bohai Sea cannot be turned into a freshwater lake. According to some estimates and calculations, annual growth of Bohai Sea is about 70 billion cubic meters. m, and annual flow of rivers surrounding Bohai Sea can reach 82.5 billion cubic meters. In addition, about 46 billion cubic meters of precipitation falls on surface of Bohai Sea every year. If dam is successfully built, more than 50 billion cubic meters of fresh water could be added to Bohai Sea every year, and total volume of sea water in Bohai Sea is 103.8 trillion cubic meters. It will take 1,800 years to replace all sea water. in Bohai Sea.
The annual net flow of Huanghe, Liaohe and Haihe rivers is too small
Furthermore, annual net flow of rivers surrounding Bohai Sea is not an efficient flow because water in river itself is fresh water, which must provide water for coastal industries, agricultural production and urban life. . According to statistics, effective annual flow of rivers around Bohai Sea is only 30 billion cubic meters.
Of course, you can count on water diversion to increase net flow of river. Join future construction of projects such as diverting Tibetan water to north so that an efficient annual flow around Bohai Sea can be achieved. If we increase net flow of rivers flowing into Bohai Sea by 100 billion cubic meters (equivalent to two Yellow Rivers), it will take 600 years for Bohai Sea to turn into a freshwater lake.
So we can dismiss Bohai Sea Dam Project just by looking at it. Let's imagine that main purpose of building a dam blocking sea is to secure fresh water resources in surrounding area. If we blindly pump more fresh water into Bohai Sea, wouldn't that be counterproductive to our goals? At present, seawater desalination technology is becoming more and more mature, and cost is getting lower and lower. It is better to directly popularize seawater desalination than to build a highly polluted Bohai Lake for a thousand years. Even if dams can be built to seal off sea and Bohai Sea can become a freshwater lake, investment in fighting pollution in Bohai Sea would be sky-high.
Comparison of seawater desalination costs
That is, from an economic point of view, we can also completely deny Bohai Sea Dam. Some people say that another economic value of Bohai Sea Dam is that it connects Liaodong and Shandong. In fact, to connect with Liaodong and Shandong, it is enough to build a sea bridge or lay an underwater tunnel.
Since construction of Bohai Sea Dam is impossible, can Bohai Sea be directly filled and turned into land? Indeed, if Bohai Sea becomes land, China's land area will increase by 77,000 square kilometers, and these lands will be plains, very suitable for construction of large cities and agricultural bases. However, volume of work to fill Bohai Sea is tens of times greater than volume of work to block sea, which is almost impossible to complete.
Some people say that instead of harnessing Yellow River, let Yellow River fill with sand and sand and always fill Bohai Sea. We can also calculate it. Sand and soil sent by rivers around Bohai Sea can form 20 square kilometers of land each year. At this rate, area of the Bohai Sea could shrink by only one-third in a thousand years. It will take at least 3,000 years for Bohai Sea to completely disappear.
Most importantly, if Yellow River continues to carry sediment, it will be an environmental disaster. Since these sediments drain from Loess Plateau, more deposits there are in Yellow River, worse ecology of Loess Plateau will be. During Qin and Han dynasties, Loess Plateau was full of dense forests, and later gradually turned into a barren land with ravines. If left untreated for a long time, Loess Plateau can turn into a desert. After Loess Plateau turns into a desert, Yellow River stops flowing, Hexi Corridor, Guanzhong Plain and Fengshui Valley will be flooded with desert. Turning Loess Plateau into a desert for sake of increasing 70,000 square kilometers of land is not worth cost.
In addition, after Bohai Sea becomes dry land, amount of ocean water vapor received by North China and Northeast China will decrease, area will shrink, oceanic climate will weaken, and continental character will increase, which may further worsen depletion of water resources in Northeast China and North China You should know that desert in Inner Mongolia is not far from Beijing. If rainfall from Beijing to Zhangjiakou decreases, desert is likely to invade south and Beijing will be threatened by sandstorms.
Therefore, both Bohai Sea Dam and Bohai Land Development Plan are unfeasible and unfeasible. The only thing that can be done now is to build an underwater tunnel in Bohai Sea to connect with Northeast and Shandong Peninsula and accelerate economic development of Northeast. When completed, Bohai Sea Tunnel project will be one of largest projects of 21st century.