First of all, the simplest earthquake-resistant South-to-North Water Transfer Project, which spans the Yangtze River valley to Beijing, Tianjin and Shandong Peninsula, is unique in the world. Such a long-distance project must pass through many fault zones and earthquake zones. If underground pipelines are used, once an earthquake occurs, it will cause irreversible collapse. Take the eastern route as an example, and it will pass through the famous Tan-Lu earthquake zone. The Middle Route and East Route of South-to-North Water Transfer Project are located in densely populated plain areas, where ground production and labor are very intensive. The problem comes: excavation involves the pressurization of the ground water tower, and the engineering quantity and cost will increase exponentially, but it is easy to collapse in the case of intensive ground activities.
Secondly, the cost is the reason. Not all the routes of the South-to-North Water Transfer Project are newly built, but a large number of existing rivers are used, the most typical of which is the utilization of the East Line Beijing-Hangzhou Grand Canal, which not only saves huge costs, but also makes the Beijing-Hangzhou Grand Canal play its value again. In addition, connecting the lakes along the line in series can comprehensively dispatch and optimize the water resources of the lakes along the line and promote the ecology along the lake. However, if underground pipelines are used, the existing rivers will only be abandoned, and when water resources are to be dispatched to the surrounding lakes along the line, high-power pumping stations need to keep working. The open-air river connects the lakes along the line in series, which can reduce the workload of the Yangtze River pumping station hub and save costs when the lakes flood in the rainy season in the north.
One is fault maintenance. Undeniably, many water conservancy projects in China have used underground pipelines (water tunnels), such as the project of diverting water from Han to Wei and the project of diverting water from central Yunnan. , and extensive use of underground tunnels. However, these tunnels are all based on natural mountains, or more accurately, they are called "mountain tunnels". After the large shield machine is dug, there is a lot of space, and the later maintenance can completely allow human equipment to enter. However, the east and middle routes of South-to-North Water Transfer Project are located in the plain area of China. Tunnels in plain areas have no mountainous terrain, so they can only take underground tunnels. Once there is a problem in the later stage of the background, not only the investigation workload is heavy, but also it is more complicated to maintain. It is impossible to dig every time, which will seriously affect the ground production operations.
Finally, to correct one point, many people think that the use of underground pipelines in the South-to-North Water Transfer Project also involves the problem of freezing in winter in the north. In fact, this question is not valid. The freezing in northern winter refers to the rivers and lakes on the ground, but the underground temperature is high and will not freeze, otherwise the groundwater and tap water supply in northern cities will be completely paralyzed in winter.