On August 8th, after a major debris flow in Zhouqu, Gansu, it caused a controversy in the society about hydropower construction and geological disasters. However, at the same time of heated debate, in the early morning of August 18th, an extra-large debris flow took place in Lidi Di Village, Puladi Township, Gongshan County, Nujiang Prefecture. More than 20 people were killed and more than 60 people were missing. The affected villages were completely buried by mudslides. . Just a few days later, on September 1st, a massacre of mudslide burial villages occurred in Hedong Village, Vama Town, Longshan District, Baoshan City, the Baoshan region of Nujiang. At present, more than 10 people have been killed and dozens missing. The relevant authorities explained that “the combined effects of multiple factors such as the special geological structure in the area and the continuous multi-day rainfall have led to the occurrence of a geological disaster in Baoshan, Yunnan.” However, what causes the special geological structure in the Nujiang area in Yunnan? Can the geological disasters in the Nujiang area be fundamentally controlled? This is what people are most concerned about.

Regarding how to treat the geological disasters caused by the special geological structures in the Nujiang region, different people have different conclusions. This cannot but remind people of a dispute about the development of hydropower in the Nu River several years ago. In the same year, an anti-build dam geologist protested that the Nujiang River area was geologically fragile in order to oppose the development of hydropower in the Nujiang River. Once the hydropower development was carried out, it would cause serious geological disasters. However, more professional hydropower and geologists pointed out that the disasters of the landslide, bank collapse, and mudslide in the Nujiang River are due to the fact that the Nu River's water contains tremendous energy, which has long impacted the river valley and caused the river bed to continuously cut down. If we cannot use the hydropower development of the Nujiang River, it will continue to create new landslide bodies and geological disasters will continue to emerge. Only the use of hydropower resources to generate electricity can fundamentally reduce the causes of geological disasters, thereby reducing geological disasters. Without the development of hydropower, geological disasters in Nujiang will never be avoided.

The reality is exactly the same as what most experts have asserted. The energy of rivers and rivers in the Nu River is extremely high. Therefore, the geological disasters in the Nu River region are particularly frequent and severe. Along the Nujiang Highway, which is several hundred kilometers away, there are at least 100 geological disasters such as landslides, bank collapses and mudslides every year. The mudslides in the town of Puladi and the Baoshan area in the Nu River are only relatively large geological disasters, resulting in relatively serious loss of human assets.

Wang Zhaoyin is a renowned professor of the Department of Hydraulics at Tsinghua University. He is the chief editor of the International Journal of Sediment Research and the secretary general of the World Sediment Research Society. He has been engaged in scientific research on sediment movement laws and river governance for more than 30 years. According to research by Professor Wang, the power of collapse and landslide is actually from the lower cut of the river, and the deeper the lower cut, the greater the potential energy of the collapse landslide. He believes that in the process of river geological disaster management, we must adhere to four directions, namely: increase resistance, reduce the flow rate; control erosion, reduce river sediment transport capacity; increase water surface area and connectivity of biological habitats; protect and restore the natural landscape of rivers.

Specifically, the key to managing the debris flow is to dissipate energy. Tsinghua University has a test site in Yunnan and has conducted field tests throughout the year. In the year before the untreated, the amount of landslides in a local river valley in 2008 reached 1.7 million square meters. By the year of 2009, only 20,000 square meters had been destroyed. Specific energy dissipation methods require different measures to be taken in response to different situations. In the trenches of seasonal floods, large stones can be placed in a staggered manner to increase the resistance of water, and at the same time, it can be used to eliminate energy. It is best to build hydropower stations in long-term rivers. Use the energy of the river to prevent it from creating geological disasters.

In particular, it should be emphasized that if we only build dams, it will not be effective. At present, disaster management in many areas in China is through the establishment of small levees in the valley to block the debris flow. Many practices have proven that mudslides cannot be blocked and must be able to eliminate energy. Many small levees that are used to block debris flow can only stop small mudslides or delay the occurrence of mudslides. Since small levees do not dissipate energy, they can only accumulate energy. In the end, once these small levees collapse, they become large mudslides. The major debris flow in Gongshan, Nujiang, has this factor.

In addition, after the completion of the hydropower station, due to the formation of the reservoir, the surrounding water vapor can be increased, the surrounding local microclimate can be effectively improved, and the rapid growth of the vegetation can be facilitated, thereby further improving the environment and reducing the occurrence of geological disasters. We know that the causes of many geological disasters are directly related to the destruction of vegetation and soil erosion. Therefore, in general, after the completion of the hydropower station, the best geological disaster reduction effect will be achieved, and it will take some time. Only a few years after the hydropower station is built, it will promote the growth of the surrounding vegetation and prevent the loss of soil and water. The geological disaster reduction effect of hydropower will be fully realized. It can be said that the longer the hydropower station is constructed, the more obvious its geological disaster reduction effect will be.

Due to the need for a process to control geological disasters through hydropower depletion, there is a significant lag. Therefore, it is normal for China’s initial geological disasters after the completion of the Three Gorges reservoir to increase. After the reservoir was built and impounded, due to the erosion and accumulation of the rising water level, the bank formation process began on the new waterfront. Especially when the reservoir is suddenly drained, the water pressure in the soil increases after the slope is immersed in the water due to the relatively high water level, and the sudden water discharge causes the water level to drastically decline and the pore water pressure in the soil is too late to change. The sudden loss of the hydrostatic pressure outside the slope, the imbalance of pressure inside and outside the soil often leads to the instability of the slope and the occurrence of landslides.

The premise of this situation is that the slope itself requires hydrological and geological conditions that produce landslides (or potential landslides). Under this geological condition, even if there is no change in the water level of the reservoir, if there is a strong continuous rainfall, as long as the soil on the slope absorbs enough water, it may cause the pressure of the same pore water to increase, which is easy to produce. Landslide phenomenon. For example, last year's 8.8 storm mudslides in Taiwan Province and our 8.8 Zhouqu mudslides this year. In fact, these are all potential landslide bodies that have been released during heavy rain.

It can also be said that if there is no potential geological condition for generating landslides, the change of reservoir water level will not cause landslides. On the other hand, if the slope itself has the geological conditions of the landslide caused by changes in reservoir water level, it means that the slope itself has a landslide (or The landslide conditions and landslides are also likely to occur under continuous heavy rainfall, or under certain special conditions (such as earthquakes). In this sense, the construction and storage of reservoirs is by no means creating landslides. Instead, it provides an opportunity for concentrated release of the original unstable landslide body.

In general, after the construction of hydropower projects, the geological conditions of the original natural slope will be improved from three aspects: 1. Hydropower development is the use of river water to cut the energy of the bank slope and use it to generate electricity, reducing the sharpness of the river to the river valley, making the river Development tends to be slow and stable, which will ultimately greatly reduce the occurrence of geological disasters. 2. Handle the main landslide body manually, or protect the slope (including concrete spraying, shear-resistant piles, and pre-stressed anchor cables). 3. The initial stage of reservoir impoundment is the period of instability and redevelopment of a new reservoir bank, which is a period of concentrated release of hidden geological disasters.

Taking the Three Gorges as an example, we must know that we cannot manage the geological disasters in the Three Gorges area of ​​the Yangtze River, and that we can use engineering measures and long-term effective mechanisms to manage geological disasters. This huge progress is due to the construction of the Three Gorges Project. The energy of the river is used to generate electricity, and it is not allowed to make a new landslide. Although this conclusion needs to be confirmed after several years of operation in the Three Gorges area. However, the current reality is that the hydropower resources in western China are rich, the development is very low, and the development time is generally relatively late. Therefore, the geological disaster reduction effect of hydropower construction is often still not fully realized. Therefore, the occurrence and loss of geological disasters in the western region are generally serious. However, due to the economic development in the eastern part of China, hydropower development and construction are relatively early, and the vast majority of hydropower resources have been basically completed. Therefore, the probability of landslides, mudslides and other geological disasters in the eastern part of the country is significantly lower than in the west.

From the international perspective, the situation is the same. France is one of the countries with the most abundant development and utilization of hydropower resources in the world. The development level is close to 100%. Since the energy of the river will no longer be used to impinge on the valley to create geological disasters, it is at the same time a very serious geological disaster in hydropower development in France, but very few. This phenomenon is almost universal in the world. The survey results show that the higher the degree of hydropower development in countries and in the disaster-stricken areas, the better the ecological environment. The occurrence of various natural disasters and the resulting losses are smaller.

In short, both science and facts have proved to us that the civilized progress and scientific development of human society is the fundamental direction for the prevention and mitigation of natural disasters. Specifically, the most fundamental measure for reducing and eliminating landslides is effective energy dissipation. The full development and utilization of hydropower is one of the most effective ways of energy dissipation and disaster reduction. Therefore, the rapid development of hydropower in the Nu River is the fundamental way to reduce the geological disasters in the Nu River.