2024, 43(1): 1-11.
doi: 10.11932/karst20240103
Abstract:
At present, there are two conflicting conclusions on the research of water leakage hazards in Dianchi lake. One is that the hidden danger points of water leakage in Dianchi lake have rapidly changed and is at a critical point, so there is a high risk of water leakage disasters. The other is that the view of hidden dangers of water leakage is not true, and hence there is no risk of water leakage disasters in Dianchi lake. Although people of both sides have done a large amount of analytic demonstration and published their research results. However, there are still more or less conceptual, systematic and normative errors or deficiencies. These deficiencies are mainly reflected as follows: unclear geological concepts and terms, insufficient hydrogeological investigation, weak research on the history of lake basin formation and evolution, and lack of verification by hydrogeological exploration, which may lead to insufficient basis for both sides to make a precise deduction. First, the terminological phrase "structural leakage" needs a clear expression. If a strong earthquake occurs in the Kunming area, it is likely to cause faults, leading to karst collapse of the funnel at the bottom of Dianchi lake, and then leading to the probable fault and connection of underground karst caves. This process will contribute to the catastrophic water leakage in Dianchi lake. Therefore, the risk of water leakage disasters may be originated from karst collapses at the lake bottom. However, the idea that the occurrence of a huge water leakage through the fault structure and the conversion of runoff between karst pipelines and faults may contradict the basic knowledge and reality of hydrogeology. It is not objective, reasonable and accurate to use the phrase "structural leakage" to express the hidden danger and its mechanism of water leakage in Dianchi lake. In addition, "funnel" is a karst term of karstology, referring to a funnel-shaped or saucer-shaped closed depression usually with a diameter of less than 100 m. At the bottom of a funnel, there are usually sinkholes leading to the underground, which can play a role of water drainage. However, the previous studies refer to the shallow and gentle low-lying landform formed on the loose cover layer of Dianchi lake as "funnel", which is obviously misused. This kind of landform is inconsistent with a funnel regardless of its formation background, genesis and components. If "funnel" is misused in this case, it is likely to cause cognitive errors and barriers in academic communication. Second, the geology, hydrogeology, engineering geology and environmental geology of the karst plateau in eastern Yunnan have been fully investigated and explored. The surveys of 1∶200,000 and 1∶50,000 have covered the whole area, and many detailed surveys and exploration with high precision have been carried out in the Dianchi basin. However, previous studies are far from enough for us to collect the detailed and reliable results of these surveys, so the inference of many phenomena and problems deviates from the reality. For example, with continuous surface divide and groundwater basin boundary, the eastern and southern parts of the Dianchi basin are blocked by thick surface divides, multi-layer Cenozoic viscous soil layers, and weak permeable layers of basalt, clastic rock and metamorphic rock. Moreover, the Jinsha river has been the most strongly invaded in this region since Pleistocene. Therefore, there are no hydrogeological conditions for the development of huge underground river channels across basins in these two parts. Third, the analysis of geological history is indispensable to understand the process and law of geological evolution. For example, through the analysis of the development and evolution of the Dianchi lake basin since Miocene, it can be found that the development of karst underground river system related to the depression at lake bottom may initially take the Hanjiacun depression as the discharge basis, and finally change to the Tanglang river as the discharge basis through the Haikou river. However, in the study of the hidden water leakage in Dianchi lake, the research in this aspect is very weak, leading to insufficiency of the basis for analysis and inference of the formation and evolution of depression at lake bottom, its genetic mechanism, and the water leakage path of Dianchi lake. Fourth, due to the complexity of geological phenomena and the multiplicity of geophysical exploration results, the conclusions drawn by geophysical exploration and geological inference are not final because they have not been verified by drilling tests. Although the thickness of Cenozoic overburden layer at the lake bottom is the key to the prediction and evaluation of water leakage hazards in Dianchi lake, it is speculated only based on the results of regional gravity measurement. The structure of overlying soil layer, physical and mechanical properties, and developmental characteristics of basement karst in the depression lack the drilling and experimental testing. The absence of drilling and testing data makes it impossible to calculate and analyze the characteristics and mechanisms of sediment consolidation of settlement at the lake bottom. If there are karst funnels and sinkholes in the basement of depression and their shapes, scales, and characteristics and locations of the blocking material are unknown, it is impossible to accurately analyze the instability mechanism of the blocking body, and thus it is also impossible to calculate and evaluate its stability and the so-called critical point of collapse. Therefore, the conclusion that "the hidden danger points of water leakage in Dianchi Lake have rapidly changed and is at a critical point of leakage disasters" is speculative. Currently, all deductions made need to be verified through drilling tests before they can be finalized.For these problems, this study makes an in-depth analysis one by one. According to the current research and data of regional physical geography, geology, hydrogeology, engineering geology and environmental geology, and combined with practical work experience, this study puts forward specific suggestions for the improvement of future research, such as standardizing basic concepts of geology, carrying out drilling tests, monitoring the depression deformation at the lake bottom, and systematically carrying out comprehensive research and field verification. It is pointed out that in order to reach the final conclusion of the hidden danger of leakage in Dianchi lake, the key is to find out the possibility of the karst collapse of depression at the lake bottom, so drilling verification must be carried out. Because the technology of underwater drilling test is difficult and the fragile environment of plateau lake cannot be disturbed excessively, the conduction of drilling test should be carefully planned and one hole can be drilled for different purposes. For sufficient representativeness and pertinence, it is appropriate to carry out drilling tests, monitor the two depressions studied, and provide specific technical suggestions for geophysical exploration, drilling test, dynamic monitoring of lake water and groundwater, and monitoring of the deformation of lake overburden layer at the lake bottom.
