Systematic Engineering Geological Research Of Reservior Leakage In Karst In Mountain Plateau Of Eastern Yunnan

Reservoir leakage, a focused issue, is one of the most complex problems in karst area, which would be a barrier of a reservoir construction success and influence economic returns. Eastern Yunnan mountain plateau possesses special landform with terrain flat, open and shallow cut, and deep incised valleys around, hundreds of meters sharp drop. However, its geological structure is complicated with open-flat fold and many high dip angle faults. The carbonatite is distributed widely and karst developed. Otherwise, most reservoirs built in the mountain plateau area in 50 s to 60 s of the 20 th century have karst leakage problems. Apparently, the geological condition of eastern Yunnan mountain plateau is complex, in where large hydraulic engineering construction will face serious challenges. It is significative to do the systematic research of reservoir leakage in karst hydraulic construction under such complex geological settings.Based on the view of systematic engineering geological research, this paper summarized the uniqueness and controlling factors of karst on the watershed zones of plateau and river valley. Main karst hydrogeological structure and aquifer system types in this mountain plateau area have been classified, so do the types and characteristic of karst ground flow system. Geological models of reservoir leakage are proposed based on the hydrogeological analysis of more than 20 reservoir in this area. In the final, leakage judgement method, process and seepage-proofing are carried out relying on the Heitanhe reservoir, especially the model of leakage to the long distance and deep valley. The main conclusions are followed.(1) In terms of the geologic structure and tectonic characteristic, the karst hydrogeological structure has been classified into three types: ① uniform purified carbonatite flat fold type, ② fault controlling type, ③ interbed fold type. The aquifer system in this area includes the single and the compound two types.(2) There are two main types of alternate cycle of groundwater, including basin or valley discharge and deep incised valley discharge. The previous one could be classified into gathering-water basin(valley) and catchment-runoff basin(valley). Meanwhile, the latter one could be classified into the type of discharge to the present drainage datum plane directly and discharge to the deep incised tributary valley. The ground water flow system in the area includes the single karst spring and ground river two types. The transfer type of ground water including the process that the rain changes into ground water, then surface water, and finally ground water, which is a special transforming process of three different types water in the research area.(3) There are three secondary karst groundwater flow systems in this research area, including the Niulan river, the Nanpan river and the Beipan river. The tertiary karst groundwater flow systems are single karst springs and ground rivers in the Niulan river and the Beipan river, while tributary type in the Niulan river, whose level four karst groundwater flow systems are single karst springs and ground rivers.(4) In terms of the runoff process of ground water, almost each tertiary karst groundwater flow system could be devided into three level four flow systems from the upstream to the downstream in the Niulan river and the Beipan river. The first part is epi-karst flow system, in which the groundwater discharges to the local drainage datum plane and many springs with little flow on the surface. The second part is deep-flow karst flow system, in which the groundwater wouldn’t discharge to the local drainage datum plane and with few springs on the surface. The third part is disappearing stream which would obtain all the water of the previous two part and the rainfall.(5) Statistical analysis showed that the reservoir leakage not only occurred in the karst area but also non-karst area. According to the difference of the location, medium and leakage distance, there are two leakage types, including the normal and a special seepage type that is long distance and great fall to the deep incised valley.(6) The distribution of the karst aquifer system and change of the flow system boundary are the important factors in the judgement, which contraposes the seepage type of long distance and great fall to the deep incised valley. What is most important is whether the karst aquifer system connects with the deep incised valley. The epi-karst flow system and the deep-flow karst flow system would became one flow system at the Heitanhe reservoir, which would cause severe seepage to the Linjiaotang ground river.(7) The seepage-proofing scheme of karst reservoir should be determined according to the geological conditions and be technical feasibility and economy reasonable. The Heitanhe reservoir adopts the impervious curtain that is placed at the key part of leakage. It is calculated that the amount of leakage by numerical analysis and investment of the seepage-proofing at different depth. In the final, the appropriate depth of the curtain is proposed after the compare of economy under the different depth, which would be the scientific proof for the reservoir construction.