Technical key points of 1∶50，000 hydrogeological and environmental geology surveys in karst areas of South China

The karst area in South China is about 520,000 square kilometers, which is controlled by the rock properties, group structure types, geological structural framework, topography and hydrodynamic conditions. The development and distribution of karst in the area is quite uneven. The special subsurface-underground double-deck structure leads to the lack of surface water and deep buried underground water. With the influence of global climate change and irrational human activities, rocky desertification, drought and flood disasters, groundwater pollution and other major environmental geological problems have occurred in karst areas of South China. These natural and man-made factors have seriously restricted the sustainable development of regional social economy, making many karst areas become one of the poorest areas in the country. In order to promote the economic development, ecological civilization construction and poverty alleviation of the karst areas in South China, it is necessary to further clarify the karst hydrogeology and environmental geology conditions, providing a basis for the development and utilization of resources, offering water resources guarantee for the residents and economic development of areas with serious water shortage, and technical support for the protection and control of ecological environments.By summarizing the six research results on the comprehensive investigations of hydrogeology and environmental geology and groundwater development and utilization in the karst areas of South China, this study suggests 10 characteristics of hydrogeological and environmental geology conditions in karst areas of South China, which are stated below, the comprehensiveness of karst development controlled by the strata structure, geologic structure frames and hydrodynamic conditions; heterogeneity of karst groundwater distribution; multiplicity of karst water-bearing media by pores, gaps, joints, pipes and holes; multiphase characteristics of karst groundwater flow; variability of karst groundwater dynamics; seasonal distribution of karst groundwater resources; alternation of drought and flood; concealment of karst groundwater pollution; big buried depth of karst groundwater; and correlation between karst groundwater and ecological economy. At the same time, this study discusses the technical points of investigations and research on the 8 key scientific problems, including carbonate rock group structure, tectonic evolution and development period of karst, karst-form combination relationship, surface karst zones, karst groundwater systems, karst underground river, the main problems of environmental geology, and development and utilization of karst water resources.