Comprehensive analysis and evaluation of the multi-information on the underground river system in construction of a pumped-storage hydropower station in Hubei

China is steadfast in promoting green and low-carbon energy transformation. Playing a pivotal role in the power industry, hydropower is at the forefront of energy transformation. Developing hydropower has always been an important strategic policy for China's energy and electricity industry. The southwest area, a main karst distribution region, is mostly concentrated with water energy resources in China. With the rapid development of water conservancy and hydropower construction, reservoir engineering in karst areas is often constructed. The characteristics of karst development are hydrogeological conditions that must be identified in the construction of hydropower projects in karst areas. What’s more solving the problem of karst leakage is the key to the success of engineering construction. A pumped-storage power station in Hubei Province is prone to serious karst leakage because its upper reservoir is located in the karst depression and the boundaries, where conditions of the groundwater system are not clear. Taking the upper reservoir of the power station as a research object, this study integrates different technical methods such as regional structural analysis, identification of geomorphic causes, tracing of underground rivers and micro-dynamic automation monitoring to extract multi-information for effective identification of the underground river system in the engineering area and to conduct a comprehensive analysis of the impact mechanism of karst development on the engineering.

Firstly, geological structures control the formation and movement of groundwater, as well as the direction and pattern of karst development. On the one hand, under the transformation of neotectonic movements, karst development in the study area has typical characteristics of vertical zoning, with surface karst zones, vertical karst development zones, and horizontal runoff zones developed from top to bottom. On the other hand, the secondary tension fractures at the turning point of the anticline provide space for groundwater to migrate in depth, and the wide and gentle distribution of strata at the sampe place increases the catchment area of groundwater. These two actions jointly provide conditions for the development of karst pipelines along the axis of the anticline. Secondly, the regional terrain and topography can roughly reflect the movement trend and direction of groundwater. Especially, the form, quantity, and scale of karst negative landforms are important bases for characterizing the development of underground karst. Through ground investigation and tracing, the distribution characteristics of underground karst pipelines can be basically obtained. Finally, the boundary and structural characteristics of the underground river system can be further clarified through high-precision tracing experiments, drilling, and verification of geophysical exploration.

The analysis results indicate, (1) There are no aquitards or water blocking structures around the upper reservoir. The vertical and secondary fractures with tensile properties in the axis of the Ziliangping anticline control the basic pattern of the groundwater system, and the secondary cracks generated in the axis of the anticline play a dominant role in karst development. (2) The upper reservoir is located in the supply area of the Dongzhushui underground river system, and the permeability rate of the rock mass is controlled by the strength of karst development, the degree of structural development, the integrity of the rock mass, and the degree of weathering and unloading of the rock mass. There are significant differences in different parts, with a high risk of leakage. (3) The karst pipeline in a structure of the single-pipe shape is not subject to the development of large-scale karst ponds. The north-south karst pipeline is not developed, and there is a risk of pipeline leakage towards the southwest side of the upper reservoir. (4) The reservoir area has undergone at least three stages of denudation, and the current stage of dissolution is still ongoing. The development and evolution of deep karst can lead to deformation in the overlying strata. After the engineering water storage, it is necessary to prevent potential uneven settlement and karst collapse. By comprehensively analyzing and evaluating multi-information of the underground river system, people can accurately identify the boundary and structural characteristics of the karst water system in the reservoir area, providing a scientific basis for the project construction of the reservoir area as well as reference for the site selection of reservoir in other karst areas.