Watershed boundaries and hydrodynamic properties of surface water and groundwater in the Luxi karst fault-depression basin

The Luxi karst fault-depression basin is located on the marginal slope of the southeast Yunnan plateau and is a tributary on the left bank of the Nanpan river system. It hosts two types of landforms, karst basins and karst river valleys. This basin also lies at the upstream in north, while the Xiaojiang karst river valley is at downstream in the south; both are connected by the underground flow system in the Maoshui cave to form a karst water system with complete recharge, runoff and discharge processes. The watershed boundary and hydrodynamic properties are the most important determinants of the watershed eco-geological environment and water flow characteristics. Accurate determination of the boundary and hydrodynamic properties of surface water and groundwater in the basins is a necessary prerequisite for runoff system simulation, water resource evaluation, searching and utilizing groundwater resources, development and protection planning of resources and environments, solution of environmental problems, and ecological restoration and protection. However, in previous work, the boundary of the groundwater basin divided by the hydrogeological environmental geological survey and evaluation is mainly along the boundary of the surface watershed, aquifer and aquiclude (band, body), most of which are not accurate enough. The hydrodynamic property of the boundary was mainly the result of hydrogeological analysis and inference. In this work, through detailed hydrogeological investigation and analysis, we initially delineated the boundary between surface water and groundwater basins in the Luxi karst fault-depression basin, and then revealed and controlled the hidden and inaccurate sections through drilling, tracer tests, and geophysical surveys, thus making the boundaries of watersheds and water systems revised more accurate. At the same time, we clarified the hydrodynamic properties of watershed boundaries, and obtained basic hydrogeological parameters, so as to provide a basis for model construction and solution conditions to the surface water and groundwater runoff systems in the basin.