Identifying three-dimensional groundwater flow patterns

The study area is located in the eastern part of the Gaolan river basin, Xingshan county in the west of Hubei Province,South China. Uplift and erosion have produced a steep terrane of medium to low mountains and deep ravines that are characterized by complex karst landforms and great topographic relief. The terrain is generally high in the north and east, low in the south and west, with an elevation ranging from 349 m to 1,780 m amsl. The Gaolan river and its deep tributaries, Baiji river, Liangsan river, Tanyu river and Xiayang river, are successively developed from north to south. To identify 3D groundwater flow patterns in the study area , based on the results of 1∶50,000 scale karst hydrogeological survey,GIS technology and runoff segmentation were used in this paper to quantify the elevations of top and bottom of the karst aquifer system, from which we obtained infiltration recharge coefficient, groundwater runoff and other simulation data. The groundwater flow system under different rainfall conditions in the study area was numerically simulated. The results show that the development of groundwater flow patterns mainly controlled by the larger-scale potential sources and sinks, the effect of small and medium scale relief on groundwater level is not obvious. Because of the presence of deep river cut valleys, the groundwater of the Liangsan and Tanyu river basins is more powerful, which is favorable to the development of local flow systems. With the increase of recharge elevation in the east, the groundwater process is gradually increasing, and the localised flow systems are more developed; and the intermediate water flow systems that discharged to the Gaolan river are developed near the ridge areas. The simulation result also shows that once the annual rainfall in the study area is reduced from medium 1,021.1 mm to the lowest 725.5 mm, the intermediate flow system discharged from the eastern recharge area to the Gaolan river increases; in this range of rainfall intensity, there is no intermediate or regional groundwater flow system developed across the inter-mountain blocks.