Analysis of hydrological process of drip water in the aeration zone of a typical karst stone hill

Xiaoyan cave is located in Yaji village approximately 8 km southeast of Guilin City in Guangxi (N25°14′53, E110°22′33). Geomorphologically, the cave is on the boundary between adjacent peak cluster and peak forest karst systems. Xiaoyan cave is developed in massive pure Upper Devonian limestone with a bioclastic sparite to micrite texture. The limestones dip gently toward the south-west. The altitude of the cave is 197.5 m. The total length of cave measures 100 m, the width of cave is about 25 m and the thickness of the cave roof is approximately 20-150 m. XY5 is a perennial drip point, which is the largest drip water point in the cave. The overburden above the cave is about 0.3-1 m thick. The area has a subtropical monsoon climate with mean temperature of 18.9℃， and long-term mean annual rainfall of 1 886 mm.In order to study the hydrological processes of cave drip water flow, cave drip water was sampled, and water level, conductivity, and temperature were automatically monitored in Xiaoyan cave’s karst aeration zone. The response of the drip water, water chemistry and dynamic characteristics to the rain was analyzed. The results indicate that the drip water flow rate, conductivity and water temperature have a good corresponding relationship. Rainfall, rainfall intensity and the pre-rainfall water content of the rock and soil mass overlying Xiaoyan cave are the main factors affecting water flux; the flow rate ranges from 23.15 to 589.47 mL/s. Temperature has the fastest response to rainfall, while water flux and conductivity basically increase at the same time. Water temperature is mainly affected by the local temperature. Conductivity exhibits obvious seasonal changes,with higher values and lower amplitude in the rainy season, lower values and and a large amplitude in the dry season. Due to the hydrological processes of the wet and dry conditions, combined with dynamic changes in the main hydrochemical components in the dry season, conductivity and temperature exhibit three peaks. The different peaks correspond to different runoff water: preferential flow, soil-rock interface runoff and fracture water. Therefore, through the hydrological processes and the dynamic change characteristics of hydrochemical indicators, we can qualitatively reflect the drip water source, flow paths, time and the changes in environment conditions.