Development characteristics and connectivity analysis of Buquan underground river in Guangxi Province

To detect the karst development characteristics and distribution, long-term groundwater level was observed and groundwater tracer test was conducted based on the integrated 1:50 000 hydrogeological surveys in Buquan underground river of Guangxi Province. Surface and underground karst development chracteristics were summarized, and the connectivity of branches in the upstream and midstream of Buquan underground river was analyzed. The results show that this area is mainly peak cluster and depression landform with strong corrosion. The branch distribution of the underground river is along with faults, with dendritic planar form and ladder-shape profile form. Groundwater level has hysteretic response to precipitation in Buquan midstream and downstream, while it has sensitive response to precipitation in the upstream and the areas away form karst pipeline. The average flow rates are 1 166 m/d and 1 079 m/d for the upstream and midstream respectively, indicating fast groundwater flow. And groundwater in the Buquan upstream has larger hydraulic gradient than that in the midstream. Besides, the upstream has more river branches, suggesting complex groundwater connection. Pipelines in the midstream are clear and show better connectivity.