Tracer tests on distribution and structural characteristics of karst channels in Nandong underground river drainage

The high precision tracer tests were carried out to delineate the distribution of part karst channels in the Nandong underground river drainage and to analyze their structural characteristics. The results show that the No.1 underground stream has an independent water system, with its recharge area around Wabaibai. The chief channels of No.2 underground stream are overall towards to Yongning and Shidong. The channels of No.3 underground stream lead to Chenghongzai. The channels of No.2 and No.3 underground streams meet each other nearby Nandong outlets where the No.2 stream supplies No.3 stream during dry seasons. In addition, No.1 and No.2 underground streams present morphology of old and adult ages, respectively, and their courses are relatively fluent. Whereas, the No.3 underground stream developed later and has some cracks nearby its outlet. Finally, this paper infers and maps the general distribution of karst channels based on the existing data and the hydrogeological conditions in the drainage, providing a theoretical basis for the future karst hydrogeology surveys, geophysical prospecting, drilling and groundwater exploitation and utilization in this region.