Hydraulic interconnections study of Seropan-Ngreneng-Bribin underground rivers in Gunung Kidul karst area using tracer technique

Series of studies have been conducted to investigate the hydraulic connection between Seropan underground rivers with other underground rivers in Gunung Kidul karst area. Stable isotopes composition, hydrochemical contents of collected samples from several sources around Seropan cave together with tracer tests that have been conducted in the area have helped us to establish hydraulic connection of Seropan underground river with adjacent underground rivers in Gunung Kidul karst area. Several tracer tests that have been conducted in the study area have revealed that subsurface water flowed from Seropan to Ngreneng cave with average travel time about six hours and 13 minutes. Analyses of breakthrough curves found from the tracer tests hinted that the flow is a direct flow with large well developed conduit without any significant delay due to water depressions and dead zones. Although downstream flow paths of Seropan underground river were successfully determined, however, upstream hydraulic connection were not been established. Future study should focus on the upper part (upstream) of Seropan cave.