Identification of Karst Underground River Catchment Areas with Artificial Tracer Tests and Water Balance in Banteng Cave Springs (Karst Gombong Selatan, Central Java)

¹ Karst Research Group, Faculty of Geography, Universitas Gadjah Mada, Yogyakarta, Indonesia
² Department of Environmental Geography, Faculty of Geography, Universitas Gadjah Mada, Yogyakarta, Indonesia
³ Department of Science and Geographic Information, Faculty of Geography, Universitas Gadjah Mada, Yogyakarta, Indonesia

^* Corresponding Author: m.qodri.alghozali@mail.ugm.ac.id

Abstract

The karst hills of Gombong Selatan have abundant potential water resources, especially in locations that have underground springs and rivers. The connectivity between the subsurface passageways that is difficult to know can threaten the potential of water resources, one of which is due to pollution caused by uncontrolled human activities. Therefore, identification of catchment systems and boundaries of water catchment areas in karst aquifers is needed that can contribute to sustainable water resources management policies. This catchment identification needs to be conducted because previous studies have never explored the eastern side of this karst area. This study aims to (1) define the underground river flow connectivity (upstream-downstream) of Banteng Cave; and (2) limiting the water catchment area of Banteng Cave. The method used to determine the subsurface connectivity system was carried out through an artificial tracer test, while the catchment area was delineated using a water balance approach. The results showed that the underground river of Banteng Cave has connectivity with Lake Blembeng, as evidenced by a change in watercolour after the tracer test and breakthrough curve (BTC) analysis of the tracing test results. BTC analysis shows that the Banteng Cave passageway has one main passage and does not have a tunnel branch. The estimated area of the Banteng Cave catchment used a water balance approach, which is 141.73 hectares. The Banteng Cave karst catchment conditions are dominated by the formation of valleys and karst cones accompanied by the appearance of valleys and karst hills that are quite evenly distributed, indicating that the Banteng Cave karst catchment is included in the advanced karst development phase. Furthermore, this research contributes significantly to increase knowledge regarding the characteristics of void karst development in aquifers which in the future are very important for determining water resources management policies.