Mapping Underground River Flows in karst Areas with the VLF-EM Method (Case Study of the Krawak Region, Singgahan Tuban)

The Krawak Springs is a source of springs from the cracks of river rocks in the middle of a teak forest in Guwoterus Village, Montong District, Tuban. This spring is a source of irrigation water for agricultural land in the District of Montong. Based on its urgency, it is necessary maintaining its sustainability by identifying recharge areas and underground river flows. VLF is quite advantageous for use in the regional mapping underground rivers in karst areas because can describe the structure of the karst environment and predict interconnected pathways in karst. Data acquisition uses four tracks with an average length of about 300 m. Data processing was made qualitatively using MATLAB software and quantitatively using Inv2DVLF software. Qualitative results show that the conductive zone is identified as a subsurface river flow. From the processing results, it is known that the subsurface river flow zone can be identified as a zone that is conductive or has low resistivity.