Identification of Underground River Flow in Karst Area of Sumber Bening-Malang, Indonesia Based on Geoelectrical Self-Potential and Resistivity Data

Research has been conducted on karst area in Sumber Bening Malang, Indonesia. The research objective is to find out the underground river flow. Data acquisition was carried out using two types of geophysics method, namely the self-potential method and the resistivity method of dipole-dipole configuration. In the self-potential method, data acquisition is carried out as many as 176 points where each point is measured five times with the distance between points is 10 m. In the resistivity method of dipole-dipole configuration, data acquisition was carried out as much as 6 lines. Based on the results of measurement and data processing, the electrical potential value detected in the study location was around 0-14 mV and low potential values (0-1.5 mV) indicated as underground river flow. The resistivity value in the research location is in the range of 122800 Ωm, which value 1-221 Ωm interpreted as sandy marl and 222-22800 Ωm as carbonate. The results of self-potential and resistivity interpretations show underground river flow found beneath carbonate rock layers and from there it can be suspected that fluid flows from the northeast to the southwest of the