Identification of underground river using geoelectrical method to reduce drought disaster in Bayemharjo Village, Wonogiri

Abstract Bayemharjo Village in Giritontro Subdistrict, Wonogiri Regency, is located in a karst area that often experiences drought due to the absence of permanent surface water. This condition is caused by high infiltration rates in karst soil, where rainfall quickly seeps into the underground network through holes and cracks. As a result, identifying the underground river system is crucial for water resource management and drought mitigation. This study aims to characterize the underground river pathways using geoelectric resistivity methods. Three survey lines were measured using Wenner–Schlumberger and Wenner configurations for 2D mapping, supplemented by one Vertical Electrical Sounding (VES) point with a Schlumberger configuration for 1D profiling. Data collection was conducted from October 2024 to April 2025, with data processed for 2D and 1D inversions. The lithology is dominated by sandy clay, tuff sandstone, marl limestone, dense limestone, and conglomerate limestone. High resistivity anomalies (≥4634 Ωm) at depths of 10–20 m on profiles AA′ and CC′ are interpreted as karst cavities, representing main channels and branches. Profile BB′ does not show large cavities, functioning as an infiltration pathway. VES confirms the presence of cavities in AA′, interpreted as air-filled cavities during the dry season, indicating seasonal storage capacity. These results indicate a channel system parallel to the NW–SE fault structure. These cavities may function as seasonal reservoirs, offering potential for groundwater management and drought mitigation strategies in the Bayemharjo karst area.