Analysis of Groundwater Level Dynamics in Response to Seasonal Meteorological Conditions Using Integrated 2D Resistivity Profiling and ADMT Method: A Case Study of Surabaya City

Surabaya, the second-largest metropolitan city in Indonesia, faces significant groundwater challenges due to rapid urbanization and excessive extraction, contributing to land subsidence. This study investigates groundwater dynamics in relation to meteorological and tidal variations, integrating geophysical methods with geodetic data for subsurface characterization. GNSS static measurements provided orthometric elevations of 4.381 m a.s.l. for Tandes TD-01, 4.853 m a.s.l. for TD-02, and 5.670 m a.s.l. for Gayungan GY-01, ensuring vertical consistency. Groundwater data from Tandes and Gayungan (2022-2025) were analyzed alongside GSMaP rainfall data and BMKG meteorological and tidal data. Results show rainfall influences groundwater recharge, with depths varying from -190 cm to -140 cm during peak rainfall, and decreasing below -250 cm in dry periods. Temperature and humidity show inverse seasonal trends, affecting recharge via evapotranspiration, while tides have no effect due to the inland location of both wells. Geoelectrical surveys revealed resistivity variations. Tandes exhibited higher permeability and rapid recharge, with resistivity values ranging from 2.5 to 10 ω·m during the rainy season, while resistivity increased above 10 ω·m in the dry season. Gayungan showed more stable groundwater levels, with semi-confined aquifer characteristics. ADMT millivolt readings ranged from 0-43 mV at Tandes and 0-50 mV at Gayungan in the dry season, indicating lower groundwater conductivity. The groundwater levels in Tandes are more responsive to seasonal changes due to its permeable aquifer, while Gayungan's semi-confined aquifer shows greater stability. Geophysical data confirms seasonal groundwater saturation variability, highlighting the importance of sustainable groundwater management in Surabaya to mitigate seasonal fluctuations in groundwater resources.