Characterization of subsurface lithology based on resistivity grain gradation data in Mon Ikeun, Village, Aceh Besar, Indonesia

VES-based characterization of lithological heterogeneity for potential groundwater development in the quaternary floodplain of Jashore Sadar, Bangladesh

Subsurface geology in deltaic floodplains is highly heterogeneous, strongly influencing groundwater development. In response to growing groundwater stress and the need for potential management, this study investigates the capability of vertical electrical sounding (VES) to characterize lithological variability and infer hydrostratigraphic conditions within the active floodplain of the Quaternary deposits of Jashore, Bangladesh. A total of 18 VES surveys were conducted using the Schlumberger array with investigation depths of 90–150 m. One-dimensional inversion modeling using IX1D was validated against nearby borehole logs, showing strong agreement for layer depth and thickness (R² > 0.95) and approximately 75% agreement in lithological classification. The results show five geoelectric layers with resistivity values ranging from 6 to 60 Ωm, corresponding to topsoil, clay, silty clay, and sandy lithologies, indicating considerable lateral and vertical heterogeneity across the floodplain. Furthermore, geo-electric cross-sections indicate that shallow or thick sandy units are concentrated around VES-3–7, 9–11, and 14–17, whereas clay-rich deposits dominate VES-1, 12, 13, and 18. In particular, the sandy layers characterized by relatively high resistivity (36–60 Ωm) and substantial thickness (32.35–94 m) are interpreted as potential aquifer zones, while the overlying clay and silty clay units suggest as confining to semi-confining layers. Moreover, the absence of very low resistivity signatures suggests limited saline water intrusion within the investigated depth range. Although hydrochemical and pumping-test data are still required for confirmation, our study develops a conceptual framework of lithological heterogeneity using VES for potential groundwater management applicable for similar floodplain environments.

Assessment of hydrogeophysical delineation of groundwater zones using vertical electrical sounding (VES) in Jeypore Block, Koraput District, Odisha

Groundwater occurrence in hard-rock terrains is complex and spatially heterogeneous, controlled by weathered and fractured zones with limited surface expression. This research integrates Vertical Electrical Sounding (VES) with remote sensing, GIS and Analytical Hierarchy Process (AHP) for groundwater potential mapping of Jeypore Block, Koraput District, Odisha. This area is underlain by Eastern Ghats Mobile Belt rocks such as khondalites, charnockites, and granite gneisses. Fifteen VES surveys using Schlumberger configuration were conducted across the study area, with electrode spreads up to 800 m. Resistivity data were interpreted using IPI2WIN software, producing one-dimensional resistivity models and Dar-Zarrouk parameters. Subsurface profiling revealed distinct lithological layers consisting of topsoil, laterite, sandstone, weathered/fractured granite, and compact bedrock. Layer thicknesses ranged from 0.6 to 20.4 m in the first layer to 99.5 m in the third layer. Iso-resistivity maps generated using Surfer-25 showed significant lateral heterogeneity. Low-resistivity zones (2.6–105.2 Ωm) indicated saturated formations, whereas high-resistivity values (> 150 Ωm) represented compact basement rocks. Curve-type analysis identified predominantly AAA-type curves, which indicate increasing resistivity with depth. HA-type curves observed at two locations suggested the presence of conductive, water-saturated layers favourable for aquifer development. VES-derived parameters were integrated with twelve geospatial thematic layers, including geology, geomorphology, soil, NDVI, lineament density, drainage density, rainfall, slope, physiography, land use, groundwater fluctuation, and hydrogeology, using the AHP framework. The consistency ratio of the model was 2.36%, indicating reliable thematic weighting. Validation via pumping tests and ROC analysis (AUC = 0.86) confirmed model reliability. This approach offers a scientifically robust framework for sustainable groundwater management in structurally complex hard-rock terrains.

PATTERN OF ELECTRICAL RESISTIVITY IN REGOLITH AQUIFER AND THEIR IMPLICATION FOR GROUNDWATER MANAGEMENT IN ILORIN METROPOLIS, NIGERIA

Groundwater development in basement complex terrains is largely dependent on the occurrence and characteristics of the regolith aquifer, making geophysical investigation a vital precursor to borehole siting. This paper examines the pattern of electrical resistivity in the regolith aquifer of Ilorin metropolis, Kwara State, Nigeria. Forty (40) Vertical Electrical Sounding (VES) points were established across the study area to delineate subsurface lithological layers, determine resistivity patterns, and estimate weathering depth. The resistivity data were processed and interpreted using computer iteration techniques, while an aquifer potential index was used to evaluate groundwater potential. The findings reveal a geo-electric sequence of five lithological layers, comprising topsoil, lateritic layer, clayey soil, weathered basement, and fresh basement, with resistivity curve types identified as H, K, A, and Q. The regolith aquifer, represented by the weathered basement, recorded resistivity values ranging from 3.57Ωm to 297Ωm, while weathering depth varied from 3.30 m to 31.28 m, with both parameters showing higher values in the south-western and north-eastern parts of the study area. Analysis indicated that 45% of the study area exhibited optimum weathering and groundwater potential, whereas correlation analysis revealed a weak inverse relationship (r = -0.361) between regolith resistivity and aquifer potential, suggesting that resistivity alone is insufficient predictor of groundwater yield. The study concludes that the regolith aquifer constitutes the principal groundwater reservoir in the study area. Recommendations include the adoption of pre-drilling geophysical surveys as a mandatory practice and the prioritization of boreholes in zones identified with optimum aquifer potential.

Hydrogeophysical investigation for groundwater development in the crystalline terrain of Ohagainyi area of Lokoja, North-Central, Nigeria

DELINEATION OF QUATERNARY AQUIFER USING VERTICAL ELECTRICAL SOUNDING (VES) IN OGBIA AREA, BAYELSA STATE, NIGERIA

Electrical resistivity method using the schlumberger configuration were employed to delineate the quaternary aquifer in Ogbia area of Bayelsa State, Nigeria. The aim of this research is to determine the viability of the aquifer for borehole drilling. 10 VES points were carried out in Ogbia Area. They were interpreted by the use of IP12Win software. The interpreted VES data revealed 4-5 delineated layers of silty-clay, clay, clayey sand, sandy-clay, fine to coarse sand. Five sounding curve types were identified in the study area and they are of the KA, HA, QH, AK, and HKH types. The 4-layer geo-electric section were dominant compare to the 5-layer. The first aquifers were delineated at average depth of 24m and 34m with thicknesses ranging from 9.2m to 26.5m and resistivity ranging from310 to 8254Ωm while the 2nd aquifer were delineated at average depth of 37m to 43m with thicknesses ranging from 19.2m to 27m and resistivity values ranging from 740 to 9086Ωm. The second aquifer in the area are more reliable as sources of groundwater because they are less vulnerable to infiltration of surface contaminants and as well as possess better indices for higher groundwater yield due to their texture and greater thickness when compare to the first aquifer.

Hydrogeophysical Assessment of Groundwater Potential in the Deccan Basalt.

Groundwater occurrence in the Deccan basalt is highly uncertain. Non-invasive hydro-geophysical techniques, when integrated with a priori geological information, can aid in delineating saturated zones. This study uses electrical resistivity anisotropy with direct current (DC) resistivity and time-domain induced polarization (IP) for delineating groundwater prospects. We utilized the geophysical responses of DC resistivity, induced polarization, anisotropy and available borehole litholog data to locate the potential aquifers. Anisotropic inversion of DC resistivity data enables the identification of fractured basalt. We observed shallow saturation zones where fractured basalt overlies less permeable layers and deeper confined zones below the intertrappeans within fractured amygdaloidal basalts. The most productive shallow aquifers exhibit low to moderate resistivity (1 to 36 Ωm), and moderate to low chargeability (1.1 to 8 mV/V) and anisotropy (1.1 to 1.21). Finally, we conducted aquifer tests in different wells in the study area to quantify the aquifer parameters. This study offers a strong scientific basis for the assessment of groundwater potential zones and their management in the complex basaltic terrains of the Deccan province.