Groundwater aquifers in Akungba-Akoko, a basement-terrain town in southwestern Nigeria, hold only low yield potential and receive limited natural protection from surface contaminants, according to a new geophysical assessment published in Environmental Geochemistry and Health.
Researchers led by Temitayo Olamide Ale conducted eighteen Schlumberger vertical electrical soundings across recharge, discharge, and intermediate zones of the area. The survey aimed to evaluate both groundwater potential and aquifer vulnerability by combining geoelectric measurements with index-based models, including transmissivity estimates, hydraulic conductivity, longitudinal conductance, the GLSI, GOD, and DRASTIC methods.
The soundings identified four geoelectric layers, with curve types classified as HA, AA, AK, and HK. Aquifer depth ranged from 3.5 to 9.0 metres, and aquifer thickness from 4.1 to 9.8 metres. Topsoil resistivity values between 87.9 and 405.2 ohm-metres indicated low corrosivity of the near-surface materials.
Hydraulic estimates pointed to modest water supplies. Transmissivity ranged from 0.71 to 3.48 square metres per day, and hydraulic conductivity from 1.27 × 10⁻⁶ to 1.53 × 10⁻⁵ metres per second, values the authors interpret as indicating low yield potential. The intermediate zones offered better prospects than the recharge and discharge zones.
Protective capacity was also weak across most of the surveyed area. Longitudinal conductance was below 0.1 mhos at 89 percent of the vertical electrical sounding points, indicating poor natural shielding of the aquifer. The GOD classification rated 56 percent of the sounding points as highly vulnerable, while the DRASTIC index classified the entire study area as moderately vulnerable.
Sensitivity analysis of the DRASTIC parameters identified the impact of the vadose zone, depth to groundwater, and net recharge as the factors contributing most strongly to the calculated vulnerability index. These results suggest that the thin, clayey sand overburden characteristic of the basement terrain provides limited natural protection, leaving the aquifer susceptible to contaminants originating at the surface.
To test the reliability of the vulnerability mapping, the team validated the maps quantitatively against published soil and groundwater quality data, alongside published groundwater sample results. The DRASTIC index showed a significant correlation with total dissolved solids from the hydrochemical validation dataset, with a Pearson correlation coefficient of 0.771 and a p-value of 0.009.
The authors state that the study advances methodology by combining zonation-based vertical electrical soundings with effective recharge estimates and quantitative validation. They describe the work as providing a practical framework for groundwater resource management, land-use planning, and targeted monitoring in rapidly urbanizing basement terrains.
Because the aquifers are shallow and poorly protected, the findings underscore the importance of careful land-use decisions in areas where groundwater is a primary water source. The study, published as an Original Paper in Volume 48 of the journal, was released online on 20 October 2026.
Subject of Research: Geoelectric assessment of groundwater potential and aquifer vulnerability in the basement terrain of Akungba-Akoko, southwestern Nigeria
Article Title: Geoelectric and vulnerability assessment of aquifers in recharge, discharge and intermediate zones of Southwestern Nigeria
Article References: Ale, T. O., Faseki, O. E., Aminu, M. B., Ololade, I. A., Daramola, S. O., Ayeniyo, O. O., & Olotu, E. J. (2026). Geoelectric and vulnerability assessment of aquifers in recharge, discharge and intermediate zones of Southwestern Nigeria. Environmental Geochemistry and Health, 48(16), Article 650. https://doi.org/10.1007/s10653-026-03536-7
Image Credits: AI Generated
DOI: 10.1007/s10653-026-03536-7
Keywords: groundwater, aquifer vulnerability, vertical electrical sounding, DRASTIC, GOD, hydraulic conductivity, transmissivity, longitudinal conductance, basement terrain, Nigeria, geophysics, water resources
News Source: Bethany Barker. (October 28, 2026). Shallow basement aquifers in southwestern Nigeria show limited natural protection, study finds. Scienmag.
