Evaluation of groundwater potential, aquifer parameters and vulnerability using geoelectrical method: a case study of parts of the Sanaga Maritime Division, Douala, Cameroon

A geoelectric survey was carried out in parts of the Sanaga maritime division where the limited quality of surface water sources, insufficient geophysical knowledge and a growing population have had a significant impact on the assessment and development of groundwater in the area. Forty-six vertical electrical soundings (VES) involving the Schlumberger electrode configuration were carried out across the study area to assess the groundwater potential and vulnerability which will assist in the proper siting of wells/boreholes. The VES survey was carried out using the ABEM SAS 1000 instrument with a maximum current electrode spread (AB/2) of 120 m. Field data obtained were curve-matched and iterated using the JOINTEM software to estimate groundwater repositories. The modelling results revealed three to five geoelectric layers including the topsoil, laterite, weathered formation, cracked gneiss and gneiss. VES curves obtained included the A, AA, H, HA, HK, HKH, KH, KHK, and QH. A correlation between borehole logs and the VES lithology was made and is in agreement. The aquifer unit was identified at the third and fourth geoelectric layers with thickness and resistivity ranging from 18 to 47 m and 93-16500 ohm m, respectively. The evaluated aquifer parameters (longitudinal conductance, transverse resistance, hydraulic conductivity, transmissivity, reflection coefficient and fracture contrast) ranged: 0.0026 to 0.28 mhos, 1981 to 702,405 ohm m(2), 0.05 to 5.67 m/day, 2-150 m(2)/day, -0.67 to 0.93, and 0.19 to 29, respectively. Contour maps were drawn from the estimated aquifer parameters to show their distribution in the study area, from which groundwater potential areas were delineated. The distribution of longitudinal conductance showed poor to moderate protective capacity throughout the study area. The findings of this study hold significant value as a reference for guiding groundwater exploration and development activities in the study area.