Hydro-geophysical mapping of occurrences and lateral continuity of aquifers in coastal and landward parts of Ikorodu, Lagos, Southwestern Nigeria

Abstract

Hydro-geophysical investigation of groundwater resource of Ikorodu area, SE Lagos was carried out using vertical electrical sounding (VES), lithologic, resistivity, and gamma ray logs. This was with the aim of evaluating the lateral and vertical variations of lithologic sequence and also delineates the aquifers within the subsurface. Fifty (53) VES of which six (6) traverse lines were selected and their geo-electric logs along these profiles were correlated to highlight the extent of continuity of different layers and evaluate their hydrogeological significance in the study are. The field data were curve-matched and computer iterated. Both modelled VES curves and borehole logs showed the alternation of subsurface layers of clay, sandy clay, “upper” sand, “lower” sand, and ferrugenized sand. The resistivities (Ω m) of these layers are: 3.3–93.9, 102.6–155.5, 219.9–1140, 250.6–1020.2, and 1428.8–6141, while the thicknesses in metres are: 0.5–62.6, 0.5–30.9, 1.4–34, 15–112.4, and 6.2–60.1, respectively. Lithologic, geo-electric, and gamma ray logs revealed the occurrence of confined/semi-confined and unconfined aquifers/semi-unconfined which correspond to lower and upper sands, respectively. Domestic water needs are largely supplied by two aquiferous horizons—the upper and the lower sands. While the upper sand supports only shallow hand-dug wells exclusively around the coastal area, the lower sand provides groundwater supply in the landward area. The present study has provided some useful insights in the understanding of the groundwater resource in the area which is useful for groundwater management.