John Adeyemi Eyinade*
Groundwater remains a vital and strategic component of global freshwater resources, sustaining domestic, agricultural, and ecological needs, particularly in areas with limited access to surface water [1,2,3]. In Nigeria, reliance on groundwater has intensified due to the inadequacy of centralized water infrastructure, especially in urbanizing regions like Ile-Ife, Osun State [4, 5]. Consequently, borehole drilling has become widespread, often proceeding without scientific site assessment—resulting in failed wells, excessive abstraction, and poor resource planning [6]. Despite this growing dependency, few studies have systematically integrated electromagnetic geophysical data, borehole records, and terrain elevation models to evaluate groundwater table depth in Nigerian basement terrains. This methodological gap is particularly critical in areas underlain by crystalline rocks, where aquifers are highly discontinuous and their occurrence is governed by the extent of weathering and fracturing [7, 8, 9]. Topography plays a crucial role in groundwater distribution, influencing recharge patterns, surface runoff, and aquifer depth [10 11, 12]. Lowland zones often coincide with shallow water tables, while elevated terrains tend to host deeper groundwater systems due to their role as recharge zones [13]. Understanding this relationship is essential for improving borehole siting and optimizing resource extraction. To characterize subsurface properties, geophysical techniques—especially electromagnetic (EM) and electrical resistivity methods—have been widely employed across basement terrains [14]. While effective, these methods can be time-intensive, equipment-heavy, and spatially limited. In response, newer devices such as the ADMT-200S (an audio-frequency domain electromagnetic tool) offer real-time data acquisition with lower logistical demand, making them attractive for rapid field deployment. Complementing field-based surveys, remote sensing products like the Shuttle Radar Topographic Mission (SRTM)-derived Digital Elevation Models (DEMs) provide high-resolution surface data, offering insights into terrain-induced controls on groundwater recharge and discharge [15]. Several regional studies have shown the value of integrating DEMs with geophysical and borehole data for groundwater assessment, though such applications remain limited in Nigeria's crystalline environments [16, 17]. This study investigates the spatial relationship between surface terrain configuration and groundwater table depth in Ife Central and Ife East Local Government Areas of Osun State. By combining terrain elevation (SRTM-derived), geophysical data (ADMT-200S), and borehole depth measurements, this research presents an integrative methodology aimed at predicting water table variability across complex basement terrain. The goal is to improve groundwater targeting strategies, reduce borehole failure rates, and offer a replicable framework for groundwater exploration in similar settings across sub-Saharan Africa.
2. Materials and Methodology
This section outlines the materials used and the methodological framework adopted to investigate the relationship between surface terrain configuration and groundwater table depth in Ile-Ife. The research process involved the collection of field-based geophysical and hydrogeological data, acquisition of remote sensing datasets, and the integration of these through spatial and statistical analysis. The methodological flow integrates borehole records, electromagnetic soundings, and digital elevation modeling to develop a comparative framework that evaluates how topographic variability correlates with water table distribution. The approach is structured into three main components: definition of the study area, data collection and types, and data processing and analysis.
2.1. Study Area
The study was conducted in Ile-Ife, located in Osun State, southwestern Nigeria. Specifically, the study focused on Ife Central and Ife East Local Government Areas (LGAs), which are known for their growing population and increasing demand for groundwater resources. The region lies between latitudes 7°28'N and 7°34'N and longitudes 4°31'E and 4°36'E. This location is characterized by tropical wet and dry climatic conditions, with a bimodal rainfall pattern that contributes significantly to groundwater recharge. The area is geologically situated within the Precambrian Basement Complex of southwestern Nigeria. This complex comprises predominantly crystalline rocks such as granite gneiss, quartzite, and migmatite. These rocks are typically impermeable in their fresh state but become water-bearing when intensely weathered or fractured. The hydrogeological characteristics of the region are thus controlled by the thickness of the weathered overburden and the extent of fracturing, both of which influence groundwater storage and movement. Topographically, the region features an undulating terrain with elevation values ranging between 240 and 350 meters above sea level. The landscape includes ridges, gentle hills, and depressions, which play a critical role in defining surface runoff and potential recharge zones. The locations of Ife Central and Ife East Local Government Areas (LGAs) used in this study are shown in Figure 1. Hydrologically, the region is drained by tributaries of the Opa and Ooni Rivers, which are seasonal and directly influenced by rainfall. The proximity of the water table to the surface in lowland areas, coupled with anthropogenic activities such as construction and uncontrolled borehole drilling, underscores the need for a detailed spatial understanding of groundwater conditions. Groundwater is the main source of domestic and agricultural water supply in the area, as public water infrastructure remains insufficient to meet the growing demand. The selection of this region for the study was motivated by the hydrogeological diversity, surface topographic complexity, and prevalence of groundwater reliance. It provides a suitable natural laboratory to examine how surface terrain variations influence the spatial distribution and depth of underground water tables across different geomorphologic settings.
10.5281/zenodo.15779739