Integrated Geophysical Investigation of Gully Erosion in Ukpor Metropolis, Southeastern Nigeria Using Vertical Electrical Sounding and Electrical Resistivity Tomography Methods

Abstract

This research investigates the geophysical aspects of gully erosion in Ukpor Metropolis using Vertical Electrical Sounding (VES) and Electrical Resistivity Tomography (ERT) methods. We identified distinct subsurface lithological layers by interpreting resistivity curves and geoelectric sections across multiple sites, including clayey sands, dry sands, water-saturated sands, kaolinite clays, and shales. The resistivity data reveal a complex stratigraphy with varying aquifer depths and thicknesses, such as 39.5 meters and 97.3 meters. The study found that high resistivity values near the surface, indicative of porous and air-filled structures, significantly contribute to the area’s susceptibility to erosion. Soils with resistivity over 50 Ωm have an 87% probability of being highly erodible, which correlates with the gully-prone zones identified. The ERT results depict unstable heterogeneous zones, particularly those with sand lithology, prone to gully formation and potential landslides. Conversely, areas with consolidated kaolinite sand exhibit higher resistivity and lower susceptibility to erosion due to compaction and cement deposition in the sand’s pore spaces. The findings of this study underscore the critical role of subsurface lithology and resistivity characteristics in gully erosion processes. The study highlights the need for targeted erosion control measures and sustainable land management practices to mitigate the impact of gully formation in Ukpor Metropolis.