Assessment of Gully Erosion Through Combined Electrical Resistivity Surveys and Soil Testing in Enugu North, Southeastern Nigeria

Abstract

A geophysical investigation was conducted to assess gully erosion in selected parts of the Enugu North zone, Southeastern Nigeria. The study employed the electrical resistivity method alongside soil test analyses to evaluate subsurface conditions contributing to erosion. Four electrical resistivity tomography (ERT) profiles were acquired using the Wenner electrode configuration, with a maximum electrode spread of 200 meters. The resistivity data revealed zones of both low and high resistivity. Low resistivity values are indicative of loosely consolidated, sandy materials, whereas high resistivity values are associated with more compact subsurface features, likely comprising silt, clay, and bedrock. The two-dimensional ERT inversion delineated three distinct subsurface layers: an upper layer of loose, sandy soil; a transitional layer of sandy clay; and a deeper, compacted layer predominantly composed of dry clay. Complementary soil tests further confirmed that the surface materials are primarily composed of loose, non-cohesive soils, including sandy loam, coarse sand, and fine sand. These characteristics suggest a predominance of non-plastic and non-cohesive soils, which significantly contribute to the region's vulnerability to gully erosion.