Paleochannel Detection and Groundwater Targeting Using Transient Electromagnetic and Seismic Methods Near Aguleri, Anambra State

Paleochannels buried beneath the alluvial plains near Aguleri in Anambra State are hypothesized as significant repositories of groundwater yet remain uncharacterized by systematic geophysical surveys. This study employs transient electromagnetic (TEM) and shallow seismic refraction methods to detect buried paleochannel systems and identify optimal groundwater targets near Aguleri. TEM soundings were conducted at thirty-five stations on a 500 m by 500 m grid using a 100 m by 100 m transmitter loop and a Geonics EM47 receiver. Shallow seismic refraction profiles were established along six traverses oriented perpendicular to the inferred paleodrainage direction. TEM data were inverted using the Occam smooth inversion approach to generate one-dimensional resistivity-depth sections, which were subsequently stitched into two-dimensional geoelectric sections. Resistivity sections reveal elongated low-resistivity bodies (8 to 30 ohm-m) at depths of 15 to 60 m interpreted as water-saturated coarse-grained paleochannel fill materials. Seismic refraction velocities within the inferred paleochannel (700 to 1,100 m/s) contrast with velocities of adjacent sandy clay sediments (300 to 500 m/s), confirming the presence of denser saturated coarse fill. Two principal paleochannel segments are delineated with widths of 150 m to 320 m, trending broadly northwest-southeast in alignment with the inferred path of an ancestral Niger River tributary. These paleochannel systems represent high-priority targets for borehole development, with estimated aquifer thicknesses of 30 to 45 m. This study provides a framework for paleochannel-targeted groundwater exploration in the Niger floodplain region.

Keywords: transient electromagnetic, seismic refraction, paleochannel, groundwater, Aguleri