Resistivity and Induced Polarization Survey for Characterizing Saline Water Intrusion into Shallow Aquifers in Ebonyi River Floodplain

The Ebonyi River floodplain supports a dense agricultural and domestic population whose groundwater supply is threatened by saline water intrusion linked to seasonal flooding and geological salt deposits associated with the evaporitic facies of the Benue Trough. This study applies combined resistivity and induced polarization methods to characterize saline water intrusion into shallow aquifers in the Ebonyi River floodplain. Fourteen profiles were acquired using a Syscal R1 Plus instrument in combined resistivity and IP mode with Wenner-Schlumberger configuration. Two-dimensional inversions were performed simultaneously for resistivity and chargeability using ZondRes2D software. Resistivity values below 3 ohm-m in the shallow zone (0 to 8 m) are interpreted as indicative of saline water-saturated sediments, while chargeability values exceeding 10 ms identify zones of clay-bound ionic exchange characteristic of transitional salinity conditions. Three distinct saline intrusion fronts are mapped across the floodplain, with lateral extents of 80 m to 350 m from the main river channel. Seasonal comparison using data from wet and dry season surveys reveals that saline intrusion advances an average of 55 m inland during peak flooding periods. Domestic wells within 100 m of the identified saline fronts are flagged as at-risk water sources. The study provides a geophysical basis for groundwater protection zone designation in the Ebonyi River floodplain.

Keywords: induced polarization, saline water intrusion, floodplain aquifer, Benue Trough, Ebonyi River