Vulnerability assessment of hydrogeologic units in parts of Enugu North, Southeastern Nigeria, using integrated electrical resistivity methods

摘要

Aim/objectives: This research is geared towards integrating Vertical Electrical Soundings (VES) and Electrical Resistivity Tomography (ERT) profiles constrained with geoelectric sections and borehole logs to assess the vulnerability of the aquifer units employing Aquifer Vulnerability Indexing (AVI) method.Method: The dataset used in this study comprises of fifty VES, five ERT profiles surveyed in parts of Enugu north in Enugu state, two geoelectric sections and three borehole logs. The computer and manual interpretation of VES resistivity data using WinResist software gave values of resistivity, depth and thickness of each geoelectric layer using half current electrode spacing of 1.0 to 450.0m and maximum current electrode spacing of 900 m. 2D imaging data from the measured field resistance values were processed using RES2DINV 32 version 3.71.115 software. The geoelectrical sections show the variation of resistivities with depth along transcent lines. The geohydraulic parameters were also estimated. Finding: Interpreted VES data revealed five to six geoelectric layers and fundamental parameters generated were used to estimate the values of hydraulic conductivity (s ) and hydraulic resistance (C) of the covering layers ranging from 0.010 to 0.769 mday??1 and 40.47 to 8292.0 day??1 respectively.This research revealed high hydraulic conductivity in the western part implying good groundwater potential with moderate to high protective capacity while areas with low hydraulic conductivity correspond to areas with high resistivity indicating little or no pore space and total devoid of water. The hydraulic resistance quantifies groundwater vulnerability using AVI and reveals that the area of study is characterized by low to high AVI with moderate AVI dominanting.Originality and novelty: The estimated geohydraulic properties from resistivity data and their spatial spread are promising and could increase the depth of knowledge on groundwater vulnerability within and around the study area.