2-D Resistivity Imaging Applied In Groundwater Exploration in Awka, Se Nigeria

By Ehirim, C. N. and Ebeniro, J. O.

Abstract

The groundwater resource of Enugu-Agidi to the SE of Awka was investigated using 2-D resistivity imaging. The survey was conducted along four profile lines each of length 1000m; with inter-traverse spacing of 250.0m within a (1x1) km2 area. Data acquisition was performed using Wenner-alpha array with a 10m electrode spacing to a maximum of 60m, and the Abem Terameter (SAS) 1000C. The data was processed by using RES2DINV software, and results were presented as inverse resistivity sections with RMS errors of between 2.2% to 6.6%. The resistivity of these inverse models varies from 15.25Om to 99927.0Om. Three promising confined aquifers were delineated to the NW and SE of profiles 1 and 2, respectively, at depths of between 62.0m to 90.0m. These were overlain by low resistivity hemispherical structures of confining clay / shale bed of resistivity < 205Om. This revelation was confirmed by the abandoned artesian well situated 20m to the east of traverse one. Unconfined aquifers were delineated at shallow portions of the sections along the traverses at an average depth of about 37.0m. The resistivity of the confined and unconfined aquifer materials varies from 243Om to 19037Om. The subsurface topography generally dips to the NW and SE of the river valleys in all the traverses, with major bedrock upwarp along P2-Profile in agreement with surface topographical expressions.

 

Key Words : 2D Resistivity Imaging, Confined Aquifer, Unconfined Aquifer, and Groundwater.

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