Geo-hydraulic evaluation of aquifers of the Upper Imo River Basin, Southeastern Nigeria using Dar-Zarrouk parameters

Abstract

Aquifer geo-hydraulic evaluation of the Upper Imo River Basin, Southeastern Nigeria, was carried out to estimate aquifer parameters from surface resistivity data. Forty (40) vertical electrical sounding data were acquired with the ABEM™ Terrameter SAS 4000 using the Schlumberger array with a maximum current electrode separation of 1000 m. Seven (7) parametric soundings were carried out close to the location of existing boreholes with pumping test data to geologically constrain the predictive process. The vertical electrical sounding data were processed using a combination of curve matching and computer modeling using the OFFIX™ Software. Aquifer resistivity of the study area ranged between 136 and 4640 Ωm. The depth to water table varies between 23.6 and 94.5 m, while the aquifer thickness varies between 1.7and 126.2 m with Ibeku and environs having the thinnest aquifers. Estimates of the Dar-Zarrouk parameters revealed that the transverse resistance varies between 534.8 and 196,092 Ωm2, while the longitudinal conductance ranged between 0.001737 and 0.7211 Ω−1. Estimates of the geo-hydraulic parameters using Dar-Zarrouk parameters calibrated with local geology revealed that aquifer hydraulic conductivity ranges from 1.902 to 42.85 m/day and 0.4195 to 5.339 m/day for the areas underlain by the Benin and Ameki Formations, respectively. Similarly, aquifer transmissivity values on the other hand ranged between 71.97 and 1810.91 m2/day and 1.448 and 424.985 m2/day for the Benin and Ameki Formations, respectively. The range of aquifer hydraulic parameters interpreted in the study area revealed that the groundwater potentials of the area vary from fair to good with the areas underlain by the Benin Formation having higher groundwater potentials.