Aquifer geo-hydraulic characteristics of Enugu and environs, southeastern Nigeria using pumping test and geo-sounding data

Direct current resistivity and pumping test data were used for this study to estimate the characteristics of the aquifer hydraulics of Enugu and its environs. Eighty-five vertical electrical sounding (VES) points were carried out using the digital ABEM™ Terrameter 4000 model. Nineteen parametric soundings out of 85 VES were carried out near existing productive boreholes where pumping test data were available for correlative purposes and to constrain the model predicting parameters. The Schlumberger electrode configuration was adopted for data acquisition across the study area. The study results from VES revealed the presence of three to nine geo-electric layers with the aquifer zone lying mainly between the fourth and fifth layers. Similarly, 25 curve types were encountered in the area with the QH type being the most prevalent. The aquifer’s resistivity in the area ranged from 2.8–88,745.0 Ω m, with a mean value of 5434.60 Ω m. The area’s aquifer depth ranges from 23.4 to 375.0 m, with a mean value of 132.53 m while the aquifer thickness in the area is highly varied, ranging from 10.0 to 224.0 m with an average value of 86.96 m. The longitudinal conductance across the study area varies from 0.001 to 29.714 mhos/m with a mean value of 1.073 mhos/m while the transverse resistance varies between 42.0 and 8,430,775.0 Ω m² with a mean value of 560,402.8 Ω m². Aquifer hydraulic estimation was carried out using a new set of formation-specific models proposed and used in this study in addition to the pumping test measurements made in the productive monitoring wells across the study area. The estimation of hydraulic characteristics of the area showed values which varied between 1.05 and 34.06 m/day with an average value of 5.59 m/day while transmissivity values varied between 25.70 and 2767.81 m²/day) with a mean value of 500.05 m²/day. The hydraulic conductivity estimated from pumping tests when compared with the values estimated from the new geologically constrained hydro-geophysical models exhibits results that show they are closely related. Thus, we recommend the integration of both methods for better and more accurate aquifer geo-hydraulic estimation in the study area.