Litho-stratigraphic characterization of hydrogeological and hydraulic flow units via electrical resistivity, Stratigraphic Modified Lorenz Plots, and flow zone indicator models

Abstract

Litho-stratigraphic characterization within hydrogeological units of a major aquifer system in Southern Nigeria was carried out using Electrical Resistivity (ER), Stratigraphic Modified Lorenz Plots (SMLP), and Flow Zone Indicator (FZI) algorithms. The aim of integrating these technologies was to generate hydraulic flow units (HFU) that would describe the speed of flow and efficiency within the aquifer's stratigraphic units. Electrical Resistivity technology delineated four geoelectric layers within the study area: motley topsoil, coarse sand, fine sand, and sandy clay, with the aquiferous formation being the third layer. Via measures obtained from geo-electrical data, major geo-hydraulic parameters were estimated. The hydraulic conductivity ranged from 3.1 x 10⁻⁵ to 9.3 x 10⁻⁵ m/s, effective porosity ranged from 0.33 to 0.54, permeability ranged from 4362.9 to 13143.4 mD, tortuosity ranged from 0.85 to 0.97, Aquifer Quality Index (AQI) values ranged from 3.57 to 4.88 and Flow Zone Indicator values ranged from 4.11 to 7.00. The Stratigraphic Modified Lorenz Plots delineated the presence of three hydraulic flow units within the region. The first hydraulic flow zone was a superconductor with good efficiency ranking; the second and third flow zones were conductors having fair efficiency rankings. Results obtained from measures of Aquifer Quality Index (AQI) were employed to generate Discrete Rock Typing (DRT) results which indicated the presence of two distinct aquifer rock matrix types. The Dykstra-Parson co-efficient, employed in evaluation of aquifer heterogeneity, gave a value of unity, indicating perfect heterogeneity of the aquifer.