Geoelectrohydraulic parameters of shallow sandy aquifer in Itu, Akwa Ibom State (Nigeria) using geoelectric and hydrogeological measurements

Abstract

Knowledge of geoelectrohydraulic parameters is paramount in the management of groundwater resource and the design and construction of safe engineering structures. Results obtained from integrated borehole-constrained geophysical analyses and interpretations, in situ measurements on water samples and laboratory analyses of aquifer units were employed in estimating the basic geoelectrohydraulic parameters such as formation factor, porosity, tortuosity, coefficient of permeability, bulk and interface conductivities. Other parameters estimated are Dar-Zarrouk parameters and transmissivities. The application of empirical and semi-empirical models in the analyses of sixteen evenly spread resistivity and hydrogeological data of sixteen nearby aquifer repositories measured in laboratory were combined with the results of in situ measurements of water samples to obtain the geoelectrohydraulic properties. The ranges of results obtained and their variations established through computations and graphical illustrations show goodness of fit when compared with other ranges and variations documented in literatures. From the results, the upper hydrogeological units have bulk resistivity range of 804–6001Ωm with mean value of 4118Ωm. The range of water resistivity and the mean are respectively 21.9–612.0Ωm and 237.7Ωm. Formation resistivity factor ranges from 9.8 to 36.7 with an average value of 21.6. The estimated range and mean values of porosity were 16.7–29.69% and 21.8%. The tortuosity values range from 1.79 to 2.48 with a mean value of 2.11. The hydraulic conductivity values of the aquifer units gave a range spanning between 3.03×10−5 (2.6) and 2.38×10−4m/s (20.60m/day) with an average value of 7.46×10−5m/s (6.45m/day). The economic aquifers have thicknesses ranging from 27.9 to 103.0m and a mean value of 63.1m. The range and the mean values of Dar-Zarrouk parameters are 9.0×10−3–3.5×10−2Ω−1 and 1.8×10−2Ω−1 for longitudinal conductance and 22,432–565,882Ωm2 and 28,6393Ωm2 for transverse resistance respectively. The transmissivity also lies between 73 and 1186m2/day with a mean value of 672.0m2/day. The deduced parameters can be used as the physical basis for predicting groundwater flow and a guide to designing geofluid flow modelling programmes in the saturated subsurface of the study area. The estimated models and spatial spread of parameters from data processing are promising and suitable for use in contaminant migration modelling. They can also be used to improve the quality of existing models in the study area.