Determination of aquifer parameters from geosounding data in parts of Afikpo Sub-basin, southeastern Nigeria

Abstract

Aquifer parameters (e.g. hydraulic conductivity and transmissivity) are routinely determined from pumping tests. Pumping tests are very expensive and researchers have continued to explore cheaper and reliable alternatives to determine these parameters at locations without producing wells. Electrical resistivity method was applied to determine hydraulic conductivity and transmissivity in areas without boreholes in the present study area. Fifteen (15) vertical electrical soundings with a maximum current electrode spacing of 300 m, in the Schlumberger configuration, were acquired. Seven (7) of the soundings were carried out near existing boreholes for comparative analysis between geologic and geoelectric sections. Modelling was done using the IPI2™ software. Cross-plot of hydraulic conductivity (K) obtained from pumping tests and aquifer resistivity (ρ) extracted from sounding interpretations was used to generate a linear relation of the form K = 0.0426ρ + 0.8584. A similar cross-plot between transmissivity (T) and transverse resistance (R) gave another linear relation of the form T = 31.92–0.0019R. These relations, which connects geoelectrical properties with aquifer hydraulic properties, were used to estimate aquifer properties in areas away from well locations. Results show that depth to water ranges from 11.5 m at Mgbom to 52.1 m at Immama Ozizza, while aquifer thickness varies from 14 m at Poperi Primary School, Amasiri (VES 1) to 47.6 m at Immama Ozizza (VES 11). Hydraulic conductivity values range from 1.344 m/day at Mgbom (VES 2) and 2.792 m/day at Okpotokun Primary School Amata-Akpoha (VES 15), with a mean of 2.068 m/day. Transmissivity on the other hand varies between 28.18m2/day at Immama Ozizza (VES 11) and 31.73 m2/day at Mgbom (VES 2) with a mean of 29.96 m2/day. The derived results correlates well with those obtained from pumping test analysis and have provided a cost-effective method for estimating aquifer hydraulic parameters in areas away from well locations.