Abstract
A geo-electric survey employing the Vertical Electrical Sounding (VES) was carried out in order to access the distributions of electrical and hydraulic parameters of hydro-geologic units in some locations of Makurdi where groundwater resources are difficult to tap. A total of fifteen geo-electric soundings were acquired. The contour maps were generated using the results. From the bulk aquifer resistivity and water resistivity values, the formation factor was calculated and it ranges from 4.12 to 10.07. The porosity with a range of 24.58 to 39.36% and hydraulic conductivity with a range of 0.85 to 45.1 m/day were estimated. The porosity values confirm that hydro-geologic units in the study area consist mainly of sandstone. The high resistivity in the northern part of the study area is due to high water quality while the southern part has lower resistivity due to the presence of argillaceous materials. It is also observed that the areas with low resistivity have high porosity. The observed low resistivity zone with high porosity is believed to have poor interconnected pores, the condition for high total or absolute porosity in argillaceous materials. The analyses of the geophysical data constrained by geological and borehole information revealed that potable water can be extracted within the depth of 35 to 50 m in the study area.
Key words: Porosity, formation factor, hydraulic conductivity, aquifer resistivity, Makurdi, geo-electric survey.
