Modelling aquifer parameters using surficial geophysical techniques: a case study of Ovwian, Southern Nigeria

Abstract

Vertical electrical sounding (VES), pumping test and grain size distribution techniques have been used to model the hydraulic parameters in Ovwian, Nigeria. Twenty-two depth soundings were carried out with a maximum current electrode separation of 400 m to delineate the aquifer layers while the pumping test and grain size distribution procedures were conducted by drilling two boreholes where thirteen representative soil samples were collected at an interval of 3.048 m. The field data obtained from the resistivity sounding were modelled using the Win Resist software and the results when correlated with borehole log identified five geoelectric units made up of the topsoil, clayey sand, sandstone, fine grain sand and coarse grain sand. The sands of the third and fourth geologic layers constitute the aquiferous units with depth which varied between 6 and 42 m while the aquifer resistivity ranged between 100 and 2100 Ωm. The pumping test was analysed using the Copper Jacob method and the results revealed that the hydraulic conductivity and transmissivity of the aquifer from the reference well are 30.467 m/day and 495.072 m2/day, respectively. These results together with results from the vertical electrical soundings were used to model the hydraulic conductivity and transmissivity values for the area. This showed that the hydraulic conductivity of the area ranged from 28.595 to 38.435 m/day, with a mean value of 30.757 m/day while the transmissivity ranged from 185.697 to 1310.636 m2/day, with a mean of 495.752 m2/day. The grain size distribution analysis also revealed the hydraulic conductivity value of 1.46–171.94 m/day with an average of 38.880 m/day, while transmissivity ranged from 23.725 to 2794.025 m2/day with an average values of 631.738 m2/day. The close approximations of the results revealed the reliability of the VES, pumping test and grain size distribution analysis in the estimation of aquifer hydraulic parameters for groundwater resource development. Analyses of the results obtained in this study suggest that the aquifer is prolific and highly permeable with a high degree of rechargeability.