2-D Resistivity Imaging and Determination of Hydraulic Parameters of The Vadose Zone In A Cultivated Land In Southwestern Nigeria

A combined 2-D resistivity imaging survey and determination of hydraulic parameters of the vadose zone in a seasonally-flooded part of southwestern Nigeria that has been cultivated for the past 18 years is presented. The survey area is about 22 000m2 (2.2 ha) with the bedrock geology comprising Pre-Cambrian granite gneiss. Imaging data were measured along 11 lines, with a minimum inter-electrode spacing of 1 m; control data were obtained along two lines nearby. Soil samples were collected from 30 shallow pits at depths of 0.5, 1.0 and 1.5 m, respectively. The resistivity of the near-surface sandy-clay lithology is low at less than 50 Ωm while that at the control site is much higher. The natural moisture content ranges between 3.3 and 27.4% with a mean of 12.2%; porosity ranges between 9.9 and 36.8%, with a mean of 14.4%. The coefficient of permeability ranges between 9.61x10-7 and 1.01x10-5 cm sec-1. The study has shown that<br>changes in electrical properties of the soil could be due to variations in moisture content and that there is a close relationship between the sandy clay lithology and the recharge. Moreover, the soil could constitute an environmental problem at the peak of the rainy season.