Hydrogeophysics of tropical Africa: recent advances and perspectives

Abstract

In the present work an attempt is made to put into perspective the hydrogeophysical investigations for rural water supply carried out over the last two decades in tropical Africa, paying special attention to groundwater targets in the weathered rocks in and above the crystalline basement. The applicability of geophysical techniques in groundwater investigations in tropical Africa, particularly the DC resistivity and electromagnetic techniques is discussed in the light of recent developments in instrumentation, data collection and interpretation procedures. Although there has been an increase in the use of 2D resistivity surveying systems, standard VES is still the main tool of geophysical surveys for groundwater in Africa, where it is often used to characterise the lithology of the weathered layer. In the present work, two automatic 1D inversion schemes based on iterative least squares procedures with singular value decomposition are presented. In order to reinforce the convergence of the inversion schemes towards a global minimum, the standard least squares procedure is combined with other measures of robustness and search strategies in the parameter space. Tests with synthetic and field data prove their usefulness for fast interpretation of DC resistivity data. Compared with plane wave RMT data DC resistivity data generally seem to have less resolving power for the models tested.