The role of surface geophysics in the assessment of regional groundwaterpotential in Northern Nigeria

Abstract

Abstract An analysis has been made of the usefulness of surface geophysical site investigations as part of a rural water supply programme carried out in southern Kano State, northern Nigeria. Field work was undertaken under the auspices of the Kano State Agricultural Rural Development Project in conjunction with Groundwater Development Consultants (International) Ltd, Cambridge. The database for this study consists of the results of surface geophysical site investigations at over 200 rural villages and comprised electrical resistivity and/or electromagnetic ground conductivity methods together with hydrogeological data from boreholes drilled as tubewells. The groundwater potential of southern Kano State was determined as a result of field studies of hand-dug wells, water table levels, geological and geomorphological mapping, the use of aerial photographs and, in particular, surface geophysics. Areas with poor groundwater potential were successfully highlighted. A drilling programme was planned on the basis of these field studies which allowed the drilling rigs to be used to maximum effectiveness providing successful tubewells whilst the more problematical sites were investigated further. Wildcat wells sited without the aid of geophysics and drilled in the Basement Complex of the Younger Granite terrain in Kano State resulted in unacceptably high failure rates ( c. 70%). Once geophysical methods were introduced, the failure rate fell to less than 32% and, following further development of geophysical field and interpretation techniques, the final failure rate was around 17%. For a project whose target was 1000 successful tubewells, each costing of the order of £15,000, the saving to the client as a result of reduced number of failures was of the order of £5 million. The use of resistivity surveys, especially in conjunction with electromagnetic induction methods, has proved invaluable in the evaluation of groundwater potential and the planning of extensive drilling programme in southern Kano State.