Groundwater exploitation in the Abakaliki metropolis (southeastern Nigeria): Issues and challenges

摘要

This paper assesses and evaluates geologically related problems and issues associated with five ‘abortive’ boreholes drilled within the Abakaliki metropolis, southeastern Nigeria. Results of the vertical electrical geophysical soundings (VES), carried out in these borehole locations, show that the underlying Abakaliki Shale Formation in those areas has six layered model. While the uppermost layer has an apparent resistivity value of range 240 to 1120 ohm-m and a thickness of range 1.0 to 1.2 m, and is interpreted as lateritic overburden. The 2nd to 5th layers have apparent resistivity values that range from of 25 to 1025 ohm-m, with depth that range from 0.8 to 25 m. The 6th layer has mean apparent resistivity value of 443.25 ohm-m and undetermined thickness. The range of the apparent resistivity values and a correlation with local geological data reveal that the formation, although layered, is predominantly shaley, which become fresh, unweathered and ‘unfractured’ at greater depth. Although the studied boreholes all exceeded the depth to watertable of some functional boreholes in the area (28-50 m below the surface), they are all sparsely productive to abortive, suggesting that the concept of a ground water table with regional flow is very likely to be unrealistic in the area. Hence, an integrated geophysical survey method is required to identify productive spots.