Identification of hydrogeological features using remote sensing and electromagnetic methods in the hard- rock formations of the Cameroon coastal plain (Central Africa): implications for water borehole location

Abstract

Sustainable access to groundwater in rural areas such as the coastal plain of Cameroon (Sub-Saharan Africa) is an ongoing challenge due to the lack of knowledge on hydrogeological features favorable to the identification of potential groundwater targets. In this study, remote sensing imagery and electromagnetic surveys were used to assess the hydrogeological potential of the Ngwei locality hard-rock. Automatic extraction of lineaments from Landsat-8 images indicated 200 lineaments with a total length of 293 km corresponding to 0.6 km of lineament per square km, suggesting a median groundwater potential. The main directions are NNW-SSE, N-S and NNE-SSW while the secondary directions are NW-SE; NE-SW and E-W. Surface geophysical investigations showed an electromagnetic field of 0 to 0.57 mV. These surface and borehole investigations confirmed basement fracturing and spatial variations in weathering profiles whose aquifer structure and yields (4.4 m3/h on average) are similar to what is commonly observed in the hard rock aquifer. The correlation between borehole productivity and the nearest lineament suggests that these lineaments are not (at least not all) surface traces of regional discontinuities that may act as major groundwater flow paths. This implies that the productivity of the Ngwei aquifers appears to be dependent on the fissured/fractured horizon, so exploration should be based on a contextual rather than general approach.Analysis of the consistency of the results with the field data allowed to propose a preliminary electromagnetic log model and also shows the value of using this approach to assess the availability of potential groundwater zones in hard rock areas. However, the methods used should be supported by further investigations to allow a better understanding of the hydrogeological characteristics of this part of the Central African basement so that no one is left behind in the achievement of the SDGs.