Detection of groundwater flow in fractured media through remote sensing techniques — some Nigerian cases

Abstract

About a decade or two ago, groundwater supply was always associated with regions of sedimentary basins and consequently, exploration for groundwater was carried out almost exclusively in such regions. However, recent advances in exploration techniques have shown that groundwater can be found in abundance even in rocky terrains devoid of deep sedimentary covers. The occurrence of groundwater in these crystalline basement areas is due primarily to secondary porosity and permeability created by the presence of discontinuities in such regions. The discontinuities in and through which groundwater occurs and flows are in form of fractures. The extent, width, roughness and nature of the fractures; their patterns of distribution in a given area; frequency of occurrence and type and amount of infilling in these fractures determine the amount of groundwater stored and the case with which it can be extracted for possible domestic and/or commercial uses. Most of the fractures occur deep within the basement complex and thus their detection by means of conventional geological field mapping techniques is not very feasible. However, remote sensing techniques such as radar imageries can be conveniently used to detect these fractures or zones where they occur. By carefully analysing imageries obtained through remote sensing, favourable sites could be selected for the location of boreholes that could tap the groundwater in these areas. This paper deals with the techniques for detection of fractures and siting of boreholes in rocky terrains. Few cases in which remote sensing techniques have been successfully used in the detection of groundwater in parts of southwestern and northern Nigeria are also cited.