Estimating the productivity of boreholes in fractured crystalline basement using lineaments extracted from remote sensing data

Crystalline basement formations are originally without any hydrogeological potential  due to the poor primary porosity of rocks that they content. Therefore, finding productive zones of groundwater in those area becomes possible by a better knowledge of fracturing. The mapping of linear features on remotely sensed data is one of the keys to understand groundwater occurrence, in those area. For that purpose, The extraction of lineaments is a preliminary step in the selection of favorable sites for exploration of basement aquifers. The purpose of this work is to study the hydraulic role of the major lineaments of the Mayo-Banyo department (Adamawa Region, Cameroon) in the productivity of the boreholes through the analysis of the correlation between the productivity parameters of the high flow boreholes and the proximity to the major lineaments associated with other productivity index parameters such as topography, drilling depth, proximity to the nearest fracture node, lineament density and alteration thickness, and to suggest favorable areas for future hydraulic surveys. The application of the Canny filter and the shaded relief respectively on the Landsat 8 and SRTM image of the study area shows after statistical analysis a good correlation between the two methods in view of the obtained directional rosettes for lineaments. The main directions of the extracted lineaments are N-S, NNE-SSW and NNW-SSE. The NNE-SSW direction as indicated by several structural studies carried out in the region corresponds to the orientation of the D1 phase of tangential tectonics that the region underwent. The correlation analysis between the productivity of high flow boreholes (Q> 5 m3/h) and the proximity to major lineaments (L> 5km) of the NNE-SSW directional class shows a positive and relatively significant correlation (0.41). This result shows that the productivity of the boreholes in the department is influenced by the proximity to the main fracture directions. In addition, the analyses also show a combined effect of lineament density, topography (slope), borehole depth and alteration thickness on the productivity of high flow boreholes. The northeast and west of the study area have a greater density of lineaments. These areas would have been affected by greater structural deformation and therefore may have a higher potential for groundwater infiltration due to a greater density of lineaments that serve as weaving. Therefore, more local analysis with geophysical data in those areas should help to better locate future wells. 
Keywords: lineaments, basement aquifers, Mayo-Banyo.