Contribution of Sentinel Radar Images 1Ato the Extraction of Lineaments from the Lobo Watershed (Center-West of the Ivory Coast)

Abstract

The improvement of the conditions of access to drinking water for the populations of the Lobo watershed requires the exploitation of groundwater because of the surface water which remains exposed to climatic hazards and the impacts of anthropic activities. And yet, these underground waters finds himself bedrock aquifer which are complex aquifers. Thus, the objective of this study is to characterize those fissure aquifers that who govern underground run-off in the aquifer system of the Lobo catchment area. The methodology adopted consisted in using 1A sentinel radar images to map fractures and their spatial distribution. The validation of the lineaments first consisted in comparing and highlighting the lineaments from the radar images and the fractures revealed from photo-geological images. Next, we superimposed the map of lineaments on the map of boreholes with a flow rate greater than or equal to 5 m3/h, which were considered as productive boreholes. To determine the traffic corridors, this fracturing map was superimposed on the piezometric map. This work made it possible to extract 9,753 lineaments over a surface area of 7,000 km². The various validation techniques enabled us to confirm 121 major fractures with an average length of 9 km. In addition, the most productive boreholes are located on average less than 300 m from the fractures. The analysis of the distribution of the orientations of these fractures revealed a heterogeneity of direction and a predominance of the N-S; NW-SE and NE-SW families. The Fracturing density maps and density of the number of fracture crossing points highlight the spatial heterogeneity of the fracture network which is controlled by geomorphology, geological formations and lithological contacts. The river Lobo and its main tributary the Dé, flow preferentially in fractures. This river and its tributary drains the aquifer system. The results obtained from different thematic maps are useful for the realisation of future high-yield hydraulic wells (Q ≥ 5 m3/h).