Multi-Scale Lineament Mapping and Fracture Network Characterization in the Tenkodogo Square Degree (Burkina Faso): Hydrogeological Implications

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Résumé

Groundwater development in crystalline and metamorphic basement terrains is hampered by the difficulty of locating productive fractures from optical lineament mapping alone, even when it is combined with surface geophysics. This study assesses the influence of geological structures on the geometry and functioning of the aquifers of the Tenkodogo square degree (Burkina Faso) through a multi-scale, multi-sensor approach combining aeromagnetic data, radar imagery and multispectral optical imagery. Magnetic lineaments were extracted manually from derived products and the analytic signal, whereas optical and radar lineaments were extracted automatically (PCI Geomatica) after enhancement (PCA, Laplacian, directional and Lee filters). In total, 502 aeromagnetic, 4476 optical and 39,764 radar lineaments were corrected for anthropogenic and topographic biases, then validated against existing geological data and checked locally through structural measurements at 17 field stations. The three networks were then merged, and the lineament intersection node density, an indicator of fracture network connectivity, was computed by quartic kernel estimation with a search radius of 5 km and a cell size of 100 m. Fracturing displays a scale-dependent hierarchical organization: aeromagnetic lineaments (median lengths of 7 to 16 km, locally exceeding 100 km) delineate regional structural corridors, whereas the shorter and denser optical and radar networks, the latter consisting of surface linear features potentially associated with shallow fracturing, provide local connectivity. The 192,030 retained nodes yield densities of 1.2 to 31.6 nodes/km2. Of the 1307 existing boreholes in the study area with a known yield, only 80 (6.1%) exceed 15 m3/h at the end of drilling. The proportion of boreholes yielding 3 m3/h or less decreases from 64.1% where node density is below 15 nodes/km2 to 45.1% where it exceeds 20 nodes/km2, but the rank correlation between node density and yield remains weak (Spearman’s ρ = 0.13). Two boreholes sited at Tenkodogo (23.5 nodes/km2) and Garango (23.7 nodes/km2), i.e., within the densest 6% of the study area, yielded 50 and 18 m3/h (airlift), respectively. These results argue for integrating multi-source structural analysis upstream of drilling campaigns in basement areas.

Mots-clés

Tenkodogo, Crystalline Basement, Fissured Aquifer, Lineament, Multi-Sensor Remote Sensing, High-Yield Borehole