IMPACT OF BAUXITE MINING ON AQUIFER HYDRODYNAMICS IN THE COGON CATCHMENT (SANGARÉDI, GUINEA): A SEASONAL PIEZOMETRIC APPROACH

Abstract

Open-pit bauxite mining on the duricrust-capped plateaus of the Boké region reshapes the land surface, yet its effects on groundwater remain poorly documented. This study assesses how the activity affects aquifer hydrodynamics in the Cogon catchment, within the concession of the Compagnie des Bauxites de Guinée (CBG). Thirty-one piezometers were monitored during two campaigns, one in the dry season (March–April) and one in the rainy season (July–August). Hydraulic heads, derived from a digital elevation model, were interpolated by ordinary kriging to map depth to water and the seasonal amplitude ΔH, and saturated thickness was integrated to estimate the geometric volume of the saturated zone. The water table is generally shallow (less than 20 m below ground over most of the catchment) and flows from northwest to southeast. Seasonal amplitude ranges from 5 to 24 m (mean ≈ 14 m); it peaks in the northeast (P1–P3) and stays moderate in the west-central sector (P19, P22, P23). The geometric saturated volume increases by 1.40 × 109 m³ (+29.5%) over an area of 371.4 km². A closed piezometric depression centered on wells P18–P19, which coincides with active mining sectors, forms in the dry season and fades during the rains. This local signature is consistent with the effect of mine dewatering or industrial abstraction, although two campaigns are not enough to establish a causal link. Confirming it will require multi-year monthly piezometric monitoring and an inventory of abstractions.