Piezometry-surface permeability statistical approach for identifying topographic zonation patterns of groundwater flows in the shallow weathered hard rock aquifer of the Olézoa watershed (Yaoundé–Cameroon)

Shallow weathered hard rock aquifers are an important source of water supply, particularly in areas where water supply systems are deficient. The efficient use of water resources in these environments, therefore, requires additional knowledge of the hydrogeological processes of these aquifers. On the basis of statistical analysis of the piezometric data and hydraulic conductivity of the soil, this study permitted us to determine the hydrodynamic properties of the most superficial part of the hard rock aquifers of the Olézoa watershed in Cameroon. The vertical evolution of permeability at a depth of about 13 m was investigated by considering an exponential decay of permeability throughout the portion of the weathering profile overlying the coarse saprolite. The model was applied by simulating a range of exponential ( α coefficient) relationships defining hydraulic conductivity versus depth. In this aquifer, piezometry generally follows the topography and the hydraulic conductivities are relatively weak and have a heterogeneous distribution which can nevertheless be related to morphopedological features. The hierarchical cluster analysis of hydraulic conductivity data and piezometric levels revealed links between these two parameters. This study made it possible to identify a variability in hydrogeological environments as a function of the value of α , the investigated depth in the field (piezometric level or bottom of the well) and the considered hydraulic conductivity (variable, K s ; estimated, K m and identical, K e ). It also made it possible to understand the dynamics of groundwater and to specify the groundwater table conditions which is useful for the sustainable management of groundwater. Understanding the effect of exponential decay of hydraulic conductivity on piezometric levels may be useful in future modeling efforts of shallow weathered hard rock aquifers.