Review: Hydrogeology of weathered crystalline/hard-rock aquifers—guidelines for the operational survey and management of their groundwater resources

Abstract Hard rocks or crystalline (i.e., plutonic and metamorphic rocks) constitute the basement of all continents, are particularly exposed at surface in large shields Africa, India, North South America, Australia Europe. They were, still some cases, to deep weathering processes. The storativity hydraulic conductivity hard rocks, thus their groundwater resources, controlled by these processes, which created profiles. Hard-rock aquifers then develop mainly within first 100 m below ground surface, Where partially noneroded, profiles comprise: (1) a capacitive but generally low-permeability unconsolidated layer (the saprolite), located immediately above (2) permeable stratiform fractured (SFL). development SFL’s fracture network is consequence stress induced swelling minerals, notably biotite. To much lesser extent, further weathering, conductivity, also develops deeper SFL, periphery preexisting geological discontinuities (joints, dykes, veins, lithological contacts, etc.). demonstration recognition this conceptual model have enabled understanding functioning such aquifers. Moreover, has facilitated comprehensive corpus applied methodologies hydrogeology geology, described review paper as water-well siting, mapping hydrogeological potentialities from local country scale, quantitative management, hydrodynamical modeling, protection hard-rock resources (even thermal mineral aquifers), computing drainage discharge tunnels, quarrying, etc.