Résumé
Hard rocks (granites, metamorphic rocks) occupy large areas of Africa and India. Well yields from hard rock aquifers are modest, commonly 2-3 m (super 3) .h (super -1) compared to those from other types of aquifers. However, these resources are geographically widespread and well suited to scattered settlement and small-to medium-size cities. They contribute greatly to the economic development of such regions, especially in arid and semi-arid areas where the surface water resources are limited. Significant advances have recently been made regarding the genesis, geometry, and hydraulics of hard rock aquifers, particularly in India. The hydrodynamic properties of these aquifers appear to be mainly related to weathering processes. The weathering profile, up to more than 100 m thick, is mainly composed of two layers: saprolite which provides groundwater storage; and saprock (fissured bedrock) which affords adequate transmissivity to sustain well discharges. These two layers constitute an aquifer system. New geological and hydrogeological conceptual models enable the spatial distribution and remnants of such weathering profiles to be mapped at the catchment scale and give rise to numerous practical applications: (1) mapping of groundwater potential on a regional scale; (2) sustainable water resources management at the watershed scale through multilayer mathematical modelling tools; and (3) management of groundwater quality issues such as non-point source pollution.