ABSTRACT
A macroscopic vision of the hydrogeological conditions of the world cannot be based on only one typology deduced from the predominant regional geological features. It could, and should, also identify and outline all first-order aquifer systems on the basis of analyses of their structure. Just as hydrographic structures come in various sizes, so too do groundwater systems. Less well-known than the “giant river systems”, there are nevertheless around forty very large aquifer systems with a surface area ranging from 100,000 to 1,000,000km2 or more, distributed across the continents and all the climate zones.
These first-order aquifers are usually linked to great sedimentary basins which are generally multilayered and whose maximum thickness may exceed 10,000 m. Altogether, they occupy 35 million km2 and probably contain the greater part of the continental fresh groundwater reserves. They often have multinational drainage basins, and social and economic problems have to be overcome in order to study them and manage their resources.
