Hydrogeological Units

The distribution of underground water resources in mainland Portugal is closely related to the geological actions that shaped our territory. In the Mesocenozoic basins, mainly occupied by decritical or carbonated rocks, little or nothing affected by metamorphism phenomena, there are the most productive aquifers with the most abundant resources. The Old Massif, consisting primarily of eruptive and metasedimentary rocks, generally has few resources, although some exceptions are noted, usually related to the presence of limestone mass. The correspondence between the distribution and characteristics of the aquifers and the geological units had already been noted by several authors, having formed the basis for the establishment, by INAG, of four hydrogeological units, corresponding to the four large morpho-structural units in which the country is divided: Ancient Massif, also known as the Iberian Massif or Hespérico Massif. *Western Mesocenozoicorla, abbreviated as the Western Rim. Southern Mesocenozoic Dorla, abbreviated as the Southern Rim. *Tejo-Sado Tertiary Basin, abbreviated as the Tagus-Sado Basin.