Hydrogeology of the Picos de Europa National Park (northern of Spain)

The Picos de Europa National Park, with a total area of 675 km(2), is located in the North of Spain, in the provinces of Asturias, Cantabria and Leon. Carbonated materials predominate in the North and central areas of the Park, whilst to the South rocks are mainly siliceous. The complex geological structure caused by the superposition of two orogenies has conditioned the presence of a very karstified limestone series more than 2 km thick. The karst development is really important and it is well known that the Picos de Europa high mountains contain 14 % of the deepest discovered caves in the world. As far as hydrological planning is concerned, the park is integrated into the 016.214 Picos de Europa-Panes and 016.218 Alto Deva-Alto Cares groundwater bodies. The geological formations present in the Picos de Europa National Park, considering the permeability characteristics of the materials, can be classified as either aquifers or aquitards. The main aquifer is karst in nature and includes a powerful series of carboniferous limestones with an O-E orientation. The presence of siliciclastic formations, which behave like aquitards, determine the compartmentalization of the aquifer into "smaller underground water bodies" (hereinafter SGWB, the acronym for the English terminology, "smaller groundwater bodies") with dimensions of between 2 and 108 km(3) in volume. The piezometric level in the different SGWBs varies between 120 and 1,200 m a.s.l., descending in a staggered way to the North. It should be noted that in the Central and Eastern Massifs the piezometry is more uniform and is located between 300 and 500 m a.s.l. To the northern of the limit of the park, the main points of discharge of the carbonated aquifer are located between 120 and 150 m a.s.l. The aquifer recharge, preferably by direct infiltration, has a clear snow influence. The karst springs jointly discharge the water from the surface runoff infiltrated into the aquifer and the groundwater that comes from the different SGWBs. The presence of siliciclastic units, with general W-E directions that function as permeability barriers has caused the circulation of the underground flow to be directed predominantly northwards, and therefore, has led to the main springs being located in the northern part of the park.