Occurrence and flow of groundwater in crystalline rocks of Sardinia and Calabria (Italy): an overview of current knowledge

Crystalline rocks constitute aquifers that are of interest for water supply in many countries. In Italy, the hydrogeological characteristics of crystalline rocks are not well known and the interest in these aquifers is generally scarce. Nevertheless, the large extent of these rocks in Sardinia and Calabria regions and the local scarcity of water resources justify this preliminary analysis. Crossing the information derived by the available data on climate conditions, type of crystalline rock, structural setting, characteristics of wells and springs, base flow of streams and rivers and pumping test results, a preliminary quantification of the potential yield of the crystalline aquifers of both regions was performed. The processing of data involving different aspects confirmed that the crystalline rocks of Sardinia and Calabria form low-permeability aquifers where groundwater circulation occurs in the weathered layer and, mainly, in the most fissured layers closest to the surface. In the heavily fractured zones, it was seen that the groundwater flow is more active and can also occur at a greater depth. Groundwater mainly outflows in the valleys, feeding streams, numerous low discharge springs and surrounding aquifers. Climate, rock covers and tectonic style influence the aquifer yield, which has been evaluated herein to range from 1 to 2 L/s per km² and from 2 to 12 L/s per km² in Sardinia and Calabria, respectively. This preliminary characterization shows that there are reasons to deepen the present knowledge on these aquifers in order to optimize the present use of their groundwater resources