Lithostratigraphical and Hydrogeological Characteristics of the Aquifers of the Low Friuli Plain and Sustainability of Groundwater Extractions

The hydrogeological characteristics of the Friuli Plain derive from the depositional processes which occurred in the Upper Pleistocene. Such processes led to a sedimentation of materials whose geometry and development were conditioned both by the geological-structural evolution of the pre-Quaternary substratum and by sea level fluctuations connected with climatic events of Quaternary glaciations. The consequent changes in the dynamics of the alluvial plain hydrographic network led to a subdivision of the area into two distinct sectors: High Plain, formed by coarse-grained detrital sediments, prevalently gravels, irregularly cemented in conglomerate horizons and intercalated with layers of sand and, less frequently, of clay; Low Plain, characterized by sandy-pelitic deposits intercalated with gravel horizons which become increasingly deep and rare southwards. The progressive transformation of the alluvial body in the north-south direction from a homogeneous and highly permeable predominantly gravel body to a differentiated structure with superimposed permeable and impermeable layers, determines the transition from unconfined aquifer to a multilayered aquifer system, the two being strictly interconnected. It is along this transitional belt between the two aquifer systems that a springs zone occurs extending approximately 100 km in an EW direction either side of the Tagliamento river. The reconstruction of the aquifer systems of the Low Friuli Plain, using stratigraphic data collected from a set of 339 water-wells, enabled the identification of: - a confined aquifer system, formed by 8 variously branched superimposed artesian aquifers (A, B, C, D, E, F, G, H) at average depths between 20 and over 500 m below sea level (bsl); - a transition aquifer system, comprising two confined layers (S1, S2) at average depths between 27.2 m above sea level (asl) and 12.2 m bsl; - an unconfined shallow aquifer system, laterally discontinuous, at average depths between 44 m asl and 18 m bsl. The groundwater of the Friuli Low Plain is exploited by means of a dense network of water-wells for drinking, agricultural, industrial and trout breeding purposes. The total quantity of groundwater drawn from the Low Plain has been estimated to be approximately 701×106 m3 annually, 75% of which derives from the confined system. The most exploited artesian aquifers are A and B with a volume of 443×106 m3 per year. These data allow the evaluation of the sustainability of current levels of exploitation of the confined aquifer system of the Friuli Low Plain.