CALIBRATION OF THE GROUNDWATER FLOW MODEL AND ASSESSMENT OF THE SALTWATER INTRUSION IN A MULTI-LAYERED AQUIFER SYSTEM OF THE IONIAN COASTAL AREA (TARANTO GULF, SOUTHERN ITALY)

In some Mediterranean karst areas, groundwater is often the only available supply for freshwater. Besides the contamination induced by human activities, coastal aquifers often suffer from the saltwater intrusion phenomenon, which can be enhanced by both extensive withdrawals and climatic changes. Establishing an effective set of regulatory and management measures to ensure the sustainability of coastal aquifers requires a deep knowledge about natural and anthropic stresses involved in groundwater dynamics. In this regard, a prior conceptualization of aquifer systems and a deeper characterization of balance terms through mathematical modelling are of paramount importance. In the gulf of Taranto (southern Italy), these issues are particularly pressing, as the multi-layered, carbonatic aquifer is the only available resource of freshwater and satisfies most of the human water-related activities. Especially during the last decades, proper management plans and decisions seem to be compelling, as the national government included Taranto in the list of the contaminated sites of national importance, due to the presence of highly-polluting activities nearby the Mar Grande and Mar Piccolo seawater bodies, whose relationship with the underground resources is matter of concern, as they host important freshwater springs. Furthermore, the Taranto area is particularly sensitive to the phenomenon of seawater intrusion, both for the specific hydrostratigraphic configuration and for the presence of highly water-demanding industrial activities. These problems, strictly related to the protection and preservation of groundwater quality and quantity, have triggered several actions. Among them, the Flagship Project RITMARE (la Ricerca Italiana per il Mare - the Italian Research for the Sea) took into account criticalities involving several environmental components within the Mar Piccolo ecosystem, including groundwater. In this thesis, a full charactrization of the multi-layered aquifer system of the whole Province of Taranto is presented, with the purpose of supporting monitoring activities, land-use plans and management decisions. The preliminary outcomes refer to the identification of the conceptual model, namely the reconstruction of the hydrostratigraphic structure of the underground and the qualitative assessment of the groundwater dynamics. The successive development of a numerical model permits to produce a tool for quantifying the hydrogeological balance and simulating the system response to climate or man-induced changes. Generally speaking, thorough evaluation of model adequacy and/or accuracy is an important step in the study of environmental systems, due to the uncertainties on hydrodynamic properties and boundary conditions and to the scarcity of good-quality field data. This commonly results in groundwater models being calibrated and often leads to the development of many candidate models that can differ in the analysed processes, representation of boundary conditions, distribution of system characteristics, and parameter values. In this framework, calibration of alternative models allowed to identify the main challenges which limit the reliability of model outcomes and test model adequacy while proposing a new calibration methodology, which represents tha major scientific contribution of this thesis.