Caratterizzazione idrogeologica avanzata dell’acquifero alluvionale della piana costiera di Muravera

Many coastal areas around the world, especially low-lying delta areas, have a high density population and host important economic activities. In such context groundwater abstraction for public water, irrigation and private water supply can lead to over-exploitation and seawater intrusion phenomena. Saltwater intrusion is a critical socio-economic and environmental issue in the coastal plain of Muravera, south-eastern Sardinia (Italy). Since the early fifties the natural hydrodynamic equilibrium between groundwater, surface-water and seawater has been deeply modified by human interventions mainly related to the development of agriculture and tourism activities. The aim of the work was to contribute to the definition of a sustainable water management system to assure the equilibrium between the freshwater inputs to the plain aquifer and the withdraws, thus containing the extent of saltwater intrusion. A density dependent groundwater flow and coupled solute transport model was built for the plain taking into account input and output to the hydrogeological system. Three main tasks were developed to implement the model addressing the following questions: i) what is the amount of natural recharge? ii) how fast do the aquifer respond to the recharge? iii) where do the further recharge to the aquifer come from? iv) how do the salt wedge extend inland and at depth? The Soil Water Balance code (SWB) and the Water Table Fluctuation (WTF) method were applied to estimate the natural recharge and the behaviour of the aquifer to the indirect recharge. A monthly piezometric and electrical conductivity monitoring survey was carried out to recognize eventual trends, main contribution on aquifer recharge and salinization mechanisms. Water chemistry evolution and flow path were investigated through chemical and isotope analyses of δ18OH2O e δ2HH2O, δ11B, δ18OSO4, δ34SSO4, 87Sr/86Sr. Moreover, analyses of 3H, 3He, CFC-11, CFC-12 and SF6 were carried out to date groundwater and to evaluate recharge time. The SEAWAT based iMOD-WQ software developed by Deltares was used to implement the numerical model, which allows the simulation of groundwater management scenarios contributing to the sustainable use of water resources in the coastal environment, addressing human and environment needs.