Conceptualization, modelling and management of alluvial aquifers: case studies of Sangro and Vomano plains (central Italy)

The analysis of complex hydrogeological problems related to alluvial aquifers through conceptualization and numerical modelling is of great relevance particularly for defence and management of groundwater and surface water systems. Assessment of conceptual models and uncertainties related to system geometries, parameter distributions, boundary and internal conditions are essential in application of density-dependent flow and transport numerical modelling. Investigations and numerical analysis have been carried out on Sangro and Vomano rivers alluvial plains (Central Italy), supported by specific hydrogeological and hydrochemical geodatabases within ESRI ArcGIS platform and developed using finite-difference MODFLOW and densitydependent finite-element FEFLOW numerical codes. These studies highlight the role of aquifer geometry, recharge conditions and hydrodynamic processes related to main hydrological features and applied stresses. The management of well fields exploitation for drinking and irrigation purposes has also been assessed, considering hydraulic connections with surface water bodies and groundwater hydrochemistry. The alluvial plains waters are characterized by facies of both Apennine origin and up flow from deep underlying mineralized systems; there is also evidence of marine intrusion phenomena along coastal areas. The found chemical-physical layering of groundwater proves to be important to environmental characterization and monitoring. By focusing on the key-role of rivers as recharge and drainage bodies and hydrogeological properties of major palaeo-rivers, numerical modelling supported an overall analysis of the underground hydrology, including analysis of fundamental components of local hydrogeological balance, flow pathlines and velocity fields, as well as possible problems related to contaminants migration. After calibration processes, models have been used to investigate some major issues, concerning optimisation of well fields pumping regimes as well as establishment of wellhead protection areas. The salt water intrusion dynamics, which often play a major role along the eastern Italian coastline, are amplified by localized groundwater exploitations as proved by physical- chemical evidence. Simulated scenarios confirm risks of marine intrusion due to groundwater over-exploitations related to civil uses and irrigation; mobilisation of salt waters normally requires some years to take place but is a persistent phenomenon once established. Long-term environmental monitoring, system conceptual refinement, numerical models uptuning are of fundamental importance for confidence building on simulation results for comprehension of relevant hydrological processes and adequate decision-making in socio-economic changing times. KEY WORDS: alluvial aquifers, Central Italy, conceptualization, density-dependent conditions, groundwater modelling.