Inflow–Outflow Behaviour of a Coastal Karst Aquifer Based on 3D Geostatistical Reconstruction of the Thermal Field

Abstract The spatiotemporal patterns of groundwater temperature may effectively delineate groundwater flow systems and help to identify aquifer recharge areas and preferential flow pathways. In coastal aquifers, they may also offer valuable insights into the spatial extent of seawater intrusion and saltwater upconing. Applying simple Kriging interpolation and variography techniques on a high-density three-dimensional temperature dataset derived from groundwater temperature–depth profiles has enabled the reconstruction of the three-dimensional thermal field for the southernmost part of the Salento coastal karst aquifer (Southern Italy). This region shows structural complexity, which poses challenges for conceptual modelling assessment. The 3D temperature model produced is a groundbreaking reconstruction derived from field data that highlights crucial insights into a shallow hydrogeological environment. Given the hydrogeological complexity and the regional scale of the aquifer, which pose challenges to straightforward groundwater flow modelling, the information on temperature distribution from maps and cross sections of the three-dimensional thermal field emerges as a pivotal tool in identifying crucial hydrogeological features. This study, bolstered by geological, geomorphological, and structural data, demonstrates that the analysis of the groundwater thermal field, which encapsulates information about aquifer permeability heterogeneity and anisotropy, is instrumental in deducing the hydraulic behaviour of faults and revealing aquifer properties. From a geostatistical perspective, this study underscores the comprehensive nature of the 3D Kriging model: it incorporates all available groundwater temperature data from all explored depths, resulting in temperature maps that show a more accurate spatial distribution than those created by Kriging within ± 2 m of selected depths.