Beyond Piezometers: Integrated Supersite Monitoring Framework for Seawater Intrusion in the Brenta and Adige Coastal Plain, Italy

Saltwater intrusion poses an increasing threat to groundwater sustainability in coastal aquifers worldwide, where relative sea-level rise, climate variability, and drainage management jointly alter groundwater recharge and flow regimes. To properly understand these forcings and implement effective management strategies, adequate monitoring approaches are required. However, conventional regional monitoring networks, typically based on sparse and infrequent measurements, often fail to capture these coupled dynamics, complicating the development of regional models and long-term assessments.
This study presents the design and first observations of an integrated coastal “supersite” monitoring framework implemented in strategic areas of the coastal plain between the Brenta and Adige rivers (northern Adriatic coast, Italy), within the SWAMrisk project. The region hosts a multi-layer aquifer system composed of a shallow unconfined aquifer and several deeper confined units, separated by discontinuous silty–clayey aquitards, and is heavily modified by a dense network of drainage channels and pumping stations that regulate groundwater levels. Two supersites were established at Gorzone and Buoro, characterized by contrasting hydrostratigraphic settings and located next to pumping stations hydraulically connected to tidally influenced drainage networks. Each supersite integrates three multilevel piezometers equipped with fixed-depth conductivity–temperature–depth sensors, periodic high-resolution vertical electrical conductivity (EC) profiling, surface-water level monitoring in canals and pumping stations, and information from nearby meteorological and tide-gauge stations.
Despite the limited initial observation period (July–September 2025), the combined approach reveals consistent and site-specific fresh–saline groundwater structures and dynamics. Both sites exhibit vertically layered systems, with small fluctuations in groundwater level and pronounced vertical variability in EC. A persistent freshwater cap above more saline groundwater was identified in both aquifer systems. At Gorzone, where a thicker and laterally continuous aquitard promotes hydraulic isolation, the upper confined aquifer remains relatively fresh (~2.3 mS/cm) and stable, increasing to ~12 mS/cm at depth. The phreatic aquifer shows EC values rising from ~2 to 18 mS/cm in the upper part, driven mainly by pressure perturbations associated with tidal propagation and drainage management. At Buoro, a thinner and discontinuous aquitard allows partial vertical connectivity, resulting in faster phreatic responses to local recharge and pumping, and subtle, delayed confined-aquifer responses linked to inland rainfall. Here, the phreatic aquifer hosts a thicker fresh-to-brackish lens (~3–10 mS/cm), stabilizing at ~15 mS/cm near its base, while a thin freshwater lens (~2 mS/cm) caps the confined aquifer and rapidly transitions to saline conditions (~24 mS/cm) at depth.
These observations support a dual-forcing conceptual model in which short-term groundwater and salinity fluctuations are dominated by local mechanical controls, whereas longer-term stratification and freshwater preservation in confined aquifers are governed by regional recharge and density-driven processes. The results demonstrate that integrated coastal supersites provide a robust, scalable, and management-relevant platform for improving process understanding, model calibration, and adaptive management of coastal aquifers under climate change and increasing human pressures. 
Research funded by the Interreg Italy–Croatia 2021–2027 Programme, Project ID: ITHR0200479—SWAMrisk “Subsurface Water Monitoring and Management to Prevent Drought Risk in Coastal Systems”.