Tidal dynamics and saline intrusion in coastal aquifers: A case study of the Flumendosa Coastal Plain, Sardinia

Coastal aquifers are essential sources of freshwater that support human populations and ecosystems. The threat of saline intrusion, a complex phenomenon that is being exacerbated by various anthropogenic and natural factors, is posing a growing threat to these invaluable sources. When seawater infiltrates freshwater aquifers, it results in saline intrusion, which compromises their quality and potability. Tidal fluctuations have a significant impact on these aquifers, altering groundwater dynamics and exacerbating saline intrusion. Fluctuations in groundwater levels within coastal aquifer systems are linked to the ebb and flow of the sea due to tidal activity. The influence of tides on the aquifers towards inland gradually diminishes in accordance with the hydraulic characteristics. Understanding the effects of tidal patterns and aquifer salinization is crucial for effective management and preservation of groundwater sources. Monitoring the influence of tides on groundwater behaviour is fundamental to develop predictive models and implement adaptive strategies, ensuring the sustainable utilization of coastal aquifers amidst mounting challenges of saline intrusion. The Flumendosa coastal plain, in southeastern Sardinia, hosts a complex hydrogeological system affected by saline intrusion due to aquifer overexploitation for various anthropogenic activities. Agriculture is the prevalent activity that persists within this area and in particular, the eastern sector was dedicated to rice cultivation. The eastern part of the valley lies at elevations close to the sea level that have a significant influence on piezometric fluctuations due to tidal variations. Tidal changes in coastal aquifers play a pivotal role, leading potentially to an increase in soil salinization. The relationship between tidal variations and aquifer salinization is the focus of this study because this phenomenon can change the interface between freshwater and saline water. To register tidal fluctuations and the subsequent piezometric changes influenced by the aquifer response, a monitoring system has been implemented. It includes continuous measurements of sea levels at the S. Giovanni fish-farm site, and groundwater levels at two piezometers located within a 3 km buffer inland from the coastline. Electrical conductivity of groundwater is also measured at one piezometer site. Additional monitoring points will be implemented in the coming months. Monitoring results will enhance our understanding of the mechanisms affecting aquifer response and saline intrusion dynamics with respect to tides and concomitant effects like aquifer exploitation. Analysing tidal response data offers also valuable insights into aquifer parameters, complementing approaches like pumping tests. Furthermore, these tidal insights yield crucial information on hydrogeological aspects, including aquifer confinement, spatial variations in hydraulic properties, and connectivity patterns within the aquifers. This data enhances our understanding of aquifer dynamics, improving comprehensive aquifer characterization efforts.