Numerical Modelling of Countermeasures against Saltwater Intrusion in Heterogeneous Porous Media

Saltwater intrusion (SWI) is a worldwide issue affecting coastal aquifers due to climate change and increasing demand for fresh water. The worst scenario occurs during summer periods when the lack of rainfall results in the reduction of groundwater recharge. This process leads to seawater advancing inland for many kilometres, causing environmental pollution and groundwater contamination. The problem is exacerbated by the fact that 70% of the global population lives in coastal regions, where freshwater availability depends on the balance between precipitation and sea levels. Moreover, saline irrigation results in high salt residues in soil, contributing to desertification. Research on saltwater wedge intrusion over time using physical and numerical modelling is used to improve predictions and design effective countermeasures. Physical and numerical models are reliable tools used to help coastal aquifer management agencies suggest rational water resource exploitation and ensure proper freshwater flux to limit inland rising of the saltwater wedge. In this work the physical model of a heterogeneous porous medium is presented that reproduces a coastal aquifer. The model and was used to develop experiments of saltwater intrusion during drought periods and to test the effectiveness of surface recharge as a countermeasure. In this work, an experiment that lasted 72-hour is presented: during the initial 64 hours, the so-called free intrusion, the saltwater wedge evolved without any external forcing, while in the last 8 hours, characterized by a drought period, an artificial recharge of freshwater was chosen as a possible countermeasure against intrusion. Photos, acquired with 1-minute frequency during the experiment, were used to calibrate a numerical model developed using Saturated-Unsaturated Transport computer program. According to the physical model results parameters of the numerical model were varied in order to ensure that the latter’s’ results well reproduce the former’s ones. During the drought period, the impact of the artificial freshwater recharge chosen to lessen the infiltration of seawater was assessed, studying the evolution of the curve how much it has compacted and how much the toe of the wedge is protruded. Despite its complexity and various influencing elements, numerical modelling of seawater intrusion in heterogeneous formations coupled with physical experiments or in-situ surveys represents the most valuable tool for understanding the process and managing and controlling water resources. Since this is a global problem, in the future, efficient countermeasures will be necessary to combat this phenomenon and protect groundwater resources from such pollution. Accordingly, the results obtained in this thesis will be used as a basis for future laboratory experimental analyses and subsequent field studies to find the best and most efficient ways to mitigate saltwater intrusion.