Technical note: an alternative approach to laboratory benchmarking of saltwater intrusion in coastal aquifers

Abstract. Saltwater intrusion is a worldwide problem increasingly affecting coastal aquifers, due to climate changes and growing demand of freshwater for irrigation and human consumption. Therefore, research efforts on this topic have been intensified, aiming to achieve better predictions of the saltwater wedge evolution and design suitable countermeasures to limit the saltwater intrusion. Both physical and numerical models are essential for these purposes. This work presents a laboratory facility designed and built to simulate saltwater intrusion in coastal aquifers, with the overall goal of providing benchmarks for numerical models by means of different measurement techniques. The laboratory facility has been specifically designed to limit errors and provide redundant evaluation in the measurement of hydraulic heads and discharged flow rates. Moreover, the size of the facility allows us to monitor the saltwater wedge evolution by electrical resistivity tomography (ERT). A specifically designed ERT monitoring system was developed and verified by comparison with photos of the saltwater wedge collected at regular intervals during an experiment in a homogeneous porous medium. The experiment consisted of two phases: for the initial 24 h, the saltwater wedge evolved without any external forcing, while in the following 12 h, freshwater was pumped out through a channel drain, to simulate aquifer exploitation. The SUTRA code was adopted to reproduce the experimental results, by calibrating only the longitudinal and transversal dispersivities. Overall, the agreement between observed data, numerical simulations, and ERT results, albeit preliminary, demonstrates that the proposed laboratory facility can provide valuable benchmarks for future studies of seawater intrusion, even in more complex settings.