Saltwater intrusion modelling for the safeguard of crop production in the Mediterranean

In coastal aquifers seawater intrusion is a worldwide problem caused by natural processes but significantly worsened by aquifer overexploitation for irrigation and drinking water supply, land subsidence, sea level rise and climate changes, which contribute to the reduction of groundwater natural recharge.

Seawater intrusion represents a relevant environmental issue along the coastal aquifers of the Mediterranean Sea, including the coast south of the Venice Lagoon, a peculiar ecosystem characterized by a fragile equilibrium between reclamation and irrigation activities, whereby salinization is significantly reducing the annual local crop production of about the 25% on average.

Here, we present the test case of Ca’ Bianca, located near the city of Chioggia - Italy. A numerical flow and transport model has been set up with SEAWAT, aimed at reproducing the complex saltwater intrusion dynamics in the area. To pursue this goal, real field water table and concentration measurements are combined to aid in the calibration and validation of the model. Particular attention is devoted to the evaluation of the dynamics and uncertainty associated with seawater levels, an essential forcing of the model. Then, mitigation strategies, such as drains supplying freshwater in the first layer of soil, are simulated to test their effectiveness against the saltwater intrusion in a way that their application can be reproduced also in other sites affected by the same phenomenon.

Results show a good match between the simulations and the data, with errors of about 10 cm for the water table, which is acceptable if we consider the scale of the project and its topographical and stratigraphical uncertainties. Even though matching observed concentrations proved to be more difficult, the model realistically reproduces the saltwater spatio-temporal behaviour. The comparison between the scenarios with and without mitigation strategies shows that, in the latter case, significant enhancement in crop production can be achieved.

As a future development, climate change effects on the sea levels will be considered and predictive scenarios will be developed and quantitatively analysed.