Numerical Modelling of Groundwater Level and Salinity Evolution in a Low-Lying Coastal Area Under Intensive Agricultural Activity

The groundwater salinity changes of the coastal unconfined aquifer of the Po Delta (Italy) from 2010 to 2020 were assessed via a density-dependent numerical model implemented with SEAWAT 4.2. The temporal discretization was defined on a monthly basis, allowing for detailed analysis of the evolution of salinity stratification within the aquifer and of the vertical fluxes induced by the reclamation drainage network. The validated model was used to unravel surface-groundwater interaction fluxes and the long-term impacts induced by the ongoing climate change. The simulation highlighted that deeper layers experienced a salinity increase due to the presence of hyper saline low permeability lenses, while shallow layers experienced both increasing and decreasing salinization trends, depending on the temporal and areal distribution of local factors such as recharge and evapotranspiration, the connection between the shallow aquifer and the drainage network, and the presence of a seawater wedge along the coastline. The sensitivity analysis performed on the maximum plant salt uptake due to evapotranspiration revealed a slight variation in the accumulated salinity mass and concentration within the aquifer, resulting in a maximum error of less than 2% at the end of the simulation