Groundwater Freshening Following Coastal Progradation and Land Reclamation of the Po Plain, Italy

Many coastal areas historically were inundated by seawater, but have since undergone land reclamation to enable settlements and farming. This study focuses on the coastal unconfined aquifer in the Po Plain near Ravenna, Italy. Fresh water is present as isolated, thin (1-5 m) lenses on top of brackish-salt water. Historical maps show large areas of sea inundation until approximately 150-200 years ago when coastal progradation and construction of the drainage canals began. Since then, the aquifer has been freshening from recharge. A 3D SEAWAT model is used to simulate a 200 year freshening history, starting with a model domain that is saturated with sea water, and applying recharge across the top model layer. Calibration to the observed concentrations is remarkably good for discrete depths within many monitoring wells despite model simplicity. The distribution of fresh water at the end of the 200 year period, representing current conditions, is controlled by the drainage network. Within and adjacent to the drains, the groundwater has high salinity due to up-coning of salt water. Between drains, the surface layers of the aquifer are fresh due to the flushing action of recharge. The modeling results are consistent with cation exchange processes revealed in the groundwater chemistry.