Saltwater intrusion in the unconfined coastal aquifer of Ravenna (Italy): A numerical model

Summary The Ravenna pine forests represent an historical landmark in the Po River Plain. They have great environmental, historical and tourist value. The San Vitale pine forest is located 10 km north of the town. It is surrounded by an urban area, the city industrial infrastructure and the waterworks of the agricultural drainage system. Most land in this area is below mean sea level. As a result, no natural freshwater hydraulic gradient contrasts the density gradient of saltwater. In the last century, many events (land subsidence; land reclamation and drainage; urban and industrial development and gas and deep groundwater extractions; coastal dune destruction) led to the intrusion of large volumes of brackish and saline groundwater. Today the freshwater in this coastal aquifer consists of low salinity water lenses floating on the saltwater wedge. This study is aimed at understanding how past and present human activities have affected the saltwater intrusion process in the phreatic aquifer and how the predicted future sea level rise will affect the salinisation process. We used a numerical model to quantify these effects on the density-dependent groundwater flow, hydraulic head and salinity distribution, seepage and salt load fluxes to the surface water system. The simulations show that over the last century artificial subsidence and heavy drainage started the salinisation process in the study area and a relative sea level rise will accelerate the increase in salt load in the coming decades, affecting the entire aquifer. Climatic conditions in the area result in limited precipitations throughout the year and preclude efficient aquifer recharge, especially in spring and summer when saltwater seepage is extensive. The lack of a continuous coastal dune system favors salt wedge intrusion.