Evaluation of a well-injection recharge system to contrast saltwater intrusion in a coastal forest: the S. Vitale Pinewood, Ravenna (Italy)

The roman time S. Vitale forest near Ravenna represents an historical landmark in the Po Plain. Today, the forest is surrounded by the complex urban system of Ravenna, by the city industrial infrastructure, and by the waterworks of the agricultural drainage system. Several natural and anthropogenic features threaten this area: - Saltwater intrusion in the freatic aquifer and seawater encroachment inland along the rivers; - Natural and anthropogenic land subsidence (caused by gas and deep groundwater winning, mostly after 1950); - Direct contamination from water bodies open to sea. Destruction of coastal dunes and reduction of its barrier effect; - Land reclamation drainage system. Insufficient aquifer recharge; - Sea level rise. Land subsidence has dropped most of the territory below mean sea level and it has modified the river regime and the normal groundwater flow. A drainage system is necessary to lower the phreatic level and keep dry the agricultural land. A second objective of the drainage system is to keep above the watertable the roots of the trees in the coastal areas. The result of the drainage system management, however, is an unstable freatic aquifer that is not able to contrast saltwater intrusion and is not helping much to maintain healthy the pinewood forests that are also very sensitive to salinity. The objective of this study is to evaluate the feasibiliy of an aquifer recharge system able to contrast saltwater intrusion. For this purpose, the first thing we need to do is to characterize the freatic aquifer with special concern for its hydraulic characteristics, such as porosity and hydraulic conductivity. In order to do that, we carried out a series of slug tests and we integrated their results with some geo-electric resistivity and tomography studies. The hydraulic properties of an aquifer are very important to calculate the depth of the freshwater-saltwater interface and, therefore, to better plan water management strategies aimed to find the optimal watertable depth for pine growth under the forest. In order to show the importance of the aquifer’s hydraulic characteristics, we show how they can be used in the design of a simple well-injection recharge system aimed to reduce saltwater intrusion under the pinewood forest