Artificial recharge assessment in salinized coastal aquifers: Comacchio case study (IT)

Within the many solutions that have been investigated to solve the decrease in freshwater for coastal regions, Managed Aquifer Recharge (MAR) has been attracting an increasing interest as a mechanism to store and later supply an alternative water source for various uses. In salinized coastal systems, one of the main purposes of aquifer recharge is to use the freshwater as a barrier to prevent saltwater intrusion. The area that was investigated is a topographic depression located along the Adriatic coast (Italy), within the alluvial plain of the Po River. The coastal aquifer consists of unconsolidated Holocene sands, with intercalation of peat and silt. In this area, groundwater has undergone heavy salinization due to natural and anthropogenic factors. The study is based on monitoring data (groundwater samples, core logs, temperature and EC profiles) collected via multilevel sampling techniques in piezometers located a few meters from the canals. The hydrometric stages in the canals are artificially controlled by the drainage system and they are periodically varied based on the seasonal irrigation pattern. Multilevel pressure head measurements highlight the presence of steep upward vertical gradients induced by the drainage system, which is used to reclaim the lowlands for agricultural purposes. This drainage causes the upward transport of salts due to the presence of hypersaline groundwater in the lowest portion of the aquifer. Results emphasize that salinization affects almost the entire aquifer. The complete salinization of the aquifer is prevented by the hydraulic conductivity that decreases from the top to the bottom of the aquifer, from natural recharge and by the induced infiltration of freshwater from the canals. These permeability features lead to a vertical separation of the aquifer into two zones, which roughly coincides with the fresh and saline groundwater zones. The artificial and natural recharge generate a fresher shallow zone (TDS < 1500 mg/l), 2.5 m to 4.5 m thick, which is influenced by the seasonal variation of the canal levels and precipitation. This study demonstrates the efficacy of MAR technology to significantly improve water quality and reduce saltwater intrusion into coastal aquifers