Artificial recharge of the phreatic aquifer in the upper Friuli plain, Italy, by a large infiltration basin

To cope with the general reduction of water availability and increase the subsurface storage of highquality surficial waters, an artificial recharge project is ongoing in northern Italy within the WARBO LIFE+ Project funded by EU. WARBO is aimed at implementing large-scale use of artificial recharge in Italy where water directives still strongly limit its application. In this context, the Mereto recharge site was selected in the upper Fruili plain where the water availability is guaranteed during winter period by the Tagliamento and Ledra Rivers. An infiltration basin, about 5.5 m deep and 45 x 7 m^2 wide, was built at Mereto in the early 2000s but the possibility of implementing the recharge has been allowed only very recently. The site is characterized by an elevation of 105 m asl and the depth to the groundwater table averages 50 m.Below a few meter-thick organic soil, the aquifer is composed by coarse deposits with an estimated thickness of 100 m and an average vertical hydraulic conductivity on the order of 10^(-4) m/s. A ~0.1 m^3/s infiltration flow has been preliminary estimated (corresponding to an infiltration rate of 60 cm/h). Geophysical investigations (electrical resistivity tomography, high-resolution seismic surveys) together with infiltration and pumping tests have been carried out to characterize the vadose zone and the unconfined aquifer in the study area. Functional approaches and three-dimensional (3D) Finite Element numerical computations have been used to predict the effect of the artificial recharge. The results of these investigations will greatly reduce the hydrogeological knowledge gaps and will be used to fine tune the recharge program and to define the monitoring concept. This contribution aims to provide a methodology for the implementation of managed aquifer recharge programs using existing structures.