Groundwater monitoring at a building site of the tidal flood protection system “MOSE” in the Lagoon of Venice, Italy

To protect Venice against tidal flooding, the MOSE system (Experimental Electro-mechanic Module) has been under construction since 2003. This safeguarding system is composed of four batteries of mobile barriers at the Lagoon’s inlets (Lido, Malamocco, Chioggia), which will be lifted before the occurrence of exceptional high tides (>1.10 m above the mean sea level), isolating the Venetian Lagoon from the sea. The end of the construction work is foreseen by 2016. In this paper, the results of the groundwater monitoring at the building site of Punta Sabbioni at the Lido inlet are described. A large dewatered basin (tura), formerly occupied by the sea and close to the shoreline, was used for the precasting of the mobile barriers, and the impact of groundwater control was therefore monitored in the phreatic and shallow confined aquifers. Although a slurry wall barrier was excavated to isolate the tura, a drawdown cone in the confined aquifer was observed, extending to 1 km from the construction site. In contrast, the phreatic aquifer was only influenced by tides, rainfall and evapotranspiration, and the slurry wall of the tura had a positive effect of decreasing the groundwater salinity by limiting the seawater intrusion, as confirmed by the electrical conductivity profiles measured inside the piezometers. The monitoring activity was successful in assessing the impacts of the construction work on the aquifer system and in distinguishing them from the effects of natural driving forces.