Monitoring of the groundwater levels in the framework of Mo.S.E. project of Venice

In the framework of Mo.S.E. project for the protection of Venice against exceptional high tides, the development of Treporti (Lido’s inlet) and Ca’ Roman (Chioggia’s inlet) harbours in the Venice Lagoon required the realization of two provisional sea basins, positioned below the sea level, which have been isolated with impermeable barriers and then drained with dewatering well systems to ensure their accessibility. These basins are now used to build the concrete lodging caissons of mobile barriers, and will be reopen after their installation. Two networks of piezometers (25 and 2 respectively) have been installed to monitor the impact of dewatering on the first and second aquifer levels close to the constructions sites. Hydraulic heads and groundwater electrical conductivity profiles are continuously measured. The anthropogenic impact on groundwater is determined by comparing the time series of hydraulic heads with the natural driving forces (rainfall, evapotranspiration, tidal oscillations) acting on the aquifers. After five years of monitoring activities, it has been ascertained in both sites that no depletion of the phreatic aquifer has been produced by dewatering pumping; in the confined one, instead, a depression cone is observed around the dewatered basin. The impermeable barrier isolated a portion of the phreatic aquifer, resulting in a progressive groundwater desalinization. Electrical conductivity profiles show that seawater intrusion has not been enhanced by construction works.