Hydrological Effects of Bounding the Venice (Italy) Industrial Harbor by a Protection Cutoff Wall: Modeling Study

To prevent erosion of polluted land and discharge of contaminated groundwater and surface water into the Venice Lagoon, a 57 km long cutoff wall has been designed by the Venice Water Authority and is currently under construction along the canal banks of the Venice, Italy industrial harbor. To predict the impact on the hydrologic regime and mitigate the related inundation hazard in the nearby urban areas, a complex three-dimensional finite-element model has been developed and implemented over the multiaquifer system down to a depth significantly larger than the wall bottom. The model is initially calibrated against the regional piezometry and then refined locally to reproduce the groundwater volume drained along a 5-km long bank of a harbor canal already bounded. Major results from the simulations show that after the wall completion the subsurface discharge into the lagoon is successfully abated by as much as 85% relative to the preexisting rate with, however, an expected 1-m increase of the water table in the inland city of Mestre, Italy thus pointing to the need for implementing a drainage trench upstream the wall to properly reduce the raised groundwater level. The model would also indicate that the shallowest aquifers may receive underground water from a large number of old deeper boreholes abandoned in the past and not properly sealed. From a more general perspective, the present study constitutes an important example where the reliable and sustainable design of a complex engineered structure bound to impact significantly on the surrounding environment can be much helped and improved by the use of advanced numerical models capable to capture the essential features of the underlying geohydrological processes