Modeling the saltwater intrusion in the lowlying catchment
of the southern Venice Lagoon
P. Teatini, M. Putti, C. Rorai, A. Mazzia, G. Gambolati
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
L. Tosi, L. Carbognin
Istituto per lo Studio della Dinamica delle Grandi Masse, CNR, Venezia,
Italy
ABSTRACT
The coastland surrounding the southern Venice Lagoon, Italy, is a precarious environment subject
to both natural changes and anthropogenic pressure. One major environmental problem is the
saltwater intrusion in shallow aquifers. The salt contamination is generally the result of seawater
encroachment, but significant contributions can also be due to the water exchange between the bed of the
major rivers and the subsurface. In fact, the reduced freshwater discharges that occur in the
Brenta and Bacchiglione rivers during the dry periods allow the saltwater to flow up from the river
mouths for several kilometres. Saltwater intrusion is enhanced by a land elevation well below the
mean sea level and by the presence of several ancient sandy fluvial ridges and buried paleo-channels,
crossing the farmland with a main direction from inland to the lagoon boundary, that can act as
preferential pathways for groundwater flow and solute transport. Using as input data a geological
, geophysical, hydrological data set collected around the Casetta pumping station over 2004-2005,
a numerical model has been developed to investigate the saltwater intrusion process along the
margin of the southern Venice Lagoon. The model solves the coupled density dependent flow and
transport equations by a highly accurate numerical approach based on the mixed hybrid finite element
(MHFE) method and a combination of MHFE with high resolution finite volumes (HRFV) for the
discretization of the flow and transport equations, respectively. A set of simulations has been
initially carried out to analyze the effect of the natural factors forcing the saltwater intrusion
in the coastal aquifer system. Preliminary results provide evidence of the strong influence exerted
by the river freshwater that can represent an effective hydraulic barrier to salt contamination from
the lagoon. By contrast the river can be a strong source of salinization for the phreatic aquifer
if seawater encroaches along the final 15-20 km of the watercourses.
