L'intrusione salina nel comprensorio lagunare veneziano. Il bacino meridionale
(Saltwater intrusion in the Venice watershed, Italy. The southern catchment)
L. Carbognin, F. Rizzetto, L. Tosi
Institute of Marine Sciences, National Research Council, Venezia, Italy
P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
G. Gasparetto-Stori
Consorzio di Bonifica Adige Bacchiglione, Conselve (Pd), Italy
ABSTRACT
The salt water contamination process in the Venice watershed between the
southern edge of the lagoon of Venice and the Adige River was investigated
through hydrogeological and geophysical surveys and a new monitoring
network of surface water and shallow groundwater (ISES Network). The results
show that: the presence of saline water extends up to 20 km inland from the
coast; the depth of the fresh/salt-water interface varies from 2 to 30 m below
the ground level and exhibits a significant, mainly seasonal, time variation;
the bottom of the contaminant plume penetrates from 10 even to 100 m depth in
the subsoil. Further investigations, still in progress, are showing that the
dynamics of the soil salinization process is especially sensitive to the
changes in the river (Brenta, Bacchiglione, Adige, Gorzone) discharge, water
levels in a complex drainage network regulated by a number of pumping stations,
and climatic conditions. Other important factors are fresh-water releases for
irrigation purpose and riverbed seepage. The latter is influenced by the tide
dynamics which, together with river discharge, control the sea water
encroachment along the river mouths. In summer 2003, for example,
characterized by a severe drought, salt water flowed up the Brenta and
Bacchiglione rivers for about 20 km. The saltwater intrusion has been enhanced
by the ground elevation generally below the mean sea level, especially in the
southern sector where land subsidence, mainly due to peat soil oxidation, has
induced an elevation loss greater than 1 m over the last few decades.
