Groundwater contour mapping in Venice by stochastic interpolators: 2. Results

Reliable and flexible tools are required to keep under control the subsurface flow field of the Venetian lagoon and the related land subsidence. One such tool is given by the stochastic interpolator developed in paper 1 (Gambolati and Volpi, 1979) and used to map the 1973 and 1977 piezometry of three major Venetian aquifers. A fairly small number of test holes unevenly scattered across the mainland, Venice, and the littorals provide the input data. The output is the reconstructed hydraulic head together with an assessment of its reliability. The 1973 results show the existence of a pronounced cone of depression centered upon the industrial area of Porto Marghera, which turns out to be by far the major pumping site in the whole area. Local withdrawals produce a minor cone in Venice, but they do not account for the overall head decline recorded there. The 1977 contour maps show a substantial recovery of the flow field in the upper 250 m of the groundwater basin, thus providing documentary evidence for the recently observed rebound of the land surface (Carbognin et al., 1976). Significant residual withdrawals still occur in the lowest unit (∼280 m) of the aquifer system.