A new hydrogeologic model to predict anthropogenic uplift of Venice
P. Teatini N. Castelletto, M. Ferronato, G. Gambolati
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
L. Tosi
Institute of Marine Sciences, CNR, Venezia, Italy
Recent numerical studies based on a simplified lithostratigraphy of the Venice
subsurface suggest that the city may be raised by pumping seawater into deep
aquifers through 12 wells located on a 10 km diameter circle. Using an updated
3-D reconstruction of the Quaternary deposits, developed very recently from about
1050 km of multichannel seismic profiles and eight exploration wells, along with
a more accurate representation of the injection boreholes, novel finite-element
predictions are performed. The new model simulates the lithostratigraphy of the
lagoon subsurface and allows for a reliable assessment of the water volumes
injected into the geologic formations based on the actual bottom hole overpressure
that can vary both in space and time. Pumping occurs into two Pleistocene sequences
that are originated from the Alps and Apennine sedimentation and terminate just
south and north of Venice, respectively, and the shelf portion of a Pliocene
sequence that is rather continuous below the central lagoon with arenite layers to
depths as much as 1000 m below mean sea level. With a proper tuning of the injection
pressure the new hydrogeologic model allows for a prediction of a quite uniform 25-30
cm uplift over 10 years after the inception of injection. The gradient of the vertical
displacement ξz does not exceed 5×10-5 and
1×10-5 in the whole lagoon and Venice, respectively, i.e., well below
the most conservative bound recommended for the safety of the structures. If ad hoc
calibrated injection overpressures are implemented in each single well, may be
reduced to as much as 0.1×10-5 throughout the city.
