A new hydrogeologic model to predict anthropogenic uplift of Venice

Abstract

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 ε z 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, ε z may be reduced to as much as 0.1 × 10 -5 throughout the city. Copyright 2011 by the American Geophysical Union.