Can Venice be raised by pumping water underground? A pilot project to help decide

Recent field evidence suggests that injecting fluids below the ground surface can induce an anthropogenic land uplift of a few tens of centimeters over a time interval that may range from a few months to a few years. At the same time, new modeling studies using a lot of realistic hydrogeological and geomechanical information from the northern Adriatic basin indicate that pumping seawater into a 600–800 m deep brackish aquifer below the Venice Lagoon might help raise the city uniformly by 25–30 cm over 10 years (a). This could provide Venice with an important innovative defence from and a substantial mitigation to the so-called ‘‘acqua alta", i.e., the increasingly frequent floods that plague the city. To test the feasibility of an actual program of anthropogenic Venice uplift, a pilot project is designed with the aim of investigating the occurrence over a limited area selected on purpose within or in the margin of the lagoon where three boreholes down to 800 m are drilled and seawater properly treated for geochemical compatibility is pumped into the selected aquifer during 3 a. Using an improved reconstruction of the geology and lithostratigraphy from a new seismic survey to be carried out in the lagoon subsurface, the pilot project plans the instrumentation of the injection wells and other boreholes for the continuous monitoring and accurate measurement of (1) pore water overpressure; (2) expansion of the injected unit by the radioactive marker technique; (3) compaction, if any, of the upper fresh water aquifer system with the aid of an extensometer; and (4) vertical and horizontal motions of land surface via spirit leveling, GPS and interferometric synthetic aperture radar. Preliminary numerical simulations show that a constant saltwater injection rate of 12000 m3 s-1 from each well might provide a maximum 7 cm uplift at the center of the selected site over a 3-a time, namely, a limited amount that is nevertheless accurately measurable and should not raise concerns for the stability of the buildings and the preservation of the infrastructures in the area. A continuous control of the experiment is envisaged based on much refined hydrologic and geomechanical models properly updated and calibrated to the detailed lithostratigraphy resulting from the new seismic campaign, the ad hoc field analyses, and the current field observations of the event. The completion of the pilot project is expected to require 4 a including an initial year needed for the necessary authorizations and the operative implementation of the injection program. The planned cost is in the range of 5 MEuro/a. The present paper addresses the major issues concerned with the design of the pilot project and discusses the results from the experiment simulations with a glance at their prospective application to an actual project of anthropogenic uplift of Venice.