Can Venice be raised by pumping water underground? A pilot project to help
decide
N. Castelletto, M. Ferronato, G. Gambolati, M. Putti,
P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
ABSTRACT
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.
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 years.
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 12x10-3
m3/s 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 years 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/year. 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.
