Modelling possible structural instabilities of the Po River embankment,
Italy, due to groundwater pumping in the Ferrara Province
M. Ferronato, P. Teatini, G. Gambolati
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
M. Gonella
Med Ingegneria S.r.l., Ferrara, Italy
C. Bariani, G. Martelli
CADF S.p.A., Codigoro, Italy
ABSTRACT
Land subsidence due to groundwater pumping is a
major environmental problem in flat alluvial
coastal plains. In the eastern Po River plain, Italy,
CADF, a local Water Distribution Company
serving a 1300 km2 territory, is producing water
from a well-field established since the 1930s at the
Ro Ferrarese village. The 107 m3/year current
pumping rate is withdrawn from a 20-60 m deep
confined aquifer. In order to cope with the
increasing water demand, CADF has planned in
2006 the development a new field 5 km east of the
old one. The new field is made of 9 wells located
in the Po River overbank and produces from the
same shallow aquifer.
To provide the establishment authorization, the
Regional Environmental Agency has required the
evaluation of the environmental impact in terms of
land subsidence and possible structural instability
of the Po River embankment (that is more than 10
m above the surrounding farmland) due to
differential displacements.
In order to comply with the previous requirements,
a modeling study supported by in situ
investigations has been performed. Advanced
three-dimensional finite element flow and poroelastic
models have been implemented with a
realistically detailed lithostratigraphic sequence
obtained by integrating a number of borehole
stratigraphies and 2D electrical resistivity
tomographies. The models have been calibrated
against the outcome of available pumping tests and
records of land settlement taken at the old wellfield.
A "best fit" scenario along with other three
plausible scenarios have been simulated in order to
account for the major data uncertainties of the
hydrologic parameters, i.e. hydraulic conductivity
of the pumped aquifer and sand and clay vertical
compressibility.
The models have been used to simulate the
anthropogenic land subsidence from the
establishment of the Ro well-field (1930) to the
present time (2005), and to predict the expected
occurrence up to 2035.
The results show a cumulative maximum land
settlement of 15±4 cm at the Ro well-field over
the simulated 105 years. A value of 6±2 cm
of land subsidence may be expected from
2005 to 2035 at the new well-field. The
displacement gradient is of the order of
10-4-10-5.
Hence, it may be concluded that the activation of
the new well-field and the joint groundwater
pumping from the old one should not generate any
instability of the Po River embankment.
