Long-term geotechnical response of Venice coastal defences detected by Persistent Scatterer Interferometry
L. Bincoletto
Geological consultant, San Vito al Tagliamento, Italy
P. Simonini
Department of Hydraulic, Maritime, Environmental and Geotechnical Engineering, University of Padova,
Padova, Italy
T. Strozzi
Gamma Remote Sensing, Gumligen, Switzerland
P. Teatini
Dept. Mathematical Methods and Models for Scientific
Applications, University of Padova, Padova, Italy
L. Tosi
Institute of Marine Sciences, CNR, Venezia, Italy
ABSTRACT
With a surface area of about 550 km2 the Venice Lagoon is the largest Italian wetland,
open to the tides of the Upper Adriatic Sea (the highest tides in the Mediterranean Sea).
The lagoon is connected to the sea through three inlets, which divide the narrow littoral strip
separating the inner water body from the Adriatic. Several nearshore and offshore structures have
been constructed over the decades to protect such a unique city and its coastal environment from
sea storms and high waters, whose frequency and level are increasing due to relative sea level rise.
Long jetties have been built at the inlets between the end of the 18th and beginning of the 19th
centuries and then reinforced between 1994 and 1997. Since 2003, in the framework of the MOSE
construction (i.e., the project of mobile barriers for the temporarily closure of the lagoon to
the sea), the jetties have been extended, new breakwaters have been constructed in front of the
inlets, and a small island has been realized within the Lido inlet to support the MOSE gates.
An accurate quantification of the movements of these coastal defenses due to long-term consolidation
has been carried out by Persistent Scatterer Interferometry (PSI) using ENVISAT ASAR and TerraSAR-X
images acquired from April 2003 to December 2009 and from March 2008 and January 2009, respectively.
The displacements range between few mm/yr for the structures older than 10 years up to 50-70 mm/yr
for those realized few years ago. The PSI measurements have been combined with the outcome of a
detailed geomechanical characterization of the lagoon subsoil down to -50 m depth below msl.
The geotechnical dataset has been collected at a test site located on the northern littoral where
an instrumented 20 m radius, 6.7 m high vertically-walled reinforced sand embankment was built at
the end of 2002 and monitored till to 2007. The use of the derived stress-strain properties together
with the actual lithostratigraphy below the structures, which is available from several piezocone
profiles and boreholes, allow for the computation of secondary compression rates that match very well
the PSI-derived movements. The results provide important information on the expected time-dependent
settlement of these structures and prove the potentiality of PSI in controlling the geomechanical
response of large coastal structures.
