Keeping Venice
afloat
High accuracy
pressure transmitters from Keller are helping to keep Venice
afloat through their integration into the foundations of the
city's flood prevention system
The idea
thatVenice might sink into the sea has been circulating in the
media for many years now.Around one hundred years ago, the city
was 25 centimetres higher out of the water than it is today.When
its industries moved to the mainland in the 1960s and began to
grow and expand rapidly, there was a great need for fresh water,
and Venice therefore decided to pump groundwater out from under
the Venetian Lagoon.That's when the city began to sink.
The problem was actually identified in the I 960s, and Venice
then began restricting the volume of water that was pumped out
- but this could not stop the process entirely.The situation
was exacerbated when the channels in the lagoon were expanded
to accommodate ships travelling to Mestre.Tourism also increased
and the water connection from the city to the Adriatic Sea was
widened.The huge amount of water thus introduced carries sediment
away and out of the lagoon, and this phenomenon is being reinforced
by the effects of global warming.
Over the years, various proposals were presented to deal with
the problem, but there were also corruption scandals and protests
by the local population. Finally, the parties involved agreed
to launch a project known as M.O.S.E. (Modulo Sperimentale Elettromeccanico
- "Electromechanical Experimental Module").
This flood prevention project uses moveable flood gates installed
at the four entrances to the Venetian Lagoon.The idea is to protect
the historic centre ofVenice from floods that are becoming ever
more frequent.The concept is not completely new, as similar flood
barriers have also been built in London (Thames Barrier) and
Rotterdam (Maeslant Barrier).
When a flood alert is issued, the four entrances to the lagoon
are closed off using floating barriers.The flood prevention system
consists of a total of 78 movable elements. The technology used
here is tried and tested, as it is been employed for quite some
time at the gates of large ship docks. MO.S.E. is a lot bigger,
however, and its gates are also
networked with one another and equipped with intelligent control
and monitoring systems. Data from throughout the system is sent
to a control centre. Information on weather conditions and sea
currents is also analysed and used as a basis for decisions on
when to close the flood gates.
KELLER TRANSMITTERS
IN THE FOUNDATION
Secured by giant hinges set in concrete, the steel gates are
20 metres wide, five metres thick and up to 30 metres high.When
there is a danger of flooding, air is pumped into the gates,
which causes them to rise up to form a protective barrier against
the Adriatic Sea and block off the lagoon like a floodwall.When
the water is at a normal level, the gates lie retracted beneath
it.
Extremely precise data is needed to control and monitor the gates.
In order to monitor the structure of the caissons, geotechnical
specialists at Agisco s.rl. therefore installed
digital (bus) profilometers in the concrete elements.The prof
lometers work with highly accurate KELLER X series transmitters
with IP-68 protection.This solution guarantees impressively high
precision - down to onetenth of a millimetre over a length of
several kilometres.
HIGH-PRECISION
PRESSURE TRANSMITTERS THE X SERIES
The pressure transmitter's extremely high accuracy of 0.01 %FS
is available as an option; the standard precision of the X series
(33X, 35X and 36X) is 0.05%FS.This high degree of measurement
precision is achieved by combining a stable, floating, built-in
piezoresistive transducer with an XEMICS microprocessor with
an integrated I 6-bit A/D converterThe latter uses mathematical
compensation to eliminate the temperature dependencies and non-linearity
of the sensor. The transducer registers even the tiniest pressure
fluctuations, In order to ensure that this high sensitivity is
effectively exploited, the measuring element must be well shielded
from disruptive external influences. For example, the floating
installation setup completely decouples the transducer from mechanical
tension in the outer housing.
June 2019
