In 2002, the flooding of the city of Venice by seawater lasted a month. A worrying situation, and different from the one recorded in 589 BC, when the water rose for only a few days and did not bother the inhabitants. What used to be a rare event 2,600 years ago has become commonplace in last few decades, and is a threat to the future of part of the heritage of humanity. The damage caused by the floods over the centuries has brought irreparable consequences for the city washed by the Adriatic Sea, in the north of Italy.
For a long time, the first floor of the buildings has no longer been used, because of the recurrent floods. This has made the population fall from 250,000 in the Middle Ages to some 60,000 nowadays. But it was only in 1966, with the arrival of the worst flood ever up to that time, that a real solution for the problem started to be thought up. At the end of 2002, approval was given for the construction of submersed gates that, when raised in the period of high tide, are capable of blocking the three inlets from the sea to the Venice Lagoon.
Conceiving the gates was able to count on the collaboration of one of the dwellers of the city who lived through the great flood of 1966. Paola Rizzoli, aged 58, today a professor at the Massachusetts Institute of Technology (MIT), in the United States, recalls that the water ran through her own house. “For three days, it was impossible to go out. There was over 2 meters of water, we spent the whole time without any electricity, and the people who lived on the first floor had to go up to their neighbors’ apartment”. The marks of the flood remained ingrained in Paola’s memory in such as way that she decided, years later, to give up theoretical physics, after having received her doctorate in quantum physics, and to study the circulation of the waters of the oceans. “I became an oceanographer because of the high tide in Venice. That was 20 years ago”, says Paola.
In 1995, Professor Rafael Bras, from the MIT, was invited by the Magistrato alle Acque, or Venice’s Water Department, to head up a committee to supervise the work of designing, planning and constructing the Mose (Experimental Electromechanical Module), the official name given to the gate, in the form of a prototype, which was built ten years before. Bras then invited Paola and Professor Donald Harleman, also from the MIT, as well as Andrea Rinaldo, a professor from the University of Padua, in Italy, to take part in the committee, which had to assess whether the gates would not cause damage to the marine environment. In 1998, the researchers concluded that there would not be any environmental problems with the blockage of the three inlets (Lido, Malamocco and Chioggia) of the lagoon.
Islands and canals
Venice was built on 117 small islands interspersed with 150 channels and over 400 bridges. It began to be designed during the barbarian invasions in the 5th and 6th centuries BC, when the inhabitants of the Veneto region left the continent and took refuge on the islands. The problem with the flooding in the totally inhabited archipelago, with so much history to tell, has been intensified by two factors. The city is sinking, and the level of the sea rising. The first began at the end of the Second World War, when industries in the region started to pump water from the subsoil for their daily activities.
With the lowering of the subterranean water table, Venice began to sink rapidly. The 1966 flood put an end to the pumping of this water, and Venice is today sinking 0.4 millimeters a year. But the great problem is that the level of the Adriatic Sea has been going up 1.4 millimeters a year over the last century. One of the drastic consequences of this rise in the level of the sea is the multiplication of the number of times that the floods have happened. In 1997, for example, Venice suffered a hundred inundations.
“Today, the high tide is so common that, in November last year, the Piazza San Marco stayed under water for the entire month. My house is three bridges (blocks) from it. The only way of getting there, after crossing one bridge, was to walk on top of tables (actually, iron trestles with wooden planks, set up by the city hall), which continue to be there”, comments Rizzoli.
Prototype in the sea
In 1975, the Italian government ran an international competition to receive proposals for solutions to the inundations. But it was only in 1989, after a project based on five solutions presented in 1975, that the Mose was approved in a preliminary fashion, as a solution for Venice’s floods. At a cost estimated at between US$ 3 billion and US$ 4 billion, the Mose should take ten years to become ready.
Its 79 gates, each one 30 meters in height, 20 meters in width and 5 meters in thickness, will remain under the water for the greater part of the year – the estimate is that they will be raised for the equivalent of six days during this period, adding together all the times that they come in to action. They will be located in the three inlets to Venice Lagoon, and will only be raised if the tide rises more than 1.10 meters. Accordingly, the gates will work as physical barriers that will prevent the sea from inundating the city.
Installed at the back of the three outlets to the sea and commanded electronically, each gate will be able to be raised individually, making a strict control possible of how much sea water is entering the lagoon. The project indicates that the construction of the gates should start with Malamocco, then Lido (the place where the ships go in and out), and, finally, Chioggia.Republish