17/02/2006

The Moses Gates

Michele Jamiolkowski, ICON: World Monuments Fund Quarterly Magazine

Although Venice has been slowly sinking into the marshy soil upon which it is built for centuries, the historic city is confronting a modern-era condition that is threatening coastal regions throughout the world, global warming. In Venice, global warming has exacerbated the effects of extreme storms, which batter the city four to six times a year. Over the past decade, the Italian government has embarked on a massive and complex plan to preserve the city with measures ranging from raising the city's sidewalks to installing new breakwaters in the lagoon. The costly and controversial centerpiece of the plan, however, is the installation of the so-called MOSE (Modulo Sperimentale Elettromeccanico) Gates, a system of 78 300-ton barriers across the three inlets to the lagoon that are intended to protect the city during the worst of storms.

ICON correspondent, Alex Ulam, recently caught up with Michele Jamiolkowski, president of Studio Geotecnico Italiano, a firm which is helping to design the gates. A professor at the Technical University of Turin and a geotechnical engineer known for his innovative approaches to solving such problems as reducing the precarious tilt of the Leaning Tower of Pisa, Jamiolkowski explains why the gates are critical to saving Venice.

ICON: The extraction of water from the underground aquifers and the extraction of natural gas have been blamed for Venice's sinking. To what extent is the annual flooding in Venice related to these activities?
MJ: Human induced subsidence was triggered first by the extraction (pumping) of water and later by the extraction of gas, which began around 1920. More than a decade ago, the Italian government stopped the extraction of the gas from the upper Adriatic and moved the pumping of water to deeper strata. Generally, they have also forbidden deep wells in the historic part of Venice. Once they curtailed these activities, the problems of human induced subsidence was reduced practically to zero.

Today, the problems caused by the human induced subsidence are quite small in comparison to the rise in the sea level and the high tides, which are caused by very specific weather conditions. Yet, the city continues to sink as a result of natural subsidence caused by the compression of the subsoil under the weight of recent river deposits, especially those of the Po River Delta. The rise in the sea level is linked to global warming and the melting of the polar ice caps. The special weather conditions in the Adriatic, where there is an unusual combination of low barometric pressure and high winds, are causing the frequent high tides.
The historical areas of Venice are extremely vulnerable as they are located at very low elevations with respect to the mean sea level. This past November, for example, a large part of the historical part of the town was flooded during high tides, which rose to elevations of 1.36 meters above sea level, the Venice datum for which is close to the Church of Santa Maria della Salute.
 
ICON: How is Studio Geotecnico involved in the design and construction of MOSE Gates?
MJ: SGI is acting as Geotechnical Consultant to the Engineering Company TECHNITAL, responsible for the design.

ICON: Has Studio Geotenico worked on any other World Heritage Sites aside from Venice?
MJ: Yes, we have also been involved in safeguarding the Bell Tower in St. Mark's Square.
 
ICON: What is most challenging aspect to designing and installing the MOSE Gates?
MJ: The baseless opposition by the Green Party, both from a scientific and an environmental point of view, as well as the differential settlements of the MOSE caissons and the maintenance of the mobile gates in the lagoon environment.
 
ICON: Will the barriers be completely watertight?
MJ: No. One cannot have the steel gates touch each other, so there are some small gaps between them, which will allow some seepage of the water from the sea into the Venice lagoon. However, this will not cause any significant rise in the Venice lagoon during high tides.
 
ICON: There has been some concern that the water in the canals will stagnate during the periods when the gates are up. How will you avoid this?
MJ: The gates will only be operating when the high tides exceed 1.1. meters above mean sea level. Under the present conditions they will only be raised a few days a year. Of course, the longer the gates need to be closed, the greater concern there will be about the adverse environmental impact resulting from a lack of circulation within the lagoon.
 
ICON: You mentioned that the MOSE Gates wouldn't necessarily help with the problems in New Orleans.
MJ: New Orleans flood was caused by an accident-failure of the dikes-while MOSE is conceived to defend a relatively small area from high tides occurring roughly every year. In the case of Venice, three relatively narrow inlets will be fitted with gates. The area to be protected in New Orleans, however, is so large that a system such as the MOSE would not be affordable. The way out for New Orleans is to make the dikes safer and to implement an efficient monitoring and maintenance procedure.
 
ICON: This past fall, you were asked to evaluate a proposal put forth by scientists from the University of Padua, which would involve the injection of water into the depleted aquifers to elevate the city. Would this help protect Venice against the floods.
MJ: Injecting water into the aquifers is not technically feasible. Even if it were, this intervention would raise Venice not more than a hundred millimeters, which is not enough to provide any degree of protection from the floods. Further, this solution would result in a differential heave to the soil, which would damage historical buildings. This solution would also cause a great deal of environmental harm because it would contaminate the freshwater aquifers with salt water.
 
ICON: In addition to Venice, you have worked on the containment of Chernobyl and on reducing the tilt of the Leaning Tower of Pisa. Of these projects, which has been your most challenging?
MJ: The Leaning Tower of Pisa was much more challenging and difficult to solve for several reasons. As one of the most important icons in Italy, any work on the tower was politically charged, with the public opinion and the media being particularly sensitive to even a slightly invasive intervention on the monument. Every attempt to solve the problem of the lean since the close of the eighteenth century had failed. When we began our project in 1993, the tower was on the verge of collapse, so any intervention to its foundation or masonry was highly risky. By excavating sediments beneath the north side of the tower and installing thousands of pounds of counterweights, we were able to reduce its lean by .5°, buying the tower another three centuries (see ICON Spring 2003).