Letter: Protecting Venice

Protecting Venice

MICHAEL McCARTHY'S report (21 April) highlighted the threat of catastrophic flooding facing Venice. For nearly two years I chaired the international panel of experts that supervised the preparation of the environmental impact statement for the proposed movable gates that would protect the lagoon against high tides and storm surges. We could not agree more with the conclusion that inaction endangers the city and the rest of the lagoon environment.

Unfortunately, I must strongly disagree with statements attributed to Professor Edmund Penning-Rowsell. The gates are the only solution to long range flooding. They will protect the whole lagoon against flooding; they respect the commercial activity of the lagoon; they benefit the environment by protecting against flood; and they provide the opportunity to increase, through operation, circulation and water quality in the lagoon.

Professor Penning-Rowsell asks, "What happens when the gates have to be closed every day, as they will?" It is very reasonable to assume that the relative sea level will be 20cm higher a hundred years from now. At that point the gates would have to be closed 70 times a year for 250 hours. That is accounting for false alarms. If we were to assume a rise of 50cm in the next 100 years, consistent with some of the predictions of the UN Inter-governmental Panel on Climate Change, the above situation would be reached in 50 years. Although frequent, the closures would be far from permanent. A life of 50 to 100 years for such an engineered solution is very reasonable.

The article suggests "small-scale local flood defence works" as an alternative to the gates. Such works, called "insulae" are already under construction. These raised walls on the perimeters of many small islands are being built to their maximum feasible elevation without being physically and aesthetically intrusive. They will significantly reduce the number of gate closures required under medium flood conditions, but cannot possibly protect the city and lagoon against the extreme and most damaging flood events.

If indeed the worst of the sea level rise scenarios do occur, the movable gates provide protection and time for the Italian and world community to react. The present design includes locks to permit emergency transit even while the gates are closed. If sea level rise were ever to force permanent closure 100 or more years from now, the gates would not only have served their purpose but would provide the platform to implement the only solution possible: gates and locks. Ask the Dutch about their successful experience!

The gates are made of steel, not concrete, and are invisible except during operations. The cost quoted is too high by at least a factor of two. With the correct numbers the gates will not be a "waste of money".

RAFAEL L BRAS

Head, Department of Civil and Environmental Engineering

Massachusetts Institute of Technology

Cambridge, Massachusetts, USA