Corinne Podger BBC science correspondent

A multi-billion dollar scheme to save Venice, the famous Italian city of canals, from being submerged by stormwater floods, may be obsolete within decades, according to a study published in the journal of the American Geophysical Union (AGU), Eos.

Venice lies in a lagoon which protects it from the open sea.

But water levels in the lagoon are rising and in 1996 alone the city was inundated with metre-high floods more than 100 times.

A long-standing scheme to prevent flooding was set in motion at the end of last year by the Italian Government.

It will see a series of massive floodgates being built at the lagoon's three entrances to prevent surges from stormwater floods from entering the ancient city.

The $3bn gates are expected to take eight years to build but they may not be able to cope with the effects of global warming on sea level.

'Good for 100 years'

Paolo Pirazzoli, a geophysicist at the French National Centre for Scientific Research, has published a critique of the floodgate scheme in the journal Eos.

In it, he says the gates were originally designed more than 20 years ago and have not been adapted to cope with forecasted rises in sea level as a result of global warming.

As a result, he says, the barriers could be obsolete within a few decades of their completion.

But his views are contested by a team of scientists at the Massachusetts Institute of Technology in the US who have been commissioned by the Italian Government to assess the floodgates.

They say the gates will protect Venice from floods even if sea levels rise dramatically over the next century.