A conservation group yesterday claimed Italian authorities' plans to expand Venice's port will further endanger the fragile lagoon and contribute to the sinking of the treasured city.

Venice in Peril, a fund that works to preserve the city, said a report it obtained from the local port authority showed plans to accommodate more and bigger ships in a bid to compete with other European harbours.

The Venice port authority confirmed it had written the report, but insisted the works will respect the environment and are necessary to deal with the growing flow of tourists and goods.

The debate illustrates the complex and often controversial balancing act between protecting the Unesco World Heritage Site and exploiting a sea port that gives easy access to prosperous areas of northern Italy and central Europe, as well as rapidly developing markets in the Balkans.

The report drawn up for the Italian Senate outlines ongoing and future works including the continued dredging of passages in the shallow lagoon to allow larger vessels in and the construction of a new shipping terminal in the declining mainland industrial zone of Porto Marghera.

The port authority is spending at least €260 million to dredge inlets and navigation channels to allow the passage of ships of up to 400 metres in length.

This is particularly concerning for conservationists because dredging and heavy ship traffic are seen as one of the causes of the rising sea level in the lagoon, which threatens the low-lying islands on which the historic city is built.

"The big shipping channels through the lagoon are bad for its health," said Jane da Mosto, a researcher for Venice in Peril. "They aggravate erosion processes and since more water is exchanged between the lagoon and the sea, the higher water levels in Venice infiltrate the building fabric causing damage."

Under the combined effect of rising water levels and settling of the land, Venice has sunk 23 centimetres in the last century.

Most experts agree that the waves generated by large ships and the currents that run through the deep passageways play a big part, displacing and dragging out to sea the sandbanks and other sediments that help keep water out.

In winter, Venice periodically goes through bouts of acqua alta (high water), when strong winds and high tides conspire to push the sea into streets and piazzas.

The rising sea level has increased the frequency of the floods, and in December Venice suffered its worst deluge in 22 years. Experts warn the problem could further worsen in the coming decades as climate change causes sea levels to rise globally. The port authority report dismisses environmental concerns by declaring them solved thanks to a project to build towering movable barriers designed to rise from the seabed and prevent flooding.

The €4.3 billion system, named Moses, is expected to be operational by 2014.

"The problem of the hydraulic equilibrium is solved because it will be manageable through judicious use of the Moses system," the report says.

But opponents say the Moses barriers block shipping so they would only be raised when an exceptionally high tide is expected. That would not lower the average sea level and stop the waters from slowly eating away at Venice's bricks and stones.

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