Street Flooding, “high water” in Piazza San Marco, Venice

Street Flooding, "high water" in San Marco: Venice City Guide

Acqua alta (High tides)

We’ve all heard about Venice flooding and seen the news shots of people wading through the waters in St Mark’s Square. But actually Venice only has Acqua Alta (high water) in Autumn and Winter when some streets and squares flood, and even then there are only a few days when the waters get really high and cause disruption.

The main difficulties result from the water rising in the canals so that boats can’t get through them (public transport schedules are shot!). There are plenty of pedestrian routes equipped with special raised walkways (passarelle: see photo) to avoid the flooding so you can reach most parts of Venice.

You often see claims that Venice has acqua alta on more than forty days a year, but there are different levels of severity. Basically, less than 80 cms is a normal tide with no flooding. A tide above 100 cms will cause minor flooding, whilst tides above 120 cms will begin to cause extensive flooding.

According to this page on Acqua alta , the tides can be classified as follows:

• 100 cm : about 4% of the city is under shallow water
• 110 cm : about 12% of the city is under shallow water
  sirens wailing over the city three-four hours before the peak – small nuisance.
• 120 cm : about 35% of the city is under shallow water ; sirens … – medium nuisance.
• 130 cm : about 70% of the city is under shallow water ; sirens … – high nuisance.
• 140 cm : about 90% of the city is under shallow water ; sirens … – emergency.

When a higher than usual tide is expected in the city, sirens are sounded 3-4 hours in advance to warn the public, but they only go off if the level is expected to be above 110 cm (12% of the surface under water).

Maps of Acqua Alta routes

Maps are posted at the boat stops showing 11 alternative pedestian routes around the city equipped with special footbridges to avoid the high water. You can also pick up a brochure with a map of the walkways at the tourist office.

These wooden walk ways (passarelle) allow movement around the city in the main areas in tides up to 120 cm. (35% of the surface under water).

Of course, the tides ebb and flow, and the peak only lasts a couple of hours, so it’s just a matter of waiting before things get back to normal.

Current tides predictions can be found on the Commune de Venezia website , at the Rialto vaporetto stop, at the bottom of the Campanile in San Marco, and on a neon sign in Piazzale Roma.

For further information call the Venetian Tide Information Service on 041-522-8662

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