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Acqua AltaHigh Tides and Flooding in Venice
ABOVE: Tourists wade in the Piazza San Marco. INSET BELOW: An intrepid visitor tests the waters. by Durant Imboden Acqua alta, or "high water," can make Venice feel like Atlantis. At its worst, in 1966, acqua alta flooded the city with more than a meter of salty lagoon water; more typically, visitors notice water splashing over canal banks or bubbling up through drains in the Piazza San Marco.
Why (and when) acqua alta floods the city:Acqua alta occurs when certain events coincide, such as:
The phenomenon is most likely to take place between late September and April, and especially in the months of November, December, and October, in that order. The Comune di Venezia's Acqua Alta publication explains: "In the remaining months, frequency is very low, while there has never been an event from June to August." Not all parts of the city are equally susceptible to flooding, as the following chart from the Comune di Venezia indicates. Also, the actual depth of water in the streets is far less than the "level of tide" might suggest. (See the "extreme case" below, where 135 cm of flooding translated into 40 cm of water in the Piazza San Marco.)
An extreme case:On October 31, 2004, when some of the photos in this article were taken, the acqua alta reached 135 cm. The Piazza San Marco was indundated by at least 40 cm or 16 inches of water in what was billed as the worst acqua alta of the decade (and the 10th worst since the record flood of 1966). More recently--on December 1, 2008--the acqua alta reached 156 cm and flooded most of the city.This was the most extreme acqua alta in 22 years. (The worst deluge in Venice's history was in 1966, when floodwaters topped out at 194 centimeters.) Possible solutions:The Comune di Venezia and various international organizations have been working on solutions that range from MOSE Project floodgates at the Lagoon's entrances (due to be completed in 2014) to raising of pavements in low-lying areas of the city. Much construction of the latter has already taken place, but it remains to be seen whether acqua alta can be tamed without closing off the Lagoon from the sea and turning it into a freshwater lake. Next page: What to expect, how to prepare
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