Last night's flooding in Venice

Last night, Venice had its first acqua alta (high water) of 2011. The 112-cm water level was relatively minor, compared to some acqua alta tides, but it was enough to inundate the Piazza San Marco and other low-lying areas of the city.

Below is a short video that was taken around 11 p.m., at the high point of the acqua alta in our San Polo neighborhood. (If you've spent time in Venice, you'll probably recognize the Fondamenta del Vin, a pedestrian street near the Rialto Bridge where several restaurants have outdoor tables alongside the Grand Canal.)

Friday update: We noticed that the city's warning sirens didn't sound before the acqua alta, as they're supposed to do when the tide is expected to reach 110 cm. A local newspaper, Il Gazzettino, is now reporting that the sirens weren't working because the Centro Maree (Tide Center) hadn't received maintenance funds.


It's spring, and the canal walls are greening up

Moss on Venice canal walls

Q. Is the moss on the canal wall above a sign of (a) spring, or of (b)  something worse?

A. If you guessed (b), you've nailed our pop quiz.

The photo above was taken at low tide, when water from the Adriatic Sea and the Venetian Lagoon had receded enough to show moss growing on the brick walls of a canal.

The picture below is similar but more worrisome, because the moss shows that acqua alta, a.k.a. "high water," has soaked into the brick above a building's marble foundations. After a few decades of repeated exposure to salt water, the brick will start to crumble, and chunks of the damaged building wall (or canal walls, for that matter) are likely to begin falling into the canal.

Venice has an ongoing program of canal maintenance, and in recent years the city has responded to ever-higher acqua alta levels by replacing damaged water-damaged brick with layers of white marble or Istrian stone. The stone is far more resistant to salt water than brick is, and it's said to offer protection against water damage for hundreds of years. 

To see how canals are drained and repairs are done, see "Maintaining Venice's Canals" at our travel-planning site, Venice for Visitors.

Acqua alta damage to building walls  

The Sound of Sirens

Acqua alta garbage bags
ABOVE: During acqua alta, necessity is the mother of improvisation.

No, the title of this post isn't a misspelled homage to Simon and Garfunkel--it refers to the alert sirens and warning tones that tell Venetians and visitors when acqua alta flooding is on the way and what level of inundation to expect.

Several hours before a flood tide, you'll hear one blast on a World War II-style air-raid siren followed by a series of warning tones that forecast the expected water level at high tide:

  • One prolonged single-frequency tone means the water will peak at 110 cm above the benchmark of zero.

  • Two tones, each ending in a rising note, indicate an expected level of 120 cm or more.

  • Three tones, each ending in a rising note, indicate an expected level of 130 cm or more.

  • Four tones, each ending in a rising note, indicate an expected level of 140 cm or more.

Note: The tones may be repeated two or more times, so don't assume the worst if you hear two or three sets of tones with gaps between them.

What to do when you hear the sirens:

  1. Don't panic. Alta acqua can be annoying, but it won't hurt you unless you slip on wet pavement or are foolish enough to step off a flooded fondamenta into a canal.

  2. The area around the Piazza San Marco is the most flood-prone tourist area of the city, so avoid it unless you're willing to get your feet wet.

  3. Put on rubber boots or, if you're in a flooded tourist area, consider buying a set of overpriced temporary plastic boots from a street vendor.

  4. Stay close to buildings if you're walking along a fondamenta without a wall or railing. Canal edges are usually indicated by a border of white--and possibly slippery--Istrian marble, but why risk falling into a canal when it's just as easy to be sensible?

  5. Try not to splash when you're walking around--you'll just get yourself and other people wet, and you'll annoy Venetians who take little pleasure in the flooding of their streets, shops, and ground-floor apartments.


To hear samples of the initial acqua alta warning siren and the tones that indicate what tide level to expect, click here and scroll down to "Scarica i Segnale" for links to sound files in MP3 format.