Acqua alta doesn’t hit Venice as a surprise. There are simple “laws” that can help predict it, and in this post we are going to reveal them to you.
As a rule not all parts of Venice are flooded when acqua alta strikes. If you’re prepared to stick to a special part of town on higher ground, you might even escape without boots or ruining your shoes.
Last November, I was closed in by acqua alta after breakfast in a restaurant. Within half an hour, we watched how the tide rose from normal to +50 cm above ground level. The terrace was completely flooded, and the door was shut and boarded up. The birds – sparrows and sea gulls – remained perched on the tables outside. The chairs on the terrace were fastened with a chain to prevent them floating off. Life continued like it was routine, inside and outside. Ten minutes of heavy rain were followed by sunshine.
I was able to “escape” through a “secret” back door – leading out upon another calle to higher ground. Making a little detour I was able to reach home without getting wet at all. It really depends on where you are in Venice when acqua alta hits.
Times have changed in the sense that acqua alta now hits town all year, with more severe bouts in the cold season. If you know a few facts about the Lagoon, you can predict when acqua alta occurs, and what are its effects when you would like to go for a walk in town.
#1 Duration: From October through February we experience severe high tides. These happen because of adverse meteorological conditions in the cold season, such as heavy rain and scirocco wind causing the water masses to swell. I’ve experienced acqua alta bouts in the last few years that didn’t recede for 10 hours on end. The bouts are less severe in September and April. From June to August, acqua alta occurs 1-3 times a month, while you experience it up to 20 times per month in winter.
# 2 The laws of the tides: Tides on the northern Adriatic shores are more accentuated because they are channeled in northern direction along the natural currents and via the bocche di porto into the Lagoon. This is why the Lagoon experiences higher natural tides than any other location on the Adriatic sea.
When the force of gravity of the moon is strongest, high tide – alta marea = marea sigiziale (marea viva) occurs with full moon – luna piena and new moon – luna nuova. With the rising moon – luna crescente (crescent moon) and waning moon – luna calante, tides are more regular, called marea di quadratura (marea morta).
#3 Summer and winter tides: Twice a day in winter, tides peak. That is, high tide – alta marea and low tide – bassa marea occur twice a day in winter but as a rule only ONCE a day in summer !!! During full moon and new moon, water enters the Lagoon faster than it recedes. During the periods of rising and waning moon, water enters more slowly than it recedes.
#4 Acqua alta: Acqua alta is an exceptional alta marea (high tide). Even if the Lagoon wasn’t altered in its landscape features there would still be acqua alta once every 2-3 years, and an excessive one once every thousand years. That means the Lido would be flooded and the water masses submerge all parts of Venice.
That’s why the stone barrier called I Murasi (Murazzi) were built from the year 1714 on the long-stretched island of Pellestrina. This monumental wall made of huge Istrian boulders, built by the Republic of Venice, saved Venice almost 200 years after its end, during the exceptional high tide of 1966 !!
It takes about half an hour for the high tide to reach Piazza San Marco and even longer to arrive in the northern Lagoon. Salinity is thus higher at the bocche di porto than it is around the island of Torcello located nearer to the river mouths. This is why fresh water-loving fish live there, while the sea fish farming grounds valli da pesca are located in the southern Lagoon next to the open sea.