The sea is a fickle mistress. Built on marshland within a salt-water lagoon off the Adriatic, Venice owes her fortune to the sea. At her birth, at 12pm on 25th March 421 AD (according to legend), the lagoon protected Venice from her enemies. Later, in her heyday, water-based trade and naval warfare made the city very rich. But water can also bring damage and destruction as Venice knows all too well. Venetians call the phenomenon Acqua Alta, or high water.

Acqua alta in Piazza San Marco, June 2014

Wading through

So what causes acqua alta? Here comes the science bit! Acqua alta is produced when a number of factors combine to cause an exceptionally high tide which floods the city. These factors include –

1. Normal and seasonal high tides
2. Low pressure weather and prevailing winds pushing the high tide into the Venetian lagoon like a storm surge
3. Subsidence or sinking…