Venice has been keeping flood records for 150 years, though it is generally understood that the city has been regularly flooding since the very beginning. It usually happens between the fall and the spring and the earliest record is believed to be from the 6th century.
This past week, Venice saw its acqua alta (or high water) peak at 187cm (6'2") above its normal level. This is the second highest number on record and is just below its 1966 peak. At these numbers, about 80% of the historic center is underwater. Here is a chart from the WSJ explaining that:
Venice has been working on a flood management project called MOSE since the 1980s. The name is an acronym, but there's a deliberate biblical reference here. Remember when Moses parted the red sea?
The project has been mired in engineering delays and corruption scandals, and so it's not yet operational. If it were, it would have, in theory, protected the city this past week. 2022 is the anticipated completion date, but I don't know if that's realistic or not.
The system consists of 78 mobile gates that fill with water and sit flat on the seabed when the tide is low. When a high tide is predicted, the gates are then to be pumped with air so that they rise (hinged on one side) and close off the three inlets that connect the Venetian Lagoon to the Adriatic Sea.
As I was reading about this project and everything else that has been going on in Venice this past week, I became curious about how exactly the Dutch have been managing to hold back the sea. I mean, a big chunk of the Netherlands sits below sea level.
If you're also curious, here's a video that explains how they do it.