Flooding in Venice's St. Mark's Square

Lots people wear the disposable protective show covers that look like cellophane stockings. You can also walk on the elevated platforms which will be set up all around the flooded areas.

If you want to avoid flooding then avoid the St Mark's Square area which is the lowest ground in Venice.

Based on my research for our trip I don’t feel like late September flooding should be much of an issue. But as the poster above says, if it is, just buy some over-shoes and enjoy a wet experience you won’t forget!

I had once the acqua alta and found the boardwalks adding to the experience. Put two small plastics bags in your suitcase to be prepared.

On average March and November have been the rainiest months for Venice.
I have been to Venice in March and there were days with slight flooding. I would
not worry about September, however we brought our "Wellies" stuffed full of socks etc to fit in suitcase.
We had the best day in Venice sloshing in puddles while others tried not to lose their balance
on the elevated sidewalks. Just a suggestion. Bon Voyage.

Check the cycle of the moon. If it is a full moon or new moon, the tides will be higher and flooding can occur at high tide. So in between those two extremes, half moon, the tides will be the lowest and flooding unlikely at high tide.
The full moon will be Sept 25 this year. Half moon is on Sept 17 and Oct 2.

Funny, I was actually HOPING I would get to see acqua alta in Venice (and I did)!

What we did was just take off our shoes and walk barefoot.

For short term aqua alta forecast: http://www.veniceforyou.com/highwaterprev.html

During Venetian Aqua Alta events backpacks would be preferable over rollers. While the canal water will be diluted, getting your clean clothing soaked with contaminated water isn't a good idea. Wash clothing and body parts that come into contact with flood waters: https://www.cdc.gov/nceh/ehs/publications/guidance_flooding.htm

We saw flooding in St. Mark's during a May trip. We tried to use the elevated walkways where possible, but it wasn't possible 100% of the time. You should find many people willing to sell you plastic foot/leg covers, though.

My tactic - if the shoes were already wet, I'd just suffer through them again because I wanted to keep one pair dry for post Venice.

I was actually looking forward to the flooding in St. Marks square. Where else in the world would you get to see it except in a big rain storm. We were on a RS tour and planned to go into St. Mark’s at noon when our tour guide got a text that the square was going to flood so he postpone the tour until 4:00 pm and suggested that we might stick around for a few minutes to watch it. The day before our guide showed everyone how to get from the hotel to St. Marks Square and back. He told everyone that they could always find St. Mark’s Square so wouldn’t get lost. Those of us that have downloaded Maps2Go had no problem getting back to our hotel avoiding the rising water. Those who didn’t, ended up with wet feet. We all had a good laugh at dinner that night.

This website shows tide projections for locations worldwide. Plug in "Venezia, Italy" for Venice, and the date range you want at the bottom. It will show tide times and heights (in centimeters) by dates, plus moon phases.

This article in Wikipedia discusses the acqua alta, and includes a table showing what percentage of the city is submerged at what water levels.

Using the two tables helps you predict the water levels you might experience on given dates and how much of the city they will affect. One problem is that St. Mark's Piazza can be affected even when most of the city won't. The other is that water level depends not only on the astronomical tide (influence of sun and moon), which can be predicted far ahead, but also on rainfall and winds pushing water up the Adriatic, which can't be predicted far enough ahead to be useful in scheduling a trip.

I'm hoping for relatively dry, calm weather on my early November trip, and for a healthy market in those lightweight boots if I don't get the weather I want!