High tide in Venice

The High Tide is a natural phenomenon linked to the influence of the moon on the waters of the seas. With the rotation of the earth around the sun and on its axis and the moon around the earth, the stars, attracting the mass of water, in fact create the tides, water moving attracted to celestial bodies and, in the case of matching, tides are created more or less supported.

Being precise and known the movement of the stars, you know perfectly well the movement of the tides.
When, during the alignment condition of the sun and moon, you add a wind from the south pushes the water of the entire Adriatic Sea, and more abundant rainfall occur that swell the rivers that flow into sea, then you will have the conditions for a tide supported that submerges part of Venice.
The first parts of which are under water are the older ones, those on which it was not possible to add layers of earth or new flooring, as in the case of the areas in the vicinity of the Rialto's Bridge or St. Mark's Square, already under water with 85 cm to tide over the mean sea level, as you can see in the Time Lapse below, shot by Venicewiki.org October 22, 2014.