High water, a phenomenon Venetians have always been used to, is nothing else but a tide peak, usually occurring in autumn and winter, mostly between November and December, when the astronomical tide, the strong Sirocco wind, the “sessa” phenomenon in the Adriatic – or a combination of these elements – determine a higher inflow of water in the Venetian Lagoon.
The height of the tide varies according to different meteorological factors. The tides are higher when the barometric pressure is particularly low or when the Sirocco wind is blowing. The widest tide excursions usually occur at new and full moon periods, in the first and last quarter of the moon the abundant high tide phenomenon is less likely to happen.
High water in Venice follows the tidal cycle, that rises for 6 hours and then lowers in the next 6: in the days with high water, this phenomenon persists only in the central hours of the rising phase. High water in Venice usually lasts about 3-4 hours, and when the level of the water lowers, the city goes back to normal.
But how high can the high water get? When the tide level is measured, the point of reference is the average sea level measured at Punta della Salute. To let you better understand, nearly all of the city (97%) is at about 100 cm over the average sea level. This means that the quantity of water that can flood the streets is always much lower than the maximum forecast tidal level. For instance, an exceptional tide of 140 cm corresponds in reality to about 60 cm of water in the lowest points of the city (Saint Mark’s Square) and floods about 54% of the historic city centre.
the tide level is between +80 cm and +109 cm over the average sea level
very sustained tide
When the value is between +110 cm and +139 cm;
When the value reaches or exceeds +140 cm.