Acqua Alta and The Rising of The Tides

Throughout it's history the city of Venice has seen its share of environmental changes, but none pose a greater threat to the preservation of the city than what the locals refer to as acqua alta. Acqua alta is the name given to an exceptionally high tide that floods all but the most elevated parts of the city for several hours at a time. The most recent, significant, occurrence of this phenomenon, which most often takes place between the fall and spring, occurred on December 1, 2008 when it was documented that 156 cm of water flooded the city streets. Not only is this a disturbance to everyday life, but more importantly it is a direct threat to the overall structure of the city. When the bricks in an old wall are exposed to sea water they absorb the salt which, as it accumulates, hastens their decay. Both the frequency of acqua alta and the height reached by the tides have increased over the past 30 years due to the slow rising of sea levels and sinking of the land surface of Venice. It is believed that the sea level rises by an average of 3 mm per year according to a 100 year study conducted at the tide gauge station known as the Punta della Salute. This study concluded that from 1897-1997 the sea level rose by a total of 30 cm, which gives an average of 3 mm per year. As a natural occurrence the sea levels will continue to rise thus resulting in more frequent and severe cases of acqua alta as well as more severe and hastened deterioration to the foundations of the city. This is most certainly an issue that cannot be overlooked for much longer.

Source