Acqua alta

The main winds involved are the sirocco, which blows northbound along the Adriatic Sea, and the bora, which has a specific local effect due to the shape and location of the Venetian Lagoon.

The particular shape of the Venetian lagoon, the subsidence which has been affecting the soil in the coastal area, and the peculiar urban configuration all magnify the impact of the high waters on city dwellers and on the buildings.

The study provided Venetians with the following reference guide:[9] To assist pedestrian circulation during floods, the city installs a network of gangways (wide wooden planks on iron supports) on the main urban paths.

The Tide Monitoring and Forecast Centre of the City of Venice is fed information via a network of hydrographic stations, located in both the lagoon and the Adriatic Sea (on a scientific platform belonging to the Italian National Research Committee, CNR).

Forecasts are then announced to the population via the centre's website and dedicated phone lines, through local newspapers, on electronic displays, and at some stops of the vaporetti (public transport).

When an acqua alta event is forecast, owners of commercial and residential property that is likely to be affected are contacted by phone (a free service provided by the municipality) or SMS.

The project should significantly reduce the effects of "exceptional high waters" (but not those of lesser, yet detrimental, tidal events) by completing the installation of 79 separate 300-ton flaps hinged on the seabed between the lagoon and the Adriatic sea.

The Venetian Institute for Science, Literature and Arts was appointed to the task by the newly formed Italian Kingdom, thus replacing the Magistrato alle Acque in 1866[2] upon annexing the city.

After the unprecedented acqua alta of 1966, the city set up a dedicated service to analyse data, monitor fluctuations, and forecast high tides, which is also charged with continuously keeping the population informed.

In 1110 the water, following a violent sea storm (or, possibly, a seaquake and its subsequent tsunami), completely destroyed Metamauco (ancient name for Malamocco), Venice's political centre before the Doge's residence was moved to Rialto.

The latter event was probably remarkable, since there are also records of very violent sea storms that, having "broken indeed the shores in several places, entered the towns of Lido Maggiore, Tre Porti, Malamocco, Chiozza, et cetera".

Several chronicles of the time, among them one written by a scientist, concur in reporting that "the waters reached the outdoor floor of ... [Sansovino's] Lodge", which is the monumental entrance to the Campanile di San Marco.

These are the highest water levels documented by the Tide Monitoring and Forecast Centre of Venice:[2] In Kozue Amano's utopian science fantasy manga series Aria and its anime adaptation, acqua alta is a phenomenon that happens in the lands on Mars referred to as Neo Venezia.

This season introduces the phenomenon of Aqua Laguna, an annual event in which rising water levels completely floods the lower part of the city, causing massive damage to it.

A satellite image of the Adriatic Sea , highlighting the long and narrow rectangular shape which is the source of an oscillating water motion (called seiche ) along the minor axis. The oscillation, which has a period of 21 hours and 30 minutes and an amplitude around 0.5 meters at the axis' extremities, supplements the natural tidal cycle, so that the Adriatic sea experiences much more extreme tidal events than the rest of the Mediterranean.
Acqua alta in Venice , fondamenta di Borgo , December 2019
Fondamenta del Squero flooded in December 2019
Tide Monitoring and Forecast Center
Tourists on the gangways queueing to enter the San Marco Basilica
Monument to sea and land soldiers , sculpted by Augusto Benvenuti, to commemorate the help given by the army during the catastrophic 1882 flood (Biennale gardens)