Aqua Alte in Campo San Marco, Venice
The Flooding of St Mark's Square and the Solution to the Problem
Mar 22, 2009
Water has made Venice what it is – a canal-based city – and water could well be the unmaking of Venice, if the Venetian authorities are unsuccessful in controlling the Aqua Alte (high water) flooding that is now a frequent occurrence.
What is Aqua Alte?
Over the centuries, Venice always experienced occasional flooding – an infrequent natural disaster faced by many other cities in the world. However, in recent decades, a combination of factors has resulted in major flooding of low-lying areas at high tide. Worst flooding occurs at those times when strong winds blow into the canals, slowing the normal tidal outflow, so that a fresh high tide ‘catches up’ and backs up the water. As well, the lunar cycle dictates that there is a short period of ‘king tides’ every month.
Ancient drainage systems are inadequate to deal with such volumes, minor canals silt up, and, as all buildings are supported by wooden piles driven into the mud, many buildings are slowly sinking. Around the famous Campo San Marco (St Mark’s Square), minor flooding, according to information boards placed by the Venetian authorities, is “an almost daily occurrence”.
St Mark’s Square
The Venetian municipal authority is particularly concerned about damage that is occurring to buildings and precious artwork in Camp San Marco. It indicates that, even with moderate tides, water rises around the basilica itself, possibly unnoticed by tourists. Many home owners are familiar with the problem of rising damp – this is rising damp on a very large scale.
There are three ways that high tides impinge on Campo San Marco. Water rises through the subsoil, weakening the massive structures; it flows up through the drainage system and out drain gratings; and, on really high tides, it sloshes over the canal edges, as from an over-full swimming pool, and spreads out across the city squares and narrow lanes to a considerable depth. Basements get flooded.
Problems for Tourists at Aqua Alte Periods
Clearly, the chief danger and concern of Alte Aqua is for this magnificent city itself, unique among the cities of the world, a long-standing treasure. Nevertheless, the present Venetian economy depends on the tourist dollar, and the needs of tourists are strong in the minds of the city fathers. When Alte Aqua threatens, a siren is sounded throughout the city.
Those premises that are equipped to do so, seal off low doorways. Boardwalk segments which lie ready along the edges of certain streets are hauled into line to form a metre wide footpath about 30 centimetres above the water. Crowded streets become super-crowded boardwalks and visitor need to negotiate these narrow paths with care and patience.
Many hotels now keep a supply of gumboots to issue to their guests during Aqua Alte. The determined tourist will still manage to see Venice, and may even carry home the memory of St Mark’s Square looking like a vast swimming pool.
Protecting San Marco from Flooding
- The Venetian municipal authority is attacking the problem in three wayThe sub-structures of buildings in Campo San Marco are being strengthened with a new infrastructure network.
- Pavement is gradually being replaced and, at the same time, better drainage is being installed underneath the square.
- The edges of the canal where the main flooding occurs are being raised.
The Mose System
These measures will support the Mose system, which is the major hope for the preservation of Venice against the ravages of the sea. The Mose system is an integrated chain of mobile barriers that can be positioned across the three main sea entrances of the Venetian lagoon. Work has been progressing on this project for the past five years. The authorities believe this system will be proof against flooding, even if sea levels rise as predicted by many scientists.
Anyone who has ever had the joy of visiting this spectacular city with its long history of trade and opulence will hope that the Venetian authorities are right in their belief that they can save Venice from destruction.
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