FLOOD CAUSES HAVOC IN BELOVED ISLAND CITY
BY PATTY CIVALLERI
Recent dramatic photographs and headlines regarding the flooding of the city of Venice, Italy, are causing global speculation as to the long-term outlook for the iconic city. Heavy winds, dramatically high tides, a sudden change in air pressure, and an incomplete underwater tidal barrier system known as MOSE, have combined to create a ‘perfect storm’ that has resulted in the massive flooding of one of the most beloved cities in the world.
The city of Venice is made up of 118 islands connected by over 400 bridges that span 150 waterways between the islands. This network of manmade islands is located within a large lagoon with three openings through which ships can enter and exit the lagoon.
THE TIDES & WINDS
Lunar tides known by Californians on the Pacific Coast are not the same kind of tides experienced in the northern Adriatic Sea. In Venice, a local phenomenon occurs that is known locally as the Acqua Alta or High Water. It occurs mainly in the Spring and the Autumn when astronomy combines with Sirocco and Boro winds from the south, which push the waters northward. The north end of the Adriatic, where Venice is located, is nearly surrounded by mountains creating a cul-de-sac where the north-moving waters back up and raise before receding back southward again.
DRASTIC CHANGE IN AIR PRESSURE
Another ingredient in the mire of havoc-creating events this week in Venice was a rapid change in air pressure. “Monday, this difference has reached 0.44 to 0.59 inches of mercury (15 to 20 millibars), which is quite significant. This pressure difference tends to lift water at the north end of the Adriatic Sea (thus Venice),” said AccuWeather Meteorologist Jim Andrews.
THE MOSE PROJECT
After the ‘great flood’ of Venice in 1966, the city met with engineers from around the world to formulate a project that would prevent these periodically dangerous floods from doing further damage to this historically preserved city. After many years, a solution was decided upon, and the project began construction in 2003. It was designed to place an underwater ‘gate’ of sorts at each of the three entrances to the Lagoon: the Lido, the Malamocco, and the Chioggia, from north to south. During normal weather and tides, the gates are passively withdrawn. When a high tide is in the forecast, the gates could be raised enough to create a barrier against the influx of waters from the Adriatic Sea.
This is all well and good. However, the project has stalled on many occasions due to heavy-handed politics, as well as deeply-saturated corruption and arrests of city officials ‘on the dole.’ The consistent slowing of the project has deflated the confidence of many local Venetian residents, who roll their eyes at the mere mention of the project. Although the project has seemed to pass the 90% completion mark, a growing number of voices are now protesting the total completion of the project since it has already cost more than $5 billion euros, and its design uses what is now considered to be old technologies.
HOW THE ISLANDS WERE CONSTRUCTED
During the early 400s in the area that we know today as Northern Italy, Attila the Hun’s formidable army ransacked many of the townships and left a path of frightened citizens scattered throughout the countryside.
Questioning their fate, many folks decided to move to the islands to escape the onslaught. This was a difficult decision because the hundreds of little islands in the Venetian lagoon were not much more than swampy, muddy, mushy, marshland. But flee they did, to the island of Torcello (pronounced tor-CHEH-lo).
With limited materials, they created temporary shelters in which to live until they knew it was safe to return families back to their original homes on the mainland. Most did return, but some enjoyed the marshy life on the island of Torcello and began to build further.
The marshy land was not easy to dominate. They had to find ways to not only strengthen the soft land but also to claim more land from the surrounding waters. They built a wall of pilings to widely surround the swampy land that stuck up above the water, pounding them deep into the natural clay foundation. They filled this newly-created basin-like area with rocks, shells, and any other hard materials that could easily be acquired and transported. They covered this layer with another thick layer of dirt which they pounded to make it hard and flat. This was the new land that could be inhabited.
Over time as the population grew, they repeated this process, adding more islands as needed. These efforts left them with many pieces of usable land. Small foot-bridges were then added so that they could easily walk from one island to the other.
Venetians are probably the most creative and resourceful population in the world when it comes to dealing with flood waters. This little city has championed flood-related issues for over 1,500 years and are considered experts at the complications caused by living in a water-surrounded community. So much so, that Venetian city engineers have been teaching other cities how to manage flood waters, fires, refuse, and health emergencies for many years. Adding to the complexities of an island population of 54,000 residents is the fact that the little city of Venice, over 30 million visitors each year. Tourism causes a completely different kind of flood to the city, the kind that is doing more damage than the seasonal waters. But as elegantly as the city handles this myriad of complex scenarios, it still needs to deal with the long-term issues creating by flooding waters and the flood of tourism.
IS VENICE SINKING?
Every time the waters rise in St. Mark’s Square, the world asks this question. Here is the answer: Since the 1890’s, the altitude of Venice has had a measurable loss of 23 cm (approximately 9 inches). In the 1970’s, Venice stopped extracting water from under her skirts. Freshwater is now pumped in from the mainland. “Due to the elasticity of the aquifer,” said Andrews, “Venice has actually regained 2 cm since the 1970’s.”
The melting of the polar ice caps is causing all coastal cities in the world to think about their own future. Venice, because of her geological makeup and position, is more vulnerable than many other coastal cities. But if any city will devise answers to solve this global problem as it unfolds, it will be Venice.