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Venice Offers Lessons on Coping with Rising Seas

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Bianca
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« on: January 08, 2008, 06:34:26 am »









                                   Venice Offers Lessons on Coping with Rising Seas





by Sylvia Poggioli

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http://www.npr.org/templates/story/story.php?storyId=17910734

All Things Considered, January 7, 2008 ·

As the Earth warms up, rising sea levels will increase the threat of storm surges and flooding. In some places, that will make exisiting problems worse. Venice, Italy, offers a glimpse at what may lie ahead.

For years now, Venice has topped the world's most endangered cities list. Built 1,300 years ago on mudflats in the center of a lagoon, the sinking city is subject to increasingly frequent winter flooding, from high tides known as "acqua alta" in Italian.

A major engineering project has now begun aimed at protecting the Venetian lagoon from rising sea levels, but most Venetians seem to take high water in stride.

Elevated walkways ensure dry feet, boutiques provide fashionable rubber boots, and residents are comforted by the conviction that nothing evil can come from the sea, Venice's oldest friend and protector
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« Reply #1 on: January 08, 2008, 06:37:22 am »









A boat ride in the Venice lagoon is a discovery of how humans and nature have created one the world's most extraordinary experiments.

Starting in the 16th century, the Venetians diverted major rivers outside of the lagoon to prevent silt from filling it up.

Left alone, lagoons like the one in Venice either tend to dry up and become land or they are overwhelmed by the sea and turn into bays.

The lagoon covers 212 square miles. Along with the city of Venice in the center, there are some 50 smaller islands, as well as dozens of mudflats and sandbanks — havens for thousands of aquatic birds that flock here even in winter.

This delicate and fragile ecosystem is the largest wetland in the Mediterranean.

If Venice is to be saved, the lagoon must be protected.

But today, rising seas threaten the Venice lagoon. All along the Grand Canal, windows of buildings near sea level have been closed and filled with cement.

"Those windows have been closed as they are too much exposed to the waters," says Francesca de Pol of Consorzio Venezia Nuova, the consortium entrusted with the task of safeguarding Venice.
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« Reply #2 on: January 08, 2008, 06:38:33 am »



On the central canal in Venice, people have cemented ground-floor
windows to protect against the floods.

Nobody lives on the ground floor in Venice anymore.









Moving Upstairs



No Venetian lives on the ground floor any more.

In the last century, the city sank 11 inches, mostly due to the pumping of groundwater and methane gas for local industries. But it has also being affected by rising sea levels.

What that means is that the same tides that were not flooding the city 100 years ago are now high-tide events. It's called acqua alta.

High water afflicts Venice mostly in the winter. A century ago it happened seven times a year, now it's more like a hundred.

The visionaries who first began building Venice 1,300 years ago used materials for the foundations that could withstand water. But with the seabed sinking, brick walls on the ground floors are being corroded and waterlogged buildings are crumbling.

Sophisticated technology is now being used to rescue the lagoon. MOSE, the acronym in Italian for experimental electromechanic module, is the biggest public works project in Italian history.

MOSE is also the Italian word for Moses, recalling the biblical parting of the Red Sea.

The project is building 78 floodgates at the three inlets that link the Venice lagoon to the Adriatic Sea. Del Pol says one of the gates' characteristics is their flexibility.

Depending on the type of tides, there are differing ways to manage the gates.

"You are not obliged to close the whole lagoon," she says. "You can close one inlet and not the other.

"In case of wind coming from a certain direction, you can chose not closing the whole system but only parts of the gates for certain types of tides.

"So you continue to have an exchange of water, not totally blocked."
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« Reply #3 on: January 08, 2008, 06:39:26 am »



Work is under way on one of the 78 giant gates to protect Venice
from flooding.

Rising sea levels due to climate change are causing more frequent
floods in the city. Here, a mobile sea barrier is being constructed
at the Malamocco inlet on the Venice lagoon








Giant Gates Filled with Air



At the Malamocco inlet, the walls of the MOSE project are being built just like the original walls in Venice. But workers are driving 125-foot-long steel and concrete pilings into the lagoon bed, instead of wooden pilings.

When the giant doors are at rest, they will be lying on the bottom of the inlet channel, invisible to the world. Each gate will be up to 92 feet long, 65 feet wide, and will weigh 300 tons.

When a dangerous tide is forecast, compressed air will be released inside the gates, emptying the gates of water. They will then rise and block the entrance of the tide.

In another effort not to alter the landscape, the worksite is on a specially built artificial island that will be demolished once the project is completed.
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« Reply #4 on: January 08, 2008, 06:40:57 am »



A key feature of the massive
MOSE project to protect Venice
from flooding is a navigation lock,
shown here under construction
at the Malamocco inlet.

When completed, there will be
78 giant mobile floodgates that
can be raised against high water.

Boats wishing to gain entry into
Venice will pass through this lock.

 







Protests Fail to Slow Construction



A debate over the floodgates has been under way for nearly four decades. The design was finally approved by the Italian government in 2003. Costs now stand at $7 billion.

Claudio Mantovan, supervisor at the Malamocco worksite, says the project is on schedule. Some 37 percent of the work has been completed, and MOSE should open as planned in 2012. One key element already finished is a navigation lock to allow large ships to enter the lagoon when the gates are up.

Mantovan says a few days of work have been lost due to peaceful protests by environmentalists and others.

"In order to build trenches for the MOSE gates, they are going to dig up millions of cubic meters of seabed and replace it with cement, which could seriously alter the ecosystem," says Alberto Vitucci, a journalist who has been covering the project for years.

"The entire mechanism will be underwater, making maintenance extremely difficult and costly. And the authorities never took any alternative projects into serious consideration."

Other proposals to control flooding in Venice have included narrowing the inlet channels to reduce the water flow from the sea into the lagoon, and banning tankers and large ships from entering.

Some criticize the project as irreversible and outdated. They say it was designed without taking into account predictions on rising sea levels over the next century.

MOSE engineers respond that the mobile gates are designed to last at least a century and to protect Venice from a difference in water level between the sea and lagoon of up to six and half feet.

The latest prediction of the United Nations Intergovernmental Panel on Climate Change is for a one- or two-foot increase by the end of this century.

Despite opposition, the MOSE project is moving ahead, and it's being closely watched not only by Venetians.

Coastal cities all over the world, from New Orleans to Singapore to Bombay, know that due to rising sea levels, Venice's seasonal flooding could soon become a shared, global phenomenon.



 
Related NPR Stories
Aug. 20, 2007

Donna Leon's Venice: A Tale of Two Cities
Aug. 11, 2007

Venice Awaits New Bridge over Grand Canal
Aug. 6, 2007

Venice Exhibit Traces the Migration of Culture
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« Reply #5 on: January 08, 2008, 06:53:26 am »



At St. Mark's Basilica in Venice, floods force people to walk on risers
to stay dry.

Flooding is more frequent as climate change brings higher tides into
the Venice Lagoon.



http://www.npr.org/templates/story/story.php?storyId=17910734
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« Reply #6 on: January 08, 2008, 07:03:49 am »


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« Reply #7 on: January 08, 2008, 07:16:38 am »








                                         MOSE system for the safeguard of Venice: how it works





The problem. High waters



Since the beginning of the 1900s, high waters have becoming ever more frequent as the level of the land has dropped with respect to the sea.  Flooding causes inconvenience for inhabitants and damage to architecture and buildings. There is also an ever present risk of a catastrophic event such as the 4 November 1966 flood when Venice, Chioggia and other built up areas in the lagoon were completely submerged under more than a metre of water.

 Some figures:

a) High waters above 140 cm recorded in Venice since 1966

4 November 1966: 194 cms
3 November 1968: 144
14 February 1979: 140
22 December 1979: 166
1 February 1986: 159
8 December 1992: 142
6 November 2000: 144
16 November 2002: 147

b) Increase in the frequency of high waters in Venice from 1926 to 2005 (number of events equal to or higher than 110 cm per decade)

years:                         no. events
1926 - 1935:  7 events
1936 - 1945: 3
1946 - 1955: 11
1956 - 1965: 22
1966 - 1975: 31
1976 - 1985: 39
1986 - 1995: 23
1996 - 2005: 53
« Last Edit: July 12, 2008, 05:25:40 pm by Bianca » Report Spam   Logged

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« Reply #8 on: January 08, 2008, 07:17:41 am »








What is the MOSE and how does it work?



The Mose System is a project for the safeguard Venice from high waters and consists of mobile barriers able to temporarily separate the lagoon from the sea.  It is being constructed at the lagoon inlets of Lido, Malamocco and Chioggia, the three openings in the barrier island through which tides propagate in the lagoon.

The mobile barriers consist of rows of gates.  In normal tidal conditions, the gates (a type of pontoon) rest in caissons on the bed in the inlets, completely invisible and without modifying exchanges between sea and lagoon. During high waters, they are raised and prevent the tide from entering.  At present, the tidal level at which the gates will be raised has been set at 110 cm, the level to which Venice has been protected by raising quaysides and paving.  This means that the gates would be activated an average of 3/5 times per year for a period of 4/5 hours each time.  However, the level at which the gates are raised can be changed whenever necessary. When the gates are in operation, the continuity of port operations will be guaranteed by a lock for large shipping being constructed at the Malamocco inlet. 
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« Reply #9 on: January 08, 2008, 07:23:33 am »













The above illustrate the movements of the gates of the MOSE system.

The Mose system can protect the lagoon and its cities from tides of up to 3 m and will therefore

be effective even if the level of the sea rises significantly during the next few decades. 
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« Reply #10 on: January 08, 2008, 07:28:54 am »








Mose system:

Progress

The go-ahead to construction of the Mose System was given by the "Comitatone" in April 2003, with the collaboration of all levels of State, Regional and Local Government.  Work has been underway for three and a half years and will last a total of eight years. A further ok was given by the comitatone in november 2006. According to the project, by 2012 (expected year of completion) Venice will be definitively protected from all high waters and the ever present risk of a catastrophic event such as 1966.





Work sites - For the last three and a half years, work has been proceeding in parallel at the three inlets of Lido, Malamocco and Chioggia.

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« Reply #11 on: January 08, 2008, 07:30:15 am »



LIDO INLET






Lido inlet -




At the centre of the inlet, the new island which will act as the intermediate structure between the two rows of mobile gates has already been constructed.  At the side of the island, work is underway on the deep structure which will house one of the "abutments" for the row of mobile gates. The island will also accommodate the control buildings and barrier operation installations

The coast on the north side of the inlet (Cavallino- Treporti) has been extended and redesigned with the construction of two sizeable small craft harbours, large areas of protected water equipped with a lock to allow small craft to shelter and transit when the gates are raised during a high water event.  The sea side area of the small craft harbour has already been "impermeabilised" and will be used to construct the gate caissons.

Along the south side of the inlet (San Nicoḷ), the existing jetty has been enlarged to avoid siphoning and flow-over of water when the gates are raised to close the inlet.  The deep structures to house the "abutment" for the second row of gates are under construction.  For the last few months, major work has been underway to prepare the bed for installation of the gates. 




VIEW OF THE WORKS AT LIDO INLET
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« Reply #12 on: January 08, 2008, 07:31:43 am »









Malamocco inlet -




Outside the inlet, a 1,280 m long curved breakwater has been constructed with the dual role of attenuating the vivacity of the tidal currents and creating a basin of calm water to protect the lock for large ships heading for Marghera, already finished some time ago.  The lock will avoid Mose interfering negatively with port activities during construction and when the gates are raised.  The size of the lock, present in numerous large ports in the north, allows the transit of large ships up to 280 m long and 39 m wide.

Beside the lock, a temporary area has been prepared to construct the gate housing caissons for this inlet. 



In the photo: the works at the Malamocco inlet.

On the left, on the south side of the inlet (Pellestrina littoral), works for the construction of the abutment of the gates and for the creation of the navigation lock that will allow large ships to pass through when the barriers will be closed. In the foreground, the new breakwater (completed) outside the inlet. It attenuates the vivacity of currents nd creates a calm basin sheltered from wave motion and wash to facilitate the transit of boats. On the background, the city of Venice)
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« Reply #13 on: January 08, 2008, 07:34:42 am »



CHIOGGIA INLET








Chioggia inlet -



Outside the inlet, a 520 m long curved breakwater has been completed.

Work at the north side of the inlet is also at an advanced state of completion, with construction underway of a protected small craft harbour with two locks to guarantee access to the lagoon for a large number of fishing vessels when the gates are in operation during a high water event. The "abutments" for the row of gates are also under construction. 



CHIOGGIA AND THE ISLAND OF PELLESTRINA ARE AT THE SOUTHERN END OF THE LAGOON



Lastly, large sections of the bed have been protected with layers of rock near the areas where the rows of gates will be installed.





 Employment -


Currently about 700 people are employed directly, while after completion.

When in full activity, the work sites will guarantee a total of about 1.500 direct jobs.


http://www.veniceword.com/news/8/mose.html
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« Reply #14 on: January 08, 2008, 07:42:52 am »








Young Professionals visit MO.S.E project in Venice

On 5 and 6 July 2007 the Young Professionals Commission organized its first technical visit to the MO.S.E. project in Venice and to the Experimental Centre for Hydraulic Models in Voltabarozzo (Padova). Objective of these technical visits was to offer YP's the opportunity to visit hydraulic projects of world wide interest. The technical visit was attended by YP's from Germany, France, The Netherlands and Italy.








www.pianc-aipcn.org/august2007/index.html
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