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Can engineering save the sinking city of Venice?

By intouch * posted 09-08-2018 11:05

  
By Chelsea Wallis. 

Human intervention is at the heart of the Venetian legend, earning the mythological status it retains today thanks to residents pursuing the knowledge to master nature. Not all of these efforts have been positive in the long-term.


Screen_Shot_2018-08-09_at_11_01_54_AM.pngVenice is now sinking at a rate of about 2mm per year, with climate change threatening ever higher, more frequent tides upon the already fragile World Heritage Site.

Today’s interventions are necessarily more robust. While much of the focus is on the city’s sea wall project – and on whether it will be enough – it is only part of the solution that Italian engineers are putting in place to protect Venice.

MOSE

In 1966 Venice suffered its worst flooding in history, with high tides reaching 1.94m prompting action. After years of study, the Consorzio Venezia Nuova (CVN), the consortium of construction companies undertaking the design and construct task, proposed mobile barriers to protect the lagoon inlets to the city.

The innovative Modulo Sperimentale Elettromeccanico, or MOSE, is a series of gates positioned at three inlets to the lagoon: Lido (with two separate gate installations), Malamocco and Chioggia.

The unique steel gates are designed to lie on the sea floor out of sight, their hollow chambers filled with water. Once the tide levels reach 1.1-3m, the gates are raised remotely by pumping in air to displace the water and float them into position, temporarily isolating the lagoon from dangerous seas.

Alternate design options

Screen_Shot_2018-07-05_at_11_27_17_AM.pngThe design is not without criticism. Massive cost overruns and the long lead-up to implementation have not ingratiated the project to locals, nor did the corruption scandal that involved the mayor of Venice and 30 others siphoning millions from the project and covering up design flaws.

Italy’s Higher Council of Public Works approved the plan in 1994, with construction beginning in 2003. The first gates were installed in 2013, which means maintenance, on a five-year cycle, is due while the full system is not yet operational. There are reports of saltwater corrosion on gates waiting to be installed and questions about the 1.1m minimum barrier, which leaves low-lying areas such as St Mark’s Square still vulnerable to flooding from 80cm. The latest estimates put completion around 2020.

However, UTS architecture professor and specialist in sustainable urban environments Rob Roggema says this is a necessarily unique solution for an equally unique location. There are three phases of engineering thought progression to protect cities vulnerable to flooding, he explains.

“The first phase is to construct a rigid wall,” Roggema says. “The second phase is to build something temporary and artificial, only to be used in extreme circumstances. Both of these options hold harmful ecological implications. Those implications are very difficult to predict, with effects only revealing themselves in the long term.

“There is a third phase where we build with nature. It could be as simple as planting mangroves that grow the landscape to match the rise in sea level, or introducing sand into the sea for the tides to create natural dunes and beaches. Nature could well be our strongest ally for protecting hinterlands while creating the highest ecological value.”

Not just a wall

Screen_Shot_2018-07-05_at_11_26_44_AM.pngIt therefore shouldn’t be surprising that the MOSE project encompasses more than the mobile barriers. Venice is not the only town along the lagoon under threat, not to mention the semi-lacustral habitat of the lagoon itself: barrier islands and 550km2 of marshlands, including 40km2 of salt marsh and a 1500km network of canals.

For instance, in the fishing town of Chioggia, the “Baby MOSE” project will assist the main floating barriers and improve overall flood management. This consists of two gates on the Canal Vena that isolate it and prevent the tide from flowing over the quaysides or rising up through the drains.

Measures have been taken to combat the Venice littoral affect along 63km of coastline. This includes beach reconstruction to halt erosion and dissipate wave energy, and six jetties at the lagoon inlets installed between 1994-97 have been upgraded to reinforcement breakwater efforts.

Is it enough?

MIT professor of environmental engineering Andrew Whittle doesn’t doubt the quality of the engineering behind the MOSE gates. MIT has had a long relationship with the MOSE project, and Whittle previously consulted on the project prior to 2013.

“I think the frustration is there because all of these flood projects take a very long time between inception and completion,” Whittle explains. “People think the Netherlands is highly efficient – it took them 40 years between the inception and completion of the delta works, and that was 16 separate projects over 40-odd years.

“Evidence of a working system is what everyone is waiting on at the moment. The proof of MOSE is when the gate starts drying the city out and stopping these big flood events. By all counts we ought to be very close in the next few years.”

This story first ran in the August edition of IPWEA's inspire magazine as 'Against the tide'. View the full magazine now. 
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