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A tale of hazards, risks and resilience

A tale of hazards, risks and resilience

Nov 7th, 2018

A tale of hazards, risks and resilience came to my mind while in Venice, end of October. I lived though an extraordinary “acqua alta” (high tide) which submerged approximately 70% of the city and was reportedly the fifth event of such magnitude in 924 years.

Aqua alta is a complex event combining high tide and wind driven surge in the Venetian Laguna: South winds hinder the tide outflow and “push” in the Laguna open sea water. Aqua alta is not uniform through the city as vertical settlement in the laguna were not uniform. That was the effect of varying foundation conditions as well as buildings of different mass and size.

 

A tale of hazards, risks and resilience

An ambitious mega project called MOSE is not yet operational. MOSE’s movable dams should protect the city from this type of events. Completion, hindered by budget and schedule overrun should occur around 2020.

A long long time ago

From the lower Middle-Age on, for centuries, merchants, adventurers and an unending desire to expand and dominate transformed the tiny Republic in the Master of the Sea. The character of Marco Polo and his contacts with the Khan are only one aspect of the incredible ascension and span of the Republic’s reach.

Perils of the Sea, hazards of all sort, both internal and external lurked all along.

For example, Venice faced a terrible crisis in the middle of 1300. In those times a plague followed a quake. Furthermore competitors from Genoa created a blockade in the Bosphorus, which lead to a war.

Thus, in 1473, the Venetian Senate ordered the building of a mighty facility, the Arsenale. Its aim was to ensure timely production of warships. The Arsenale, still a very impressive presence in the city, was manned by up to 1600 workers. They received particular benefits from their employer.

Vessels were built thanks to a chain process similar to modern industries. The vessels were of many types, including the Galeazze. These altered the naval warfare in those times with their fire power from the sides. In 1574 the King of France and Poland witnessed the construction of a Galea, complete of all the accessories and weapons in one single day!

Nevertheless the Republic started declining. It ended up falling as a side-effect of the French-Austrian conflict during the Napoleon Bonaparte reign.

A tale of hazards, risks and resilience

Venice stands on floating foundations made of short wooden piles lowered to a weak strata of Laguna sediments. There are sometimes 10 such piles per square meter of foundation. These foundations allowed the Venetians to slowly expand the initial Laguna islands on which they settled to seek refuge from other hostile populations. The foundations also featured variable vertical settlements, depending on the soils geotechnical parameters, weight and size of the buildings.

Storms, tides, perils of the Sea and natural settlement of the foundations have forever been part of the Venetian life.

Perhaps the permanent exposure, continuous uncertainty and the need to cope have forged the DNA of the inhabitants. The heritage of Marco Polo and the Venetian conquerors lives despite the “political decadence.”

In the short film below you will see how the resilience of the staff of a restaurant and the public has played during the extraordinary event I witnessed.

The most incredible thing I witnessed though was next morning.

I looked through the window and saw the water had receded.

I took off for a walk.

The bakery downstairs smelled of freshly baked bread and sweets.

The florist had the best flowers exposed on the street.

No one complained, although many had lost stored goods, business hours, and in some cases appliances. However, many were still scooping water out of their premises.

Morale of the tale

Venice has learned to live with the hazard.

The early warning system worked egregiously, the population knows what to do.

Segmented elevated movable paths equip the lowest points of the city. These appear “like magic” hours before the alerts.

The electrical grid is protected against sea water raises.

Of course some people, especially tourists, acted stupid and had some consequences.

San Marco was damaged by this 1/200 event. Experts have reportedly stated “the Basilica lost 20 years of life in one day”.

One could wonder if the MOSES mega-project with its enormous initial price estimate over-budget and delays is justified or if other solutions could have been implemented, faster and at lower capex and foreseeable opex.

We will soon realize if climate change will increase the frequency of similar extreme events.

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Category: Risk analysis, Risk management

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