Tag Archives: sea levels

Sinking Cities

As sea levels rise, ground levels in coastal mega cities are also falling. This presents potentially disastrous consequences for insurers. Sinking cities are being submerged at a phenomenal rate

Large property insurers in the world’s coastal cities are concerned. They have taken into account the effects of climate change into their calamity models.

Underwriters fear the combination of sea water deluge and flood damage. New Orleans suffered an ensuing cascading collapse of critical infrastructure following Hurricane Katrina. The city is constructed on multiple layers of soft soil which compresses when built upon.

The causes of sinking cities varies. Ground water extraction for drinking water and industrial processes is one of the problems. In Los Angeles, oil and gas extraction is to blame.

Tokyo has been one of the most severely affected sinking cities. In the middle of the last century it grew rapidly. It sunk over 4 metres. In the 1970s radical corrective policies were instituted. Extraction of ground water was reduced.

The fastest subsiding city is Jakarta, Indonesia. It is sinking 5 to 10 centimetres a year. Key commercial districts of the city are threatened. These districts are where major Asian, American and European companies are based.

A water management specialist from Dutch research Deltares confirmed that the project known as the Giant Sea Wall (GSW), is one of the solutions to Jakarta’s problems. This project would protect four to five million people who could see their current homes sinking between 4 to 9 metres below sea level.

The city of Venice, Italy, built on a salt marsh, as charming as it looks, is sinking. Venice has always survived on borrowed time. A major threat are the extreme high tides known as “acqua alta”. Acqua alta is when the water level is over 90mm (3.54 inches) above normal.The most common occurrence of the acqua alta is in and around Piazza San Marco. Abnormal high tides are becoming more common place. Venice now experiences more than 60 days a year of extreme high tides.

Heavy and often reckless boat traffic speeding through the canals is another one of Venice’s problems. The wake caused by these motor boats and large cruise ships create small but powerful waves that lap the stones lining the canals. This is eroding away the mortar holding the city in place.

A popular as well as the most controversial solution to the sinking of Venice is called the MOSE Project (Modulo Sperimentale Elettromeccanico). The plan is to create adjustable barriers at the Venice Lagoon entrances. These barriers are designed to rest on the sea floor until Venice is threatened by an acqua alta event. The barriers, when needed, spring into action by rising to form a dam across the three entrances to the Venice Lagoon. High water is thus kept away from the city.

The project, still incomplete, was caught in a scandal of corruption and bribery. Thirty five people were arrested and one hundred politicians investigated.