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Shanghai – sinking by the second?

 | July 19, 2012

The physical weight of Shanghai’s tall, high-density structures is weighing down the earth, wearing it out and causing the city to sink.

FEATURE

The glittering metropolis of Shanghai with its larger than life landscape of concrete and steel is sinking at an alarming rate of one-and-a-half centimetres every year.

Several factors have been attributed to its gradual descent, the three biggest being the sheer weight of its massive structures, excessive pumping of its groundwater and rising water levels due to global warming.

According to a report by the Shanghai Geological Research Institute, Shanghai’s skyscrapers impressive though they are, account for 30% of the city’s subsidence.

Professor of earth sciences at Hong Kong University Jimmy Jiao said, “Usually groundwater pumping is the key factor but in Shanghai, development is also important because the building density is high, and most of the high-rise buildings are sitting on the areas with soft soil.”

In other words, the actual physical weight of Shanghai’s tall, high-density structures is so enormous, it is weighing down the earth, wearing it out and causing the city to sink.

This catastrophe is compounded by the over-pumping of its water table to meet the demands of industrialisation and the city’s growing population that now stands at 13 million. Preventive measures were taken in 2005 to limit the pumping of ground water and Shanghai now uses river water to satisfy most of its needs rather than traditional well water. Although a corrective move, it is sadly a case of doing too little too late.

There is also the possibility that Shanghai could be deluged by the angry waters of the Huang Pu river that flows too close for comfort at just 3 metres below the city. As the threat of floods, wrecked buildings and a ruined economy loom, the people of Shanghai go about their business with a carefree attitude, choosing to believe the government will do enough to prevent any tragedy of mega proportions.

At the old city centre, known to locals as the Bund, and where most of the city’s skyscrapers have sprouted up in, a flood wall was built in the early 1990s as a preventive measure against the rising summertime waters of the Huang Pu River. That was a good move considering that in 1997, the rain-gorged Huang Pu rose 1.5 metres above Sun Yat-sen Road and rose just shy of 1 metre from the top of the floodwall.

A close call by most counts yet on many days, the Huang Pu actually runs higher than the streets of Shanghai during high tide. One can only guess at the kind of devastation that would ensue should a hurricane, tsunami or tropical storm unleash its fury on the city, breaking the sturdy floodwall in a flash.

However there are ways to reduce the city’s slow slide into oblivion. For one, groundwater pumping can be banned altogether and laws can be implemented to decrease the density of high-rises in the city. Though many don’t see this happening anytime soon considering China’s economic and population boom, there is yet another option that may bring some relief to the problem – the pumping back of water into the shallow water tables that once were over-used. Shanghai now pumps some 5.2 billion gallons of water a year into these water tables in the hope of helping the city regain its footing. So far, the city has risen by almost 11.5 cm.

LINKS

http://www.china.org.cn/video/2012-02/21/content_24692583.htm

http://ecocentric.blogs.time.com/2012/05/21/soaring-to-sinking-how-building-up-is-bringing-shanghai-down/


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