China's largest and most populated city, Shanghai, built on the marshy banks of the Huangpu River, is slowly sinking, though at a slower rate than before, a report said yesterday.
The modern metropolis is home to nearly 17 million people and although over-exploitation of underground water is the main cause, its 3,000 high-rises built on soft, wet ground have contributed to the problem of subsidence, experts said.
The eastern port sunk 8.7mm last year, more than the target rate of 5mm a year hoped for by 2010, the Shanghai Daily reported, citing a geological survey.
The subsidence rate in 2003 was 10.4mm, down slightly from 11.1mm in 2002. If Shanghai continued to sink at 10mm per year it would reach sea level in 40 years.
To counteract the problem, underground water must be pumped out a rate of 865 million tonnes annually, the figure recorded last year, the report said.
Subsidence is clearly seen in Puxi District's Nanpu Bridge and the Lujiazui financial district in Pudong, which is littered with new skyscrapers.
"Once any increase in subsidence is observed, we will suggest the government take actions such as further controlling the pumping of underground water," said Yu Junying, an engineer with the Shanghai Institute of Geological Survey.
Researchers calculate the rate of subsidence by hammering two tubes underground and observing the distance each moves.
There are more than 100 buildings over 100m in Shanghai.