The rate of land subsidence in this city seems to have slowed
last year, geologists said.
Shanghai sank only 7.5 millimeters during the period, or 1.21
millimeters less than in 2004 and 4.8 millimeters less than in
2000, according to measurements taken by the local subsidence
monitoring system.
Local government officials said they expected to keep subsidence
to less than 7 millimeters this year and to less than 5 millimeters
by 2010.
Yan Xuexin, an engineer at the Shanghai Institute of Geological
Survey, said land subsidence was no longer a major threat to
Shanghai because the authorities had taken effective steps to
control the problem.
"However, subsidence is not only caused by human beings, but
also by natural changes, such as rising sea levels. It is difficult
for the city to completely avoid land subsidence," he said.
Shanghai has been suffering from serious land subsidence
problems since early in the last century. A survey done by the
Ministry of Land and Resource showed that the city had sunk by more
than 2 meters since 1921.
Shanghai reportedly experienced its worst land subsidence in the
1960s, when it sank by more than 10 centimeters per year.
Even now, subsidence poses a bigger threat to Shanghai than to
any other city in China.
Economic losses
According to Xinhua News Agency, an area of more than 1,000
square kilometers in the city has been affected by land subsidence.
Some places have sunk by as much 2.8 meters in recent years. Land
subsidence has caused economic losses worth more than 100 billion
yuan ($12.9 billion) for the city.
"Subsidence was a much more serious problem a couple of years
ago, when the city was sinking at a rate of more than 10
millimeters per year," said Yan.
He attributed the problem to over-exploitation of the city's
underground aquifer and the rapid and dense construction of
high-rise buildings around the city.
"The overuse of underground water resources is the main culprit
for the subsidence," he said.
The city now pours a large amount of water back into its
underground reservoirs to fill up the vacant space. The local
government has also taken measures to cut down on the exploitation
of underground water and has closed up some of the city's
wells.
In 2003, the municipal government also passed a regulation to
limit the height of new buildings and density of construction in
the downtown area in a bid to alleviate land subsidence.
Last October, Shanghai passed an administrative regulation on
preventing land subsidence.
It stipulates that special projects that are located in
subsiding areas or whose groundwork goes deeper than 7 meters
should receive a special appraisal before construction starts.
Efforts paid off
"Such efforts seem to have paid off. Shanghai has taken a
leading position in the country in terms of its efforts to control
land subsidence," said a source surnamed Zhang at the Shanghai
Housing and Land Administrative Bureau.
"But the situation concerning the uneven rate of land subsidence
in different parts of the city still poses a serious challenge for
the city to tackle," he said.
According to media reports, more than 70 cities in China have
land subsidence problems, representing a combined subsiding area of
640,000 square kilometers.
In addition to Shanghai, the cities of Tianjin, Taiyuan and
Xi'an have all sunk by at least 2 meters. The affluent cities in
East China's Jiangsu Province, Suzhou, Wuxi and Changzhou also
suffer from serious land subsidence.
(China Daily February 14, 2007)