A noted marine geologist warned yesterday that land subsidence
remains a major issue for Shanghai, the country's financial
hub.
"As the local economy booms, the widespread construction of
skyscrapers has become a new challenge for land stability," said
Wang Pinxian, an academic at the Chinese Academy of Sciences.
It has been estimated that every millimeter of subsidence costs
Shanghai as much as US$20 million.
Wang, a professor of marine geology at the Shanghai-based Tongji
University, issued the warning at the second session of summer
school for 30-plus doctorate students from both home and abroad.
The theme of the meeting was Sustainable Use of Water
Resources.
Wang said over-exploitation of ground water beneath the city and
the density of high-rise buildings were causing subsidence in
coastal cities.
According to data from the State Key Laboratory of Marine
Geology at Tongji University, more than 90 medium and large cities
on the mainland suffer from land subsidence.
The land in Shanghai subsided at a rate of 5-7 mm per year from
2001 to 2006.
In 2004, the city's land sank 8 mm, causing alarm and spurring
the local government to act.
Shanghai has restricted the pumping of ground water,
particularly downtown.
Wang said that people who pump groundwater have also been told
to replace it.
"People who use ground water are requested to pump in the same
amount of water during the winter that they pumped out in summer,"
Wang said.
Meanwhile, the city government has shifted most of the
industrial use of ground water from downtown to the suburbs.
Wang said such measures have proven successful in controlling
the speed of land subsidence, but more needed to be done.
"We have established a network of experts to monitor subsidence
and ground water levels," Wang said. "A research centre will be set
up soon."
The professor said he believes that by combining all the
measures mentioned above, the city will keep the pace of subsidence
at less than 5 mm per year by 2010.
Land subsidence in Shanghai became a real hazard in the 1950s
when the city's ground water resources were extensively exploited
for cooling during the summer by the city's newly developed
industrial sector.
Land subsidence hit a pace of 38 mm per year in the late 1950s
and early 1960s. The city sank by 110 mm per year during the period
from 1957-61.
The rapid pace of subsidence during that period caused cracks to
form in the land, buildings to slant and tidal flooding.
(China Daily August 21, 2007)