Scientists have developed a three-dimensional map of Shanghai's
underground geology, which they say will help authorities tackle
the problem of subsidence.
Wei Zixin, director of the Shanghai Institute of Geological
Survey, said that although recent figures had shown the rate of
subsidence was falling, it remained a problem.
The city of
Shanghai
However, with the new map, areas that are most at risk can be
quickly identified and appropriate action taken.
Speaking at a forum on geological studies held in Shanghai on
Wednesday, Wei said that once an area has been identified, water
can be pumped underground to boost the groundwater level.
By doing so, the city's skyscrapers will be free from the threat
of subsidence for up to 100 years, he said.
According to figures presented at the forum, in 2004, Shanghai
sunk 7.76 mm, and this year 7.5 mm. With the help of the new map,
which details 6,700 sq km of the city's subterranean environment,
the level could be cut to just 5 mm by 2010, Wei said.
While helping reduce the threat of subsidence, the map can be
used by planners to determine the most suitable areas for
construction and the selection of digging routes, he said.
Subsidence has been a longstanding problem in Shanghai, mostly
as a result of the over-exploitation of underground water and the
construction of skyscrapers, Wei said.
More than 1,000 square kilometers of the city have been affected
by subsidence, with the most serious case seeing the ground level
fall by 2.6 meters.
Although hot springs have been discovered in five separate areas
of Shanghai, Sun Jianzhong, director of the information department
at the city's urban development information center, has warned
against exploitation of the natural resource.
"The priority must be to protect Shanghai's water environment,
not exploit it," he said yesterday.
Shanghai is built on the alluvial plain of the Yangtze River and
any exploitation of underground water has a serious impact on the
geological environment and can cause subsidence, Sun said.
In a bid to halt the city's slow decline, the municipal
government has introduced various measures including limiting the
exploitation of underground water sources and pumping water into
the subsurface.
Industrial consumers of water have also been moved out of the
downtown area and are required to draw water from deep
underground.
(China Daily November 23, 2007)
