While this coastal city is sinking at a slower rate than in the
1980s, local geological experts said efforts to ease the surface
subsidence in east China's Shanghai-centered Yangtze-River Delta
are still urgent.
Statistics from the Shanghai Institute of Geological Survey show
the surface of the city has been sinking around 10 millimeters
annually since the late 1990s, the slowest rate in the past two
decades and almost one quarter of the average rate between the
1920s and the 1960s.
In
2000, the surface of the city sank 12.12 millimeters, according to
the institute.
Wei Zixin, chief engineer with the institute, described the fight
against land subsidence as "arduous." The tendency, which can be
eased but is almost impossible to reverse, still poses a threat to
the city's development, Wei said.
Shanghai started exploiting its underground water in 1860 and the
surface of Shanghai has been continuously sinking since 1921.
Shanghai was under sea water 3 million years ago and the city is
still in danger of sea water invasion, according to the Shanghai
Geological Bulletin published by the institute.
The main cause of the city's subsidence is the over-use of
underground water, according to the institute.
The Shanghai municipal government has taken strict measures against
such over-exploitation since 1995 by requiring each deep well in
the city to have an official permit.
In
addition, underground water usage is limited to less than 10
million cubic meters per year under the measures.
Such measures against the over-exploitation of underground water
are "long-term" and require "consistent" support by the government,
said Wei.
In
1996, the city government began to invest in a global positioning
system (GPS) to monitor land subsidence in the city with a coverage
of 700 square kilometers (270 square miles).
Wei also remarked on the "grim" land subsidence situation in
neighboring Jiangsu and Zhejiang provinces.
"The situation there is even more severe than that in Shanghai,"
said Wei.
China Environmental News reported earlier this year that
experts think Shanghai suffers a loss of more than 10 million yuan
(US$1.2 million) for every millimeter it sinks.
The country's total land subsidence losses are estimated to exceed
100 million yuan (US$12.1 million) annually, according to the
report.
(China
Daily September 10, 2002)