Subsidence has become a topic often bemoaned in China and as of
today, this plague is far from reaching its end. More than 70
cities in china have different subsidence problems, covering a
total area of 64,000 sq kilometers.
Shanghai is the city most seriously affected, with the deepest
settlement at 2.6 meters. Since subsidence was first identified in
1921, Shanghai has seen direct economic losses of one trillion
yuan.
Underground water systems have been destroyed in some of north
China's cities, while water quality has frequently been affected by
the issue. In Xi'an, where famous architecture dates back to Tang
Dynasty, the Big Wild Goose Pagoda, has tilted thousand millimeters
due to surface subsidence.
Other cities, like Tianjin, Taiyuan and Suzhou, are also
tortured by such problems.
Heavy use of local groundwater and excessive urban construction
are cited as the reason for subsidence. Consequentially, many
cities hit by subsidence have substantially reduced groundwater
extraction. In Suzhou, Wuxi and Changzhou in eastern China,
underwater extraction dropped to 3 million cubic meters from 290
million in 2000. The annual rate of subsidence has been controlled
at below 25 millimeters per year in the three cities, with no terra
crack disasters occurring in the cities since 2003.
One scholar from Chinese Academy of Science, Lin Xueyu suggests
that, "the settlement is degenerative and undetectable. Its
monitoring is therefore equally important and difficult."
A Subsidence monitoring project has recently been approved in
eastern China's Jiangshu Province. With 249 GPS points located
along the Yangtze River, the monitoring system has played an
important role in subsidence prevention.
(CRI February 14, 2007)