A diminishing water table, combined with a
growing number of skyscrapers, is causing large areas of China to sink,
increasing flood risk and endangering the rail network, according to a survey
released recently by the China Geological Survey.
The
government has already launched a number of measures to combat the problem and
a plan of action was approved by the State Council in February.
Research
shows the most vulnerable spots are in the North China Plain, the Yangtze River
Delta and the Fenwei Basin, covering a combined total area of 79,000 square
kilometres - more than 100 times the size of Singapore.
More
than 50 cities in these areas are now at least 20 centimetres lower than they
were in the 1970s, the survey said.
The
problem is worsening and could spell potential disaster for millions of
residents, said Li Tiefeng, head of the group's geological disaster office.
Statistics
for Cangzhou in Hebei province, for example, show its average surface level has
sunk 2.4 meters since the 1970s, mainly due to the excessive reduction of the
water table.
The
city's low-lying location has made it vulnerable to urban flooding during rainy
seasons since the 1980s.
Unlike
Cangzhou, Shanghai is suffering land subsidence due to dense high-rise
construction.
In
February, a crack about 10 meters long appeared between the 492-meter tall
World Financial centre and the under-construction Shanghai Tower with a
designed height of 632 meters.
"The
frantic building boom has contributed a lot to Shanghai's ground sinking,"
Li said.
There
are about 65 buildings higher than 200 meters in Shanghai, while Tokyo has 45,
according to Emporis, one of the world's leading providers of building
statistics.
A study
released by the China Geological Survey in 2008 showed that total economic
losses due to land subsidence reached nearly 333 billion yuan ($53 billion)
from 1956 to 2008 in the North China Plain.
The
plain covers an area of 140,000 square kilometres, including Beijing and
Tianjin.
The
situation may become worse with the construction of high-speed rail, Wu Aimin,
director of the geological survey and technology department at the China
Geological Environment Monitoring Institute, told the Economic Herald.
As
China enters a boom period for high-speed rail construction, authorities should
monitor subsidence near railways, such as the high-speed rail linking Beijing
and Shanghai.
"If
the ground sinks, even by a few millimetres, it will threaten the safety of
high-speed rail," Wu was quoted as saying.
However,
the government is taking measures to tackle the situation with the first
national land subsidence control plan from 2011-20 approved by the State
Council in February.
It
includes a nationwide survey, the establishment of monitoring networks in
affected areas and increased control over underground pumping.
A land
subsidence research project will be completed by 2015 in key areas such as the
North China Plain, the Yangtze River Delta and the Fenwei Basin in Shaanxi and
Shanxi provinces, especially areas with high-speed rail, according to the plan.
Han
Mukang, a retired professor at Peking University who has studied the issue for
decades, said controlling underground water extraction is an urgent task.
Authorities
of the affected areas are combating subsidence by recharging groundwater and
reducing pumping.
Shanghai
Water Authority said that in 2015 the city will reduce extraction to 10 million
cubic meters from more than 13 million cubic meters in 2011 and the water table
recharge will reach 20 million cubic meters in 2015.
Beijing
is also planning to recharge groundwater to avoid further land subsidence when
conditions are proper.
Wang
Qian
China
Daily
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