China's largest land subsidence monitoring network has passed appraisal, the China Geological Survey, a bureau of the Chinese Ministry of Land and Resources, said on Friday.

 

The network, focusing on Suzhou, Wuxi and Changzhou cities in east China's Jiangsu Province, covers 30,000 square kilometers of land along the Yangtze River valley.

 

Experts from the geological survey bureau said that the network has begun to play an important role in controlling land subsidence on the Yangtze River Delta.

 

Besides the Suzhou-Wuxi-Changzhou network, another land subsidence monitoring network, covering nearly 5,000 sq. km, has been launched for the Hangzhou-Jiaxing-Huzhou city group in Zhejiang Province.

 

The bureau has recently conducted a series of geological surveys on the Yangtze River Delta, one of the nation's economic engines, covering Jiangsu and Zhejiang provinces and Shanghai.

 

Shanghai is the Chinese city most affected by land subsidence.

 

According to the bureau, the metropolis has records of land subsidence going back to 1921, and has seen 1,000 square kilometers of land subside, at depths of up to 2.6 meters.

 

Land subsidence has cost Shanghai more than 100 billion yuan (US$12.9 billion). The city loses 10 million yuan (US$1.3 million) when the land subsides by one millimeter.

 

Another seriously affected area is the Suzhou-Wuxi-Changzhou city group in Jiangsu. About 5,700 sq. km of land, or half of the total area of the three cities, subsided, with the deepest subsidence measuring 2.8 meters.

 

Tianjin, an economic center in northern China, has reported land subsidence of 3.1 meters. Other cities affected include Taiyuan, capital city of north China's Shanxi Province, and Xi'an, capital of northwestern Shaanxi Province.

 

The geological survey bureau said that more than 70 Chinese cities suffer from land subsidence.

 

Inappropriate siphoning of underground water and poorly thought-out urban construction projects have contributed to land subsidence, said Lin Xueyu, an academician with the Chinese Academy of Sciences.

 

"It is very important for China, a nation with insufficient water supply, to tap underground water resources in a reasonable way," said Yin Yueping, a senior engineer with the China Geological Survey.

 

The Suzhou-Wuxi-Changzhou city group has brought underground water exploitation under control. The cities now exploit 30 million cubic meters of underground water annually, as against 290 million cubic meters in 2000.

 

Thanks to the mammoth south-to-north water diversion program, Tianjin will have a stable annual water supply of 800 million cubic meters in 2010. The water will be used for agricultural and ecological protection purposes and also to replenish water resources underground.

 

Shanghai is striving to reduce land subsidence year by year. Last year, land subsided by 7.5 mm on average in the city, 4.8 mm less than the 2000 level.

 

(Xinhua News Agency February 10, 2007)