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Subsidence rates in Yangtze River Delta have slowed down for the first time in 10 years, it was announced yesterday.

Hong Jingxin, vice-chairman of the Standing Committee of Jiangsu Provincial People's Congress, said observations over Suzhou, Wuxi and Changzhou reported marked drops over the past 12 months.

The three cities had been suffering the most severe subsidence in the country.

They each sank by 8, 12 and 8 millimetres respectively in 2005. "It has greatly improved from the previous years when the numbers were much higher," Hong said.

Suzhou, Wuxi and Changzhou were sinking with annual rates of 25, 100 and 120 millimetres respectively during the 1990s. Losses of about 2.6 billion yuan (US$ 325 million) have been suffered because of the damage brought by subsidence, according to the Yangtze River Delta Ground Water Resources and Geological Disaster Survey conducted by the Ministry of Land and Resources between 2000-04.

Over-exploitation of underground water was believed to be the main reason for the subsidence in the three delta cities.

Many enterprises turned to underground water for industrial use due to ground water pollution caused by a fast-growing economy, said experts.

Jiangsu provincial government began measures to control the excessive pumping from 2000.

The Jiangsu Provincial People's Congress set up a regulation in the same year prohibiting pumping of underground water in the most severely sinking areas by 2002 and any exploitation in all the three cities by 2005.

A total of 4,831 wells have been closed in the three cities, leaving only 86 for emergency uses.

The province has also required the three cities to co-ordinate water resources.

The province invested more than 9 billion yuan (US$1.12 billion) to establish a pipe water network, providing industrial and drinking water supplies within the three cities in order to prevent them from pumping the underground water.

According to Xu, the prohibitive measures during the past five years have protected 288 million cubic metres of underground water from being exploited, which ensured that 99 per cent of those previously sinking areas maintained a higher or stable underground water level.

The research institutes set up by the Provincial Land and Resources Bureau among the three cities obtained the recent findings after years of research, Xu said.

"Those prohibitive measures and the co-ordinative network between the three cities have obviously worked," said Guo Kunyi, vice-director of the Nanjing Geological Study Centre, who took charge of the 2000-04 survey.

But he warned that to ease the subsidence tendency in the whole Yangtze River Delta, there still needed to be long-term and consistent efforts.

Guo suggested that all the cities in Yangtze River Delta should co-ordinate their use of water resources.

"As all the underground water circulates, it makes no sense that one city restricts its underground water pumping, while the other doesn't. All the cities should put their hands together," said Guo.

The survey also pointed out that 46 cities from 16 provinces were sinking in the country, among which the urban districts of Shanghai, Suzhou, Wuxi and Changzhou in Jiangsu Province, and Jiaxing in Zhejiang Province were suffering the biggest problems.

(China Daily January 11, 2006)