Shanghai is to pump 15 million cubic metres of water back underground this year to prevent land subsidence in the metropolis and save the precious resource for future generations, the city's water supply administration has claimed.

According to the Shanghai Municipal Water Supply Administration, the city plans to feed 15 per cent more ground water back through 30 wells than it did last year.

The water drawn from underground sources this year shall not exceed 90 million cubic metres, the administration said, 8 per cent less than in 2003.

In the first six months of the year, 42.56 million cubic metres of underground water was drawn.

The administration, which has issued 896 water exploitation permits, said it would continue to enhance the management of the permits and no new wells should be allowed, according to the administration.

"Subsidence is still the most serious chronic geological disaster the city suffers and you will know how terrible it is, thinking that some day Shanghai will be immersed underwater," said Zhang Xianlin, a professor and also director of the Geo-Environment Division under the Shanghai Municipal Land and Resources Bureau.

To safeguard the city, the administration has put forward specific goals. By next year, the yearly subsidence is not to exceed 10 millimetres and by 2010, the figure will be reduced to five millimetres.

Since 1860, when the first well over 100 metres down the earth was drilled, it took a long time for the city to realize the importance of planning its water use instead of drawing water extravagantly from underground sources.

In late 1950s, the city annually drew 200 million cubic metres of water from underground sources, which resulted in a yearly subsidence of 10 centimetres.

Data showed that since 1921, the downtown area has sunk by two metres on average and in some area, the figure reached three metres.

After identifying excessive exploitation of ground water as the major cause of subsidence, the city took effective countermeasures since 1966 -- asking large industrial water consumers to pump correspondent amounts of water back underground.

Subsidence has slowed noticeably since then and in the 1970s, the city even saw itself grow a little higher, three millimetres a year. The subsidence from 1966 until 2002 was 20 centimetres, which means 6.5 millimetres per year, according to data provided by the administration.

The city also has water quotas for each of its subsidiary districts and counties. Those who exceed the allocated amount shall be fined 10 times the cost for the extra water, Zhang said.

The city's pricing authority is also working on plans to make the price of valuable underground water higher than that of ordinary tap water.

(China Daily August 2, 2004)