The local legislature in Shanghai started to discuss a draft regulation on preventing land subsidence, which aims to improve supervision of high-speed rail, underground transportation and other major municipal construction projects in the city, state media reported today.
Gan Zhongze, a lawmaker said that the city of about 30 million people sank by 29 cm in the past 40 years.
"The speed of sinking has slowed down, especially since 2005, but it remains a major hazard for the city," official news website China.org.cn reported.
Feng Jingming, director of the Shanghai Planning and Land Resources Bureau, said a diminishing water table, combined with a growing number of skyscrapers, is causing Shanghai to sink.
The average altitude of Shanghai is only four meters above sea level.
Earlier this year, public concern was triggered when a road crack that was 10 meters long emerged in Shanghai's Lujiazui area, where dozens of skyscrapers, each taller than 100 meters, are located.
Officials later concluded that the crack was "caused by a usual settlement of the foundation ditch, which is in a controlled and safe state".
"The crack was caused by the increased pressure of foundation, but it didn't come from one high-rise or two, it came from the area where the 101-story Shanghai World Finance Center and 88-story Jin Mao Tower sit," said Chen Junhong, from Guangzhou Institute of Geography's environmental research center.
Hongqiao area, Pudong's Sanlin and Zhangjiang areas have had the most severe land subsidence.
The most seriously affected area has sunk about 3 meters in the past five years, becoming even lower than the level of the Huangpu River, which cuts through the city, the report said.
The draft regulation stipulates a monitoring network to measure land subsidence for Shanghai's major municipal projects.
It also requires construction companies to evaluate land before digging pits of 7 to 15 meters deep, which is considered a deep-foundation ditch.
Violators could face a fine up to 500,000 yuan (USD 80,200), according to the draft. Critics say such a fine is too little for top builders.
Land subsidence in Shanghai became a real hazard in the 1950s when the city's groundwater resources were extensively exploited for cooling during the summer by Shanghai's newly developed industrial sector.
It has been estimated that every millimeter of subsidence costs Shanghai as much as USD 20 million for restoration and maintenance.