Image credit: Gregory Jordan.
The Shanghai legislature has opened discussions on new regulation to prevent land subsidence, which remains a major hazard for China’s most populous city.
According to a report earlier this year, Shanghai has sunk over 1.8 metres since 1921. “The speed of sinking has slowed down, especially since 2005, but it remains a major hazard for the city,” lawmaker Gan Zhongze said. Shanghai is at high risk of subsidence due to its position at the mouth of the mouth of the Yangtze River basin; the highest points in the city are a mere 4 metres above sea level. Numerous parts of the city are in fact below sea level, only protected from flooding by concrete walls. Rising sea levels and increased meteorological activity caused by global warming means a hurricane, tsunami or tropical storm could potentially be disastrous for the city.
The new regulation will introduce stringent requirements for developers, particularly when buildings (such as high rise skyscrapers) require deep foundations. Developers must seek third party evaluation of their plans if the foundation is deeper than 15 metres.
Shi Yishao, a professor at Tongji University, estimates that every millimetre that Shanghai sinks costs the city as much as 125 million yuan in restoration and maintenance.