For those unfamiliar with Shanghai’s history, the city was once a giant, stinking swamp. While some say things haven’t changed much since then, others have noticed a bit of development going on. Given other coastal cities (on deltas) like New Orleans and Tokyo, it shouldn’t be much of a surprise that Shanghai is sinking.
Basically, the extracting of water from the moist soil of Shanghai is causing the land to subside so perhaps “sinking” isn’t quite the right words to use, although, it is a bit more dramatic. Ever since 1921, Shanghai has been “sinking” into the ocean. Shanghai’s government has been working on the problem and they are “winning” the battle against land subsidence.
Last year the city, whose name means “above the sea” in Chinese, sank a mere 7.5 millimeters (0.3 inches), the Shanghai Daily newspaper reported on Tuesday, quoting the Shanghai Engineering Administrative Bureau.
That was an improvement on 8.3 mm in 2005 and 8.7 mm in 2004, but more had to be done, the paper quoted officials as saying.
While scientific evidence points to environmental factors as being the leading cause of the water displacement and the inevitable “sinking”, “human-induced subsidence” accelerates this process precipitously. Shanghai is particularly prone to this problem because of the heavy construction of skyscrapers (which displaces water), as well as the increasing demand for groundwater. Always up for an engineering challenge, Shanghai’s government is on the case.
The city’s Metro authority is planning to install sensors and cameras inside subway tunnels to detect distortion and leakage caused by land subsidence. The system will enable Metro operators to oversee the safety of tracks and tunnels 24 hours a day. At present maintenance workers check for tunnel distortion only two to three times a year.
All future Metro lines will have subsidence sensors installed every five to 10 meters. If any problems are found, repair crews can be dispatched immediately.
The map above, courtesy of Flood Maps, shows the effects of a 5 meter increase in the water levels in Shanghai. With the ocean levels rising and the ground below us sinking, it’s not looking good.