Move over Venice, Italy. There’s a new city grabbing all the headlines because it is sinking. The newcomer, Beijing, may not be the most likely choice, but a new study shows the situation is dire. Venice, famous as a city composed entirely of islands, has been fighting erosion and land loss issues for centuries. Its floating buildings even feature prominently in movies, including The Italian Job and the James Bond film Casino Royale. Beijing’s situation is more likely to appear on Engineering’s Greatest Challenges rather than in a feature film.
The new research study, conducted by the National Natural Science Foundation of China, stressed that water was the foundational problem behind the sinking. In particular, the 20 million residents of the Chinese capital city consume nearly 925 million gallons of water (3.5 billion liters) per year. That consumption includes homes, industry, and agriculture. In all, two-thirds of all water comes from groundwater aquifers. This water has accumulated over millions of years, but similar to the slurping noise a straw makes in an empty glass, there is a limit to how much can be removed. At the current pace, the ground under Beijing is drying out. Areas where there was once water are now air voids. When these collapse, the ground sinks. When these voids are near the surface, they create the many sinkholes that plague China’s cities.
As Beijing’s population continues to grow, the situation is due to worsen. Based on GPS data collected from 2003-2010, scientists analyzed the topographic changes around the city. Their findings show that the center of the city and the districts of Changping, Tongzhou, Shunyi, and Chaoyang are most affected. Chaoyang, an eastern suburb descending four inches annually, has sunk the most over the last two decades. While the current infrastructure is still functional, without significant changes in the next five years, some power lines, roads, and railroads in Beijing will be on the brink of collapse. Efforts are currently under way to divert more water from the mountains to the northern cities. In total, there are 46 Chinese cities sinking due to depleted groundwater supplies.