Ho Chi Minh City and provinces of the Mekong Delta region in southern Vietnam are sinking at an alarming rate, posing grave danger to the local economy and livelihoods, experts have warned.
Alarming numbers about land subsidence in Ho Chi Minh City have been published in a study by a group of scientists at the Ho Chi Minh City University of Technology, led by Assoc. Prof. Dr. Le Van Trung.
The scientists looked at remote sensing images of the area taken between 1992 and 2010, with updates added in 2016, to observe changes in land level over the years.
The results were shocking – the districts of Binh Chanh, Binh Tan, 8, 7, 2, 12, Thu Duc and Nha Be in Ho Chi Minh City are all suffering from complete or partial subsidence at a rate of 5-10 millimeters per year.
The sinking of land was attributed to excessive extraction of groundwater, as well as rapid urbanization that has placed tremendous pressure on the ground.
Its consequences include the expansion of areas affected by high tides, as well as the salinization of water stored at different levels underground, threatening farming and sustainable agriculture.
According to Dr. Trung, land subsidence has been warned of by local and foreign experts for years, though the situation is not yet “frightening” enough.
To give a comparison, Trung said that China’s Shanghai had subsided by 2.4 meters since experts began tracking, while Ho Chi Minh City had subsided around 0.4 meters in total.
Trung warned authorities not to be comforted by those numbers. “We need to come up with a solution to the problem now, or some parts of the city will submerge once our subsidence gets as bad as Shanghai’s,” Trung said.
In some areas of the southern metropolis, the consequences of land subsidence had already become apparent.
At the foot of a pedestrian bridge on Vo Van Kiet Boulevard in Binh Tan District, the ground has sunk by up to 20 centimeters, revealing parts of a bridge that were previously underground.
At the residence of Nguyen Van Ut in the same district, walls have been damaged by the constantly shifting foundation.
“It’s not hard to notice the subsidence,” Ut said. “My house was the most solidly built in the neighborhood, but you can see it’s clearly leaning if you look down from the roof.”
Four years ago, Ut’s house was 0.5 meters above ground level, but has since sunk to the same level as the street.
The study led by Dr. Trung also looked at land subsidence in the Mekong Delta region, where they said it was most noticeable in the districts of Ninh Kieu, Binh Thuy and Cai Rang in Can Tho City.
According to Dr. Le Xuan Thuyen from the Ho Chi Minh City University of Science, Ho Chi Minh City and the Mekong Delta provinces are built on soft geological layers, causing the area to sink faster than other regions.
Excessive and illegal sand mining on southern rivers has also played its part in accelerating the process, Thuyen said, citing a statistic saying that the reserves of sediment in the Mekong River had dropped by half since 1984.
According to Nguyen Huu Thien, an independent expert on the Mekong Delta ecosystem, land subsidence was a more urgent threat in southern Vietnam than rising sea level.
Sea level is rising at the average rate of three millimeters per year, Thien said, while land subsidence is occurring up to ten times faster.