Mekong Delta sinking as groundwater gets depleted

By Cuu Long   October 11, 2018 | 05:00 am PT
Mekong Delta sinking as groundwater gets depleted
Nguyen Van Cu Street in downtown Can Tho is flooded during high tides on Wednesday evening. Photo by Cuu Long
The Mekong Delta is subsiding faster than the rise in sea level, causing urban flooding, and humans are to blame.

For the past four days, seasonal floods and high tide have flooded Can Tho City, said to be the capital of the Mekong Delta region.

As a result, many streets and houses in the city’s inner area are almost two feet under water.

The tide on the Hau River, one of the two tributaries of the Mekong, reached 2.23 meters on Wednesday, the highest ever.

Explaining the high tide, Le Anh Tuan, a researcher at Can Tho University, said it was partly due to climate change but also a result of human activities.

Left to nature, the water would flow to low lying areas in the watershed, but rapid urbanization has seen the building of irrigation systems and dykes to prevent flooding.

Since the natural flow is blocked, the flood waters will hit downstream areas, including Can Tho, and combined with the subsidence, the impact of flooding gets worse, Tuan said.

Tuan, deputy head of the university's Research Institute for Climate Change, said the region now subsides two to three centimeters each year, 10 times faster than the sea level rise.

The subsidence has serious implications for the region, as can be seen in the flooding of its biggest city, Can Tho.

Areas with heavy construction or where groundwater is exploited more has seen worse subsidence, Tuan said.

Ky Quang Vinh, head of the climate change office in Can Tho, shared the idea that humans are to blamed for flooding in the area.

Vinh said the main reason for the flooding in Can Tho was subsidence caused by overexploitation of groundwater.

“It is possible that Can Tho residents do not use much of the groundwater, but other locations in the delta do,” he said.

Results of a study released in 2016 by the Vietnam Association of Hydrogeology said that by 2015, the level of groundwater in the Mekong Delta had dropped by 15 meters. It did not compare the drop with a previous figure.

The study said that if, in the past, residents could hit water by digging around 100 meters into the ground, they would have to go twice as deep for fresh water now, and worse, most of the groundwater was contaminated with salt or chemicals.

A study on the impacts of 25 years of groundwater extraction on subsidence in the Mekong Delta, released by the Dutch University of Utrecht last year, found that between 1991 and 2015, the Mekong Delta had sunk an average of 18cm, with the sinking levels ranging between 9cm and 53cm in different places across the region.

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