City goes down the sink

City goes down the sink

Caught between rising seas and subsidence, and hit by alternate droughts and floods, Bangkok is fighting for dry ground like never before

Bangkok is slowing sinking and parts of the city may be permanently under water within two decades.

Wat er rising: Parts of Lat Phrao flood during heavy downpours.

The chilling warning comes from the National Reform Council’s committee to prevent Bangkok subsidence which says unless decision-makers take rapid action millions of homes in the capital will disappear under the water.

It may sound like an exaggeration, but committee members presented Spectrum with alarming figures to back the claim. Bangkok is sinking at a rate of 1cm a year due to subsiding land. The nearby province of Samut Sakhon is sinking 2-4cm annually.

The bad news is the existing 3m-high dykes along the Chao Phraya River only have the capacity to handle an additional 60cm of rising water levels. Bangkok and adjacent provinces are only 50cm to 2m above sea level, which is rising 4mm every year. Rising sea levels are flushing more water into the Chao Phraya, while the dykes are subsiding along with the rest of the city.

“We cannot come to an exact conclusion. But you do the maths and figure out what’s happening,” said Vithaya Kulsomboon, chairman of the committee and an associate professor.

“It may be too early to conclude when Bangkok will be submerged. But it will be too late if there is no national mechanism to look into the problem because the subsidence may be more severe than we think.”

On July 22, the committee presented the study, based on five months analysing available research and evidence from various academic resources, to the NRC. They are due to present it to the cabinet this week.

“People have been talking about the possibility of Bangkok under water for some time but this is the first time a government committee has officially presented such findings for the cabinet’s consideration for reform,” Mr Vithaya said.

The committee members hope the cabinet endorses its findings and recommendations, and Bangkok’s subsidence be set high on the national agenda with a response devised quickly.

UNSTEADY GROUND

Standing on soft clay on the coast, Bangkok has been gradually sinking for hundreds of years. But in addition to natural phenomena, such as the earth’s shifting tectonic plates, humans have sped up the process with an excessive extraction of groundwater and adding weight on top of the clay via construction and landfills.

According to the committee’s report, the use of groundwater contributes to as much as 69% of the subsidence, extra weight 29% and natural causes only 2%.

In the past, some areas in Bangkok were sinking as much as 3cm per year, due to excessive groundwater extraction.

The use of groundwater was banned 38 years ago, with exceptions made for some industries and areas where tap water cannot reach. That had a positive outcome. Bangkok, on average, now sinks about 1cm a year, according to committee member Sucharit Koontanakulvong, also head of the Water Resources System Research Unit at Chulalongkorn University.

But the recent drought prompted some business operators to start using groundwater again. Some in areas without tap water still use groundwater for their households. Areas with heavy industry — such as Samut Prakan, Samut Sakhon and Lat Krabang district — are sinking faster than Bangkok partly because of the amount of industry there, Mr Sucharit said.

Department of Mineral Resources surveys on sea levels, which go back 60 years, show an average annual rise of 4mm, compared to the global average level of 1.8mm. The department says this is largely because of climate change. Mr Sucharit said it was still unclear why Thailand’s rise was more than twice the global average, but this will be the subject of further study.

Mr Sucharit said global warming is the result of human activities that emit heat-trapping carbon dioxide: this leads to sea surface temperatures being raised and the overall sea level rising.

He cited the report by the UN Intergovernmental Panel on Climate Change, which says the global temperature is likely to rise by more than 1.5C by the end of the century, given the current concentrations and ongoing emissions of greenhouse gases. This means the world’s oceans will warm and the ice melt will continue. The average sea level rise is predicted to be 24-30cm by 2065 and 40-63cm by 2100.

Countries have been urged to monitor the level of greenhouse gas emissions to minimise the effect on global warming and the sea temperature. But so far, efforts have not been fruitful.

Mr Sucharit said under the worst-case scenario, if greenhouse gas emissions are not controlled, the sea surface temperature will rise 3.7C in the next 50 years, raising the mean sea level by about 70cm.

“Once it happens, it cannot be reversed, even after the emissions are stopped,” Mr Sucharit said.

For now, the rising seas are being held back in Bangkok by the 3m dykes along the Chao Phraya River. After the last Bangkok floods, the water level rose to 2.4m, leaving the dykes with the capacity to block another 60cm of water.

“What if the water level rises beyond 60cm, what should we do? Do we have to increase the height of the top of the dyke? Would that be adequate, or must we do something more?” Mr Sucharit asked.

Dense urbanisation is also speeding the rate at which Bangkok sinks.

Buildings or skyscrapers constructed on solid pilings are not likely to be affected, but they can cause disruption to the earth in surrounding areas, said Sornchai Tovanitchakul, director of the Analysis and Research Division at the Bangkok Metropolitan Administration’s Department of Public Works.

FEAR FACTOR: Bangkok sinks about 1cm a year on average, according to NRC committee member Sucharit Koontanakulvong, who is also head of Chulalongkorn University’s Water Resources System Research Unit.

“Usually, the buildings are constructed on pilings more than 21m deep, so they reach the hard soil below. Those are safe from subsidence. But the surrounding area can be affected by the weight of these heavy buildings,” he said.

Bangkok also faces the problem of land erosion, with the capital's 4.8km of coastline being worn away — in some areas at a rate of more than 4m a year.

Mr Sornchai said authorities had attempted to solve the subsidence problem through the enforcement of zoning, with planners trying to spread building density evenly across the city. But he acknowledged it is difficult to curb the growth of urbanisation. “We cannot prevent the city from growing,” he said.

DEPTH OF THE PROBLEM

Mr Vithaya said the potential severity of future subsidence is the subject of fierce debate. “People still argue about what would be the worst possible rate of subsidence. Will Bangkok continue to sink at a rate of 1.4cm or more per year?” he said.

“If Bangkok continues to sink at 1.4cm, we still have lot of time to prepare for it. But even the Survey Department said they cannot provide an exact conclusion. Also, there are questions about how to measure Bangkok. It is a big city,” he said.

Subsidence is currently measured every three years. It takes time and effort because of the number of locations involved. In some areas, officials use satellite imaging to measure changes in the ground level.

“Which locations provide good indicators for measurement? These questions are still unanswered,” Mr Vithaya said. “There is no mechanism to settle these issues. The committee made this recommendation to the cabinet to set up a national strategic committee to do the research thoroughly. Once we’ve come up with a set of assumptions we all agree on, then we can work from there.”

The committee spelled out three possible scenarios for Bangkok and its surroundings, concluding the subsidence risk ranges from “medium” to “crisis”. “We are able to prepare. But we need specific agencies and measures,” Mr Vithaya said.

The committee has proposed the cabinet set up a panel to deal with rising sea levels and subsidence because the effort will involve several government departments. It estimates solving the problem will take 20 years.

Under the proposal, the first year would be spent laying out the work plan. The research would be conducted between three and five years after. The detailed design of the plan and environmental effects would then be analysed and addressed in the next six to 20 years.

Policies must be in place to ensure the appropriate use of land, the proposal says, while relevant agencies should have proper regulations and monitoring to prevent flooding and further subsidence.

WORSE THAN THE FLOOD

It does not take too much imagination to picture Bangkok under water. In 2011, massive flooding hit Thailand and the capital for several months.

But Mr Sucharit said man-made subsidence will lead to more severe problems than natural events. Flooding from rain can be fixed by pumping water out of the city, even though it may take several months. But if the city is under water because of subsidence and rising seas, it will be hard to fix.

Bangkok is also looking to the Netherlands and the Italian city of Venice for models to address subsidence. The Netherlands prevents floods by using dams and floodgates to defend the country from surging sea levels, and Thailand is now emulating that model.

Venice also faces subsidence due to years of pumping groundwater and ground compaction from centuries of building. Venice has established a massive system to block rising seawater, which took a decade to complete. 

“Although the water is the city’s signature, rising levels have started to affect tourists because it is not quite convenient to get around,” Mr Sucharit said.

“The effort took several years. We may not have the problem to that extent yet. But we have to figure out how we should deal with the problem now.”
One option is to construct a massive seawall stretching from Si Racha in Chon Buri to Hua Hin, protecting greater Bangkok from the surge of seawater, Mr Sucharit said.

“The seawall is roughly estimated to cost 500 billion baht. Therefore, we have to discuss whether it is necessary to do that,” he added.

Mr Sucharit said the debate over Bangkok’s subsidence may offer an opportunity to discuss city planning seriously. Finding ways to spread out urban density would help alleviate Bangkok’s sinking problem.

Public participation is also required, he said, since any solution will involve mega projects which require taxpayers’ money and affect people’s lifestyles.

Caught between droughts, floods, rising seas and lower groundwater tables, city planners will have to prioritise one element in particular.

“Water management has not been sufficiently incorporated in the city planning discussion. But it has to be in the future,” he said.

Sucking it up and soaking it in: how to live with floods

Buamas Sirikomol, 86, recalls how her family members learned to live with water and dampness when the massive Bangkok flood of 1980 inundated their house in Bang Kapi.

“We did not know where to go so we decided to stay here. Although the water level reached around one foot [30cm] inside the house, we were still able to live on the second floor.”

There were heavy monsoons that year. Located in one of the lowest areas of Bangkok, Bang Kapi was hard hit by the downpour. “We were able to commute," Mrs Buamas said. "Our neighbours did not evacuate either. Children in the soi went out and played in the water.”

After about a week, the flood water subsided and she had to fix the hardwood floor in the family home. But Bang Kapi was not hit by the most recent major flood in 2011. “The government had by then installed a system to prevent floods,” Mrs Buamas said.

For Raviwan Artsamang, a 57-year-old resident of Din Daeng, the flood waters come every year, though the severity varies depending on the downpours.

“It was worse in the past. The rainwater used to flood the garage, but not inside the house,” she said. To protect the garage, she was forced to raise the foundations of the floor.

“In recent years, the situation has improved. The water levels are under control, even though there is still a lot of water on the street after it rains,” she said.

“Once I was driving through floods on Mit Maitri Road and I could feel the tyres almost floating on the water.”

Ms Raviwan said she has learned to live with floods. “When the road is full of water, we just try to avoid the flooded route by choosing an alternative road.”

Nitsara Srihanam, 43, evacuates her family during heavy floods, such as in 2011. She, her husband and their daughter hurriedly left their house in Bang Bua Thong, Nonthaburi in November 2011, after news broke that nearby dykes were unable to contain water from the north.

“We had been following news about floods elsewhere. And we were checking the level of the water in a small canal at the back of the house every day. The housing villagers' committee members met almost daily to discuss what we should do if the flood came,” Ms Nitsara said.

One evening, her husband saw the water level in the canal rise sharply. Her neighbours said there was news that water had breached the dyke. “That evening we decided to pack our necessities. We drove out of the house after midnight.”

Her husband came back to check the house a few days later to see whether it was habitable. “The water had reached knee level. He told us that we had to stay away for a while.” Ms Nitsara’s family lived at a hotel outside Bangkok for one month during the floods.

Asked if she was aware that Bangkok might sink to dangerous levels in the next 20 years, she said: “Yes, but I think we will be safe because Nonthaburi stands on higher ground. People in Paknam or Samut Prakan are likely to be affected first. And that will give us time to evacuate.”

WHERE THE CITY MEETS THE SEA

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