Sinking Bangkok

For the more or less 10 million people living in Thailand’s capital city of Bangkok, flooding is a common and recurring phenomenon. This is partly due to the city’s geographic location at the southern end of the Chao Phraya River Basin, as well as its low-lying terrain of around 1.5 metres average elevation above mean sea level. The city normally experiences six months of rainy season every year from May to October.

However, conditions are soon expected to worsen for much of Bangkok. This is due to the ongoing sinking or land subsidence that is threatening the city. The implication is that while the sea level rises, the lowering of ground level continues, leaving the city doubly vulnerable to urban flooding.

On 12 May, the National Water Resource Commission (NWRC) approved a US$412 million plan to combat drought and floods as well as improve drainage and water quality in Thailand’s main interprovincial canal – the Klong Prem Prachakorn. 

Thai media reported that the plan will be sent to the cabinet for final approval. While rainfall in Thailand is expected to be five to 10 percent lower than usual over the next two months, the Office of National Water Resources (ONWR) is keeping a close eye on weather reports.

Other Southeast Asian megacities as Jakarta and Manila are being hit hardest. Thailand landed on the vulnerability list after the 2011 flood event, which cost the nation US$46 billion in repairs and rehabilitation. US$8 billion was spent on Bangkok alone. More than 800 deaths were recorded and 13 million people were affected by the flooding.

While adapting to its environmental and geological limitations is key to maintaining and improving Bangkok’s liveability by reducing the occurrence of urban flooding, other factors such as the issue of land subsidence can be more important. Bangkok, along with Venice and New Orleans, are three cities which are sinking 10 times faster than the rising sea level. According to some estimates, parts of Bangkok are sinking by two centimetres annually. For some parts of the city that are now only half a metre above sea level, these estimates are very worrying.

Built on soft clay

The city of Bangkok was developed on a marshy stretch of land in the Chao Phraya delta to accommodate a new capital after the fall of Ayutthaya to the Burmese Empire in the 18th century. It is built on highly compressible layers of soft clay. The sinking of the city is mostly driven by the sheer weight of the built-up urbanisation, as well as uncontrolled groundwater extraction.

Geological description 

Bangkok is situated on the tidal flat of marine clays of the Chao Phraya River delta. Hence, the ground surface of Bangkok is entirely underlain by marine clay, 15 m to 30 m in thickness, known as Bangkok clay. Unconsolidated and semi-consolidated sediment overlying the basement have a totally thickness of about 400 m to more than 1800 m. The aquifer system consisted mainly of sand and gravel separated by clays. Eight aquifers within the depth about 600 m have been identified. The water in the top most aquifer is not potable due to high salinity occurring since the deposition. The subsequent three aquifers (PD-100 m, NL-150 m, and NB-200 m) are the most used. However, the high production and newly developed wells at the greater depths are mostly served for industrial purposes. Due to the past uncontrolled over pumping of groundwater, certain aquifers and overlying clay layer are under substantial stress, leading to serious land subsidence which at its most severe amounts to 10 cm/year (1978-1981). In certain places, with combined surface loading, this has amounted to a maximum recorded settlement of 100 cm over a 21-year period (1978-1999) and groundwater level has declined to 55 m from ground surface. The increasing of groundwater abstraction reached it maximum at 2.6 MCMD in 1999. The mitigation actions have been required if they are to be reinstated and stabilized. The subsequent strict mitigations such as declaration of "Groundwater Critical Zone" covered large area totally seven provinces including Bangkok. The mitigation included reducing the permissible pumpage of registered wells, promoting public awareness in groundwater conservation, and finally implementing "No permission for new well rule" in the Bangkok metropolis. All these mitigations have been determined to control the total abstraction to meet permissible yield which has been studied at 1.25 MCDD. The strict mitigations finally return the good result. The current groundwater abstraction is under 1 MCMD. The overall subsidence rate has been improved to less than 2-3 cm/year in central Bangkok and less than 1 cm/year in overall area. Water level has been recovered to 40 m from ground surface. While, the ground water cone of depression areas are shift to the newly developed zone at the skirt of Bangkok metropolis. Subsidence is not the only problem when considering groundwater pumping, salt-water intrusion has become one of the major problems of groundwater. The rapid lowering of the water table by excessive extraction of groundwater has caused the shallow aquifers in Bangkok to become contaminated by salt water from the nearby ocean.

References:

https://urbanland.uli.org/sustainability/bangkok-the-sinking-city-faces-severe-climate-challenges/

https://theaseanpost.com/article/bangkok-sinking-fast

Bangkok under environmental siege

Bangkok, the capital of Thailand has a population of around 10 million people in the urban sections and more than 15 million in the metropolitan area. Its growth is the consequence of internal migration in Thailand and immigration from neighboring countries.

Many individuals in Bangkok have a connection with the Thai ethnicity. There are a couple of groups in the country as an outcome of migration. This incorporates the Vietnamese, Lao and Mon. The most known ethnic gatherings are the Chinese, who were 75% of the city’s population in 1828, which dropped to half by the 1950s. The Chinese community is situated in Yaowarat, which is otherwise called the Chinatown of Bangkok. There is an Indian community as well in Phahurt.

The rapid growth has created serious environmental problems, the periodic floods related to its low topography and sinking due to groundwater pumping and lately air contamination producen thick smog. A brief description of Bangkok's smog in the following article.

Smog in Bangkok

The small park in Bangkok's Rama III district is mostly popular with runners circling its neatly trimmed garden track to the sound of birdsong.

But on Thursday, they were joined by a convoy of fire trucks and half a dozen military drones, drawing dozens of curious onlookers.

After an hour setting up, the drones and water cannon were pumping thick plumes of water into the empty sky above. Speakers blared warnings about the operation and instructed runners to keep their distance.

The odd display was the Thai government's latest attempt at curbing the alarmingly high levels of pollution that have been plaguing the capital for weeks. The drones, geared with water tanks and fire-fighting sprinklers, were supposed to break up the smog that has been smothering the city of around 10 million people for at least a month.

Initially, Thailand's authorities said the worsening pollution was being blown over from China, predicting that it would be gone within a week or so. Then, as the smog persisted, they tried cloud seeding. Now, drones and water cannon are their latest salvo.

"Do they actually think this is going to help?" asked Gong, a 50-year-old man who comes to the park often to use its free-weight gym.

"The only thing happening today is that runners are getting wet and they have to watch out for these drones," he said, drawing laughter from weightlifters nearby.

Thailand deployed water cannon and drones to a local park in Bangkok to try and disperse the toxic smog that's been hanging over the city for weeks [Caleb Quinley/Al Jazeera]

Toxic air

As amusing as they might have found the scene, Bangkok residents are welcoming any attempts to combat the toxic smog that has forced authorities to close more than 400 schools, advise people to wear a mask when they're not indoors and limit the time they spend outside.

New research from Thailand's National Institute of Development Administration (NIDA) suggests Bangkok's air has reached particularly concerning levels of toxicity, with the lingering smog being full of dangerous heavy metals and various carcinogenic compounds.

Professor Siwatt Pongpiachan, director of NIDA and a global leading expert on urban pollution, told Al Jazeera he was concerned to find that Bangkok's air contained dangerous levels of cadmium, tungsten, arsenic and polycyclic aromatic hydrocarbons (PAHs) inside the fine dust air, known as PM 2.5.

Siwatt explained that their levels are particularly dangerous, based on the World Health Organization's (WHO) standards for measuring safe air, adding that Bangkok's pollution was largely coming from within the city itself.

Drones have been used as part of Thailand's efforts to shift the smog that's settled over the city [Caleb Quinley/Al Jazeera]

PAHs are toxic carcinogenic compounds that can be sourced to forest fires, car exhausts, cigarette smoke and insecticides, among others.

The Thai capital, meanwhile, has some 10 million registered vehicles, pollutant-pumping factories and numerous daily cremations.

Siwatt said the widespread burning of sugarcane fields in northern provinces is also contributing to the crisis, which makes tackling the problem extremely difficult.

The WHO has been campaigning to decrease toxic pollution around the globe for years, educating the public on the dangers to health and urging governments to prioritise clean air as megacities such as New Delhi and Beijing struggle with debilitating levels of pollution. Its guideline for PM2.5 is for an annual average of no more than 10 micrograms/cubic metre.

'Sense of urgency'

Bangkok has never seen pollution on this scale, and many residents were shocked at the smog lurking above. On social media, where Thais often go to express their outrage, memes comparing the city to post-apocalyptic backdrops in films such as Bladerunner 2049 and Mad Max have been widely shared.

Many are concerned the government is focusing on the symptoms rather than the cause of the problem.

"I think we need to push the government with a sense of urgency if we want to see positive results," said Sirima Panyametheekul, an academic in the Department of Environmental Engineering at Thailand's Chulalongkorn University. "We need urgent measures to be implemented, like reducing the density of traffic and cleaning the streets."

Thailand also needs to adopt more stringent measures for PM2.5, she added.

The density of the microscopic particles can reach 50 micrograms for each cubic metre volume before the government has to act, according to Sirima, who recommends that level be halved.

Currently, air quality is sitting around 61 to 93 micrograms/cubic metre depending on the location.

"I know that's challenging," she said. "But it's important. If not 25, we can at least start at 35 or 30."

Women covering their face with protective masks at a bus stop in heavily polluted Bangkok last month [File: Sakchai Lalit/AP]

Need for legislation

The government, which dropped a plan to use sugar water that was supposed to "capture" the toxins, stands by its approach to the current air crisis.

"It's going to work," said Somjiak Nonthagaew, the director of Bangkok's Fire and Rescue Department, on deploying drones and fire-fighting equipment to combat the smog.

"It should definitely help, but of course not 100 percent. We would have liked to do more, but we have limited options and resources. But we sprayed at six locations today, and we think it was a success," added Nonthagaew, between shouting loud updates into his phone as the mist began to descend over the park.

But Siwatt is not convinced.

He says Thailand needs to develop policies that would reduce the toxic compounds in the air, citing neighbouring countries such as Singapore and the Philippines. He's also urging authorities to introduce a Clean Air Act, like the one the British government rolled out after the deadly 1952 London Smog, which blanketed the UK capital for several days.

Thai authorities say that the current smog should lift in a few days as a result of their tackling operations. According to Somjiak, they plan to deploy water cannons and drones until the air quality improves.

But without major changes, the smog is bound to return.

"It's going to take a few years before we see any Clean Air Act laws," Siwatt said. "And before thinking about the timeframe, we need to convince the government and all the future political parties to agree that Thailand really needs clean air."

Reference:

https://www.aljazeera.com/news/2019/02/bangkok-chokes-pollution-busting-efforts-falter-190201040547251.html