Thailand is preparing a 165-billion-baht flood-diversion canal from Chai Nat through the Pasak basin to the Gulf of Thailand, but a water-management academic has questioned whether it addresses the flooding now affecting Bangkok and surrounding provinces.

The proposed Chai Nat-Pasak-Gulf of Thailand floodway is one of nine main plans intended to reduce flooding in the lower Chao Phraya basin. Its environmental impact assessment is being revised for submission in 2026, with construction potentially starting in 2027 if approved and lasting seven to eight years.

Associate Professor Dr Sitang Pilailar, a water-resources engineering lecturer at Kasetsart University's Faculty of Engineering, raised concerns in a Facebook article posted on 28 September 2026. She questioned whether failures in water management were caused by incompetence or intention.

Designed to divert northern water

According to plans from the Office of the National Water Resources and the Royal Irrigation Department, the project would divert northern runoff and water from the Pasak River before it reaches the lower central plains.

It would involve improving existing waterways and digging new canals over a combined 270 kilometres. The newly excavated Pasak-to-Gulf section would cover about 135 kilometres and would be designed to discharge up to 600 cubic metres of water per second.

Supporters say this could reduce pressure on the Chao Phraya River and lower the risk of river flooding in Ayutthaya, Pathum Thani, Nonthaburi and Bangkok during a major northern-water flood similar to that seen in 2011.

Limits for Bangkok's rain flooding

Dr Sitang's central point is that the proposed canal would not solve flooding caused by intense rainfall falling directly on Bangkok. Recent flooding in the capital has been linked to heavy rain, low-lying urban terrain and drainage problems, rather than the Chao Phraya overtopping its banks.

Even a completed floodway would not remove water trapped on roads in areas such as Sukhumvit, Rangsit, Ram Inthra or Vibhavadi if drains are blocked or pumping systems fail, the article argued.

Sea levels and coastal concerns

The article also raised concerns about high tides, land subsidence and possible effects on coastal ecosystems. It cited the World Meteorological Organization as saying Bangkok could rank fourth among the world's cities at high risk of flooding by 2030, with climate change, higher sea levels and subsidence among the factors.

It argued that water discharged towards the Gulf could be unable to drain effectively during high tides without adequate sea walls or coastal defences. The project may still form part of wider national water planning, but the article said Bangkok also needs better drains, more green retention areas and practical protection against sea-water intrusion.

Pictures courtesy of Manager Online

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30 September 2026

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Lovely picture of blue water in the deign canal, doubt it will be that colour as none of the natural flow rivers are that colour.

First question to be asked is, what are the relative levels of the areas to be drained compared to the min/ max sea levels and their effect on drainage?