Bangkok City Hall is developing a long-term drainage master plan designed to handle rainfall of up to 100 millimetres an hour, as the capital prepares for heavier downpours linked to climate change.

The Bangkok Metropolitan Administration (BMA) is working with the Japan International Cooperation Agency (Jica) on the five-year Thai-Japanese cooperation project. Deputy Bangkok governor Wisanu Sapsompon chaired the steering committee's first meeting on Monday at the city's drainage and sewerage department.

The current system is designed for rainfall of about 76mm an hour. Studies indicate that hourly rainfall could reach 80-97mm between 2046 and 2065 under climate-change scenarios, an increase of 5.4-27%, Mr Wisanu said.

The BMA has therefore set 100mm an hour as the benchmark for future planning.

More than drains and pumping stations

The proposed Urban Drainage Grand Design will cover expansion of drainage networks and pumping capacity, but will also look at creating more drainage routes, controlling runoff and protecting water-retention areas.

For residents, including foreign homeowners, tenants and visitors, the project is intended to reduce the disruption caused by intense rain: flooded roads, difficult journeys and waterlogged neighbourhoods.

City Hall wants urban areas to play a larger role in holding rainwater. Roads, pavements, public parks, schools and public buildings could be fitted with permeable surfaces, detention areas, rain gardens, underground storage and additional green space.

Officials have also proposed runoff-control targets for individual drainage zones, measured by the volume of water that can be reduced.

Under possible land-use and building-control measures, at least 50% of open space would be designated permeable, in line with the Open Space Ratio. The BMA is also considering changes to the Biotope Area Factor, which requires part of a development plot to serve as ecologically green space, to reflect different land uses.

Data from public parks and projects subject to environmental impact assessments will be used in preparing the plan.

Canal levels and floodgate operations under review

The project will also assess how Bangkok manages pumping stations and floodgates before heavy rain arrives.

One proposal, called the Pink Plan, would lower canal levels below existing targets at selected stations when severe rainfall is forecast. Officials will assess the measure against concerns including water quality, sediment levels and odours.

The BMA said it would review operation records, maintenance information and station checklists to produce clearer manuals. At present, flood responses rely heavily on local officials' experience and judgement.

Four working groups will cover the grand design, facilities, land-use and development controls, and operational improvements. Jica experts will provide technical advice.

The BMA drainage and sewerage department proposed the cooperation in May 2023. Jica approved it in February 2024, followed by discussions on its scope and joint field surveys. The project has two phases: an initial three-year stage followed by a further two years.

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23 September 2026

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I wonder if it will be better than Pattaya where after their work it still floods

they need to build an effective network/system of storm drains like they have in singapore and tokyo.

Bangkok trying to engineer its way out of flooding is a bit like bailing out a boat built with holes in the hull. You can reduce the pain, but you’re never going to eliminate it!

The city sits on the Chao Phraya delta floodplain, with large areas barely above sea level, and parts are still subsiding a few centimetres a year. Anyone who’s been around Rangsit or Bang Na after a decent downpour will have seen the water sitting everywhere. The low‑lying high‑rise zones in Nonthaburi aren’t much better and are a future flood disaster just waiting for the right storm.

Add climate‑change rainfall spikes and upstream runoff and you’ve got a structural problem no amount of pumps or canals can fully solve. The new Thai–Japan plan of permeable surfaces, detention areas, more green space, better canal management is sensible, but it’s still incremental mitigation, and while useful, it is not transformative.

This isn’t a new concern though. Don't forget that Thaksin famously “floated” the idea of relocating the capital to higher ground when he was PM. While that suggestion went nowhere then, it remains the only option that would fundamentally change Bangkok’s long‑term flood‑risk profile.

For now, the only realistic approach is to improve what you can, hope the next storm isn’t too big, and accept that living on a major river delta comes with permanent water problems.

https://www.uspowtbr.com/wp-content/uploads/2022/02/hx-VctMt-flooded.jpg

1 hour ago, scubascuba3 said:

I wonder if it will be better than Pattaya where after their work it still floods

Probably did last night as we got some heavy rain.

I hear the new drainage isn't big enough, so the water pops up in different places now.

We have heard this many times before.

Considering that parts of Bangkok are below sea level, and overall the average height of Bangkok is 1.5 metres above sea level, I await the brilliant plan to move so much water so quickly.

When they finally realise water doesn't run up hill?

Bangkok was once the Venice of the east, but some bright spark thought it a good idea to fill in the canals to make more room for road traffic.

I can remember the Dutch offering to assist with the flooding problem, many years ago. They were told outside help was not required.

Dumb and Dumber!?

I bet someone will regurgitate the old idea of tying up boats to bridge piers and running them to push the water downstream quicker.

4 hours ago, it is what it is said:

they need to build an effective network/system of storm drains like they have in singapore and tokyo.

Storm drains work when the outlets are above the average surrounding water level.

That's not the case in Bangkok

I remember decades ago being told by a friend who worked for the Dutch Embassy that Dutch engineers had offered Thailand a plan for Dutch style dike system, which has proven to be incredibly effective in Holland.

They offered it free of cost, and Thailand always turns down a great project that's free of cost, because there's no money to be made for the officials.

The backwards march continues unabated.

5 hours ago, scubascuba3 said:

I wonder if it will be better than Pattaya where after their work it still floods

What work was done in Pattaya?

I have not encountered any floods here recently: what am I missing.

3 hours ago, jacko45k said:

Probably did last night as we got some heavy rain.

I hear the new drainage isn't big enough, so the water pops up in different places now.

Please can you explain these problems further, and describe the effects and their primary locations.

Thanks!

14 minutes ago, spidermike007 said:

I remember decades ago being told by a friend who worked for the Dutch Embassy that Dutch engineers had offered Thailand a plan for Dutch style dike system, which has proven to be incredibly effective in Holland.

They offered it free of cost, and Thailand always turns down a great project that's free of cost, because there's no money to be made for the officials.

The backwards march continues unabated.

“Incredibly””? In what sense?

5 hours ago, Georgealbert said:

City Hall wants urban areas to play a larger role in holding rainwater.

And urban areas want City Hall to find the necessary finances to play that role. Where are Parliament leaders?

1 hour ago, Surasak said:

When they finally realise water doesn't run up hill?

Bangkok was once the Venice of the east, but some bright spark thought it a good idea to fill in the canals to make more room for road traffic.

I can remember the Dutch offering to assist with the flooding problem, many years ago. They were told outside help was not required.

Dumb and Dumber!?

2011 I beleive what did they do ignore the advice.