Why Bangkok Floods

[Guest fountainhall]

We all know that Bangkok suffers from a degree of annual flooding, partly due to heavy monsoon rainfalls, partly because drainage cannot handle the volume, and partly because the meeting point for the water inflow from the high tides in the Gulf of Thailand meets the downflow from the north at Bangkok.

 

The Nation has an article today which reminds us we sometimes forget the other reason. Bangkok is situated virtually at sea-level. On average, roads in the capital are just one meter above sea-level. As a result of subsidence, though, land in some parts of the city is bowl-shaped and therefore below sea-level. And subsidence continues at a rate of 1 to 2 centimeters per year, according to a drainage engineer at the BMA.

 

A road survey by the BMA's Public Works Department found that on average roads in Bangkok were only about one metre higher than sea level. So, when it rained heavily - more than 60 millimetres in an hour - or when the level of the Chao Phraya River was higher than two metres, Bangkokians could not avoid flooding . . .

 

"We have to use pumps to pump out water from low level areas. A system to release water through a lot of canals in the capital could also help," said Sansern.

 

He said each residence should have "monkey cheek" areas to hold floodwater in its compound and release floodwater after it stops raining instead of get rid of flood-water from residences while public areas were still flooded.

 

Apart from releasing floodwater along the canals in areas west and east of Bangkok, the BMA planned to increase water release

 

http://www.nationmul...e-30192300.html

[Guest]

Bangkok clearly needs some sort of long term strategy to deal with this.

I'm thinking of:

1 Substantial flood defences and pumping stations.

2 Also, if any area is redeveloped, potentially raise the height of the buildings and the street.

3 Thirdly, sort out the river capacity by dredging or routing a large canal around the edge of the city.

 

The Dutch seem to manage flood defences well.

[ceejay]

It's not really the same for the Dutch. Their principal concern is keeping the sea out. Bangkok has the problem of getting a huge volume of water through from the Chao Praya basin out to sea. It has to go through or round Bangkok. Certainly, Bangkok could do with better internal flood defences. Proper dredging is important, of course, but I think that the embankments lining the river and major canals need raising as well.

I'm not sure that raising the height of streets in redeveloped areas would work. I could see that giving even worse problems with run off in surrounding areas.

A relief canal, bypassing the city from North to South seems like the best bet to me. The basic system already exists - water can be passed through the canal system from North Bangkok to be discharged into the sea at Samut Prakhan. Increasing the capacity of this part of the system would, I guess, be cheaper and quicker than building a new system entirely.

The best short term solutions are to improve the maintenance of the existing systems, and to improve their use and management as well. That includes management of water levels in the big dams.

In the long term, reforestation of the higher ground around the Chao Praya basin would help moderate the rate at which flood waters are released into the river system. That's not going to happen though. Too much agricultural land would be lost.

Whatever is done though, there will always be floods. I find it very hard to imaging any system that could have prevented last year's. There was simply too much water . It had to go somewhere. That makes the issue one of flood management, as well as flood prevention and that means balancing the interests of Bangkok and the upstream provinces.

[pong]

in several parts of BKk streets ARE raised (notably on the Thonburi side, I think)-which is clearly visible when you walk there and see make-do stairs going down to entries of houses.

To z909-BKK has-for Thai stdd, about the heaviest and best water protection there is.

I still wonder how they did that last year-coming from the north, that filthy water came down to kasert uni-also engulfing DonMuang airpt-where the office to regulate it all was located-and then miraculously was to disppear in a week or so-also by ''bigbags'' and other pumpings. Which at least show they are able to handle giant masses of waterfloods and to more orless protect the inner city.

[Guest fountainhall]

I still wonder how they did that last year-coming from the north, that filthy water came down to kasert uni-and then miraculously was to disppear in a week or so

 

Khun pong is correct to indicate that the volume of floodwaters last year was extraordinary. However, with respect it took a great deal more than a week to get rid of it. Don Mueang was under water for almost three months, as were a huge number of homes. I know a couple of Thais who could not return to clean up their homes for over 8 weeks.

 

But he also makes an interesting point. When roads off the main traffic routes are resurfaced once they are falling apart, they are raised upwards by as much as half a meter. That has happened in three sub-sois near me, and is presently taking place on Sathorn Soi 1. End result is that even run-off rainwater from these sois quickly finds its way into into either lower sub-sois or homes at the sides of the sois. I can't work out why they do it this way, unless it is a deliberate policy to keep traffic lanes free at the expense of homes.

[Guest]

Obviously raising the level of areas needs to include the properties as well as the streets. In fact, the properties should be raised before the streets.

In the short term such a policy has negative effects on surrounding areas. In the long term, presumably the majority of Bangkok would be redeveloped within a century or so. So it would be one way of keeping the city above sea level.

[Guest fountainhall]

I'm curious. How would you raise large houses and small condos?

[Guest]

Initially, I'm thinking more of new developments. Areas do get redeveloped.

If a whole area gets rebuilt, just put the floor 2 metres higher than it would otherwise be and raise the street accordingly.

 

Where individual properties are being rebuilt, have building regulations that require the the ceiling of the ground floor to be (say) a minimum height of 4.5m above sea level (exact value subject to survey). Then when the road level is eventually raised, it's a simple matter of putting in a new higher floor for that building.

 

Earlier in this thread, it was reported Bangkok is sinking at 1~ 2 cm a year. So if a building is supposed to last 100 years, why not have the facility to compensate for the sinking?

The other option is flood walls and pumping stations. Personally, I'd rather have my ground floor just fare enough above the water level.

[Guest fountainhall]

I agree entirely. The problem it is the older sois which tend to require repair and new drainage. So it's the gazillion older properties which will keep getting at least a degree of flooding.