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News Forum - Bangkok’s giant drainage tunnel ready for ‘rainy season’


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Bangkok deputy governor Wissanu Sapsompol says the city’s giant drainage tunnel will be fully operational for the “rainy season.” The new Bueng Nong Bon drainage tunnel, which began construction in January 2016, was not expected to be finished until March next year. But the city’s deputy governor insists it will be ready just in time for the kingdom’s rainy season due to start next month. Wissanu says the Bangkok Metropolitan Administration has outlined plans to use the drainage tunnel in Prawet district, and the Bang Ao pump station in Bang Na will help speed up the flow of excess water […]

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All this wet season, dry season, winter, summer, high season low season is just so much nonsense in the present climactic and economic environment. It strikes me it's pretty much ail the same and it's either hot and not raining, or hot and raining. The temperature range in my place, taken over 12 months, has a day time range over the year of 29 to 34 and a night time range of 30 to 27 and the rain is not confined to any particular month, at least not around my neck of the woods. Yes humidity changes, but that doesn't seem to be much related to the time of the year anymore. 

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14 minutes ago, Pinetree said:

All this wet season, dry season, winter, summer, high season low season is just so much nonsense in the present climactic and economic environment. It strikes me it's pretty much ail the same and it's either hot and not raining, or hot and raining. The temperature range in my place, taken over 12 months, has a day time range over the year of 29 to 34 and a night time range of 30 to 27 and the rain is not confined to any particular month, at least not around my neck of the woods. Yes humidity changes, but that doesn't seem to be much related to the time of the year anymore. 

I tend to agree that in many parts of the country, what you say is correct. There are parts of the South where you are certainly better off avoiding if you want to relax on the beach and avoid the chances of rain. In land the temperatures are as you describe.
 

I would also add that occasionally it can be wet and rainy for several days at a time during July and August. When it’s like that, Some parts of Thailand can look very depressing. The sunshine certainly allows you to overlook many drab buildings and dirty streets. The same is true of many places around the world. 

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The Bueng Nong Bon tunnel is 5 metres in diameter and runs for almost 9.5 kilometres at a depth of 30 metres

30 metres deep? I thought that Bangkok was only just above sea level. So is this tunnel well below sea level?
That strikes me as odd.

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1 hour ago, Loong said:

30 metres deep? I thought that Bangkok was only just above sea level. So is this tunnel well below sea level?
That strikes me as odd.

Powerful pumps are installed to force the water south and into the Gulf.  Should work ok as long as someone remembers to power the system on and intakes are kept free of debris ... 🙄

 

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44 minutes ago, KaptainRob said:

Powerful pumps are installed to force the water south and into the Gulf.  Should work ok as long as someone remembers to power the system on and intakes are kept free of debris ... 🙄

And the tides going out.

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57 minutes ago, KaptainRob said:

kept free of debris .

They didn't do too well with the Monitor Lizards.  The Thais are not known for their ability to keep drains clear anywhere. 

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7 minutes ago, Pinetree said:

They didn't do too well with the Monitor Lizards.  The Thais are not known for their ability to keep drains clear anywhere. 

True.  The intake was also poorly located, should have been somewhere HERE to drain the swamp properly.

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water table will be a problem, diversion to reservoir for the coming dry season's would be beneficial, especially to the farmers 

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85 square kilometer, 5 meters diameter, 9.5 kilometer, 7 million cubic meter storage. Large numbers.

Bangkok gets an average rainfall of 10 mm a day in september. Which equals 10 liters every square meter. 85 square kilometer equals 85 million square meters. So, 850 million liters. Which equals 850.000 cubic meters. 5 meters diameter means 20 square meter, roughly. Times 9500 equals 190.000 cubic meters. So in like 6 hours the tunnel is full. To get rid of the water they need to pump 32.000 cubic meter water per hour. Possible, if the pumps are big enough.

Biggest pumphouse in Holland can churn out 4.000 cubic meter a minute.

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18 hours ago, Loong said:

30 metres deep? I thought that Bangkok was only just above sea level. So is this tunnel well below sea level?
That strikes me as odd.

They use TBMs which go well below the sea level

https://tunneltalk.com/Thailand-4May2017-Terratec-tight-radius-EPBMs-for-Bangkok-drainage-tunnel-project.php

63C79587-FBBB-46C2-AD68-5C6451B0DC30.jpeg

Edited by Stevejm
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13 hours ago, harry1 said:

water table will be a problem, diversion to reservoir for the coming dry season's would be beneficial, especially to the farmers 

Water table was taken into account. Luckily you weren’t in charge of the program🤔

DD2BDC55-B115-409B-9906-024693D66C9B.jpeg

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On 6/12/2022 at 10:05 PM, Janneman said:

85 square kilometer, 5 meters diameter, 9.5 kilometer, 7 million cubic meter storage. Large numbers.

Bangkok gets an average rainfall of 10 mm a day in september. Which equals 10 liters every square meter. 85 square kilometer equals 85 million square meters. So, 850 million liters. Which equals 850.000 cubic meters. 5 meters diameter means 20 square meter, roughly. Times 9500 equals 190.000 cubic meters. So in like 6 hours the tunnel is full. To get rid of the water they need to pump 32.000 cubic meter water per hour. Possible, if the pumps are big enough.

Biggest pumphouse in Holland can churn out 4.000 cubic meter a minute.

If this pipe were the only drainage then it wouldn't cope with the flow rate. That said, given that the rainfall has many other run-off paths, it's probably more than sufficient, with room to spare.

We use the Hazen-Williams equation to calculate flow discharge rates of pipes.

If we assume that this 10mm of rain is all dumped in one hour, as would typically be the case in Bangkok, then 850,000 m3 of water in one hour equates to 236.11 m3/s.

The Hazen Willams equation says that this pipe can support a flow rate of 94.2 m3/s. So just by itself, it could drain approximately half that 10mm of rain dumped in one hour across the entire 85km/2

image.png.60fdaaa1b03b6419d2366091672080fc.png

 

The article linked by @Stevejmabove claims the pipe will have a drainage capacity of 60m3/s (which doesn't seem correct when compared to the above solution of the Hazen-Williams equation; I suspect they misreported the drainage capacity)

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8 hours ago, js89 said:

If this pipe were the only drainage then it wouldn't cope with the flow rate. That said, given that the rainfall has many other run-off paths, it's probably more than sufficient, with room to spare.

We use the Hazen-Williams equation to calculate flow discharge rates of pipes.

If we assume that this 10mm of rain is all dumped in one hour, as would typically be the case in Bangkok, then 850,000 m3 of water in one hour equates to 236.11 m3/s.

The Hazen Willams equation says that this pipe can support a flow rate of 94.2 m3/s. So just by itself, it could drain approximately half that 10mm of rain dumped in one hour across the entire 85km/2

image.png.60fdaaa1b03b6419d2366091672080fc.png

The article linked by @Stevejmabove claims the pipe will have a drainage capacity of 60m3/s (which doesn't seem correct when compared to the above solution of the Hazen-Williams equation; I suspect they misreported the drainage capacity)

I think you have to look at more detailed descriptions of the system. I think there are pumping stations at several locations which extract water from the system and discharge it to suitable receptors. I haven’t looked at Hazen Williams much since university so thanks for reminding me😁

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On 6/13/2022 at 4:05 AM, Janneman said:

85 square kilometer, 5 meters diameter, 9.5 kilometer, 7 million cubic meter storage. Large numbers.

Bangkok gets an average rainfall of 10 mm a day in september. Which equals 10 liters every square meter. 85 square kilometer equals 85 million square meters. So, 850 million liters. Which equals 850.000 cubic meters. 5 meters diameter means 20 square meter, roughly. Times 9500 equals 190.000 cubic meters. So in like 6 hours the tunnel is full. To get rid of the water they need to pump 32.000 cubic meter water per hour. Possible, if the pumps are big enough.

Biggest pumphouse in Holland can churn out 4.000 cubic meter a minute.

The last large power plant that I worked on in Thailand had two cooling water pumps each with a capacity of 72,000 cu.m per hour so it’s possible 

 

Edited by Stevejm
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18 hours ago, js89 said:

If this pipe were the only drainage then it wouldn't cope with the flow rate. That said, given that the rainfall has many other run-off paths, it's probably more than sufficient, with room to spare.

We use the Hazen-Williams equation to calculate flow discharge rates of pipes.

If we assume that this 10mm of rain is all dumped in one hour, as would typically be the case in Bangkok, then 850,000 m3 of water in one hour equates to 236.11 m3/s.

The Hazen Willams equation says that this pipe can support a flow rate of 94.2 m3/s. So just by itself, it could drain approximately half that 10mm of rain dumped in one hour across the entire 85km/2

image.png.60fdaaa1b03b6419d2366091672080fc.png

The article linked by @Stevejmabove claims the pipe will have a drainage capacity of 60m3/s (which doesn't seem correct when compared to the above solution of the Hazen-Williams equation; I suspect they misreported the drainage capacity)

This stuff is way over my head but your calculations include a drop of 30 m.

There won't be any effective drop will there. The pipe may be 30 m deep, but it will have to come up again before discharging won't it? So basically all flow will be down to the pumps?

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6 hours ago, Loong said:

This stuff is way over my head but your calculations include a drop of 30 m.

There won't be any effective drop will there. The pipe may be 30 m deep, but it will have to come up again before discharging won't it? So basically all flow will be down to the pumps?

The pipe discharges into the Chao Praya or into the Bueng Nong Bon reservoir and the outlet is almost certainly at the same depth. 

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42 minutes ago, Stevejm said:

There are pumping stations that discharge water to the river.

https://www.nationthailand.com/in-focus/40015320

Correct.  The discharge is somewhere between Bang Na and Samut Prakan as far as I know, close to the Chao Phraya river mouth.  In severe weather events and high tides the river flow may be dampened or reversed and whilst pumping continues it may exacerbate upstream flooding of low lying areas.

ThIs drainage system should mitigate flood risk under normal conditions if managed correctly.

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On 6/13/2022 at 3:21 AM, Stevejm said:

Water table was taken into account. Luckily you weren’t in charge of the program🤔

DD2BDC55-B115-409B-9906-024693D66C9B.jpeg

pumping water to where ? would be better to store the water in reservoir for the drought season that happen every year if l was running the program 

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22 minutes ago, harry1 said:

pumping water to where ? would be better to store the water in reservoir for the drought season that happen every year if l was running the program 

It’s a complex system of pipes pumps and collection chambers.

There are a few more details below but I haven’t seen the final overall design concept.

https://www.nationthailand.com/in-focus/40015320

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