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No thunder down under: Phuket's new traffic tunnel stays dry last night

Phuket Underpass Passes First Test

Monday, May 25, 2015
PHUKET: Heavy rain put Phuket's first underpass to the test last night - and the tunnel passed.

Even though above-ground roads surrounding the Central Festival Phuket underpass became flooded in the downpour, the below-ground underpass remained open to traffic, an officer from Vichit Police Station reported.

The Phuket drought, which was threatening to cause rationing and become a real turn-off for those who like long showers, also appears to be likely to end within days.

All that's needed is the onset of monsoon rains.

Meteorologists are forecasting a 70 percent chance of rain across Phuket all this week, with winds of 15-35 knots and waves of 1-2 metres not yet posing a problem for speedboat day-trippers.

Last night's storm delivered 43.8mm in Phuket City and 26.8mm in Thalang, yet the pumps in Phuket's first underpass managed to keep the tunnel afloat, as it were.


Comments have been disabled for this article.


Credit where credit is due. Well done.

Posted by Sean on May 25, 2015 10:01


@Sean maybe you didn't know, but they built the tunnel inadequately first then realised they needed more money because they essentially didn't calculate it correctly.

At least second time they got it right.

Posted by Tbs on May 25, 2015 10:40


LOL... what in a normal country should be the norm here it becomes the exception. A non-news that becomes news.

Posted by dave on May 25, 2015 13:13

Editor Comment:

It's only news because doomsayers like you predicted the underpass would flood, dave. Thailand is a normal country - except for doomsayers. Didn't you just say the sky was falling? It looks blue to the rest of us.


I would like to know where the rain recording station is in Thalang please? This station recorded 26.8mm in Thalang, near Heroines Monument I recorded 30.2mm at 14:48. ( For all the big mouths who argue, my rain gauge is an electronic gauge, calibrated to 0.2mm filling increments, self empting and set at a height of 177cm, in clear open space).

Posted by Robin on May 25, 2015 13:40


Good to see been done right


A couple of kilometers can make a big difference, quite often can be pouring in chalong and dry in rawai and vice versa

Posted by Michael on May 25, 2015 15:50



may be this one near the airport?

however it is unclear what equipment is there

30.2mm of rain was it for exactly last 24hrs?
may be you have electronic log by hour or so to understand rain intensity?

Posted by Sue on May 25, 2015 16:05


@ Michael and Sue. Thanks for the answers.
Yes Michael agree with you, but it can also be meters. I have stood at Heroines Monument in Pouring rain on the Srisoonthorn side, only to watch as not a drop fell on the Pa Klok side of the monument.
Sue the rain started at 14:48 and my meter stopped recording when the rain stopped at 19:51. 30.2mm in a 5 hour 3 minute period. Quite heavy for a short space of time.
The heaviest I recorded this year was 29 04 2015 20:00-2012 15.4mm Thunder and lightning. Supreme Storm. (15.4mm in 12 minutes.)
Thanks for the answers.

Posted by Robin on May 25, 2015 17:44


@ Robin

Anyone who has spent even 1 monsoon season on this island knows that intense showers can be so localised that while it is raining on one side of the street it is dry on the other. One district can be awash while the adjacent one is bathing in sunshine. Keep watching this link

Posted by geoff on May 25, 2015 17:56


Dear ED, there is a difference between domsayers and technicians! For doomsayers if something did not happen could happen at any moment, for the technician instead, if one thing has never happened has a chance to be equal to zero. Now, technically speaking, there is only one thing built in Phuket that has never flooded by the rain?

Posted by dave on May 25, 2015 19:23

Editor Comment:

You mean, the Big Buddha? How would it be if the statue was surrounded by huge lotus leaf shaped water tanks that could save rainwater and let it run naturally downhill when taps turned on?

Honestly, dave, have you ever offered a single constructive suggestion? Do you have a feeling the positive world is passing you by?


Dear Ed, to offer (for money) costructive suggestions, is my job, expecially in the field of hydraulics. And my suggestions would be only one: automatic closure of the acces to bypass in case of heavy rain or electricity outage. Too many thinks could happen in case of poor maintenance that, to my experience, in Thailand is the rule.

Posted by dave on May 25, 2015 20:31

Editor Comment:

Does money drive your life, dave? I hope not.


The solution to restrict usage of an underpass during high intensity rain cannot be justified unless you have some knowledge that the design is flawed. If designed correctly, the following would have been considered.
1. The underpass will not be of a design that allows the entrance and exit ramps to be subject to the flow path of surface water runoff. The extreme of both will be elevated to a height greater than the maximum calculated depth of any surface water and then additional height above that to provide a safety factor.
2. The only water that should enter the underpass will be that collected on the entrance and exit ramps plus carry over from vehicles entering.
3. The sump pumps will be designed to handle this flow at peak rain intensity. The calculations are simple.
4. Should the peak intensity rainfall be exceeded it will not matter because roads leading to the underpass will be unusable due to overland flooding beyond either side of the entrance and exit ramps.
5. The underpass forming part of a main road becomes critical infrastructure during storm events. To shut it down will delay essential services reaching any emergency.
6. The design of the pumping system and contingency for loss of power should have been considered in the underpass design. It is a common event that loss of power occurs during high intensity rain or other storm events.
I am not familiar with this underpass but let's say for example we use the following criteria.
Ramp length 200m x 2, width 15 m, rain 10mm over duration 6 minutes (120mm per hour) = 60,000 litres in 6 minutes or 166.7 l/ sec. Allow for a safety factor of 40% above mean flow = 233 l/ sec..
It's not a huge or unmanageable volume of water for a properly designed system.

Posted by Manowar on May 26, 2015 00:00


So the underpass stayed dry while the surrounding roads were flooded?

Hmm. I wonder where the water in the underpass was being pumped to?

Posted by Smithy on May 27, 2015 19:39

Editor Comment:

Check the photo and you'll see that vehicles have to rise over a protective hump before entering the tunnel. Sound engineering principles, Smithy. Not that hard to understand.Unfortunately the water was probably not preserved for use in the dry season, but there wouldn't have been much of it.


Calculation and right projects never can predict the behavior of the drivers coming in the deep point of the tunnel during a black out when all is dark with some cm of water on the road. Manowar did you try to calculate the battery pack required to power the pumps in case of power failure? Have you idea about the maintenance of its? There is no time to start an automatic generator (that also requies maintenance): few seconds are enough to flood the tunnel with enough water to create a danger to traffic.. and the poblem isn't now that all is new, but in some years when people start to be confidente passing in the tunnel even in heavy rain.. we will see...

Posted by dave on May 29, 2015 23:38


Forget battery packs, inverters and uninterrupted power supplies, there is no need. For any pumping system to be supplied adequate water it will require a sump. The volume of that sump and the flow rate entering it determines what period of time a pumping system can be offline before flooding of the road surface occurs.
I doubt any person would consider using battery backup for a pumping system as a standby generator could be online and at full output within 10-15 seconds from sensing a phase failure.
Even when normal power is restored, this can be achieved break free by synchronisation of the normal supply and generator supply, however this would be considered overkill for such task.

Posted by MoW on May 30, 2015 06:02

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