Officials are trying to piece together the cause of an unusual upsurge of water in an underpass where a businesswoman drowned on Thursday after finding a pump in the area functioned normally.
It was first thought the three-metre deep underpass, located near a section of the Bangkok-Chon Buri motorway in Prawet district, filled up with water after a pump had been turned off due to a broken pipe.
That assumption was a mistake, because the pipe was in good condition and "when Prawet district officials turned the machine on, it worked normally", Prawet district chief Thanasit Methaphanmueang said yesterday during an inspection of the underpass near the back entrance to the Golden Nakara housing estate.
This has led officials to look for another reason for the rapid rise in water which stalled a pickup truck and killed the 41-year-old who could not get out of her vehicle.
According to Mr Thanasit, "1,613.5 cubic metres of water poured into the underpass in about three and a half hours".
"The question that remains is how the water poured in."
The rate of water flow raised questions. While a pump takes nearly seven hours to drain the water, the deluge only took about three and a half hours to flood the underpass, Mr Thanasit said.
Officials are investigating nearby tap water pipes for cracks and other traces of leakage that may have led to the unusual flooding in the 95.4-metre-long tunnel.
There is an underground sump pit near the spot, but it held only 360 cubic metres of waste water, he said.
Whatever brought on the massive deluge of water, the district office and the housing estate need to find ways to prevent this from happening again.
"I've learnt that the underpass light was off that day, so you couldn't see the water," Mr Thanasit said.
He proposed changes such as constant monitoring of the electricity supply and installing more facilities, including a car pulley and closed circuit cameras. A system to prevent cars entering if water rises to a dangerous level is also required.
These preparations can serve as a model, according to Mr Thanasit, especially since there is another, similar underpass in his district.
On Thursday, the woman, identified as Panumas sae Tae, drove her pickup truck into the underpass at around 1am but water blocked her exit. She called her family for help but later lost contact.
Earlier on Wednesday night, another car in the same area stalled and would not start when the water level reached 60cm, officials said.
