Unauthorised drainage works led to severe flooding at Tampines-Pasir Ris junction, PUB to take action against contractor

• PUB found that flooding at a Tampines-Pasir Ris junction on Aug 20 was caused by unauthorised drainage works
• Construction company Samwoh had blocked off a roadside drain along Tampines Ave 10
• The firm diverted the stormwater flow to a new drain section that was still under construction
• Samwoh did not seek PUB’s approval for drainage diversion works
• PUB will take enforcement action against Samwoh

SINGAPORE — National water agency PUB will be taking enforcement action against Samwoh Corporation after investigations revealed that the construction firm had carried out unauthorised drainage works, which impeded the discharge of stormwater into a roadside drain along Tampines Avenue 10. 

This resulted in severe flooding for nearly two hours at the junction of Tampines Avenue 10 and Pasir Ris Drive 12 on Aug 20.

Thirteen vehicles were found stationary and partially submerged in water at the junction after heavy rains that morning.

The Singapore Civil Defence Force had to rescue five people from partially submerged vehicles. One person was taken to the hospital.

Commenting on the investigations on Saturday (Sept 11), Mr Yeo Keng Soon, director of PUB’s catchment and waterways department, said: “This prolonged flooding incident was entirely man-made. It would not have happened if the contractor had complied with PUB’s regulations for drainage work.”

JUNCTION NOT PRONE TO FLOODS

In a press release on Saturday, PUB said that it first alerted the public to the flood at 7.58am on Aug 20 and immediately deployed its Quick Response Team to the affected location.

The flood affected a 200m section of the traffic junction, with floodwaters reaching a depth of around 500mm, or about knee-level, in some areas.

Heavy rain in the area stopped by around 9am, but the flooding persisted and fully subsided only 40 minutes later. 

PUB said that the location is not known to be a flood-prone area or a flood hot spot.

It added that the stormwater drainage system is “more than adequate” to cope with the rainfall intensity on Aug 20. 

“The amount of rainfall observed at this location was also comparable to recent rain events that occurred on Apr 5, 2021 and Nov 22, 2020, when no flooding was observed.”

PUB NOT TOLD OF DRAINAGE DIVERSION

What PUB found was that Samwoh, which is carrying out road-widening works along Tampines Ave 10, had blocked off the existing roadside drain along the avenue and diverted the stormwater flow to a new drain section that was still under construction.

“This new drain section was not properly connected back to the existing drain and was partially obstructed by scaffoldings.

“Samwoh had also failed to seek PUB’s approval to proceed with the proposed drainage diversion works,” it said. 

This “significantly impeded” the discharge of stormwater into Sungei Api Api along Tampines Link, resulting in floodwater accumulating at the traffic junction, which is the lowest point in the vicinity, it added.

Typically, stormwater flows via the roadside drain into Sungei Api Api from the junction. The water is then discharged into the sea.

However, PUB’s water level sensors showed that Sungei Api Api was about half-full at the time of the flooding incident.

PUB said that it later instructed Samwoh to remove all obstructions and ensure stormwater can flow effectively into the drain section.

WHAT LTA SAYS

The Land Transport Authority (LTA), which contracted Samwoh for road-widening works, told TODAY that it imposed a one-day time-out immediately after the flood to check the remaining stretches of the drain to ensure the drainage is not blocked.  

It also worked with Samwoh and PUB to rectify the unauthorised drainage works and clear the obstruction to prevent a recurrence.

LTA said that it will penalise Samwoh for breaching contractual requirements.

It has also stepped up checks to ensure that its contractors comply with PUB’s guidelines.

On whether individuals affected by the flooding on Aug 20 will be compensated, LTA said that claims can be submitted to Samwoh Corporation and their validity will be thoroughly investigated and assessed..

A ‘STARK WARNING’ TO CONTRACTORS

In its statement, PUB said that it takes a serious view of contractors carrying out unauthorised works that interfere with the stormwater drainage system.

“Unauthorised alterations may affect the functioning of the system, as the drains, canals and rivers are interconnected.”

Mr Yeo of PUB said that the agency maintains a comprehensive network of roadside drains, canals and rivers that convey stormwater into reservoirs or the sea. As such, it is imperative to keep drains free flowing, especially with Singapore experiencing more frequent and intense rainfall due to climate change.

“This incident should serve as a stark warning to all contractors that any construction works carried out must not adversely affect the storm water drainage system,” he added.

Under the Sewerage and Drainage Act, offenders may be fined up to S$50,000 for works affecting the stormwater drainage system, and up to S$20,000 for unauthorised alteration of the stormwater drainage system.

The last time a contractor was taken to task for unauthorised drainage works was four years ago following a flood incident along Upper Thomson Road near Thomson Plaza on Dec 24, 2016.

At that time, contractor Sato Kogyo was fined S$14,000 for unauthorised drainage alteration works and failing to notify PUB before starting drainage works.