PUB: Unauthorised drainage works by construction firm Samwoh caused 2-hour flooding at Tampines-Pasir Ris junction on Aug. 20

Man-made reason and could have been avoided.

Fiona Tan | September 11, 2021, 12:12 PM

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The national water agency PUB revealed that the August 20's flash flood at Tampines Ave 10 was caused by a blockage of a roadside drain.

The agency will take enforcement action against construction company Samwoh Corporation Pte Ltd (Samwoh) for its unauthorised drainage works which led to the flooding at Tampines on a rainy Aug. 20.

13 vehicles were partially submerged in water that morning and a person was sent to the hospital due to leg pains.

Drainage diversion not approved by PUB

In a press release on Sep. 11, PUB said an investigation was conducted to determine the cause of flooding at the junction of Tampines Avenue 10 and Pasir Ris Drive 12 following the incident.

Image from Singapore Laughs/Facebook.

Investigations revealed that an existing roadside drain was blocked off in road widening works along Tampines Avenue 10 by Samwoh.

The flow of stormwater was instead diverted to a new and incomplete drain section, that has not been approved by PUB.

Additionally, the new drain section, which was still in the midst of construction, was not connected back to the existing drain properly, and was also found to be partially obstructed by scaffoldings.

Image courtesy of PUB.

Samwoh "significantly impeded" stormwater discharge

PUB said that Samwoh's unauthorised drainage diversion works had "significantly impeded" the discharge of stormwater downstream into Sungei Api Api.

The blockage subsequently resulted in floodwater pooling at the said traffic junction, which was the lowest point in the vicinity, even though that area is not a flood prone area nor a flood hotspot.

During the same period, PUB's water level sensors at Sungei Api Api indicated that the canal, that discharges water to the sea, was half-full.

Video from De Chen/Facebook.

Flooding was entirely "man-made"

While the "severe" flood lasted for close to two hours from 7:40am to 9:40am, the stormwater drainage system is "more than adequate" to cope with that rainfall intensity experienced on Aug. 20, PUB stated.

PUB added that there were two other occasions with comparable rainfall on Apr. 5, 2021 and Nov. 22, 2020, and no flooding occurred then.

Therefore, the amount of rainfall on Aug. 20 was not a reason for the flood.

The Director of PUB’s Catchment and Waterways Department, Yeo Keng Soon 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."

Rectification works instructed, enforcement action to be taken

PUB said Samwoh was instructed to carry out rectification works within the same day on Aug. 20.

This included the immediate removal of all obstructions and ensuring stormwater can be conveyed effectively in the drain section.

In addition, PUB said that legal enforcement action will be taken against Samwoh.

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

A similar incident in the past involving another construction company Sato Kogyo carrying out unauthorised drainage alteration works, which resulted in a flood in the Thomson area in 2016.

For that offence, and the failure to notify PUB before commencement of drainage works, Sato Kogyo was fined S$14,000.

On the flooding at Tampines-Pasir Ris junction, Yeo reminded, "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.”

According to the One Motoring website, Samwoh was awarded the tender to widen Tampines Avenue 10 to a dual 4-lane road with a bus lane in each direction.

This project will ensure the reliability of bus services when it is completed in the fourth quarter of 2022.


PUB said they were alerted to the flooding at Tampines-Pasir Ris junction at 7:50am on August 20.

The agency alerted the public and, at the same time, deployed their Quick Response Team to the site at 7:58am.

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

A total of 13 vehicles were found partially submerged in water, and several motorists required help to evacuate their vehicles.

One person was conveyed to the Changi General Hospital after experiencing leg pains.

The flooding persisted and only subsided at 9:4oam.

You can keep up-to-date with Singapore's weather forecast and latest flood advisory here and here.

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Top image from Singapore Laughs/Facebook and Samwoh/Facebook