National water agency PUB will be taking action against construction firm Sato Kogyo after it was discovered that the firm had carried out unauthorised works that affected the public drainage system in Upper Thomson Road.
PUB had conducted investigations into the drainage system following a flash flood in the area on Christmas Eve last year.
The flood affected at least eight businesses in the Upper Thomson area, one of which suffered an estimated $30,000 in losses.
Sato Kogyo is responsible for the construction of the Upper Thomson MRT station - one of the stops on the upcoming Thomson-East Coast Line - near Thomson Plaza.
Earlier investigations found that a choked drain at the construction site had contributed to the flood.
The agency found the Japanese firm had constructed an undersized temporary diversion drain along Jalan Keli opposite Thomson Plaza. The firm was also found to have altered the public drainage system near Lorong Mega, which is adjacent to the plaza.
Both of these works were done without PUB's approval.
"Contractors must seek approval from PUB and notify PUB before carrying out any works affecting the storm-water drainage systems within and near their construction sites to ensure that these do not affect the functioning of the public drainage system," said a spokesman for the agency.
She added that contractors must not "construct, alter, discontinue or close up" any storm-water drains without its approval.
PUB will take action against Sato Kogyo under the Sewerage and Drainage Act.
The contractor faces a fine of up to $20,000 for unauthorised alteration of the public drainage system.
If found guilty, it could also be fined up to $50,000 for works affecting the public drainage system.
The firm is no stranger to public infrastructure projects here.
Besides the $374 million contract for the Upper Thomson station, it is also working on several Downtown Line projects.
These include the construction of the Mattar, Bencoolen and Bedok North stations, all due to be completed by the end of this year.
A spokesman for the Land Transport Authority (LTA) said that as part of the works for the Upper Thomson station project, it has been widening the canal in Upper Thomson Road and Jalan Keli across from Thomson Plaza "to enhance the drainage system and improve the overall flood resilience in the area".
The spokesman said that Sato Kogyo, which is carrying out the works, could not build a diversion drain of the desired width because of the narrow site conditions along Jalan Keli, "resulting in a localised constriction".
After the flash flood incident, the contractor has worked closely with PUB to carry out temporary improvement works to increase the drainage capacity in the area, said the spokesman.
To prevent similar incidents, the LTA said it has instructed the firm to expedite the completion of the canal widening along Jalan Keli.
"Once the canal is completed, it will improve the recurring flash-flood situation in Jalan Keli," added the spokesman. "LTA will continue to work closely with our contractors to ensure that they comply with agencies' requirements for all our construction projects."