SINGAPORE - The rain literally put a dampener on the festive mood at the eateries along Upper Thomson Road on Christmas Eve, when soaked diners had to wade through knee high waters after rain water entered the eateries in torrents.

Investigations by national water agency PUB have shown that a choked drain within a nearby construction site for an upcoming MRT station was the cause, PUB and Land Transport Authority (LTA) told The Straits Times on Thursday.

The flash flood incident took place on Saturday at a row of shops between Jalan Keli and Jalan Todak near Thomson Plaza.

Nearby construction on the Upper Thomson station, part of a 22-station Thomson Line, started in 2014. It will be built underneath a stretch of Upper Thomson Road between Thomson Plaza and the Church of the Holy Spirit.

In response to queries from The Straits Times, the joint statement from the authorities said: "PUB has investigated the flood incident on Dec 24 at Upper Thomson Road (near Thomson Plaza) and found a localised constriction at a temporary diversion drain within the LTA worksite.

"LTA will be getting their contractor to enhance the temporary diversion drain."

The statement also said that PUB has reminded the construction industry to conduct checks on the public drains in the vicinity of their respective construction sites in preparation for the monsoon season.

"As part of works to construct Upper Thomson MRT Station, PUB is also working with LTA to upgrade the drain along Upper Thomson Road to enhance flood protection for the area," the spokesman added.

The Meteorological Services Singapore said the average rainfall over Singapore that day was 35.5mm, with the highest daily rainfall that day recorded at Tai Seng, where 86.0mm of rain was recorded.