Works in the pipeline to ease flooding in Ulu Pandan, Bukit Timah

A low-lying section of the park connector along Ulu Pandan Canal that was flooded on April 17 will be raised in tandem with future developments, Minister for Sustainability and the Environment Grace Fu told Parliament yesterday.

She was responding to questions from Mr Christopher de Souza (Holland-Bukit Timah GRC) about the flash floods that occurred on April 17 following intense rainfall, including what would be done to prevent a similar occurrence in the future.

While acknowledging that flash floods occurred at the 300m-long stretch along Ulu Pandan Canal, Ms Fu noted that major roads in the area, which is served by the canal, like Clementi Road, Clementi Avenue 6, Commonwealth Avenue West and Ayer Rajah Expressway were not flooded.

Director of PUB's Catchment and Waterways Department Yeo Keng Soon said yesterday that plans to upgrade the canal include raising its top level to enhance flood protection to the surrounding areas.

Flash floods occurred in two areas - at Bukit Timah and Dunearn Roads, and at the Ulu Pandan Canal - on April 17.

A Sumatra squall over the Strait of Malacca in the morning, largely due to the influence of Typhoon Surigae over the western Pacific, caused heavy rain across Singapore.

The daily 170.6mm total rainfall recorded at Ulu Pandan on April 17 was the highest rainfall recorded for the month. "This is the highest daily rainfall recorded in April since 1980, and is equivalent 110 per cent of Singapore's average rainfall for the whole month of April, falling in a single day," said Ms Fu.

Flash floods at Bukit Timah and Dunearn Roads took place near Sime Darby Centre, and were about 150mm deep on the roads and 50mm deep on the pavements next to roadside drains, said Ms Fu. She added that the roads remained passable to traffic, and that the waters subsided within 30 minutes.

She also said upgrades to the Bukit Timah Canal, and the construction of the Bukit Timah First Diversion Canal between Bukit Timah Road and Clementi Road, which ended in Sept 2019, proved successful in preventing flash floods.

A water level sensor installed along an upgraded stretch of Bukit Timah Canal, from Jalan Kampong Chantek to Sixth Avenue, showed that the section of the canal was half full on April 17, with no flash floods occurring along the stretch despite the heavy rainfall.

The same section is linked to the Bukit Timah First Diversion Canal, which channels water away from Bukit Timah towards Ulu Pandan.

Upgrading works for the section of Bukit Timah Canal between Rifle Range Road and Jalan Kampong Chantek, where flash floods occurred on April 17, are under way and will be completed in 2024.

Ms Fu said that, when completed, the highest water level in this section of the canal is expected to be at least one metre lower than current levels when rainfall intensity similar to that of April 17 is experienced.

She added that despite government spending on drainage works over the years - $2 billion has been spent since 2011, with another $1.4 billion to be pumped in over the next five years - it is impossible to eradicate flood risks.

"It is... not practical to expand our drains to accommodate every extreme rainfall event as this would require massive land take and much higher costs," she said.