Debated in Parliament on 10 May 2021.
Ms Hany Soh asked the Minister for Sustainability and the Environment (a) where were the places in Singapore that were flooded as a result of a heavy downpour on 17 April 2021; (b) whether flood mitigation measures were in place at these areas and, if so, what were these measures; and (c) what further flash flood measures can be implemented to safeguard flood prone areas in Singapore.
On 17 April 2021, the Sumatra squall, coupled with convergence of surrounding winds arising from the influence of typhoon "Surigae" near the Philippines gave rise to intense and prolonged rainfall across Singapore. The highest rainfall that day was at Ulu Pandan with 170.6 millimetres of rain. This is the highest daily rainfall recorded in April since 1980 and is equivalent to 110% of Singapore’s average rainfall for the whole month of April, falling in a single day. This rainfall resulted in flash floods occurring at Bukit Timah and Dunearn Roads near Sime Darby Centre and a stretch of the Park Connectors along Ulu Pandan Canal.
The water levels in Bukit Timah Canal were very high due to the intense and prolonged rain, impeding discharge from roadside drains along Dunearn Road and Bukit Timah Road into the canal. This resulted in floods of around 150 millimetres depth at Dunearn and Bukit Timah Roads, and around 50 millimetres depth on the pedestrian sidewalks adjacent to the roadside drains. All affected roads remained passable to traffic and the flash floods subsided within 30 minutes. PUB Quick Response Teams were onsite directing traffic and assisting affected residents by issuing inflatable flood bags and portable flood barriers to prevent floodwaters from entering their homes.
PUB had completed the upgrading of the Bukit Timah First Diversion Canal between Bukit Timah Road and Clementi Road in September 2019 at a project cost of $300 million to alleviate flood risks along Bukit Timah Road and Dunearn Road. Water level sensors installed along the upgraded stretch of Bukit Timah Canal from Jalan Kampong Chantek to Sixth Avenue, just upstream of the expanded Bukit Timah First Diversion Canal, showed the section of the canal was 50% full on 17 April with no flash floods along that stretch despite the heavy rainfall.
PUB started the upgrading work on the section of Bukit Timah Canal between Rifle Range Road and Jalan Kampong Chantek, where the localised flash flood occurred, and is expected to complete it in 2024. When completed, we expect the top water level in this section of the Canal to be lower by over one metre for the same rainfall intensity experienced on 17 April.
A low-lying 300-metre stretch of the Park Connector next to the Ulu Pandan canal was also flooded on 17 April even though major roads, such as Clementi Road, Clementi Avenue 6, Commonwealth Avenue West and the AYE, served by the canal did not experience flooding. PUB will raise this low-lying section of the Park Connector when PUB reconstructs the Ulu Pandan Canal in tandem with future developments.
Since 2011, the Government has invested almost $2 billion in drainage works, and will invest another $1.4 billion over the next five years to enhance our flood resilience. Drainage design standards were also raised in 2011 to cater for higher intensity rainfall, as part of PUB’s broader efforts to address the impact of climate change.
It is however not practical to expand our drains to accommodate every extreme rainfall event as this would require massive land take and much higher costs. PUB will put in place cost-effective measures to minimise flood risks and better manage flood events. For instance, PUB is currently upgrading its rainfall forecasting radar technology, which will help improve prediction of locations where heavy rainfall might occur and enhance response time to potential flash floods.
PUB also works closely with LTA and Traffic Police during heavy storms to monitor road conditions and notify motorists of flooded roads to avoid through electronic road signages, online and social media platforms and radio broadcasts. Members of the public can be alerted on flash floods by subscribing to NEA’s and PUB’s weather forecast and water level SMS alerts or access the mobile app, "myENV", for updates on impending heavy rain and the water level in drains at designated locations.
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