Reason for Recent Flash Floods and Plans to Tackle Issue

Mr Sitoh Yih Pin asked the Minister for the Environment and Water Resources (a) what is the reason for the recent flash floods in several areas in Singapore, including Sennett Estate in Potong Pasir, despite the drainage system being recently expanded; and (b) what are PUB's plans to further tackle this issue moving forward.

On the afternoon of 30 April 2020, strong solar heating of land areas coupled with convergence of winds in the region led to intense thundery showers over Paya Lebar, Punggol and Hougang. The total rainfall of 128.4 millimetres that day was one of the highest daily rainfall ever recorded in Singapore over the past 30 years.

As the capacity of roadside drains were overwhelmed by the intense rainfall, flash floods resulted at locations such as Upper Paya Lebar Service Road, Lorong Gambir, Tampines Road, Serangoon Avenue 2 and Lichi Avenue (which is close to Sennett Estate). These flash floods lasted between 10 to 30 minutes. PUB officers were on site to actively engage affected residents, provide sandbags and loan the portable Dam-Easy flood panels to prevent floodwaters from entering homes. These flood panels, which the Public Utilities Board (PUB) started loaning to residents and businesses in flood-prone areas since the start of the monsoon season in 2019, can be set up quickly during a flash flood. These flood panels were used by one of the residents during the 30 April 2020 rainstorm, who found them effective in preventing water from entering his home.

Drainage Improvement Works

As part of PUB's broader efforts to address the impacts of climate change, PUB had raised the drainage design standards to cater to higher rainfall intensity in 2011. Since then, the Government has invested almost $2 billion in drainage works, and will invest another $190 million this year to enhance our flood resilience.

In most of the areas affected by the intense rainfall on 30 April 2020, a number of flood alleviation projects have been recently completed or are ongoing. For example, PUB completed the upgrading of the Tampines Canal (from Hougang Avenue 1 to Hougang Avenue 7) in March 2019 at a project cost of $27 million to alleviate flooding along Tampines Road. The hydraulic analysis showed that the completed works had successfully reduced the flood area by 86%, including a large section of Tampines Road. As a result, the flash flood on 30 April 2020 was confined to a localised road depression at the junction of Tampines Road and Hougang Avenue 1. PUB will study the feasibility of raising the depressed road junction.

For the low-lying Upper Paya Lebar Service Road, works are on-going to divert stormflow from existing drains to larger new drains. The works are expected to complete in 2021 and will further improve flood protection in these areas. In addition, PUB will be upgrading the drains serving Serangoon Avenue 2 and Lorong Gambir to alleviate flooding. These works are expected to commence over the next two years.

In the case of Sennett Estate, which is a low-lying area and prone to flooding, PUB has been progressively upgrading the drains serving the estate between 2006 and 2015. There are on-going works to upgrade the remaining stretches of drains in the estate. When completed in 2021, flood protection for Sennett Estate will be further enhanced.

While PUB will continue with efforts to improve drainage systems, it is not practical to expand our drains to meet every extreme rainfall event in land-scarce Singapore. Besides drainage improvements, PUB will put in place cost-effective measures to minimise flood risks and better manage flood events. For instance, PUB is in the midst of upgrading its rainfall forecasting radar technology, which will help improve prediction of locations where heavy rainfall might occur and enhance its response time to potential flash floods. Members of the public can also stay updated on weather and flash flood warnings by subscribing to NEA's or PUB's mobile apps and SMS alerts. In the event of a flash flood, members of the public are advised to take appropriate safety measures, such as to avoid driving and walking in flooded areas.