Early Warning Systems for Better Management of Flash Floods

Mr Ang Wei Neng asked the Minister for the Environment and Water Resources in light of recent flash floods across the island and global climate change, whether the Ministry will work with other agencies to reduce incidents of flash floods in key areas of Singapore.

Thank you. Over the past few decades, we are observing upward trends in rainfall intensities and frequency of heavy rain events. This, coupled with growing urbanisation which increases stormwater run-off, has made flood management more challenging.

To reduce flood risk, the Public Utilities Board (PUB) adopts a holistic "source-pathway-receptor" approach that addresses flood protection, not just through drains and canals, that is, the pathway; but also in areas generating stormwater run-off, that is, the source; and areas where floods may occur, that is, the receptor.

First, the pathways. Since 2011, PUB has raised drainage design standards for new developments and redevelopments, which would increase their drainage systems' capacity by up to 50%. PUB has also been carrying out improvement works to progressively increase the capacity of existing drains and canals and rehabilitate older drains. In the last three years, drainage improvement works at 192 locations have been completed and there are ongoing projects at 90 other locations.

Given land scarcity, we cannot rely solely on more and bigger drains to mitigate floods. As such, PUB also requires developers to implement "source" solutions to better manage storm-water discharges from developments. These include on-site detention measures for larger developments. In addition, PUB also requires "receptor" solutions, such as higher platform levels, crest protection and flood barriers, especially for critical installations. These help to protect developments when floods occur.

Keeping our drains free flowing is the joint responsibility of all stakeholders, be they public agencies, private developers and contractors, and members of the public. PUB works closely with the National Environment Agency’s (NEA) Department of Public Cleanliness to regularly remove debris, litter and leaves from the drains. It also encourages the public to keep our environment litter-free and give feedback on drain conditions.

In reply to Mr Ang Wei Neng's question, PUB does indeed work with the major development agencies to get their contractors to conduct checks on the public drains near their construction sites to ensure that the drains are free of debris. This is supplemented by PUB's audit checks on approved drainage works on site. During critical stages, such as drainage diversion works and decommissioning of existing drains, more frequent checks are carried out. PUB also leverages on technology, for example, closed circuit television (CCTV) cameras, to facilitate the monitoring of work sites.

Mr Ang mentioned the recent flash floods, of which one recent occurrence is at Upper Thomson Road. PUB has investigated and found out that it was due to unauthorised work, which affected our public drainage system. PUB takes a serious view of such unauthorised works and will not hesitate to take action against errant parties under the Sewerage and Drainage Act. Any person found guilty may be fined up to $50,000 for unauthorised works affecting the public drainage system and up to $20,000 for unauthorised alteration or interference to the public drainage system. Such penalties and reputational damage, as well as being liable for civil penalties if they cause third-party damage, have been sufficient and effective in the past, and PUB will continue to review the amounts from time to time.

While PUB continues with efforts to reduce flood risks, we should be realistic to note that it is not possible to eliminate floods altogether. Localised conditions, exceptionally heavy downpour, tides and errant behaviour all contribute to flash floods now and then. As such, our focus is also to help members of the public better manage floods when they occur. To this end, PUB has put in place monitoring and alert systems to keep the public updated, through a network of water level sensors and CCTVs. Members of the public can subscribe to receive SMS alerts from selected water level sensors via PUB's website. These sensors are placed in flood-prone areas and hotspots, and could provide the public with early information on the rising water levels in drains in selected flood-prone areas.

In the event of a flash flood, PUB works closely with the Land Transport Authority (LTA) and the Police to monitor road conditions and provide real-time updates on PUB's Facebook and Twitter pages and via radio broadcast, as well as LTA's Expressway Monitoring Advisory System (EMAS) on the roads.

Our stormwater management strategies have served us well. Despite increased urbanisation and more variable weather, flood-prone areas have been reduced from 3,200 hectares in the 1970s to 30.5 hectares today. PUB will continue its efforts to reduce flood-prone areas and ensure the proper functioning of the drainage system. However, measures, such as drain upgrading, canals and centralised detention tanks, take time to implement and may not be able to cope with all extremities in rainfall.

As such, I urge all parties to play a part in ensuring that our drains are free-flowing, and to appreciate the importance of source and receptor requirements in their developments. Finally, we need to work together to manage floods when they occur through better and more extensive alerts. Through concerted efforts, we can minimise flood risks and better manage flood events.

Mdm Speaker, I thank the Minister for the very comprehensive reply. The Minister mentioned about improvements to pathways in 90 locations. Recently, there were floods in Paya Lebar and Tanjong Pagar, besides Upper Thomson. So, are Paya Lebar and Tanjong Pagar part of the 90 locations? That is the first clarification.

The second clarification is: the Minister mentioned that for the flood at Upper Thomson, PUB had concluded that the errant contractor diverted the drainage and caused the flood. So, has PUB taken action to prosecute the contractor?

For the Paya Lebar flood on 24 December 2016, it was caused by intense rain which overwhelmed the upstream section of the Geylang River, thereby causing low-lying areas to flood. Drainage improvement works have been ongoing in Geylang River. The expected completion of the drainage upgrading works is in the third-quarter of 2018. The flood protection to Paya Lebar areas will be enhanced then.

On the action against the contractor, we are taking steps right now to put up the charges. We will be investigating and putting up the charges when we are ready.

Mdm Speaker, I would like to ask the Minister specifically about unauthorised works, as he mentioned increasing urbanisation. What is the danger that some of these unauthorised works and the impact that they have on the drainage system will not be discovered until way into the future?

The flash flood at Upper Thomson Road on 24 December 2016 was due to localised constriction at a temporary diversion drain built by the contractor, Sato Kogyo, and this affected the public drainage system. The temporary diversion constructed by the contractor within the worksite was under-sized. More importantly, it did not inform PUB before commencement of works. The public drainage system across Upper Thomson Road was also found to be altered by the contractor without PUB's approval. PUB, therefore, will be taking action against the contractor.