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New PUB code to prevent flash floods

SINGAPORE — To strengthen Singapore’s resilience against floods, developers of projects with a land size of 2,000 sq m and above will have to implement on-site measures to control and slow down storm water run-off as part of national water agency PUB’s revised Code of Practice on Surface Water Drainage.

Water retention and holding facilities have been installed in several City Developments Limited building projects, such as City Square Mall, along Kitchener Road, where plants are grown on green roofs to slow down storm water run-off. Photo: City Developments Limited

Water retention and holding facilities have been installed in several City Developments Limited building projects, such as City Square Mall, along Kitchener Road, where plants are grown on green roofs to slow down storm water run-off. Photo: City Developments Limited

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SINGAPORE — To strengthen Singapore’s resilience against floods, developers of projects with a land size of 2,000 sq m and above will have to implement on-site measures to control and slow down storm water run-off as part of national water agency PUB’s revised Code of Practice on Surface Water Drainage.

Starting June 1, developers will have to install structures such as detention tanks, retention ponds, green roofs as well as design features such as bio-retention swales, rain gardens and wetlands on-site, with the aim of retaining rainwater and slowly releasing it into the public drainage system afterwards.

For example, Waterway Ridges, a Housing and Development Board project currently under construction in Punggol, will include a detention tank and landscape design features such as a bio-retention basin. During dry weather, the basin — which is covered with grass — will serve as a recreation space for residents. During wet weather, rainwater will be channelled into the basin, and slowly drained into the public drainage system to stagger peak run-off.

Currently, the PUB estimates that 80 to 90 per cent of rainwater which falls onto a development is immediately discharged into drains during a storm. After the new rule kicks in, about 25 to 35 per cent of rainwater will be detained by the on-site measures to slow down discharge and prevent the possibility of flash floods.

Said PUB’s Director of Catchment and Waterways Tan Nguan Sen: “Based on historical data that we have recorded for the past 30 years, there has been an increasing trend in rainfall and projections for the future are also likely to show increase in rainfall patterns ... These features will help to improve flood resilience and the flexibility and adaptability of our drainage system to meet future challenges.”

The revised code will be applicable to all new industrial, commercial, institutional and residential developments and redevelopments. Developments which fall within the 2,000 sqm range include Liat Towers and Tong Building on Orchard Road, which were hit by flash floods in June 2010.

New developers will have a six-month grace period to include these initiatives in their plans. Asked about the cost on developers to implement such measures, Mr Tan replied: “This will be part of their overall development and will form less than 1 per cent of their development.”

Some developers, such as Keppel Land and City Developments Limited (CDL), said they have been incorporating water retention and holding facilities in their projects.

“The new requirement may demand even larger tanks. We need to balance the sizing with the area limitations,” said a CDL spokesperson.

To facilitate implementation, the PUB, in conjunction with the Institute of Engineers Singapore, has rolled out courses to educate and certify relevant professionals on planning and designing these features. Since 2011, about 100 professionals have been trained.

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