New measures to reduce flood risks

Monica Kotwani Channel NewsAsia 22 Apr 13;

SINGAPORE: New and redevelopment building projects will have to meet stricter flood management measures from June.

National water agency PUB announced this on Monday as part of its holistic storm water management strategy for Singapore.

The strategy includes a new clause that would require projects over a certain land size to have on-site storm water management strategies.

PUB is taking a three-pronged approach to prevent heavy rain from escalating into floods.

To tackle the flooding problem at the source, it is implementing a new rule into its revised Surface Water Drainage Code of Practice.

The clause will apply to new and redevelopment projects that are of land size 0.2 hectares and more.

For example, a new residential site that has a green roof, detention tanks or ponds will collect water during heavy rain.

Once the rain stops, the water would be released over a period of several hours – thereby preventing flooding and the overflowing of the drainage system.

The new clause could mean a substantial reduction of rainwater that flows into drains immediately after a storm – from about 90 per cent to 35 per cent after green features are implemented.

PUB said developers could also design features that co-exist with public amenity spaces.

PUB’s director for catchment and waterways, Tan Nguan Sen said: “Based on the historical data that we have recorded so far in the last 30 years, there has been an increasing trend in rainfall, and projections for the future are also likely to show an increase in rainfall patterns. We are not only tackling the source, but also the pathway and the receptor, and so these features will actually help to improve the flood resilience and increase the flexibility and the adaptability of our drainage system to meet our future challenges."

As part of its 'Receptor' measures, new and redeveloped sites could also implement minimum platform and crest protection levels to protect buildings from being affected by flash floods.

PUB said if minimum levels cannot be met due to site constraints, flood barriers can also be implemented.

PUB is also on track to construct new pathway measures such as the Stamford Detention Tanks and the Stamford Diversion Canal – to be completed by 2015 and 2017 respectively.

One developer has been implementing features such as green roofs and rainwater harvesting tanks into its residential and commercial projects for more than ten years.

Deputy general manager of projects division for green building at City Developments Limited, Allen Ang said: "It requires space planning, to incorporate water tanks – rainwater harvesting tanks – into the developments. With the new measures, developers may need to review space constraints, and allocate more spaces. For residential projects with extensive green roofs, typically it costs less than one per cent of the total construction costs to build a green roof.

Developers will be given six-month grace period to implement requirements of the new clause into their building designs.

- CNA/jc/sf/ck

New PUB code to prevent flash floods
Woo Sian Boon Today Online 22 Apr 13;

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.

Stricter anti-flood measures for buildings
New laws to affect only new building projects and those being redeveloped
Feng Zengkun Straits Times 23 Apr 13;

NEW and redeveloped building projects will have to meet more stringent flood prevention requirements from June this year and January next year.

National water agency PUB said yesterday that from January, development projects with land sizes larger than 0.2ha - about the size of half a football field - will have to include features to slow down and retain rainwater, such as detention tanks and green roofs.

It also specified that from June, buildings must install flood barriers if they cannot meet minimum crest and platform height levels to stop them from being flooded.

The PUB announced in late 2011 that these buildings were required to have flood protection measures, but did not specify which ones.

The new laws will affect only new building projects and those that are being redeveloped. Existing buildings will not be affected until their sites are redeveloped.

The PUB estimated that the 0.2ha guideline would include more than 95 per cent of new projects, based on past land sales. It will enforce the new rules by checking building plans when they are submitted for approval.

The new measures are meant to better protect buildings against flash floods and allow them to be used to temporarily store stormwater. This will reduce the peak flow of rainwater into the public drainage system and reduce its risk of being overwhelmed.

The PUB's director of catchment and waterways Tan Nguan Sen said Singapore is likely to have more rain in future based on historical data and projections.

"PUB will continue... deepening and widening drains, but there is a limit to this measure given competing demands for land use," he said.

The agency estimated that a 0.2ha site would need a 1m-deep detention tank about the size of a parking space to meet the new requirement. Developers of larger sites can go beyond block-level features and use shared spaces such as playgrounds and carparks, it said.

Mr Jwee Quek, project manager of specialist contracting company Parafoil Design and Engineering, said the firm has installed about 30 flood barrier systems at residential and commercial properties since 2010.

A basic, manual barrier about 3m wide by 1m tall costs about $20,000, he said.

The company recently installed a 150m-long, automatic pop-up flood barrier system at Lucky Plaza that cost $500,000. Additional works such as pumps and drainage diversions pushed the total bill of the flood protection system to about $1 million.

Property developers said the costs of the new features may increase total construction costs by up to half a per cent. Said EL Development managing director Lim Yew Soon: "That may sound insignificant but it's a lot of money for just the storage of water.

"Still, it may be necessary, and having guidelines will make things more transparent, and developers can factor it into their costs."