Urbanisation has led to increase in storm water run-off: Expert panel

Esther Ng Today Online 11 Jan 12;

SINGAPORE - Urbanisation was officially acknowledged for the first time yesterday as part of the reasons behind the increase in storm water run-off, as the expert panel on drainage design and flood prevention measures revealed its recommendations on flood mitigation in Singapore.

"Urbanisation has undoubtedly led to an increase in storm water run-off in Singapore," the panel said in its statement. "There is therefore a strong argument for introducing measures to mitigate the effects of such urbanisation."

However, the panel - formed in June last year after flooding in the Orchard Road area in 2010 - stressed that these effects are often "complex" and will require further analysis.

The 12-member panel's recommendations include more dynamic weather modelling and infrastructural improvements, but it noted that a whole-scale up-sizing of Singapore's drain infrastructure would be expensive and disruptive.

A "better approach" was to reduce and delay run-off at source such as with storage tanks, rain gardens, roof-top gardens and porous pavements.

"We would like regulations brought into Singapore which require new developments to install source-controlled measures, so that the impact of development is mitigated," said panel member Professor David Balmforth, executive technical director of MWH UK, an engineering firm. "We also believe there's potential of retrofitting these measures to existing buildings."

These measures are to be complemented with diversion canals, storage tanks along "pathways" of drains, drain capacity improvements, and finally, flood barriers, raised platform levels - some of which is already being done, but "could be carried further", noted Prof Balmforth.

When contacted, the PUB said it will be studying the recommendations of the panel.

Minister for the Environment and Water Resources Vivian Balakrishnan had announced in Parliament on Monday that the PUB was looking into raising the capacity of Stamford Canal to reduce the risk of flooding.

Asked whether this would run counter to the panel's recommendation, Prof Balmforth said: "It would be unusual to produce a range of measures in a city that didn't involve some upgrade of some conveyance capacity somewhere, but that's not the same as investing in wholesale capacity upgrade of the city area, that's an important distinction to make."

Additionally, the panel recommended that the PUB moves towards a more integrated "risk-based" approach to better forecast the weather, said panel chairman Chan Eng Soon.

Based on additional analysis done with the Meteorological Services, the panel noted some clear trends in recent decades: Higher rainfall intensity and increased frequency of intense rains - consistent with the Intergovernmental Panel on Climate Change's findings, said Professor Chan.

The panel reiterated that the PUB has advanced modelling capabilities and has already collected high quality data, but more could be done. For instance, the error margins could be in centimetres rather than in 10 to 50 cm.

With more accurate data, PUB will have a faster lead time to react and provide the public with better information, Prof Chan said.

Use local storage tanks, green roofs to tackle flooding: Expert panel
Esther Ng Today Online 10 Jun 12;

SINGAPORE - To mitigate the effects of flooding, the expert panel on drainage design and flood protection measures has recommended the use of local storage tanks, green roofs and porous pavements.

Announcing its findings and recommendations in a media briefing today, the panel also suggested improving the pathways of water flow through means such as diversion canals, retention ponds, as well as raised platform levels.

The 12-member panel, comprising local and international experts, noted that urbanisation has led to an increase in storm water runoff and that the Stamford Canal - blamed for the Orchard Road floods - did not have the capacity to drain away the runoff generated by downpour on June 16, 2010 and June 5 last year.

But the panel did not recommend wholesale upsizing of the Canal. A better approach would be to reduce and delay runoff upstream, coupled with diverting excess elsewhere, suggested the panel.

Additionally, the PUB needs to move toward a more dynamic modelling approach to manage changing weather patterns as well as enhance its flood warning system so that the public has access to better information to make informed decisions should a flood occur, it added.

The panel was appointed on June 30 last year to review drainage design and flood protection measures that will be implemented in Singapore over the next decade. It is chaired by Professor Chan Eng Soon, dean of the faculty of engineering at the National University of Singapore.

Upsizing Stamford Canal not best solution: expert panel
Evelyn Choo/Tan Qiuyi Channel NewsAsia 10 Jan 12;

SINGAPORE: The panel of experts appointed to review Singapore's flood protection measures submitted its report on Tuesday, after a six-month consultation period.

It proposed that national water agency PUB collect high-resolution data to get a better idea of Singapore's flood modelling profile, and the government look into new ways to tackle the surface runoff upstream rather than focus all efforts on the downstream.

The panel said a general widening of drains and canals in Singapore is not the best long-term solution for flood prevention. This holds true for the Stamford Canal which, the panel noted, had been designed to the standards in place at that time rather than standards more typical today.

It said the canal no longer has the capacity to drain away the volume of rainfall generated by storms like those in June 2010 and June 2011.

The panel does not believe that the whole-scale upsizing of the Stamford Canal is the best long-term solution to addressing flood risks on Orchard Road.

It suggested the government look into ways to store water in the Orchard Road area further upstream, such as through the use of roof tops, a water retention pond, storage tanks along the Stamford Canal's route to relieve its burden or a diversion canal to bring the water elsewhere.

New buildings should have water-retention roofs to make up for increased urbanisation and existing buildings should be retrofitted, said the panel.

Pavements could also be made porous to absorb some water and preventing all of it from rushing into canals, added the 12-member panel comprising local and international experts.

These measures control flooding at the source, said a member of the panel, Professor David Balmforth.

The panel acknowledged that these measures and the gathering of more accurate higher-resolution data on water drainage will require significant investment.

But Professor Balmforth, MWH UK's executive technical director, said: "What the experience in the rest of the world shows...is that the overall cost of doing it that way is generally significantly less than if you concentrate on trying to increase conveyance capacity all the time."

The panel said Singapore should also look into drainage systems that can deliver multiple benefits, for instance, water storage solutions that can serve as a source of water in times of drought.

The panel was appointed on June 30 last year to review drainage design and flood protection measures that will be implemented in Singapore over the next decade. It is chaired by Professor Chan Eng Soon, dean of the faculty of engineering at the National University of Singapore (NUS).

- CNA/cc/ir

Quick fixes and better data to fight floods
Expert panel suggests both short- and long-term measures
Feng Zengkun & Grace Chua Straits Times 11 Jan 12;

ROOFTOP rain gardens and porous roads are some of the immediate ways to alleviate flooding problems in Singapore, says an expert panel on floods.

But in the longer term, the Government needs to gather better data about how much rain falls and how it flows and pools across the island.

It also needs to upgrade its computer modelling systems so that its flood predictions are more accurate.

The panel, made up of 12 local and foreign experts, made these and other recommendations yesterday after wrapping up a six-month study.

It had been appointed by Minister for the Environment and Water Resources Vivian Balakrishnan after a flood in June last year inundated the Tanglin area.

The thrust of the report was that solving Singapore's flood woes will require managing the entire chain of rainwater flow. While some of this will mean embarking on big infrastructural projects, other measures can be implemented quickly.

The quick fixes: mandating that rooftop rain gardens or green roofs be built on top of new buildings and retrofitting old ones; redeveloping roads to make them porous; installing flood barriers and raising buildings' thresholds.

But while these can be achieved in the short term, what is more crucial is the collection and study of topographic and weather data, they said.

Professor Chan Eng Soon, head of the panel and dean of the engineering faculty at the National University of Singapore, said most of the relevant drainage data collected by agencies here has been limited to water movement within drains and canals.

The Government needs to create a digital map of the country's landscape and ground surface types, and build a computer model that can better predict where water will go above-ground and which areas may be flooded, he said.

The panel said that currently, only some areas in Singapore are very well-mapped, such as the Orchard Road area. 'You must understand the entire catchment to know how water is going to flow,' said Prof Chan.

The experts also noted that the latest technology can measure the height of the land to an accuracy of 10cm. But Singapore is still relying on topographical data which was estimated - in some parts - using aerial photographs which can be inaccurate by whole metres, not centimetres.

Prof Chan said installing more rain gauges to measure rainfall - a project which national water agency PUB has already embarked on - will also produce more granular data on rainfall in specific areas.

But he noted that it would take time for such data to support any conclusions about changes in weather patterns. The panel had access to only 30 years' worth of consistent data, which it said was not enough.

Ms Elena Pison San Pedro, a meteorologist at research organisation DHI Singapore, said 30 years is the minimum for a climate change study, and phenomena that affect rainfall patterns, such as El Nino, can occur in cycles that take five to 20 years.

'Rainfall is still one of the most difficult variables to model due to its high... variability, especially in Singapore's tropical weather,' she said.

More robust data aside, the panel agreed with PUB that a detention pond and a diversion canal could be longer-term solutions.

The water agency is studying the possibility of building these, but Dr Balakrishnan said in Parliament on Monday that the pond would require land the size of two to three football fields, while the canal, which will re-route water from the maxed-out Stamford Canal to the Singapore River, will cost between $300 million and $400 million.

Mr Kam Yim-Fai, a panellist and chief engineer of the land drainage division at Hong Kong's drainage services department, said the Hong Kong government built an underground water storage tank in Kowloon in 2004 and reduced floods there. The project cost HK$285 million (S$47 million) and the tank was hidden under football and rugby fields.

'This could be useful in Singapore if the tank is installed in a low-lying area, so water flows there naturally. It should also be located close to the flood-prone area,' he said. The panel declined to comment on where such a tank could be located in Singapore, saying it needed more information from a modelling system.

The experts also suggested creating smaller storage tanks along Stamford Canal's route to relieve its burden. Such tanks are traditionally sited above ground to reduce cost and for easier maintenance, but underground versions have been used in Hong Kong and Chicago.

Mr Veera Sekaran, managing director at Greenology which installs green roofs, said the panel's suggestion to build rain gardens will be effective only if they cover 5 to 10 per cent of the catchment area.

Ms Lee Bee Wah, chairman of the Government Parliamentary Committee for the Environment and National Development, said the drainage solutions need to be aligned with the country's land-use master plan and global weather patterns.

Panel's suggestions


Create rain gardens to capture and retain rain

Build green roofs

Build local storage tanks and ponds at ground or underground level

Improve drain capacity

Design temporary storage space such as basement amphitheatres - for recreation but can be used to hold rain water.


Build porous pavements to soak up rain water

Build a diversion canal or canals


Raise platform levels

Install flood barriers


Enhance flood warning system for the public

Invest in modelling tools

Expanding Stamford Canal 'not a long-term option'
Kezia Toh Straits Times 11 Jan 12;

THE panel of specialists set up to look into the flooding problem has concluded that upsizing the Stamford Canal is not the best way to fend off flash floods in the long run.

It suggested that a better way would be to reduce and delay the flow of rainwater into the canal, and to divert the excess flow elsewhere.

This could be done, for example, with small storage tanks along the canal's route, or by building a diversion canal upstream of Orchard Road, leading to the Singapore River.

The 4km-long Stamford Canal, which runs along Orchard Road, has been fingered as the culprit of floods in the shopping belt for its failure to drain away the runoff from heavy downpours.

The floods of June 2010 and last December caused damage to goods in the basement shops of Liat Towers and Lucky Plaza as well as inconvenience to shoppers.

National water agency PUB had previously estimated that the canal's capacity would have to be increased by 30 per cent to prevent a repeat of such floods.

Minister for the Environment and Water Resources Vivian Balakrishnan also acknowledged in Parliament this week that widening and deepening the canal was not feasible.

The panel said that while the move to raise a 1.4km stretch of Orchard Road between Orange Grove Road and Cairnhill Road after the 2010 flood has reduced the flood risk for a large part of the Orchard Road area, more in-depth studies are necessary to determine if the road-raising 'has moved the flood risk from one location to another'.

As for speculation that the Marina Barrage contributed to the floods in Orchard Road, the panel dismissed the idea.

It said the barrage removed the impact of high tides on low-lying areas and released excess storm water from the catchment.

It did not cause the floods in Orchard Road in 2010 and last year, as its influence did not extend that far upstream, said the panel.

PUB 'has done well managing floods for 40 years'
Straits Times 11 Jan 12;

DESPITE the recent flood episodes, national water agency PUB has done well to manage the drainage and flood situation in Singapore in the past 40 years, acknowledged the expert panel.

This, despite rapid urbanisation, which makes it harder for rainwater to seep into the ground.

Singapore's storm drainage, said the panel, also compares well with other metropolitan areas.

Civil engineering professor Yong Kwet Yew, who is vice-president of the National University of Singapore and one of the panellists, noted that the number of flood-prone areas has been reduced dramatically.

From 3,200ha in the 1970s, such areas have been reduced to just 56ha today.

This will be further reduced to 40ha next year.

Over the last 30 years, the Government has invested $2 billion in upgrading drainage infrastructure.

PUB continues to spend about $150 million each year improving existing infrastructure in a bid to fend off floods.

But the panel added that the likelihood of more intense rain will burden the network of canals and drains here.

This refers to high intensity storms lasting less than an hour, to prolonged rainstorms with moderate rainfall intensities.

It cited rainfall intensity records over the past 30 years, showing a trend towards higher rainfall intensity, and the frequency of intense rain.

The data came from the meteorological services under the National Environment Agency (NEA).

These rainfall trends are also consistent with the United Nations' Intergovernmental Panel on Climate Change's Fourth Assessment Report.

In view of this, PUB needs to conduct further studies and review the design of its drains, said the panel.

It also attributes the three flooding incidents in Orchard Road over 18 months as part of the 'random nature of rainfall patterns'.

Two malls - Liat Towers and Lucky Plaza - at the premier shopping belt were hit by flash floods on Dec 23. Last June, water flowed into Tanglin Mall and St Regis Residences, and in 2010, large swathes of the Orchard and Scotts Road junction were submerged.

Panel advises getting better data before drainage review
Mapping S'pore's ground elevation digitally among recommendations
Lynn Kan Business Times 11 Jan 12;

AN international expert panel said that with mounting rainfall in Singapore, PUB has to take up more advanced and comprehensive methods to measure water levels and flow in the drainage system.

More specific and accurate data would help PUB 'review its drainage design considerations to account for these observed changes in rainfall patterns'.

In particular, PUB should map Singapore's ground elevation digitally to figure out how rainwater 'runs off' overground - not only in drains - and improve on flow monitoring to track how fast water runs through a channel in a certain amount of time.

The Expert Panel on Drainage Design and Flood Prevention Measures was formed by the Ministry of the Environment and Water Resources last June 30 to review how Singapore tackles flood risks in the next decade. It will likely submit its full report by the end of the week to the ministry.

The panel, which met over a period of six months, stressed repeatedly that PUB has collected 'decent' data in the past.

'PUB has already ventured into more advanced modelling. With time, they should be able to get there,' said panel chair Chan Eng Soon, the dean of National University of Singapore's engineering faculty.

The 12-person panel also recommended Singapore introduce a 'wide range' of solutions in infrastructure rather than delve into the costly affair of deepening or widening drains and canals.

These ideas include turning rooftops into water collection points, building porous pavements, installing tanks in canals, and erecting anti-flood barriers.

Any new ideas should have multiple uses besides flood mitigation, and so, would require agencies to work together closely.

Besides cost issues, expanding drain capacity would not be 'flexible' enough of a solution given mercurial climate change patterns. Though Singapore has experienced three flash floods in Orchard Road in the past 18 months, the panel pointed out that Singapore is equally prone to prolonged drought because dry months have become increasingly dryer.

Said panellist Yong Kwet Yew: 'Singapore's infrastructure in any intervention scheme therefore has to take flooding into account as well as consider how to use collected water in periods of prolonged drought.' Some of the recommended measures should come to pass relatively quickly, such as requiring new buildings to feature detention ponds, said panel member David Balmforth.

However, major infrastructure overhauls would need a longer time to plan and would not happen until a few years later.

The expert panel also said that 'wholescale expansion' of the Stamford Canal, which runs through the Orchard Road shopping belt, is not ideal.

The panel's comments backed what Environment and Water Resources Minister Vivian Balakrishnan said in parliament on Monday.

Dr Balakrishnan said that the Stamford Canal would ideally have to be expanded by one-third to cope with higher rainfalls going forward, but said that it was a costly and disruptive undertaking.

Said Professor Balmforth: 'It might be sensible to do limited upsizing at particular key points. It may well prove from the modelling work that the Stamford Canal would be one of these places.'