'Not feasible' for drainage design to accommodate every extreme rainfall event: Masagos

Monica Kotwani Channel NewsAsia 5 Feb 18;

SINGAPORE: While the national water agency, PUB, takes into account factors such as terrain and rainfall intensity of the area when designing drains, it is "not feasible" to build them to a capacity that accommodates every extreme rainfall event.

Minister for Environment and Water Resources Masagos Zulkifli said this in Parliament on Monday (Feb 5). He was responding to questions from MPs who asked about flash floods that occurred at nine locations in eastern Singapore on Jan 8.

PUB previously said the highest recorded total rainfall that morning was 118.8m - about half of Singapore's monthly average in January in just over four hours.

Speaking in Parliament, Mr Masagos reiterated that flash floods on the day were due to intense rainfall that temporarily exceeded existing design capacity of drains.

And with climate change, he said Singapore can expect more intense rainfall "to be the norm in future".

"To prepare for this, PUB has raised drainage design standards since 2011, so that our drains can handle up to 45 per cent higher rainfall intensities," Mr Masagos said.

Mr Masagos said PUB has also commenced and completed improvement works to drains at 327 locations, with another 77 undergoing similar works.

MASSIVE LAND, HIGHER COSTS TO ACCOMMODATE EVERY EXTREME RAINFALL

But Mr Masagos cautioned that drainage design needs to be done with practical considerations, and not for extreme conditions "all the time for all places".

Building drains to accommodate "every extreme rainfall event" would require the Government to acquire massive amounts of land and much higher costs, he said.

"Bedok Canal, which serves some of the affected areas, is being widened at a cost of S$128 million from its existing width of 38m to 44m, wide enough to accommodate an expressway of 10 lanes, five lanes each way," Mr Masagos said.

But even with this widening, he said that there is no guarantee that there will not be floods in the future.

That is because climate change could result in rainfall events of even higher intensity that could exceed design capacity, he said.

"To deal with the most extreme historical rainfall events, the Bedok Canal would need to be widened to at least 62m, displacing the Bedok Park Connector and community spaces adjacent to the canal," he said.

Mr Masagos said expanding the canal could even affect surrounding residential areas, and end up looking like a 16-lane expressway.

He said authorities have to design drainage taking into account competing needs for housing, parks and roads.

"Building our drains for extreme conditions would mean that much of the capacity would be extremely costly, but not needed most of the time."

Instead what authorities will do is ensure critical infrastructure is well-protected from extreme rainfall.

Mr Masagos said this can be achieved through PUB's source-pathway-receptor approach, a holistic approach that also includes developers having to implement on site measures to slow down stormwater run-off from inundating public drains during heavy rainfall.

Source: CNA/mn


'Not feasible' to build drains for all extreme rainfall scenarios: Masagos
LOUISA TANG Today Online 5 Feb 18;

SINGAPORE — Even as Singapore pours more effort and resources into flood prevention measures, it is “not feasible” to build drains here to accommodate all possible extreme rainfall scenarios as this would involve acquiring a lot more land as well as higher costs, said Environment and Water Resources Minister Masagos Zulkifli on Monday (Feb 5).

Citing the example of the Bedok Canal, Mr Masagos said that it would have to be widened to at least 62m — or the width of a 16-lane expressway — to deal with the “most extreme historical rainfall events”. This would displace the Bedok Park Connector and community spaces adjacent to the canal, and possibly affect surrounding private residential areas.

He was answering questions tabled in Parliament from five Members of Parliament, amid heightened public concerns over the recent flash floods.

On Jan 8, flash floods hit nine locations in the eastern side of Singapore, most of which were low-lying and susceptible to flooding. Only two — Tampines Road opposite Jalan Teliti, and Arumugam Road in Ubi — had a previous history of flash floods.

The floods were due to the Northeast Monsoon and made worse by an unexpected Sumatra squall which brought widespread thundery showers, with the eastern part of the island receiving the heaviest rainfall.

The highest recorded rainfall that morning was 118.8mm, which meant that half of Singapore’s average monthly rainfall in January fell in just four hours.

Four of the affected locations are served by roadside drains that lead to the Bedok Canal, which is currently being widened from its existing width of 38m to 44m at a cost of S$1.2 billion. These works, which began in 2016 and are expected to be completed by the first quarter of next year, means the canal will be wide enough to accommodate a 10-lane expressway.

But Mr Masagos added: “Even with this widening, we cannot guarantee that there will be no floods in future, as rainfall events of even higher capacity could still occur that exceed the design capacity. This is especially due to climate change.”

More intense rainfall will be the norm in the future, he pointed out. Flood risks from rainfall changes will increase in the next two to three decades due to global warming from greenhouse gases, according to a study by the Potsdam Institute for Climate Impact Research.

The annual number of days of very heavy rainfall — with maximum hourly rainfall exceeding 70mm — in Singapore has also been on the rise since 1980, according to national water agency PUB.

The Government, Mr Masagos noted, has to design “with practical considerations and not for extreme conditions all the time for all places”, as it will be “extremely costly but not needed most of the time”.

“The need for adaptation is significant, even in countries with good infrastructure such as Singapore,” Mr Masagos said.

To that end, the Government has invested S$1.2 billion in drainage improvement works since 2012, and will pump in another S$500 million over the next two to three years. Since 2012, drainage improvement works at 327 locations have been completed, with 22 more planned for this year.

On the Jan 8 flash floods, drainage improvement works are already being carried out at eight of the nine affected locations, Mr Masagos told the House. Works at the Tampines Canal between Upper Serangoon and Sungei Serangoon are expected to be completed by the third quarter of this year, and works at the Geylang River will be completed by the first quarter of next year.

For the ninth location at Tampines Avenue 12, a temporary construction access road built by the constructor had worsened the situation by obstructing the earth drain in an adjacent worksite.

The PUB has worked with the developer to improve drainage there, Mr Masagos disclosed. A permanent drainage system, built in tandem with the upcoming development project at the adjacent worksite, will serve as the longer term measure.

Responding to a supplementary question by Mr Murali Pillai (Bukit Batok Single Member Constituency), who asked how the ministry will oversee developers and construction companies, Mr Masagos said that contractors have to submit plans for drainage diversion to the PUB. For those who commit errors, like at Tampines Avenue 12, the ministry will take action by bringing them to court and fining them, he added.

And since flash floods cannot be completely eliminated, Mr Masagos advised members of the public to subscribe to the National Environment Agency’s and PUB’s SMS alerts or mobile apps for updates on impending heavy rain and water level in drains at designated locations.

While the PUB strives to give early warning to the public, weather systems in the equatorial region pose a forecasting challenge, he said. These weather systems comprise mainly convective thunderstorms which tend to be localised, develop rather suddenly, and are of short duration. This limits the lead time for issuing warnings of heavy rain and consequent flash floods.

Flash floods have occurred on four days in January this year. There were flash floods on 14 days last year, 10 in 2016 and six in 2015.

*CLARIFICATION: In an earlier version of this story, we reported that flash floods have occurred on three days in January this year. That is incorrect. The PUB has clarified that flash floods have occurred on four days in January.

PROTECTING CRITICAL INFRASTRUCTURE FROM EXTREME RAINFALL

Besides drainage improvement works, the PUB takes an approach called “source-pathway-receptor” to ensure the Republic’s critical infrastructure is well-protected from extreme rainfalls.

“Source” refers to where the rain falls, “pathway” refers to drains and “receptor” refers to the areas where floods may occur.

Measures to cope with “source” and “pathway” issues include detention tanks, which collect and store water from storms, potentially reducing the amount of storm water entering public drains during peak rainfall.

An example of this is the Stamford Detention Tank and the Stamford Diversion Canal, which will alleviate flooding in the Stamford Canal catchment area that covers the Orchard Road shopping belt.

The Stamford Detention Tank, to be completed by the second quarter of the year, will temporarily hold excess storm water from the drains. After the rain subsides, the water will be pumped back into the drains and discharged into Marina Reservoir.

Since 2014, developers have had to implement such source measures at all new and redevelopment projects that are 0.2 hectares or larger in size. These measures slow down surface runoff and reduce peak flow to the public drainage system by 25 to 35 per cent.

There have been about 500 submissions for plans to incorporate retention tanks, of which 138 have been completed.

For areas most at risk of flooding, the PUB stipulates that buildings should have features such as higher platform levels, crest protection and flood barriers to prevent floodwaters from damaging them.

Developers have to adhere to a minimum design standard to provide adequate drainage for buildings and infrastructure. The code of practice, last revised in December 2011, covers the minimum land reclamation levels, minimum crest and platform protection levels, and design standards for drains.

Following the 2011 revision, drainage design standards for new drains were increased to handle more intense storms. For example, the width of a typical roadside drain was increased from 1.5m to 1.8m.


No history of flash floods in most areas hit on Jan 8
Audrey Tan Straits Times 6 Feb 18;

Only two of the nine locations in eastern Singapore that suffered flash floods on Jan 8 had a history of flooding, Minister for the Environment and Water Resources Masagos Zulkifli said yesterday.

He also said that with climate change, Singapore can expect intense rainfall to be the norm in future. This means flash floods could occur in areas with no record of flooding.

But he cautioned that it was not feasible to build and expand drains to accommodate every extreme rainfall event, as that would be very costly and require setting aside large tracts of land. For instance, Bedok Canal is being widened at a cost of $128 million and the space can accommodate a 10-lane expressway.

Mr Masagos made these points in Parliament to five MPs, including Mr Murali Pillai (Bukit Batok) and Non-Constituency MP Dennis Tan, who had asked about the floods.

On Jan 8, the nine places were inundated with rain - the heaviest recorded total rainfall that morning was 118.8mm, half of Singapore's average rainfall for January - with submerged cars, flooded bus cabins and some businesses being disrupted.

Although eight of them are low-lying and susceptible to flash floods, only two had a history of flooding.

They are Tampines Road, opposite Jalan Teliti, and Arumugam Road in the Ubi area. Between 2015 and this year, five flash floods took place in Tampines Road and three in Arumugam Road.

"The flash floods were caused by the intense rainfall temporarily exceeding the existing design capacity of the drains," Mr Masagos said.

Every year, since 1980, heavy rain has been pouring down more often. Also, the annual maximum hourly rainfall has risen. It was about 80mm in 1980 and 90mm in 2016.

"Although the flood waters affected only certain stretches of the roads, and subsided within 15 to 60 minutes, we acknowledge that members of the public were inconvenienced and a number of cars had stalled," he added.

Every year, since 1980, heavy rain has been pouring down more often. Also, the annual maximum hourly rainfall has risen. It was about 80mm in 1980 and 90mm in 2016.

It has led the Government to invest in drainage infrastructure.

Since 2012, drainage improvement works have been carried out at 327 locations and such upgrading is still going on at 73 other places, with 22 more planned for this year.

On the Jan 8 case, he said drainage improvements are being carried out in eight of the nine affected areas, "to enable the drains there to discharge more water in a shorter time when completed".

In the ninth location in Tampines Avenue 12, the building of an unauthorised road had intensified the flash flood.

The PUB has worked with the developer to improve the drainage, Mr Masagos said, adding that it is now working on a long-term measure of installing a permanent drainage system. It will be built in tandem with the upcoming development project at an adjacent worksite.

Singapore saw floods on 14 days last year, compared with 10 in 2016, and six in 2015. This year, four flash flood days were recorded last month.

But there is a limit to how many drains can be built or upgraded.

Mr Masagos cited the Bedok Canal, which takes in water from four of the nine places hit by the Jan 8 flash floods. It is being widened from 38.5m to 44m, by the first quarter of next year.

With the expansion, the canal will be wide enough to accommodate an expressway of 10 lanes. But to deal with extreme rainfall, it would have to be widened to at least 62m - a 16-lane expressway.

Such a move would displace the Bedok Park Connector and community spaces adjacent to the canal, and possibly even affect the surrounding residential areas, Mr Masagos said.



PUB to charge contractor for blocking ditch at Tampines Ave 12 that intensified flooding
Monica Kotwani Channel NewsAsia 5 Feb 18;

SINGAPORE: Authorities will take action against a contractor who built a temporary access road to its construction site at Tampines Avenue 12 without approval, said Minister for Environment and Water Resources Masagos Zulkifli in Parliament on Monday (Feb 5).

In building the access road, Huationg Contractor blocked a ditch near the worksite, worsening flash floods in the area on Jan 8.

If found guilty, the contractor can be fined up to S$20,000.

Tampines Avenue 12 was among nine locations in eastern Singapore that experienced flash floods that morning, as a result of intense rainfall that exceeded the capacity of drains.

But national water agency PUB’s investigations revealed that flooding on Tampines Avenue 12 was aggravated by the blocked ditch.

At a media briefing last month, PUB explained that stormwater from the construction site and a field next to it would typically flow into the ditch before being discharged into Sungei Tampines.

However, the building of the unauthorised access road completely obstructed the flow of the ditch. As a result, stormwater ended up flowing into the roadside drain along Tampines Avenue 12, which was already overwhelmed by the heavy rainfall on Jan 8, said PUB.

Mr Masagos said contractors have to submit plans to divert drains, while keeping the original drain design intact so that rainfall meant for that drain does not “affect surrounding areas”.

“This has worked most of the time,” he said.

“When we have flash floods occurring in areas we know do not frequently experience flash floods, it’s usually because the contractors have not implemented what they are supposed to do or implemented something else to make their work site accessible or easier to work on.”

PUB confirmed with Channel NewsAsia that it would charge Huationg Contractor under the Sewerage and Drainage Act.

“The charge is under Sector 23(1) for closing up the drainage system without obtaining approval from the Board and carries a fine not exceeding S$20,000,” PUB added.

Mr Masagos also responded to questions on the Jan 8 flooding, saying that only two of the nine locations had a history of flash floods. They are Tampines Road (opposite Jalan Teliti) and Arumugam Road.

Of the nine, eight also are low lying and susceptible to flash floods. The minister reiterated that PUB is already carrying out drainage improvement works in these areas.

Source: CNA/mo
Read more at https://www.channelnewsasia.com/news/singapore/pub-to-charge-contractor-for-blocking-ditch-at-tampines-ave-12-9928242