Grace Chua Straits Times 31 Dec 11;
A PERFECT storm of factors led to the flooding of the basement of Liat Towers in Orchard Road last Friday, said national water agency PUB yesterday.
Giving its latest findings on what happened there, PUB said that prolonged and heavy rainfall that day caused some parts of Stamford Canal, which runs in front of the shopping mall, to be full.
Because the canal was full, rainwater could not flow into it any more.
Meanwhile, rainwater draining off from the roof and the back area of Liat Towers into an internal drain overflowed into the building's basement area, adding to the pooling of water there.
While Liat Towers' pumps can ordinarily pump water from the basement into the Stamford Canal, this was not possible that day. 'When the canal in front of Liat Towers reached 100 per cent, the pumps were not able to discharge water accumulating in the basement into the Stamford Canal,' said the PUB.
But, it added, the pumps were still able to pump some water from the basement onto the pedestrian walkway along Orchard Road, which is what they did.
Sustained and heavy rain last Friday caused the basements of Liat Towers and Lucky Plaza in Orchard Road to flood, although the rest of the shopping district did not experience flooding and was passable to traffic, unlike in the big flood of June last year.
The PUB's latest statement comes on the heels of a seeming disagreement between the water agency and Liat Towers on what exactly caused the basement plaza area to flood.
This was the third time in two years that the sunken area has been badly flooded, affecting the four businesses there.
Customers at coffee joint Starbucks had to make their way out using chairs as stepping stones, while the Wendy's fast-food restaurant, clothing store Massimo Dutti and high-fashion retailer Hermes were also inundated.
PUB had said last week that the heavy rain had caused 'ponding' in some places like Liat Towers and Lucky Plaza across the road, which also has basement shops.
A spokesman had said at the time that based on its monitoring, 'Stamford Canal did not overflow. If it had, it would have resulted in flooding on Orchard Road, which was not the case'.
The agency had also noted that the huge volume of rain could have exceeded the building's pumping capacity.
Liat Towers, however, insisted that its pumps had been working at full bore to push water into Stamford Canal. But because the canal was full, the water had nowhere to go, resulting in the flood.
In its statement yesterday, PUB said it understood that members of the public were concerned about the adequacy of measures taken to date.
'As the national water agency, PUB takes its responsibility for flood management seriously. While it is not possible for us to completely eliminate flash floods, we will do everything feasible to prevent it, mitigate it and keep the public informed,' it said.
It added that its officers have been working closely with the management of affected buildings to investigate the cause of the floodings and identify measures to help prevent a recurrence.
It pointed out that last Friday, 152.8mm of rain fell from 2.20pm to 5.20pm in Orchard Road.
This is about half the average monthly total - 287.4mm - of rain recorded for the entire month of December over the last 142 years.
To protect against future floods, Liat Towers and the PUB have come up with some solutions.
They are building a 60cm-high wall next to a drain that starts near Wendy's and wends round the back of the building. The 90m-long reinforced concrete wall will cost between $20,000 and $25,000, which Liat Towers will pay for, and be ready next week.
Another solution: The building's management has redirected two pipes so they are now able, in an emergency, to flush water out onto the pedestrian walkway.
Asked if water pouring out onto the walkway might create problems for pedestrians, a PUB spokesman said it would be done only in exceptional circumstances.
'We expect that when the rain is very heavy, that the pedestrian walkway would be free from users. We will pump onto the pedestrian mall only when the capacity of the canal is full,' he said.
Stamford Canal has two parallel branches under Orchard Road - one on the Forum Galleria side, and the other in front of Orchard Towers. On the Forum side, it is 2.2m deep, and across the road it is 3m deep. When the shallower side is full, water coming from upstream flows into the Orchard Towers branch.
The capacity of the Stamford Canal, the PUB acknowledged last year, was a factor in last year's flooding on Orchard Road as well.
The PUB raised a 1.4km stretch from Tanglin Road to Cairnhill Road by an average of 30cm. This was completed in June this year.
Earlier this year, the Tanglin-Cuscaden area was also hit by flash floods.
PUB yesterday said that although the rainfall on Dec 23 was higher than what was recorded in June last year, Orchard Road remained passable to traffic.
Given the constraints in expanding Stamford Canal as it is in a highly urbanised area, PUB is studying the feasibility of building a detention pond and a diversion canal for the Stamford catchment for the longer term, it said.
The study started in August and will be completed in May next year.
Half the month's rain in 3 hours
Kezia Toh Straits Times 31 Dec 11;
IN THREE hours last Friday, the rain that pelted down on Orchard Road was half of what December typically gets in the entire month.
Between 2.20pm and 5.20pm, 152.8mm of rain fell in the area. The long-term average for December - the wettest month in the entire year - is 287.4mm.
Basement shops in Liat Towers and Lucky Plaza were in ankle-deep water because of the prolonged and heavy rain.
Last year, shops in the two malls were similarly affected. In two hours, 100mm of rain was dumped on Orchard Road then.
National Environment Agency (NEA) figures show that as of last Friday at 4pm, total rainfall for the month had hit 274.4mm.
So this month looks set to finish above the average, said Assistant Professor Koh Tieh Yong from the School of Physical and Mathematical Sciences at Nanyang Technological University.
'I am fairly confident that this year's December rainfall will exceed the typical average December rainfall,' he told The Straits Times.
'As compared to the revised higher rainfall, last Friday's rain will be a smaller fraction of that, and will not be so significant,' he said.
Liat Towers flooding traced to Stamford Canal
Saifulbahri Ismail Channel NewsAsia 30 Dec 11;
SINGAPORE: The cause of flooding at Liat Towers last Friday has been traced to Stamford Canal's fundamental problem of being unable to cope with the surge in water during heavy and prolonged rainfall.
And that's why during last Friday's downpour, the canal reached its full capacity very quickly.
Explaining on Friday why the flooding occurred on December 23, PUB said that the prolonged and heavy rain that day caused some parts of Stamford Canal to flow full.
The national water agency said that 152.8mm of rain fell on Orchard Road from 2.20pm to 5.20pm that day.
This is equivalent to about half the average monthly total of 287.4mm of rain recorded for the entire month of December over the last 142 years (1869 to 2010).
The sustained heavy downpour resulted in the flooding of several roads including the Thomson/Cambridge areas as well as the basements of Liat Towers and Lucky Plaza.
At Lucky Plaza, rainwater drained into the basement via the steps.
For Liat Towers, rainwater that had drained off from the roof and the back area of the building overflowed into the basement area from an internal drain, as water could not flow out into the canal, which was full.
The pumping system at Liat Towers is able to pump out the water from the open basement area when the canal is not full.
But when the Stamford Canal in front of Liat Towers reached 100 per cent capacity, the pumps were not able to discharge the water in the basement into the canal. However the pumps were still able to pump some water onto the pedestrian walkway.
To improve flood protection during similar storms, Liat Towers will be building a perimeter wall along its internal drain as an interim measure. Construction of the wall will begin on December 31 and will take about four to five days.
Liat Towers management is also considering installing more goose-neck pumps, perhaps even at a larger capacity, to divert water onto the pedestrian walkway if water overflows past the perimeter wall.
PUB said it takes its responsibility for flood management seriously. It added that while it is not possible for PUB to completely eliminate flash floods, it will do everything feasible to prevent it, mitigate it and keep the public informed.
The agency has been working closely with the management of flood-affected buildings.
PUB's director of 3P network, George Madhavan, said: "Since 23 December, PUB officers have been meeting regularly with the management of Liat Towers to review, to enhance the flood protection for this building.
"What we are clear is that both PUB as well as Liat Towers are determined to put in measures to make sure that this (flooding) does not recur."
Liat Towers' director of property management, Lydia Tjhia said: "PUB (officers) have come down many times for discussions with Liat Towers and they have been very helpful.
"They have given us a few recommendations, one of which is the raising of the 60cm curb. This will allow more water to be held within this so-called pond and with the difference in pressure we'd be able to drain the water into the canal.
"However, when the canal is full there may be times when the water might overflow onto the pedestrian walkway."
As for Lucky Plaza, its management is in the process of putting in place flood barriers after getting in-principle approval from the Urban Redevelopment Authority (URA) in October.
But the installation could be delayed.
Lucky Plaza has been asked to tweak its design of the barriers to ensure better pedestrian flow along the walkway.
URA said Lucky Plaza has yet to resubmit the refined proposal to URA for further consideration and approval.
PUB said it will work with Lucky Plaza to ensure that an effective flood prevention system is implemented quickly.
PUB noted that although the rainfall recorded on 23 December was higher than what was recorded in June last year, Orchard Road remained passable to traffic.
This was because after the June 2010 floods at Orchard Road, PUB raised the road to improve the flood protection for the area. This was completed in June this year.
Nevertheless, recognising the constraints in expanding Stamford Canal given the highly urbanised development in the area, PUB is studying the feasibility of building a detention pond and a diversion canal for the Stamford catchment in the longer term.
The study started in August this year. PUB will share the details when it completes the study by May 2012.
- CNA/fa/ir
Stamford Canal a cause of flooding again
Saifulbahri Ismail Today Online 31 Dec 11;
SINGAPORE - The 4km-long Stamford Canal, cited as a factor in last year's floods along Orchard Road, has again been traced as the source of flooding at Liat Towers last Friday.
Explaining yesterday why the flooding occurred, national water agency PUB said the "prolonged and heavy" monsoon rain on Dec 23 caused "some parts of Stamford Canal to flow full". Then, 152.8mm of rain fell on Orchard Road from 2.20pm to 5.20pm - equivalent to about half the average monthly total of 287.4mm of rain recorded for the entire month of December over the last 142 years.
The sustained heavy downpour resulted in the flooding of several roads, including the Thomson/Cambridge areas, as well as the basements of Liat Towers and Lucky Plaza.
At Liat Towers, PUB said rainwater that had drained off from the roof and the back of the building overflowed into the basement area from an internal drain, as water could not flow out into the canal, which was full.
The pumping system at Liat Towers is able to pump out the water from the open basement area when the canal is not full. But when the Stamford Canal in front of Liat Towers reached 100-per-cent capacity, PUB explained the pumps failed to discharge the water in the basement into the canal. "However, the pumps were still able to pump some water onto the pedestrian walkway," it added.
In its statement, PUB assured the public that it takes "its responsibilty for flood management seriously". "PUB regrets the inconveniences caused by the floods to members of the public and businesses," said the agency. "While it is not possible for us to completely eliminate flash floods, we will do everything feasible to prevent it, mitigate it and keep the public informed."
At Liat Towers, for example, PUB officers have been meeting the building's management regularly since last Friday to enhance its flood protection.
"What we are clear is that both PUB as well as Liat Towers are determined to put in measures to make sure that this (flooding) does not recur," said PUB's director of 3P network, Mr George Madhavan. He said the agency has been working closely with the management of flood-affected buildings.
To improve flood protection during similar storms, Liat Towers will be building a perimeter wall along its internal drain. "This will allow more water to be held within this so-called pond and, with the difference in pressure, we'd be able to drain the water into the canal," said Liat Towers director of property management Lydia Tjhia. "However, when the canal is full, there may be times when the water might overflow onto the pedestrian walkway."
Given the constraints in expanding Stamford Canal due to the urbanised development in the area, PUB is studying the feasibility of building a detention pond and a diversion canal for the Stamford catchment in the longer term.
For nearby Lucky Plaza, where rainwater drained into the basement via the steps, PUB said it will work with the building's management to ensure that "an effective flood prevention system is implemented quickly".
An Urban Redevelopment Authority (URA) spokesperson said Lucky Plaza was granted in-principle approval for the installation of flood barriers in October, subject to the refinement of the design of the barriers. "Lucky Plaza has yet to resubmit the refined proposal to URA for further consideration and approval," added the URA.
PUB noted that, although the rainfall recorded last Friday was higher than what was recorded in June last year, Orchard Road remained "passable to traffic" because of road-raising work along a 200m stretch.
PUB working to prevent more floods
Tam Yu Ling Business Times 31 Dec 11;
FOLLOWING last Friday's flash floods, national water agency PUB says it will work closely with the management of affected buildings to find out the cause of the floods and identify ways to prevent a recurrence.
Sustained downpour over a three-hour period caused flooding in areas such as Thomson, Little India and Orchard Road, including the basements of Liat Towers and Lucky Plaza - the third time in less than two years.
That afternoon, a total of 152.8mm of rain was collected from 2.20-5.20pm in the Orchard Road area. According to PUB, this represents about half the average monthly rainfall for the whole of December over the last 142 years.
When the prolonged monsoon rains caused Stamford Canal which runs along Orchard Road to flow full, rainwater from the roof and back areas of the building started flowing into the basement via an internal drain, after it could no longer flow out into the already-full canal.
A post-flood assessment conducted by PUB also found that the internal pumping system at Liat Towers was operationally able to pump out water from the basement when the canal was not full. However, when the canal in front of the building reached 100 per cent, the pumps were not able to discharge the water accumulated in the basement into Stamford Canal.
Liat Towers has put in place floodgates to protect its premises since the June 2010 flood, which PUB said had effectively prevented water collected on the pedestrian walkway from flowing into the basement plaza.
To increase the building's flood protection, Liat Towers and PUB are looking into constructing a 60cm-tall perimeter wall along the internal drain to prevent water from flowing back into the basement in the event of a similar downpour.
When contacted by BT, a PUB spokesman said construction of the curb will start today and is expected to be completed in a week.
Another flood-affected building is Lucky Plaza, where rainwater has drained into the basement via the steps. To improve Lucky Plaza's flood protection system, the building management is in the process of putting up flood barriers, after obtaining in-principle approval from the relevant government agencies. PUB also said that it would work with Lucky Plaza's management to ensure that an effective flood prevention system is implemented quickly.
The national water agency said that after the June 2010 flood in Orchard Road, it raised the road to increase flood protection for the area. The road raising project was completed in June this year.
Comparing this month's flood with that of June last year, PUB noted that although the rainfall on Dec 23 was greater than what was recorded in June 2010, Orchard Road remained passable to traffic.
In August, the agency also undertook a study on the feasibility of constructing a detention pond and diversion canal for the Stamford catchment after recognising the constraints of expanding the canal given the highly urbanised development in the area.
PUB said that it would share details of its findings when it completes the study next May. It added that it regrets the inconvenience caused by the floods to members of the public and affected businesses.