ok this for opening sesame
ST 18 June
2010
Blocked Drain Blamed for Orchard Flood (on 16 June
2010)
IT WAS just a single drain, about the width of an SBS bus. But
it was so badly blocked by debris that it triggered the flooding of
Orchard Road on Wednesday.
The critical culvert, at the junction of Tanglin and Orchard
roads, drains into two parallel channels flowing under Orchard Road
- a drainage system called the Stamford Canal.
The first heavy downpour of the morning had carried debris and
vegetation into the 2.7m by 2.7m culvert, starting a chain of
events that led eventually to the flash flood.
It was choked where it drained into the side of Delfi Orchard,
so water was directed only into the side along Forum the Shopping
Mall.
When a second intense rainstorm the same morning added more
water to the drains within a short period of time, the canal
overflowed and water gushed up to the surface of Orchard Road,
causing the worst floods there in 26 years.
Worst-hit was the junction of Scotts Road and Orchard Road, the
lowest-lying part of the area. Near the intersection, shops at Liat
Towers and the Lucky Plaza basement were flooded.
Although national water agency PUB alerted the traffic police
when the sensors at the start of each Stamford Canal channel
indicated water levels were at 75 per cent, the water level rose
too abruptly to get the alert out to shopkeepers.
At a press conference yesterday, the PUB said the heavy rains
were responsible for sweeping the debris into the drain.
It was last checked about three months ago and was not blocked
before Wednesday's storm, said Mr Yap Kheng Guan, director of PUB's
3P (Public, Private and People) Network.
After the flood on Wednesday had receded, PUB officers combed
the canal for hours, and at 10pm that night found a third of the
culvert still blocked.
To fix the problem, the PUB would now conduct checks more often
than every three months, he said. It would also install grates in
flood-prone areas to prevent debris from being swept into the
drains.
Asked why there were no debris traps already installed in a
known flood-prone area, he said the existing canal had been
'serving us very well'.
Rain this heavy had occurred twice before, in August last year
and January 2008, without severe flooding, so the Stamford Canal
has the capacity to handle such a volume of water.
What was unusual about Wednesday's storm was its intensity and
its two peaks, he said. The first peak could have brought a certain
amount of debris, and there was no way for PUB officers to safely
check and clean it out. The next peak soon after might have brought
even more debris.
'This is a learning experience for us,' Mr Yap said. 'Perhaps
when we're dealing with a storm like this, we have to do something
differently.'
In the long run, more sensors would be added to monitor water
levels, he said. They would also serve as an early warning system
similar to that now in place at Upper Bukit Timah.
Following flash floods in the area last November, flood sensors
were installed which will trigger SMS alerts to condominium
managements if the water level in the Bukit Timah canal reaches a
certain height, so residents can move their cars and other property
to safety.
Ms Lee Bee Wah, MP for Ang Mo Kio GRC and deputy chairman of the
National Development and Environment Government Parliamentary
Committees, said the flooding was a 'timely wake-up call' that
something more needs to be done to prevent a similar
occurrence.
On Wednesday morning, 101 mm of rain fell over central Singapore
in less than three hours. The average rainfall for the entire month
of June is 162 mm.
National University of Singapore climate expert Matthias Roth
said that though June is usually dry, heavy rain is always a
possibility in places located close to the equator.
