Tuesday 15 November 2011

Flood control

Long-term flood control plan in pipeline
Hoe Yeen Nie, Channel NewsAsia, 15 Nov 2011

Singapore is at a point where it needs to embark on a long-term plan for flood control infrastructure.

Minister for the Environment and Water Resources Vivian Balakrishnan said changing weather patterns have caused more flash floods in recent years, and this will be taken into account during planning.

National water agency PUB has commissioned an independent study to assess the possibility of a new diversionary canal off the Stamford Canal in Orchard Road.

Flash floods do not just occur in low-lying areas.

They can happen anywhere, coming and going in mere minutes, but causing hours of frustration.

The flash floods can be caused by several factors, be it inadequate drainage, clogged pipes, or heavy storm flows upstream.

And they're occurring in all areas, almost in a "pseudo-random" pattern, noted Dr Balakrishnan.

"I say pseudo-random because they are predictable, but you can only predict it about 10, 15 minutes beforehand if you look at the radar map of rainfall patterns," he said.

"The point is that it's not so much that it's a local problem itself, but the heavy, intense rain in a specific spot at that point in time, temporarily - temporarily - exceeds the drainage capacity and you get a flash flood."

PUB figures show that in 2009, there were six days of flash floods.

This went up to 13 in 2010, and 12 in 2011.

One way to manage that is to slow the flow of water in some parts, while allowing water downstream to flow away faster.

"If I can just regulate that flow so that for those 15 minutes it doesn't overflow the drain, you would have overcome the problem," Dr Balakrishnan said.

Even as Dr Balakrishnan outlined plans to review and improve the flood control system, he was quick to set expectations right.

"Nature is a very, very powerful force. I will have to say that I'm very sure there will inevitably be some episodes of flash flooding, despite all our best efforts," he said.

"People have to be aware of this; they'll have to take precautions, and what we will commit to, is making sure that everything we can do to prevent it, to mitigate it, and to keep you informed, we will do so."

Among the plans is a new planning code for buildings to be released by PUB in December, that sets higher requirements on flood control.

PUB is also studying a possible diversion canal for the Stamford Canal and retention pond in Orchard Road.

The study began in August, and will be completed in May 2012.

Dr Balakrishnan said he will consult the Orchard Road Business Association, which previously mooted a similar suggestion.

But he said given the cost and limitations of space, whether construction will go ahead is not yet a certainty.

Plans are also under way to expand the meteorological service, and create a network of data points allowing authorities to monitor the impact of rain and floods.

Dr Balakrishnan said he wants the public to get involved too, by providing real-time updates of floods to PUB.

A smartphone application was launched on 10 November, which allows the public to report to PUB on flooding, broken railings or missing sewer manholes.

iPhone users are also able to view these hotspots on their phones.

Dr Balakrishnan acknowledged that social media have become a place for the public to air their frustration about the floods, and saw this as a tool that can help authorities.

"We're not trying to hide anything. If a flash flood has occurred, it has occurred," he said.

"What I want to know is where it is, how deep the water was, what was affected, were there local problems, is there something which I can fix?

"If it's something I can fix, I will fix it. In fact, I should fix it. This is actually, I believe, a model for how Singapore and Singaporeans have to solve problems in the future.

"Through transparency, through sharing, through collaborating, and being prepared to make bold design decisions and appropriate local reactions at the same time.

"I'm actually quite enthused by it because I view it as a real-life experiment in how we're going to organise Singapore in the future."

He added: "It's no longer a defensive -- you know, you make a complaint and I'm trying to deny it or I'm trying to defend it. It's not.

"We're all on the same side, we're all part of the solution."

Flood control and water security are both, in Dr Balakrishnan's view, two sides of the same coin.

The volatile weather that is causing flash floods today could well result in droughts in the near future.

The way Dr Balakrishnan intends to manage this, is to design infrastructure to deal with both purposes.

The Marina Barrage, for instance, can flush out rain water during a heavy storm, while keeping it in the reservoir during a dry period.

Tackle flood worries
GIVEN the flooding in Bangkok and recent flash floods here, what is the Ministry of the Environment and Water Resources planning to improve drainage in urban areas?

Has sufficient funding been allocated to ensure that such improvements deliver an islandwide drainage system that can tackle challenges created by the combination of increasingly severe weather patterns and increasing urbanisation.

For example, flooding is common along the stretch of West Coast Road next to Clementi Woods Park when rainstorms strike.

The heavy run-off of water from high ground to low ground in Clementi Woods Park is obvious, with frequent overflowing of drains in the area and pooling on level ground.

The situation suggests that the land and the drains can no longer absorb the water run-off, which happened as recently as last Saturday afternoon.

The flooding was serious enough to trap a car, stalling it.

To the public, such flooding in Clementi Woods Park and other parts of Singapore seems symptomatic of an increasing inadequacy of parts of the national drainage grid to tackle flooding because it was not built to handle the changed weather patterns.

What are the effective additional measures to improve Singapore's drainage system to prevent, or at least mitigate, flooding and the ancillary concerns it causes?
Julian Ho,
ST Forum, 15 Nov 2011

Looming monsoon spurs more checks on roads
WE THANK Mr Charles Chew for his feedback ('Keep scupper holes clear - that's one thing less to worry about'; Nov 2).

PUB has an ongoing programme to convert scupper holes into drop inlet chambers in areas with high volume of leaf fall, pedestrian traffic and littering.

Drop-inlet Chamber
Unlike scupper holes, the drop inlet chambers are an improved design with a rectangular opening covered by a grating through which run-off enters, leaving leaves and debris trapped on the grating for removal by mechanical sweepers.

The leaves and litter collected in these inlets or scupper holes are caused by the rainfall.

PUB has also incorporated the use of mechanical suction to improve the cleansing of scupper holes and drop inlet chambers.

For public roads, the National Environment Agency (NEA) deploys mechanical sweepers equipped with brushes and a suction device to remove litter and leaves.

In areas where mechanical sweepers cannot be deployed effectively, leaves and litter will be removed by workers manually.

With the onset of the north-east monsoon, the NEA and PUB have stepped up the inspection and cleansing of public roads, including drains, scupper holes and drop inlet chambers, especially in the flood-prone areas.

The public can call PUB on 1800- 284-6600 or NEA on 1800-225-5632 to provide feedback on specific areas of concern.
Tan Nguan Sen
Director, Catchment and Waterways Department
PUB, the national water agency
Derek Ho
Director, Environmental Health Department
National Environment Agency
ST Forum, 15 Nov 2011

Keep scupper holes clear - that's one thing less to worry about
YESTERDAY'S report ('Flash floods in north, central Singapore') made reference to rubbish clogging drains.

On a few occasions in the past, I have raised the issue of blocked scupper holes with national water agency PUB. To its credit, it has always responded to complaints swiftly.

However, there is one issue that needs to be resolved. While drains are under PUB's purview, scupper holes form part of roads and hence come under the National Environment Agency (NEA). However, the mechanical sweepers used by NEA to suck up rubbish from scupper holes are often ineffective.

Over time, more and more rubbish, especially dried leaves and twigs, accumulate. Although blocked scupper holes are only one factor that may contribute to flooding, at least one cause can be removed.
Charles Chew,
ST Forum, 2 Nov 2011

Flash floods in north, central Singapore
The Straits Times, 1 Nov 2011

FLASH floods hit central and northern parts of Singapore yesterday afternoon, bringing traffic to a standstill in some areas. The water was knee-high along Woodlands Road, near the junction with Mandai Road, from about 3.15pm.

The area is near the coast, and water agency PUB said a combination of 'intense rainfall, high tide and debris brought on by the storm' caused the flood.

When The Straits Times visited the area, PUB staff and contractors were clearing the drains of leaves and twigs.

The flood waters took 45 minutes to subside, causing a major traffic jam.

Businessman Thomas Tan, 46, was driving along this stretch when the water flooded the engine of his truck. He said it will cost more than $500 to repair the engine.

Mr Tan said he was caught in a flood in the same area last week: 'There are a lot of leaves and rubbish clogging the drains here.'

There were two bursts of intense rainfall over the Mandai area yesterday afternoon, coinciding with a high tide of 3.3m.At the Kranji Expressway slip road towards Woodlands Road, the water took an hour to clear. In other flood-hit areas - including some sections of Dunearn Road, Bukit Timah Road and Stevens Close - it took 10 to 20 minutes to subside.

The National Environment Agency issued a heavy rain warning yesterday, and a spokesman said that for the next three days, moderate to heavy showers with thunder can be expected in the afternoon.


No comments:

Post a Comment