Expanding Stamford Canal not a long-term solution

REDUCING and delaying rainwater run-off is a better way to cope with floods than expanding the capacity of Singapore's existing drainage system, including Stamford Canal, a panel recommended yesterday.

This could be achieved by introducing a wider range of drainage solutions than what is available now, said the 12-member expert panel on drainage design and flood-protection measures.

The measures should take into account every part of the drainage system, such as rainwater collection points and drains that carry away the water.

The panel was appointed by the Ministry of the Environment and Water Resources last June to look into flood-protection measures to be implemented here over the next decade.

It comprises local and international experts, and was presenting its final conclusions and recommendations yesterday.

The panel proposed that storage tanks, rooftop gardens and water-retention ponds be built to help with the collection and retention of rainwater, to relieve the heavy pressure on existing drainage areas.

The current capacity of existing drains can be improved, and adjacent canals could be added to reduce, delay and divert excess water flows, they said.

The panel added that platforms outside buildings, like walkways, should be raised to higher levels, and more anti-flood barriers built.

"Rainfall intensities and frequency of high-intensity rain in Singapore have increased over the past few decades and are likely to increase even further in the future," said Professor Chan Eng Soon, chairman of the expert panel.

"Evidence has challenged past assumptions of drainage design, and there is thus the need for PUB to review this, as well as its other flood-management and prevention measures."

One key example is Stamford Canal, said Prof Chan, who is dean of the engineering faculty at the National University of Singapore.

He noted that the canal - which has been blamed for the Orchard Road floods on June 16, 2010, and June 5 last year - had been designed to outdated standards, and so did not have the capacity to drain away the storm-water runoff generated by the more recent heavy downpours.

But the panel said it does not believe that simply increasing the capacity of Stamford Canal is the best long-term solution to address the risk of floods in the Orchard Road area.

Any drainage system, whatever the standards, has a finite capacity, the panel pointed out.

A panel member, Professor David Balmforth, who is the executive technical director at MWH Global in Britain, added that there are very few examples of municipalities in the world which make a large increase to the capacity of their drainage systems to drain away rainwater.

"It is enormously expensive and, more importantly, that sort of infrastructure investment could have a very long-term disruption to the community and significantly affect their commercial prospects," he said.

"There's a considerable amount of uncertainty, and we need to have room for flexibility to be able to respond to whatever future climate-change predictions tell us."

Overall, the expert panel said that Singapore needs a more advanced monitoring and modelling system to collect more comprehensive drainage-performance data.

"You must understand the entire catchment to know how the water is going to flow," Prof Chan said, adding that the information will help in the planning of effective long-term solutions.

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