PUB to give Orchard Rd special flood protection

National water agency PUB is going to give the prime Orchard Road area special protection to guard against flooding.

This means widening and deepening drains at the junction of Cuscaden and Tomlinson roads, possibly building a retention pond and even diverting water to other catchment areas.

But the various ideas tossed up to keep Orchard Road flood-free may prove costly, and that is something PUB must weigh.

Mr Tan Nguan Sen, PUB’s director of catchment and waterways, told The Straits Times that the drains there - planned to meet the needs of a fully built-up Orchard Road - were operating at close to full capacity, given all the development in the shopping belt.

‘Even though retention ponds and all that may work, we have to weigh the costs and benefits. Is it justifiable to spend those millions of dollars just to give the added protection?’ he said.

Earlier, the idea of retention ponds had been floated by PUB and other experts as one way to catch some of the peak rainwater flows. Another suggestion was to construct a diversion canal to the Singapore River.

The cost of damage from flooding on Sunday and last year has not yet been tallied, but it was previously reported that property and vehicle damage claims from floods last June were estimated at about $8 million.

Since then, the agency has spent $26 million raising a 1.4km stretch of Orchard Road from Orange Grove Road to Cairnhill Road, to help alleviate flooding in the area.

If not for this exercise, Sunday’s flood could have been worse, it said.

PUB also clarified that the flood that submerged parts of Tanglin Mall and St Regis Residences was not due to Stamford Canal overflowing - the cause of last year’s flood - but a smaller drain in Grange Road that had overflowed.

It maintained that unusual rainfall intensity was the reason the drains and canals were overwhelmed on both occasions.

Besides expanding the capacity of the drains at the junction of Cuscaden and Tomlinson roads, it has built a wall in front of the Grange Road drain to prevent water from spilling out. By tomorrow, the drain will also be covered.

The National Environment Agency (NEA) said Sunday morning’s rain intensity - 65mm in 30 minutes - has not been recorded over this part of Singapore for the last 15 years. ‘The rainfall in Singapore varies significantly from year to year,’ an NEA spokesman added. ‘Based on our long-term records, our analysis of the rainfall patterns in Singapore shows no significant trend in the annual rainfall.’

There were no floods in Orchard Road for 25 years prior to last year, PUB said.

Last June, the weather station at the TripleOne Somerset building recorded a peak rainfall intensity of 85mm in an hour.

Since 1995, there have been two occasions when the year’s highest rainfall intensity per hour at that station was greater than that of last June: in November 2007 and September 2008.

PUB did not give its specific planning parameters for the Orchard Road area.

However, it said that drains were designed based on the premise that nearly all the surrounding area would eventually be built up, which increases surface run-off when it rains.

Asked if it could show that more buildings did not contribute to the flooding, Mr Tan pointed out that the catchment area upstream of Stamford Canal, which includes Dempsey Road and the Botanic Gardens, had not been built up significantly in recent years.

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