By Amresh Gunasingham & Ang Yiying
THURSDAY'S deluge which submerged parts of Bukit Timah was a 'freak' event that occurs once in 50 years, Minister for the Environment and Water Resources Yaacob Ibrahim said yesterday.
'What happened was very unusual,' he said. 'The intensity was tremendous.'
Shortly after 1pm the skies opened and in the next two hours, almost 110mm of rain fell - almost half the average monthly rainfall for November.
When a diversion canal from the main Bukit Timah canal burst its banks, flood waters rose knee-high, partially submerging ground-floor buildings and cars and causing untold damage.
'We knew the diversion canal was not big enough to take this,' the minister said about the three decade-old canal which stretches more than 3km, from Sixth Avenue to Sungei Ulu Pandan.
It was built in 1972 as part of the Bukit Timah Flood Alleviation Scheme, a major government project aimed at diverting water away from Bukit Timah - a low-lying area with a history of flooding stretching back to the 1930s.
A second diversion canal built in the 1990s near Whitley Road runs into Sungei Kallang and the Marina Reservoir.
The minister said yesterday that plans to widen and deepen drainage networks in the area will be sped up.
PUB, the national water agency, has called for tenders for an engineering consultant to widen the canals in the Bukit Timah area in anticipation of increased stormwater run-off from upcoming developments in the area, a spokesman said.
Construction is expected to start by the third quarter of next year.
Dr Yaacob urged patience as reinforcement work is carried out.
The current north-east monsoon season is usually the wettest time of the year, with almost 48 per cent of the year's rainfall occurring between November and January.
But even thorough planning is not always enough to deal with extreme weather, the minister said.
'It is not possible... to plan for every event. Thursday's weather... occurs once in 50 years. If we design for the largest rainfall or highest tide, then we are going to have huge canals in Singapore.'
The most important thing is to have an adequate drainage system that is continuously upgraded, he said.
Before the canal was built, the area saw about 12 floods a year, with waters rising up to 0.7m. Since then, it remained relatively flood-free until Thursday.
Since the early 70s, more than $2 billion has been spent on building new canals and drains, including the Marina Reservoir, which in the event of a storm can pump 6.3 billion gallons of stormwater out to sea, alleviating flooding in the city area.
It was never used on Thursday as the diversion canal which broke drains into Sungei Ulu Pandan, and the Pandan Reservoir, not the Marina Reservoir, Dr Yaacob noted yesterday.
Speaking to reporters on the sidelines as he sent off a group of haj pilgrims at Changi Airport, the minister promised assistance to those affected, saying: 'We will look to do whatever we can to help.'
Mr T.C. Chua, an engineer who was involved in a project to upgrade the Bukit Timah canal in the 1980s, told The Straits Times that development activity in the Upper Bukit Timah area could have contributed to the floods.
'The clearing of shrubs and trees could increase the surface run-off into the canal as there is no build-up to constrict the flow,' he said.
According to the National Environment Agency, moderate to heavy showers with thunder can be expected in the next few days, mainly in the afternoons.
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